(Circulation. 1996;93:712-719.)
© 1996 American Heart Association, Inc.
Articles |
Abnormal Systolic Intraventricular Flow Velocities After Valve Replacement for Aortic Stenosis
Mechanisms, Predictive Factors, and Prognostic Significance
Presented in part at the 67th Scientific Session of the American Heart Association, Dallas, Tex, November 14-17; and previously published in abstract form (Circulation. 1994;90[pt 2]:I-225).
From the Cardiovascular Center, OLV Hospital, Aalst, Belgium.
Correspondence to Bernard de Bruyne, MD, PhD, Cardiovascular Center, OLV Hospital, Moorselbaan, 164 B-9300 Aalst, Belgium.
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Abstract |
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 Top Abstract IntroductionMethods Results Discussion References |
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Background Dynamic intraventricular flow velocities after valve replacement for aortic stenosis have been associated with high in-hospital morbidity and mortality. The aims of the present study were to determine the mechanisms and preoperative predictors of abnormal flow velocity (AFV) after valve replacement for aortic stenosis and to assess the clinical course of patients with AFV after surgery.
Methods and Results One hundred consecutive patients with pure aortic stenosis were studied prospectively before operation by cardiac catheterization and Doppler echocardiography. After surgery, intraventricular flow was studied by Doppler echocardiography at rest, during nipride infusion, and during dobutamine infusion. AFV (defined as a systolic dagger-shaped Doppler spectrum >2 m/s) occurred in 14 patients at rest and in 27 patients during nipride and/or dobutamine infusion. In most patients, AFV was associated with left ventricular cavity squeezing. Left ventricular end-diastolic diameter, preoperative intraventricular flow velocity and septal-to-posterior wall thickness ratio by Doppler echocardiography, and mean transvalvular pressure gradient and ejection fraction by catheterization emerged as predictors of resting postoperative AFV. Patients with resting AFV had a higher incidence of dyspnea or hypotension (64% versus 21%, P<.01) and a longer hospital stay (13.1±5.8 versus 11.1±2.5, P<.05) than patients without AFV. In contrast, at a 1-year follow-up, no patient with resting AFV died.
Conclusions First, AFV occurs in 14% of patients at rest after valve replacement for aortic stenosis and can be provoked or worsened by ventricular unloading or inotropic stimulation. Second, AFV is related more frequently to cavity squeezing than to systolic anterior motion of the mitral valve apparatus. Third, a typical pattern (small, hyperdynamic, and asymmetrically hypertrophied ventricle) is predictive for postoperative AFV and should be taken into account for the postoperative management. Finally, the presence of AFV at rest is associated with high in-hospital morbidity but good long-term prognosis.
Key Words: blood flow • hypertrophy • inotropic agents • stenosis • valves
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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Since the description of dynamic intraventricular obstruction in hypertrophic obstructive cardiomyopathy,1 intraventricular gradients have been observed in patients with left ventricular concentric hypertrophy secondary to arterial hypertension2 3 4 or aortic stenosis.5 6 7 8 9 10 In addition, intraventricular gradients were seen in the absence of left ventricular hypertrophy when contractility was increased by sympathetic stimulation11 12 13 or during hypovolemic shock14 15 or cardiac tamponade.16 Intracavitary Doppler spectrum with a high maximal velocity in late systole and a leftward concavity of the spectral envelope has been shown to reflect catheter-measured intraventricular gradient.17 An identical flow pattern has been reported in the early postoperative period of patients after valve replacement for aortic stenosis18 19 20 21 22 and has been associated with high in-hospital morbidity and mortality.18 19 21 22 However, these retrospective studies dealt with limited numbers of patients, did not specifically address the preoperative predictive factors and the mechanisms of this abnormal flow pattern, and did not study the long-term prognosis of these patients. Accordingly, we designed a prospective study with the following aims: (1) to determine the pathophysiological mechanisms leading to high intraventricular flow velocities after valve replacement for aortic stenosis, (2) to study which preoperative parameters could predict these abnormal flow velocities, and (3) to assess the clinical course of patients in whom abnormal intraventricular flow dynamics occur after aortic valve replacement.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Patients
The study population consisted of 100 consecutive patients (61 men; mean age, 65±12 years; range, 40 to 77 years) undergoing valve replacement for aortic stenosis. Patients with aortic regurgitation >2/4 (based on echo Doppler data)23 or associated mitral valve replacement were excluded. Eighty-six patients were in sinus rhythm, 12 were in atrial fibrillation, and 2 were permanently paced. There were no complications related to the study protocol.
