Donate Help Contact The AHA Sign In Home
American Heart Association
Circulation
Search: search_blue_button Advanced Search
« Previous Article | Table of Contents | Next Article »
Circulation. 1995;91:990-998

This Article
Right arrow Abstract Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Panza, J. A.
Right arrow Articles by Katsiyiannis, P. T.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Panza, J. A.
Right arrow Articles by Katsiyiannis, P. T.
Right arrowPubmed/NCBI databases
*Compound via MeSH
*Substance via MeSH
Medline Plus Health Information
*Nuclear Scans

(Circulation. 1995;91:990-998.)
© 1995 American Heart Association, Inc.

Articles

Relation Between Thallium Uptake and Contractile Response to Dobutamine

Implications Regarding Myocardial Viability in Patients With Chronic Coronary Artery Disease and Left Ventricular Dysfunction

Julio A. Panza, MD; Vasken Dilsizian, MD; Joy M. Laurienzo, RN; Rodolfo V. Curiel, MD; Peter T. Katsiyiannis, MD

From the Echocardiography and Nuclear Cardiology (V.D., P.T.K.) Laboratories, Cardiology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md.

Correspondence to Dr Julio A. Panza, Director of Echocardiography, National Institutes of Health, Bldg 10, Room 7B-15, Bethesda, MD 20892.


*    Abstract
up arrowTop
 *Abstract
down arrowIntroduction
 down arrowMethods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Background Both thallium scintigraphy and dobutamine echocardiography have been used to assess myocardial viability. However, thallium uptake and the inotropic response to dobutamine are expressions of different cellular phenomena. The present study was undertaken to investigate the relation between the two methods in patients with chronic coronary artery disease and left ventricular dysfunction to derive insights into the mechanisms related to myocyte viability.

Methods and Results Thirty patients (28 men and 2 women; age, 59±10 years) with chronic coronary artery disease and impaired left ventricular systolic function at rest (mean ejection fraction, 32±9%) were included in the study. Patients underwent transesophageal echocardiography during incremental doses of dobutamine from 2.5 to a maximum of 40 µg · kg-1 · min-1 and single photon emission computed tomographic thallium scintigraphy using a stress-redistribution-reinjection protocol. The left ventricle was divided into 16 segments for analysis of echocardiographic and thallium images. Segmental myocardial contractile function was graded as normal, hypokinesis, akinesis, or dyskinesis at each incremental dose of dobutamine. Thallium uptake in each myocardial segment was graded on a 5-point scale from 0 (absent) to 2 (normal) for each of the stress, redistribution, and reinjection images. A segment was considered viable if the assigned thallium score was 1 or higher (normal uptake or only mild to moderate defect) in any of the stress, redistribution, or reinjection images. Among 472 myocardial segments available for analysis, 311 had resting wall motion abnormalities, of which 56% (173/311) showed contractile improvement with dobutamine (usually first observed at <=10 µg · kg-1 · min-1) and 84% (262/311) were considered viable by thallium scintigraphy (P<.0001). Of the 262 segments considered viable by thallium, 167 (64%) had a contractile improvement with dobutamine; in contrast, only 6 of the 49 segments (12%) considered nonviable by thallium had a positive dobutamine response (P<.0001). Furthermore, a positive inotropic response to dobutamine was significantly related to the magnitude of thallium uptake: the proportion of segments with a positive dobutamine response rose with increasing magnitude of thallium uptake (P<.001). The disagreement between the two tests was related primarily to segments considered viable by thallium that did not show contractile improvement with dobutamine.

Conclusions These findings demonstrate the existence of a relation between thallium uptake and the inotropic response to dobutamine in patients with chronic coronary artery disease and left ventricular dysfunction. However, the proportion of segments showing a positive response to dobutamine is significantly lower than those with thallium uptake, suggesting that the cellular mechanisms responsible for a positive inotropic response to adrenergic stimulation require a higher degree of myocyte functional integrity than those responsible for thallium uptake.


Key Words: coronary disease • myocardial contraction • echocardiography • scintigraphy


*    Introduction
up arrowTop
 up arrowAbstract
 *Introduction
down arrowMethods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Identifying areas of myocardium with depressed but potentially reversible contractile function may bear important significance in the therapeutic strategy and perhaps the prognosis of patients with coronary artery disease and left ventricular dysfunction.1 2 3 4 Consequently, the noninvasive assessment of dyssynergic but viable myocardium, which may contribute to the overall improvement in left ventricular function after revascularization, has generated great interest among cardiologists and cardiac surgeons.5 6 7 8 9 10 11 12 13 14 Among the several techniques used for this purpose, thallium scintigraphy (using rest-redistribution or stress-redistribution-reinjection protocols) has been shown to be a useful method, largely based on the observations that the presence of thallium uptake in a myocardial region with depressed systolic function correlates with contractile improvement after revascularization.15 16 17 18 19 20 21 22 23 24

Infusion of dobutamine (a synthetic catecholamine with a predominant ß1 agonist effect) has been combined with echocardiography for detection of myocardial ischemia in patients with known or suspected coronary artery disease.25 26 27 28 29 30 Recently, dobutamine echocardiography has also been proposed as a tool to assess myocardial viability within poorly contractile segments of the left ventricle in patients with coronary artery disease. Thus, areas of dyssynergic myocardium that display an improvement in contractile function with dobutamine appear to have a greater probability of recovery after revascularization compared with areas in which dobutamine does not induce a significant change in contractile function.31 32 33

Although both thallium scintigraphy and dobutamine echocardiography have been used to assess left ventricular dysfunction in patients with chronic coronary artery disease, the mechanisms by which these two methods identify viable myocardium are different. Thallium scintigraphy demonstrates the ability of the myocardium to take up a cation by an active process that takes place at the level of the cell membrane.14 Dobutamine echocardiography, on the other hand, assesses the ability of the myocardium to increase its contraction in response to an adrenergic stimulus.34 Thus, although the uptake of thallium and a positive inotropic response to dobutamine both indicate the presence of viable myocardium, each reflects different cellular processes characteristic of viable myocytes. The purpose of the present investigation was to determine whether there is a differential effect of chronic coronary stenoses on these two processes by studying the relation between myocardial thallium uptake and the contractile response to dobutamine in patients with coronary artery disease and left ventricular dysfunction.