Preoperative Doppler
Echocardiography
Preoperative Doppler echocardiographic study
was performed within 7 days before operation in standard
cross-sectional views with a commercially available ultrasound
system (Sonos 1000, Hewlett Packard) with a 2.5-MHz imaging transducer.
M-mode measurements were obtained according to the criteria of the
American Society of
Echocardiography.24 Left
ventricular mass was determined with the method of Devereux
et al.25 Mitral valve position index was calculated at the
onset of systole as the ratio of the distance between mitral valve and
posterior wall to mitral valve and interventricular
septum distance.26 Relative wall thickness was computed as
the ratio of twice the posterior wall thickness to left
ventricular end-diastolic
dimension.27 Fractional shortening (in percent) was
determined to be the difference between left ventricular
end-diastolic and end-systolic diameters
divided by left ventricular end-diastolic
diameters. From the two-dimensional image, the left
ventricular outflow tract diameter was measured in
midsystole. The presence or absence of mitral annulus calcification was
noted. Systolic intraventricular velocity
and the location of the highest spectrum under two-dimensional
echographic control from the apical five-chamber view were
recorded by pulsed-wave Doppler by moving the sample volume
from the apex toward the outflow tract.
Cardiac Catheterization
Catheterization of the right and left
ventricles
was performed with the femoral approach by use of standard
fluid-filled catheters. The left ventricle was catheterized by
retrograde technique. Before the left ventricle was entered, the mean
proximal aortic pressure recorded from a pigtail catheter was
superimposed on the femoral arterial pressure from the side
arm of the arterial sheath.28 Cardiac output
was determined by thermodilution method. Aortic valve area was
calculated by the Gorlin formula. Left ventricular ejection
fraction was assessed from the 30° right anterior oblique
projection with the area-length method.29
Coronary artery angiograms were obtained from multiple
projections by the Judkins technique. Significant coronary
artery stenosis was defined as >50% of diameter reduction in
a major epicardial vessel.
Postoperative Doppler
Echocardiography
Within 10 days after operation, Doppler
echocardiography was repeated.
Intraventricular flow velocity measurements were
recorded by high-pulse repetition frequency Doppler (Irex
Meridian) at rest. Then nitroprusside was infused, starting at 1
µg·kg-1·min-1
and increasing by 0.5
µg·kg-1·min-1
every 3 minutes until a decrease in systolic pressure >20 mm
Hg occurred. The intracavitary Doppler spectrum was continuously
monitored and recorded during the last minute of nipride infusion.
After hemodynamic parameters returned to
baseline values, dobutamine was infused at 10, 20, 30, and
40
µg·kg-1·min-1
each stage for 3 minutes. Doppler velocity spectrum was
recorded at the end of the study. The end points for
dobutamine infusion were 85% of maximal predicted heart
rate, side effects, and dynamic intraventricular
velocity associated with clinical symptoms. Prolonged adverse effects
of dobutamine were reversed by intravenous
metroprol. During postoperative Doppler
echocardiography, special attention was paid to the
precise location of maximal velocity, the occurrence of a
systolic anterior motion of the mitral apparatus,
and the presence of cavity squeezing (close apposition of
ventricular walls).