*    Methods
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 *Methods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Study Population
The study included 30 consecutive patients with coronary artery disease and depressed left ventricular systolic function at rest (ejection fraction at rest <45%) admitted to the Clinical Center of the National Institutes of Health for coronary angiography who underwent both thallium scintigraphy and transesophageal dobutamine echocardiography. The 28 men and 2 women had a mean age of 59±10 years. All patients underwent cardiac catheterization as part of their evaluation for suspected coronary artery disease, systolic dysfunction, chest pain syndrome, or previous myocardial infarction. In each patient, coronary angiography demonstrated >=70% narrowing in the ID of at least one major coronary artery. Sixteen patients had undergone previous revascularization (coronary artery bypass surgery in 10 and angioplasty in 6); in these patients, the status of the coronary vascular tree at the time of the most recent cardiac catheterization (performed after revascularization in all patients) was considered for allocating the patients into the one-, two-, or three-vessel disease category. Of the 30 patients, 12 (40%) had single-vessel disease, 7 (23%) had two-vessel disease, and the remaining 11 (37%) had involvement of all three major coronary arteries.

Sixteen of the study patients (53%) had suffered a previous myocardial infarction, but not in the 3 months before the study. Eleven patients were asymptomatic; the remaining 19 had stable symptoms, including 17 patients with chest pain. Ten patients were in New York Heart Association functional class III or IV. Patients with evidence of cardiomyopathy, congenital or valvular heart disease, recent myocardial infarction, unstable angina, or uncontrolled systemic hypertension were excluded from the study. All patients were in sinus rhythm. Antianginal medications were withdrawn at least 48 hours before the studies. In 28 of the 30 patients (93%), both thallium scintigraphy and transesophageal dobutamine echocardiography were performed within the same week; in the remaining 2 patients, both studies were performed within 1 month. No patient suffered any intervening cardiac events. In 16 patients, thallium scintigraphy was performed before transesophageal dobutamine echocardiography; in the remaining 14 patients, the order was reversed. The study was approved by the National Heart, Lung, and Blood Institute Investigational Review Board, and each patient gave informed written consent for all tests.

Radionuclide Angiography
Gated cardiac blood pool studies were performed to assess left ventricular ejection fraction at rest with red blood cells labeled in vivo with 20 to 25 mCi of 99mTc. Imaging was done with a conventional Anger camera equipped with a high-sensitivity parallel-hole collimator, as previously described.35 The left ventricular ejection fraction was derived by computer analysis of the scintigraphic data. The lower limit of normal for resting ejection fraction by our technique is 45%. In each study patient, rest radionuclide ventriculography showed a left ventricular ejection fraction <45% (mean±SD, 32±9).

Transesophageal Dobutamine Stress Echocardiography
Transesophageal echocardiograms were performed with a Hewlett-Packard biplane (12 patients) or omniplane (18 patients) 5-MHz probe. The studies were performed with patients in the left lateral decubitus position. The oral pharynx was anesthetized with aerosol benzocaine spray. Intravenous sedation with midazolam hydrochloride was administered before introduction of the probe and during the study as needed (total dose of midazolam per patient was 6±3 mg). Heart rate and oxygen saturation were monitored continuously during the study. A 12-lead ECG and measurements of systemic blood pressure were recorded at the end of each stage of the dobutamine protocol while the echocardiographic images were obtained.

Dobutamine was infused starting at 2.5 µg · kg-1 · min-1. After 5 minutes, the dose was increased to 5 µg · kg-1 · min-1. Subsequently, the dose was increased by 5-µg · kg-1 · min-1 increments every 5 minutes to a maximum of 40 µg · kg-1 · min-1. Two-dimensional (2D) views were acquired during the last 2 minutes of each stage. The stress test was stopped when the maximum dose of dobutamine was reached or if severe chest pain, a severe increase in systolic blood pressure (>250 mm Hg), clinically significant arrhythmias, extensive wall motion abnormalities, or intolerance to the probe developed. A fall in blood pressure not accompanied by the development of extensive wall motion abnormalities was not considered a criterion for termination of the test.36 37 Sublingual nitroglycerin, nifedipine, and intravenous propranolol were available.

At baseline and at each stage of the dobutamine infusion, transgastric short-axis and transesophageal long-axis, four- and two-chamber views were obtained following the same sequence in all patients. First, the transgastric short-axis view was obtained at both the papillary muscle and the mitral valve levels. Subsequently, the probe was pulled out to the esophagus, and the long-axis, four-chamber, and two-chamber views were recorded. Immediately after completion of the image acquisition, the dose of dobutamine was increased to the next level, and the probe was gently advanced again across the cardias and into the stomach to start with the transgastric short-axis view during the next stage. The long-axis view was obtained by lateral flexion of the longitudinal probe when the biplane probe was used38 and by rotating the transducer 135° from the horizontal position when the omniplane probe was used.39 During acquisition of the transesophageal views, particular attention was paid to avoid foreshortening of the left ventricular cavity that would result in poor visualization of the apical segments. This was achieved by using the maximum degree of retroflexion of the scope without losing contact with the esophageal wall. In addition, visualization of the apex was ascertained by ensuring that the length of the left ventricular cavity (from the plane of the mitral valve to the apical endocardium) was the same in all transesophageal views (ie, four-chamber, two-chamber, and long axis).

Two-dimensional views were continuously recorded on videotape and digitized on-line with a Nova Microsonics Image Vue system (Nova Microsonics). The system permits creation of a continuous loop of a single cardiac cycle by displaying still frames acquired at regular intervals in a continuous fashion. Twelve sequential frames of each 2D view were captured at 33-millisecond intervals with an ECG R wave–triggered mechanism at baseline and at each dose of dobutamine.

Transesophageal echocardiographic images digitized on-line during the dobutamine stress study were transferred to optical disks for permanent storage and review. Continuous videotape recordings were not routinely used for analysis but were available during the review process. Images were analyzed by two independent observers blinded to the results of the thallium scintigraphy study. In cases of disagreement, the studies were reviewed and a consensus was reached.

At each stage of the dobutamine protocol, the left ventricle was divided into 16 segments following the recommendations of the American Society of Echocardiography.40 Regional myocardial contractile function was graded as normal, hypokinesis, akinesis, or dyskinesis in each myocardial segment; particular attention was paid to systolic wall thickening rather than to endocardial motion.

For the purpose of this study, only segments with wall motion abnormalities during basal conditions were analyzed. For each segment, a positive response to dobutamine was considered an improvement in contractile function of at least one grade, regardless of whether worsening in wall motion developed during later stages of the test. For each segment, the lowest dose of dobutamine that produced an unequivocal improvement in contractile function was determined. In addition, for each myocardial segment with abnormal resting wall motion, the behavior during the increasing doses of dobutamine was analyzed and assigned to one of the following categories: sustained improvement—progressive increase in contractile function throughout the test; biphasic response—initial improvement followed by worsening in contractile function with higher doses of dobutamine; worsening only—basal hypokinesis deteriorating to akinesis with dobutamine without initial improvement (a change from basal akinesis to dyskinesis was not considered in this category41 ); hypokinesis without change—basal hypokinesis without noticeable improvement or worsening during the test; or akinesis without change—basal akinesis (or dyskinesis) without improvement (or with development of dyskinesis) during dobutamine infusion.

Thallium Scintigraphy
After an overnight fast, all patients underwent exercise 201Tl single photon emission computed tomographic study according to a standardized multistage, symptom-limited treadmill exercise test. At peak exercise, 2 to 3 mCi thallium was administered intravenously, and the patient continued to exercise for an additional 45 to 60 seconds. Conventional stress and 3- to 4-hour redistribution images were acquired. Immediately after redistribution, an additional 1-mCi dose of thallium was administered at rest, and reinjection images were acquired 10 to 15 minutes thereafter.17

Thallium studies were analyzed by two independent reviewers who were unaware of the dobutamine echocardiography results. From the raw scintigraphic data, horizontal long-axis, vertical long-axis, and short-axis tomograms were reconstructed. The reconstructed stress, 3- to 4-hour redistribution, and reinjection images were then analyzed semiquantitatively in the basal, mid, and apical short-axis views. The left ventricle was divided into 16 segments matching the segmentation used with echocardiography. The uptake in each myocardial segment for each of the stress, redistribution, and reinjection images was graded on a 5-point scale as follows: 2, normal; 1.5, mildly reduced; 1, moderately reduced; 0.5, severely reduced; and 0, absent.

For the purpose of analysis, a segment was considered to have a reversible defect if the thallium uptake in the stress images was reduced but was increased by at least one grade in the redistribution or reinjection image. If the thallium uptake in the stress images was reduced and did not increase during redistribution or reinjection, the segment was considered to have an irreversible defect. These irreversible defects were then subgrouped on the basis of severity of reduction in tracer activity: mild to moderate (thallium score of 1 or greater) and severe (thallium score of <1) defects. We showed previously that when irreversible thallium defects on redistribution images are subgrouped on the basis of the severity of reduction in thallium activity, mild to moderate irreversible defects were found by positron emission tomography to be metabolically active and viable, whereas regions with severe irreversible thallium defects were shown to be metabolically inactive and hence scarred by positron emission tomography.42 43 Thus, for the purpose of the present study, myocardial regions with normal or mild to moderate reduction in thallium activity were considered viable.

Statistical Analysis
Proportions were compared by {chi}2 or Fisher's exact test as appropriate. A probability value of <.05 was considered significant. All data are expressed as mean±SD.


*    Results
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
*Results
down arrowDiscussion
down arrowReferences
 
Transesophageal Dobutamine Stress Echocardiography
Transesophageal dobutamine stress echocardiograms were completed in all patients without complications. The study was terminated for development of extensive wall motion abnormalities in 12 patients, after completion of the protocol in 11 patients, and because of severe chest pain in the remaining 7 patients. A significant fall in blood pressure associated with extensive wall motion abnormalities was observed in only 1 patient. In no patient was the test stopped because of intolerance to the probe or side effects. The median maximum dose of dobutamine used in each patient was 30 µg · kg-1 · min-1 (range, 10 to 40 µg · kg-1 · min-1).

Of 472 segments available for analysis (average, 15.7 segments per patient), 311 segments (66%) had wall motion abnormalities during basal conditions (134 were hypokinetic; 177 were akinetic or dyskinetic). Fig 1Down shows the distribution of the different types of responses to dobutamine in these 311 segments. Only a minority of segments that were hypokinetic during basal conditions had either no change or worsening only with dobutamine infusion (5% and 7% of all dyssynergic segments at rest, respectively).



View larger version (64K):
[in this window]
[in a new window]
  		Figure 1. Pie chart showing distribution of different types of response to incremental doses of dobutamine in the 311 myocardial segments with resting wall motion abnormalities.

A total of 173 of the 311 segments with resting wall motion abnormalities (56%) showed a contractile improvement with dobutamine (sustained improvement in 63; biphasic response in 110). A positive response to dobutamine was observed more frequently among hypokinetic segments (97 of 134, 72%) than among akinetic (76 of 170, 45%) or dyskinetic (0 of 7) segments (P<.0001).

In the vast majority of segments, the improvement was first detected with the initial three doses of dobutamine (in 148 of the 173 segments with a positive response to dobutamine [86%], the improvement was observed at a dose of 10 µg · kg-1 · min-1 or less). In only 4 segments (1%) was the improvement first detected with a dose higher than 20 µg · kg-1 · min-1 (Fig 2Down).



View larger version (18K):
[in this window]
[in a new window]
  		Figure 2. Bar graph showing dose of dobutamine at which improvement was first detected during incremental infusion in the 311 myocardial segments with resting wall motion abnormalities.

Thallium Scintigraphy
Of the 311 myocardial segments with resting wall motion abnormalities, 262 (84%) had normal or only mild to moderate reduction in thallium activity (score >=1) in at least one stage of the stress-redistribution-reinjection protocol, and 49 (16%) had severely reduced or absent thallium activity (score <1). The range of segmental thallium score was as follows: 28 segments received a score of 0, 21 a score of 0.5, 75 a score of 1, 39 a score of 1.5, and 148 a score of 2.

A total of 110 of the 311 segments (35%) with resting wall motion abnormalities had normal thallium uptake on the stress images. Of the remaining 201 segments with reduced uptake on the stress images, 124 had increased uptake on the redistribution or reinjection images and were therefore considered reversible defects; the other 77 did not have increased thallium uptake on corresponding redistribution or reinjection images and were considered to show irreversible defects.