Data Analysis
Abnormal intraventricular flow velocity
(AFV) was defined as a systolic dagger-shaped Doppler
spectrum, with concave acceleration and maximal velocity >2 m/s in the
late systole (Fig 1
). To categorize the location of AFV,
the part of the left ventricle between aortic valve and the tip of the
anterior mitral leaflet in diastole was defined as the
outflow tract. The part below the mitral valve and above the insertion
of papillary muscles was considered the midventricular
portion. In addition to sex and body surface area, the predictive value
of the following preoperative Doppler
echocardiographic parameters for the
occurrence of postoperative AFV was investigated: left
ventricular end-diastolic and
end-systolic diameters, thickness of septum and posterior
wall, the ratio of septal to posterior wall thickness, relative wall
thickness, mitral valve position index, the presence of mitral annular
calcifications, left ventricular outflow tract diameter,
left ventricular mass, fractional shortening, and the
maximal preoperative systolic intracavitary flow velocity. From
catheterization, the predictive value of the following
parameters was studied: mean transvalvular
pressure gradient, aortic valve area, ejection fraction, peak
pulmonary artery pressure, left ventricular
end-diastolic pressure, and pulmonary capillary
wedge pressure. The predictive value of these parameters
was studied for AFV occurring only at rest.
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Statistical Analysis
Results are expressed as mean±SD.
Unpaired and paired
t tests were used to compare appropriate data. Fisher's
exact test was performed for comparison of categorical variables.
One-way ANOVA, followed by Bonferroni's test, was performed for
multiple comparisons. Sensitivity and specificity were calculated as
usual. Multivariate analysis was performed
separately on Doppler echocardiographic and
catheterization data to detect their values in
predicting postoperative AFV. Optimal diagnostic accuracy
level for a given factor was defined as the value of the given factor
at which sensitivity and specificity are equal. A value of
P
.05 was considered significant.
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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All patients underwent both preoperative and postoperative Doppler echocardiographic studies. The latter was performed 7±3 days (range, 2 to 10 days) after valve replacement. After surgery, nipride was given in 93 patients and dobutamine in 96 patients. Three patients did not receive nipride because of persistent hypotension (<100 mm Hg). Four patients received neither nipride nor dobutamine because AFV was present at rest (>3.7 m/s).
Hemodynamics
In the whole population, nipride induced a
decrease in
systolic pressure and an increase in heart rate (Table 1).
Dobutamine infusion increased heart
rate, whereas systolic blood pressure remained unchanged.
Patients with resting AFV had significantly higher heart rates and
lower systolic pressures at baseline and during
dobutamine infusion compared with patients without resting
AFV. A comparison of patients according to the presence or absence of
provoked AFV showed them to be similar with respect to heart rate,
blood pressure during baseline study and nipride infusion, and heart
rate at peak dobutamine infusion. Patients with normal flow
patterns, however, presented on average an increase in
systolic pressure, whereas patients with provoked AFV showed a
decrease in systolic pressure (10±21 versus -5±16 mm
Hg, P=.007).
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Extent, Location, and Mechanisms of AFV
Infusion of both
nipride and dobutamine significantly
increased systolic intraventricular
velocities compared with baseline recordings (Fig 2). After
surgery, resting AFV was found in 14 patients.
Of the 86 patients with normal intraventricular
flow at rest, 14 developed AFV during nitroprusside infusion and 27
patients during dobutamine infusion. Thus, 41 patients
showed AFV either at rest or during infusion of nipride or
dobutamine, and 59 patients demonstrated normal flow
velocities after surgery (Table 2). The magnitude of AFV
provoked by nipride infusion was similar to that seen at rest. AFV
induced (and/or aggravated) by dobutamine infusion was
significantly higher than that occurring at rest or during nipride
infusion (Table 2). In most patients with AFV (34 of 41, 83%),
AFV was
located at midventricular level. In 7 patients (13%),
AFV was found in the left ventricular outflow tract. A
clear systolic anterior motion of the mitral valve
apparatus was observed in 5 of 41 patients (12%). Among
these, 1 had marked posterior mitral annulus calcification, and 4
others had elongated and redundant mitral valve apparatus.
In all other patients, close apposition of ventricular
walls (left ventricular cavity squeezing) was associated
with abnormal flow acceleration.
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Clinical Characteristics and In-Hospital Course
There was a
higher incidence of women among patients with resting
AFV compared with those without resting AFV (77% versus 22%,
P<.001). Patients with AFV had slightly smaller body
surface areas compared with those without AFV (1.71±0.19 versus
1.82±0.18 m2, P=.045). Patients were
similar in terms of age and preoperative symptoms.