Relation Between Dobutamine Echocardiography and Thallium Scintigraphy
The number of segments with resting wall motion abnormalities that were considered viable by thallium was significantly greater than the number of segments showing a contractile improvement in response to dobutamine (84% versus 56%, respectively; P<.0001) (Fig 3Down). A significant relation was observed between thallium uptake and response to dobutamine. Among 262 segments considered viable by thallium, 167 (64%) showed contractile improvement with dobutamine; in contrast, only 6 of the 49 segments (12%) considered nonviable by thallium had a positive dobutamine response (Fig 4Down). The rate of agreement between thallium uptake and a positive response to dobutamine was 68% (Fig 5Down); the disagreement between the two tests was related primarily to the finding of segments considered viable by thallium that did not show contractile improvement with dobutamine (95 segments, or 30% of the total number of segments with resting wall motion abnormalities) (Fig 6Down). The latter observation is emphasized by the following analysis: of the 138 myocardial segments without contractile improvement with dobutamine, 95 (69%) had normal or mildly to moderately reduced thallium uptake and were therefore considered viable by this method.



View larger version (22K):
[in this window]
[in a new window]
  		Figure 3. Pie charts comparing the proportion of myocardial regions considered to be viable with thallium scintigraphy (left) and those showing a positive inotropic response to dobutamine (right) among 311 segments with resting wall motion abnormalities.



View larger version (28K):
[in this window]
[in a new window]
  		Figure 4. Pie charts comparing the proportion of myocardial segments with a positive inotropic response to dobutamine in 262 regions considered to be viable by thallium scintigraphy (left) and in 49 regions considered to be nonviable by the same technique (right).



View larger version (65K):
[in this window]
[in a new window]
  		Figure 5. Example of agreement between thallium scintigraphy and dobutamine echocardiography in the assessment of myocardial viability in a 72-year-old patient with two-vessel coronary artery disease and resting ejection fraction of 23%. Left panels show the transesophageal two-dimensional echocardiographic images obtained from the four-chamber view in diastole (left) and at end systole (right) during baseline conditions (top) and during infusion of dobutamine at 15 µg · kg-1 · min -1 (bottom). Right panels show the thallium scans from two consecutive transaxial slices obtained immediately after stress (top), after 3- to 4-hour redistribution (middle), and after reinjection (bottom). Echocardiographic images show severe hypokinesis of the basal septum with akinesis of the apical segments and of the lateral free wall. With dobutamine, the systolic thickening of all affected segments improves significantly. This correlates with normal uptake of thallium in the redistribution and reinjection images. Stress images show reduced thallium uptake in the septum and apex, corresponding to stress-induced myocardial ischemia in these areas.



View larger version (74K):
[in this window]
[in a new window]
  		Figure 6. Example of discordance between thallium scintigraphy and dobutamine echocardiography in a 66-year-old patient with three-vessel coronary artery disease and resting ejection fraction of 26%. Format is the same as in Fig 5Up, except that the images during dobutamine infusion were obtained at a dose of 20 µg · kg-1 · min -1. Basal echocardiographic images show akinesis of the apical septum and the lateral wall with severe hypokinesis of the basal and midwall portions of the interventricular septum. With dobutamine, the systolic thickening of the basal and midwall portions of the septum improves significantly. However, no improvement is seen on the apical septum and on the lateral wall. In contrast, thallium scintigraphy shows stress-induced abnormalities involving the apex, septum, and lateral wall with complete recovery on redistribution and particularly reinjection images.

The finding of a positive inotropic response to dobutamine was significantly related to the magnitude of thallium uptake: the proportion of segments with a positive dobutamine response rose with increasing magnitude of thallium uptake (Fig 7Down). Even among the 77 segments with irreversible thallium defects, the proportion of segments with contractile improvement with dobutamine was related to the magnitude of thallium uptake: 42% (17 of 42) in segments with mildly to moderately reduced thallium uptake compared with 14% (5 of 35) in segments with severely reduced or absent thallium uptake (P<.02).



View larger version (17K):
[in this window]
[in a new window]
  		Figure 7. Bar graph showing the relation between the magnitude of thallium uptake, expressed using a 5-point score from 0 to 2, and the proportion of myocardial segments with positive inotropic response to dobutamine.


*    Discussion
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
up arrowResults
*Discussion
down arrowReferences
 
Relation Between Thallium Scintigraphy and Dobutamine Echocardiography
The results of the present investigation indicate that a relation exists between thallium scintigraphy and dobutamine echocardiography in their ability to detect viable areas of dyssynergic myocardium. Thus, myocardial regions with positive thallium uptake have a significantly greater likelihood of showing a positive inotropic response to dobutamine compared with segments with absent or severely reduced thallium uptake. Importantly, the contractile response to dobutamine is significantly related to the magnitude of thallium uptake, such that the proportion of myocardial segments with contractile improvement in response to dobutamine progressively rises with increasing magnitude of thallium uptake.

At the same time, our findings demonstrate that among regions of the myocardium with reduced contraction at rest, the number of segments with thallium uptake is significantly greater than the number of those capable of increasing their contractile force in response to dobutamine. In our study, 84% of resting dyssynergic segments demonstrated normal or only mild to moderate reduction in thallium activity on the stress-redistribution-reinjection protocol and were therefore considered to be viable by this technique. This conclusion is based on the results of previous studies showing that myocardial segments with normal or mildly to moderately reduced thallium uptake have preserved metabolic activity by positron emission tomography42 43 and a higher likelihood of contractile recovery after revascularization compared with segments demonstrating severe reduction in thallium activity.20 21 In contrast, only 56% of the dyssynergic segments in our study patients showed a positive inotropic response to dobutamine. Such a response to dobutamine has also been shown to correlate with improvement in contractile function after revascularization in patients with chronic left ventricular dysfunction.33 The rate of agreement between thallium scintigraphy and dobutamine echocardiography in our study was 68%. It is important to emphasize that the major discordance between the two techniques (32%) was found primarily in the subgroup of segments with normal or mild to moderate segmental thallium uptake but without inotropic response to dobutamine (30%). In only 6 of the 311 (2%) segments analyzed was the discordance related to the finding of a positive response to dobutamine in segments with severely reduced or absent thallium uptake.

Implications Regarding Myocardial Viability
Taken as a whole, our findings indicate that cell membrane pump integrity has a different sensitivity to the mechanisms that determine myocardial dysfunction compared with the process subserving the contractile response to adrenergic stimulation. Thus, in segments with reduced resting contractile function, the myocardial processes necessary for thallium uptake appear to be less sensitive to the inhibitory effects of chronic coronary stenoses than those needed for a positive response to dobutamine. This is not surprising because transmembrane pump activity must be more critical for the preservation of myocyte viability than the maintenance of contractile function.

From the results of the present investigation, it appears that a spectrum of myocardial dysfunction exists in patients with chronic coronary artery disease. Mild myocardial dysfunction can be characterized as a stage in which basal contractile function is reduced but cellular membrane integrity and the capacity to respond to an inotropic stimulus are both preserved. This stage, observed in 167 of the 311 myocardial segments (54%) with reduced systolic function at baseline, is identified by both thallium uptake and positive inotropic response to dobutamine. A more severe form of systolic dysfunction would be that in which there is reduced basal contractile function with absent response to inotropic stimulation but with preserved membrane integrity. This stage, observed in 95 of 311 dyssynergic myocardial segments (30%) in our study patients, is identified by positive thallium uptake but negative response to dobutamine. The mechanisms responsible for producing these discordant effects on thallium uptake and contractile response to dobutamine cannot be determined from the findings of the present investigation. Possible explanations include a reduction in blood flow insufficient to maintain a positive response to dobutamine but sufficient to maintain transmembrane pump function, a greater extent of myocardial necrosis in these regions compared with those with a positive response to dobutamine, or more frequent episodes of ischemia leading to a more severe form of chronic myocardial "stunning"44 in these regions. Finally, a state of irreversible dysfunction, found in 43 of the 311 dyssynergic segments (14%) in our study, would be that in which both the ability to respond to an inotropic stimulus and the membrane integrity are lost. This is identified by negative thallium uptake and a negative response to dobutamine. The remaining 6 segments (2%) that displayed a positive response to dobutamine in the absence of thallium uptake cannot be explained with this concept and could probably be attributed to the error inherent in the comparison of the two techniques, including poor anatomic correspondence of left ventricular segmentation in some patients.

Limitations
It must be emphasized that in the present investigation, we did not have the opportunity to assess the potential recovery in contractile function after revascularization. Therefore, we cannot ascertain whether the greater proportion of segments with positive thallium uptake compared with those with a positive response to dobutamine truly indicates a higher sensitivity of thallium scintigraphy for detection of viable myocardium than dobutamine echocardiography. However, it was not the purpose of our study to assess the relative merits of thallium scintigraphy and dobutamine echocardiography for the prediction of functional recovery after restoration of blood flow. Instead, we used these techniques to investigate the relation between transmembrane pump integrity and contractile reserve in myocardial regions with chronically depressed systolic function.

It must also be noted that in the present study, we considered only the presence or absence of a positive inotropic response to dobutamine. However, a minority of myocardial segments were hypokinetic (and therefore displayed some degree of systolic thickening) during basal conditions and did not improve their systolic function in response to dobutamine (hypokinesis without change). In addition, other hypokinetic segments showed a worsening-only type of response to dobutamine, compatible with myocardial ischemia. Although these patterns of contraction do not reflect increased inotropism, they probably represent the existence of viable myocardium45 46 and should be considered in assessments of myocardial viability with dobutamine echocardiography. It must be emphasized, however, that these types of responses were observed in only 12% of the dyssynergic segments in our study patients. Such a low prevalence may be explained by the slow increases in dobutamine dose used in our study. It is possible that if higher doses of dobutamine are used initially (eg, 10 µg · kg-1 · min-1), myocardial ischemia may develop before any contractile improvement is detected, thereby increasing the prevalence of segments with hypokinesis without change or with worsening only. Furthermore, the importance of starting with very low doses of dobutamine for detection of the response of dyssynergic segments is emphasized by the observation that in the vast majority of segments, the improvement in response to dobutamine was first detected at a dose of 10 µg · kg-1 · min-1 or lower.

An important aspect of our study is the fact that the response to inotropic stimulation with dobutamine was assessed by transesophageal echocardiography. Although this technique may not be amenable for routine evaluation of all patients with coronary artery disease, it is a highly reliable tool for investigation of myocardial response to dobutamine and other interventions in which an accurate assessment of myocardial function is critical. In a previous study,47 we reported on the safety, feasibility, and diagnostic accuracy of transesophageal dobutamine stress echocardiography in the overall population of patients with known or suspected coronary artery disease. In agreement with the findings of that study and those of other investigations related to the use of transesophageal echocardiography during different forms of stress,48 49 50 51 the technique was well tolerated by all patients, and in no case did the study have to be discontinued because of intolerance to the probe or the occurrence of serious side effects.

Finally, it must be emphasized that the assessment of myocardial viability by both thallium scintigraphy and transesophageal dobutamine echocardiography in our study was based on qualitative criteria. Because both techniques are potentially amenable to quantification, it is important to determine whether a quantitative assessment of wall thickening and thallium uptake might provide a better understanding of the relation between membrane integrity and functional contractile reserve in myocardial regions with resting wall motion abnormalities.

Conclusions
The findings of the present investigation demonstrate that in patients with chronic coronary artery disease and left ventricular dysfunction, a relation exists between thallium uptake and the inotropic response to dobutamine; such a relation is determined by the magnitude of thallium uptake. However, the proportion of segments with preserved thallium uptake is significantly greater than those showing a positive response to dobutamine. These findings emphasize the difference in the mechanisms involved in the identification of myocardial viability by the two techniques and suggest that the cellular processes responsible for a positive inotropic response to adrenergic stimulation require a higher degree of myocyte functional integrity than those responsible for thallium uptake.

Received June 9, 1994; revision received August 12, 1994; accepted September 23, 1994.


*    References
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
up arrowResults
up arrowDiscussion
*References
 

  1. Akins CW, Pohost GM, DeSanctis RW, Block PC. Selection of angina-free patients with severe left ventricular dysfunction for myocardial revascularization. Am J Cardiol. 1980;46:695-700. [Medline] [Order article via Infotrieve]
  2. Rahimtoola SH. The hibernating myocardium. Am Heart J. 1989; 117:211-221.
  3. Braunwald E, Rutherford JD. Reversible ischemic left ventricular dysfunction: evidence for the `hibernating myocardium.' J Am Coll Cardiol. 1986;8:1467-1470. [Medline] [Order article via Infotrieve]
  4. Bolli R. Myocardial `stunning' in man. Circulation. 1992; 86:1671-1691.
  5. Chatterjee K, Swan HJC, Parmley WW, Sustaita H, Marcus H, Matloff J. Depression of left ventricular function due to acute myocardial ischemia and its reversal after aortocoronary saphenous vein bypass. N Engl J Med. 1972;286:1117-1122.
  6. Nesto RW, Cohn LH, Collins JJ, Wynne J, Holman L, Cohn PF. Inotropic contractile reserve: a useful predictor of increased 5-year survival and improved postoperative left ventricular function in patients with coronary artery disease and reduced ejection fraction. Am J Cardiol. 1982;50:39-44. [Medline] [Order article via Infotrieve]
  7. Brundage BH, Massie BM, Botvinick EH. Improved regional ventricular function after successful surgical revascularization. J Am Coll Cardiol. 1984;3:902-908. [Abstract]
  8. Topol EJ, Weiss JL, Guzman PA, Dorsey-Lima S, Blanck JJ, Humphrey LS, Baumgartner WA, Flaherty JT, Reitz BA. Immediate improvement of dysfunctional myocardial segments after coronary revascularization: detection by intraoperative transesophageal echocardiography. J Am Coll Cardiol. 1984;4:1123-1134. [Abstract]
  9. Rankin JS, Newman GE, Muhlbaier LH, Behar VS, Fedor JM, Sabiston DC Jr. The effects of coronary revascularization on left ventricular function in ischemic heart disease. J Thorac Cardiovasc Surg. 1985;90:818-832. [Abstract]
  10. Dilsizian V, Bonow RO, Cannon RO, Tracy CM, Vitale DF, McIntosh CL, Clark RE, Bacharach SL, Green MV. The effect of coronary artery bypass grafting on left ventricular systolic function at rest: evidence for preoperative subclinical myocardial ischemia. Am J Cardiol. 1988;61:1248-1254. [Medline] [Order article via Infotrieve]
  11. van den Berg EK Jr, Popma JJ, Dehmer FJ, Snow FR, Lewis SA, Vetrovec GW, Nixon JV. Reversible segmental left ventricular dysfunction after coronary angioplasty. Circulation. 1990;81:1210-1216. [Abstract/Free Full Text]
  12. Nienaber CA, Brunken RC, Sherman CT, Yeatman LA, Gambhir SS, Krivokapich J, Demer LL, Ratib O, Child JS, Phelps ME, Schelbert HR. Metabolic and functional recovery of ischemic human myocardium after coronary angioplasty. J Am Coll Cardiol. 1991;18:966-978. [Abstract]
  13. Marwick TH, MacIntyre WJ, Lafont A, Nemec JJ, Salcedo EE. Metabolic responses of hibernating and infarcted myocardium to revascularization: a follow-up study of regional perfusion, function, and metabolism. Circulation. 1992;85:1347-1353. [Abstract/Free Full Text]
  14. Dilsizian V, Bonow RO. Current diagnostic techniques of assessing myocardial viability in hibernating and stunned myocardium. Circulation. 1993;87:1-20. [Free Full Text]
  15. Berger BC, Watson DD, Burwell LR, Crosby IK, Wellons HA, Teates CD, Beller GA. Redistribution of thallium at rest in patients with stable and unstable angina and the effect of coronary artery bypass surgery. Circulation. 1979;60:1114-1125. [Free Full Text]
  16. Iskandrian AS, Hakki A, Kane SA, Goel IP, Mundth ED, Hakki A, Segal BL, Amenta A. Rest and redistribution thallium-201 myocardial scintigraphy to predict improvement in left ventricular function after coronary artery bypass grafting. Am J Cardiol. 1983;51:1312-1316. [Medline] [Order article via Infotrieve]
  17. Dilsizian V, Rocco TP, Freedman NMT, Leon MB, Bonow RO. Enhanced detection of ischemic but viable myocardium by the reinjection of thallium after stress-redistribution imaging. N Engl J Med. 1990;323:141-146. [Abstract]
  18. Ohtani H, Tamaki N, Yonekura Y, Mohiuddin IH, Hirata K, Ban T, Konishi J. Value of thallium-201 reinjection after delayed SPECT imaging for predicting reversible ischemia after coronary artery bypass grafting. Am J Cardiol. 1990;66:394-399. [Medline] [Order article via Infotrieve]
  19. Mori T, Minamiji K, Kurogane H, Ogawa K, Yoshida Y. Rest-injected thallium-201 imaging for assessing viability of severe asynergic regions. J Nucl Med. 1991;32:1718-1724. [Abstract/Free Full Text]
  20. Ragosta M, Beller GA, Watson DD, Kaul S, Gimple LW. Quantitative planar rest-redistribution 201Tl imaging in detection of myocardial viability and prediction of improvement in left ventricular function after coronary artery bypass surgery in patients with severely depressed left ventricular function. Circulation. 1993;87:1630-1641. [Abstract/Free Full Text]
  21. Dilsizian V, Perrone-Filardi P, Arrighi JA, Bacharach SL, Quyyumi AA, Freedman NMT, Bonow RO. Concordance and discordance between stress-redistribution-reinjection and rest-redistribution thallium imaging for assessing viable myocardium: comparison with metabolic activity by PET. Circulation. 1993;88:941-952.[Abstract/Free Full Text]
  22. Nienaber CA, de la Roche J, Carnarius H, Montz R. Impact of 201thallium reinjection imaging to identify myocardial viability after vasodilation-redistribution SPECT. J Am Coll Cardiol. 1993;21:283A. Abstract.
  23. Bartenstein P, Hasfeld M, Schober O, Matheja P, Schafers M, Scheld H, Breithardt G. Tl-201 reinjection and improvement of left ventricular function following revascularization. J Nucl Med. 1993;34:45P. Abstract.
  24. Melin JA, Marwick T, Baudhuin T, DeKock M, D'Hondt A, Vanoverschelde JL. Assessment of myocardial viability with thallium-201 imaging and dobutamine echocardiography: a comparative patient analysis. Circulation. 1993;88(suppl I):I-535. Abstract.
  25. Berthe C, Pierard LA, Hiernaux M, Trotteur G, Lempereur P, Carlier J, Kulbertus HE. Predicting the extent and location of coronary artery disease in acute myocardial infarction by echocardiography during dobutamine infusion. Am J Cardiol. 1986;58:1167-1172. [Medline] [Order article via Infotrieve]
  26. Mannering D, Cripps T, Leech G, Mehta N, Valantine H, Gilmour S, Bennett ED. The dobutamine stress test as an alternative to exercise testing after acute myocardial infarction. Br Heart J. 1988;59:521-526. [Abstract/Free Full Text]
  27. Sawada SG, Segar DS, Ryan T, Brown SE, Dohan AM, Williams R, Fineberg NS, Armstrong WF, Feigenbaum H. Echocardiographic detection of coronary artery disease during dobutamine infusion. Circulation. 1991;83:1605-1614. [Abstract/Free Full Text]
  28. Marcovitz PA, Armstrong WF. Accuracy of dobutamine stress echocardiography in detecting coronary artery disease. Am J Cardiol. 1992;69:1269-1273. [Medline] [Order article via Infotrieve]
  29. Martin TW, Seaworth JF, Johns JP, Pupa LE, Condos WR. Comparison of adenosine, dipyridamole, and dobutamine in stress echocardiography. Ann Intern Med. 1992;116:190-196.
  30. Mazeika OK, Nadazdin A, Oakley CM. Dobutamine stress echocardiography for detection and assessment of coronary artery disease. J Am Coll Cardiol. 1992;19:1203-1211. [Abstract]
  31. Barilla F, Gheorghiade M, Alam M, Khaja F, Goldstein S. Low-dose dobutamine in patients with acute myocardial infarction identifies viable but not contractile myocardium and predicts the magnitude of improvement in wall motion abnormalities in response to coronary revascularization. Am Heart J. 1991;122:1522-1531. [Medline] [Order article via Infotrieve]
  32. Smart SC, Sawada S, Ryan T, Segar D, Atherton L, Berkovitz K, Bourdillon PDV, Feigenbaum H. Low-dose dobutamine echocardiography detects reversible dysfunction after thrombolytic therapy of acute myocardial infarction. Circulation. 1993;88:405-415. [Abstract/Free Full Text]
  33. Cigarroa CG, de Filippi CR, Brickner ME, Alvarez LG, Wait MA, Grayburn PA. Dobutamine stress echocardiography identifies hibernating myocardium and predicts recovery of left ventricular function after coronary revascularization. Circulation. 1993;88:430-436. [Abstract/Free Full Text]
  34. Sonnenblick EH, Frishman WH, LeJemtel TH. Dobutamine: a new synthetic cardioactive sympathetic amine. N Engl J Med. 1979; 300:17-22.
  35. Borer JS, Bacharach SL, Green MV, Kent KM, Epstein SE, Johnston GS. Real-time radionuclide cineangiography in the non-invasive evaluation of global and regional left ventricular function at rest and during exercise in patients with coronary artery disease. N Engl J Med. 1977;296:839-844. [Abstract]
  36. Mazeika PK, Nadazdin A, Oakley CM. Clinical significance of abrupt vasodepression during dobutamine stress echocardiography. Am J Cardiol. 1992;69:1484-1486. [Medline] [Order article via Infotrieve]
  37. Marcovitz PA, Bach DS, Mathias W, Shayna V, Armstrong WF. Paradoxic hypotension during dobutamine stress echocardiography: clinical and diagnostic implications. J Am Coll Cardiol. 1993;21:1080-1086. [Abstract]
  38. Seward JS, Khandheria BK, Edwards WD, Oh JK, Freeman WK, Tajik AJ. Biplanar transesophageal echocardiography: anatomic correlations, image orientation, and clinical applications. Mayo Clin Proc. 1990;65:1193-1213. [Medline] [Order article via Infotrieve]
  39. Seward JS, Khandheria BK, Freeman WK, Oh JK, Enriquez-Sarano M, Miller FA, Edwards WD, Tajik AJ. Multiplane transesophageal echocardiography: image orientation, examination technique, anatomic correlations, and clinical applications. Mayo Clin Proc. 1993;68:523-551. [Medline] [Order article via Infotrieve]
  40. Schiller NB, Shah PM, Crawford M, DeMaria A, Devereaux R, Feigenbaum H, Gutgesell H, Reichek N, Sahn D, Schnittger I, Silverman NH, Tajik AJ. Recommendations for quantitation of the left ventricle by two-dimensional echocardiography. J Am Soc Echocardiogr. 1989;2:358-367. [Medline] [Order article via Infotrieve]
  41. Arnese M, Fioretti PM, Cornel JH, Postma-Tjoa J, Reijs AEM, Roelandt JRTC. Akinesis becoming diskinesis during high-dose dobutamine stress echocardiography: a marker of myocardial ischemia or a mechanical phenomenon? Am J Cardiol. 1994;73:896-899. [Medline] [Order article via Infotrieve]
  42. Dilsizian V, Freedman NMT, Bacharach SL, Perrone-Filardi P, Bonow RO. Regional thallium uptake in irreversible defects: the magnitude of change in thallium activity after reinjection distinguishes viable from nonviable myocardium. Circulation. 1992;85:627-634. [Abstract/Free Full Text]
  43. Bonow RO, Dilsizian V, Cuocolo A, Bacharach SL. Identification of viable myocardium in patients with coronary artery disease and left ventricular dysfunction: comparison of thallium scintigraphy with reinjection and PET imaging with 18F-fluorodeoxyglucose. Circulation. 1991;83:26-37. [Abstract/Free Full Text]
  44. Vanoverschelde JJ, Wijns W, Depré C, Essamri E, Heyndrickx GR, Borgers M, Bol A, Melin JA. Mechanisms of chronic regional postischemic dysfunction in humans: new insights from the study of noninfarcted collateral-dependent myocardium. Circulation. 1993;87:1513-1523. [Abstract/Free Full Text]
  45. Perrone-Filardi P, Bacharach SL, Dilsizian V, Maurea S, Frank JA, Bonow RO. Regional left ventricular thickening: relation to regional uptake of 18fluorodeoxyglucose and 201Tl in patients with chronic coronary artery disease and left ventricular dysfunction. Circulation. 1992;86:1125-1137. [Abstract/Free Full Text]
  46. Afridi I, Churchill DA, Hays JT, Zoghbi WA. Dobutamine echocardiography in myocardial hibernation: accuracy for predicting recovery of ventricular function following coronary angioplasty. Circulation. 1993;88(suppl I):I-111. Abstract.
  47. Panza JA, Laurienzo JM, Quyyumi AA, Cannon RO. Transesophageal dobutamine stress echocardiography for evaluation of patients with coronary artery disease. J Am Coll Cardiol. 1994;24:1260-1267. [Abstract]
  48. Lambertz H, Kreis A, Trumper H, Hanrath P. Simultaneous transesophageal atrial pacing and transesophageal two-dimensional echocardiography: a new method of stress echocardiography. J Am Coll Cardiol. 1990;16:1143-1153. [Abstract]
  49. Kamp O, De Cock CC, Funke Kupper AJ, Roos JP, Visser CA. Simultaneous transesophageal two-dimensional echocardiography and atrial pacing for detecting coronary artery disease. Am J Cardiol. 1992;69:1412-1416. [Medline] [Order article via Infotrieve]
  50. Norris LP, Stewart RE, Jain A, Hibner CS, Chaudhuei TK, Zabalgoitia M. Biplane transesophageal pacing echocardiography compared with dipyridamole thallium-201 single-photon emission computed tomography in detecting coronary artery disease. Am Heart J. 1993;126:676-685. [Medline] [Order article via Infotrieve]
  51. Agati L, Renzi M, Sciomer S, Vizza DC, Voci P, Penco M, Fedele F, Dagianti A. Transesophageal dipyridamole echocardiography for diagnosis of coronary artery disease. J Am Coll Cardiol. 1992;19:765-770.[Abstract]



This article has been cited by other articles:


Home page
 Eur J EchocardiogrHome page
R. Sicari, P. Nihoyannopoulos, A. Evangelista, J. Kasprzak, P. Lancellotti, D. Poldermans, J.-U. Voigt, J. L. Zamorano, and on behalf of the European Association of Echocardi
Stress echocardiography expert consensus statement: European Association of Echocardiography (EAE) (a registered branch of the ESC)
Eur J Echocardiogr, July 1, 2008; 9(4): 415 - 437.
[Abstract] [Full Text] [PDF]

Home page
 JNMHome page
A. F.L. Schinkel, D. Poldermans, A. Elhendy, and J. J. Bax
Assessment of Myocardial Viability in Patients with Heart Failure
J. Nucl. Med., July 1, 2007; 48(7): 1135 - 1146.
[Abstract] [Full Text] [PDF]

Home page
 HeartHome page
F Alamanni, A Parolari, A Repossini, E Doria, F Bortone, J Campolo, M Pepi, E Sisillo, M Naliato, R Bigi, et al.
Coronary blood flow, metabolism, and function in dysfunctional viable myocardium before and early after surgical revascularisation
Heart, November 1, 2004; 90(11): 1291 - 1298.
[Abstract] [Full Text] [PDF]

Home page
 J Am Coll CardiolHome page
C. Nelson, J. McCrohon, F. Khafagi, S. Rose, R. Leano, and T. H. Marwick
Impact of scar thickness on the assessment of viability using dobutamine echocardiography and thallium single-photon emission computed tomography: A comparison with contrast-enhanced magnetic resonance imaging
J. Am. Coll. Cardiol., April 7, 2004; 43(7): 1248 - 1256.
[Abstract] [Full Text] [PDF]

Home page
 Eur Heart JHome page
A.F.L Schinkel, J.J Bax, M.L Geleijnse, E Boersma, A Elhendy, J.R.T.C Roelandt, and D Poldermans
Noninvasive evaluation of ischaemic heart disease: myocardial perfusion imaging or stress echocardiography?
Eur. Heart J., May 1, 2003; 24(9): 789 - 800.
[Full Text] [PDF]

Home page
 JNMHome page
A. F.L. Schinkel, J. J. Bax, R. van Domburg, A. Elhendy, R. Valkema, E. C. Vourvouri, F. B. Sozzi, J. R.T.C. Roelandt, and D. Poldermans
Dobutamine-Induced Contractile Reserve in Stunned, Hibernating, and Scarred Myocardium in Patients with Ischemic Cardiomyopathy
J. Nucl. Med., February 1, 2003; 44(2): 127 - 133.
[Abstract] [Full Text] [PDF]

Home page
 HeartHome page
F Beygui, C Le Feuvre, G Helft, C Maunoury, and J P Metzger
Myocardial viability, coronary flow reserve, and in-hospital predictors of late recovery of contractility following successful primary stenting for acute myocardial infarction
Heart, February 1, 2003; 89(2): 179 - 183.
[Abstract] [Full Text] [PDF]

Home page
 CirculationHome page
J. J. Bax, D. Poldermans, A. F. L. Schinkel, E. Boersma, A. Elhendy, A. Maat, R. Valkema, E. P. Krenning, and J. R. T. C. Roelandt
Perfusion and Contractile Reserve in Chronic Dysfunctional Myocardium: Relation to Functional Outcome After Surgical Revascularization
Circulation, September 24, 2002; 106(12_suppl_1): I-14 - I-18.
[Abstract] [Full Text] [PDF]

Home page
 J Am Coll CardiolHome page
F. Beygui, C. Le Feuvre, C. Maunoury, G.e. Helft, and J. P. Metzger
Coronary vasodilator reserve: a clue to the explanation of 201Tl redistribution patterns early after successful primary stenting for acute myocardial infarction
J. Am. Coll. Cardiol., September 4, 2002; 40(5): 877 - 881.
[Abstract] [Full Text] [PDF]

Home page
 JNMHome page
B. B. Chin, G. Esposito, and D. L. Kraitchman
Myocardial Contractile Reserve and Perfusion Defect Severity with Rest and Stress Dobutamine 99mTc-Sestamibi SPECT in Canine Stunning and Subendocardial Infarction
J. Nucl. Med., April 1, 2002; 43(4): 540 - 550.
[Abstract] [Full Text] [PDF]

Home page
 J Am Coll CardiolHome page
M. G. Gunning, R. R. Kaprielian, J. Pepper, D. J. Pennell, M. N. Sheppard, N. J. Severs, K. M. Fox, and S. R. Underwood
The histology of viable and hibernating myocardium in relation to imaging characteristics
J. Am. Coll. Cardiol., February 6, 2002; 39(3): 428 - 435.
[Abstract] [Full Text] [PDF]

Home page