Patients with and without resting AFV had similar preoperative values of hemoglobin and hematocrit (13.35±1.2 versus 14.04±1.45 g/dL and 39.5±3.4% versus 41.65±4.3%, respectively; P=NS). After surgery, hemoglobin and hematocrit decreased in both groups to similar levels (11.7±0.9 versus 11.6±2.5 g/dL and 34.4±3.3% versus 35.05±6.1%, respectively; P=NS).
At surgery, 25 patients received a mechanical valve (24 received St Jude valves; 1 received Carbomedics), and 75 received a bioprosthesis. The prosthesis was smaller in patients with dynamic AFV compared with those without AFV (23.5±2.01 versus 24.95±2.08 mm, respectively; P=.007).
Table 3 summarizes the postoperative in-hospital
course of patients after valve replacement for aortic stenosis
according to the absence or presence of resting AFV. One patient
without AFV died within 1 month after surgery. However, patients with
AFV at rest had a markedly higher incidence of symptoms of low cardiac
output than those without abnormal flow dynamics. Among the 14 patients
with AFV at rest, 9 complained of dyspnea and 4 had persistent
hypotension (systolic pressure 100 mm Hg). During the
postoperative period, 1 of these patients had symptoms of
cerebral hypoperfusion with mental alteration. Of the 5 patients with
abnormal flow dynamics but without spontaneous complaints, 3 had
persistent sinus tachycardia >100 beats per minute. In
addition, the duration of hospitalization was longer in patients with
AFV at rest than in those with normal resting flow pattern. In
contrast, the presence of induced AFV was not associated with a
prolonged or complicated postoperative stay.
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Long-term Clinical Follow-up
At a 1-year clinical follow up,
no patient with resting AFV in the
early postoperative period died. Among patients without AFV, 3 died
late after surgery.
Predictive Factors of AFV
Because only the occurrence of
resting AFV was found to be
associated with an unfavorable clinical course, the preoperative data
were analyzed only for their value in predicting resting AFV
(and not provoked AFV). Table 4 gives preoperative and
Doppler echocardiographic and
catheterization parameters of patients
undergoing valve replacement. By multivariate
analysis of the preoperative Doppler
echocardiographic parameters, sex, and body
surface area, left ventricular
end-diastolic diameter (LVEDD), septal to posterior
wall thickness ratio (SPR), and preoperative
intraventricular flow velocity (IVFV) emerged as
independent risk factors for the occurrence of AFV at rest after valve
replacement. An optimized combination of these factors associated with
the occurrence of postoperative AFV was calculated by discriminative
analysis as follows:
y=-0.11LVEDD+1.4IVFV+2.6SPR+1.5. Fig
3 shows the sensitivity and specificity for each value
of these individual factors and their combination for prediction of
postoperative resting AFV. The 95% sensitivity level in the prediction
of postoperative resting AFV (ie, a value associated with a 95%
probability that AFV will occur after surgery) was found for values of
left ventricular end-diastolic diameter
42 mm, intraventricular flow velocity 
1.23 m/s,
septal to posterior wall thickness ratio 1.45, and combination index
1.9
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By multivariate analysis of the catheterization parameters, the mean transvalvular pressure gradient and left ventricular ejection fraction were found to be predictors of postoperative AFV at rest.
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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The present prospective study investigates the occurrence of AFV shortly after valve replacement for aortic stenosis (Fig 4
). The results can be summarized as follows. First, AFV
occurs in 14% of patients after valve replacement. AFV may be provoked
or worsened by inotropic stimulation or left ventricular
unloading. These velocities are related more frequently to left
ventricular midcavity squeezing than to systolic
anterior motion of the mitral valve apparatus. Second, AFV
is associated with high in-hospital morbidity but excellent
long-term survival. Third, preoperative indexes accurately predict
the occurrence of postoperative abnormal ventricular flow
dynamics.
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Previous Studies
Previous case
reports21 22 and retrospective clinical
studies18 19 20 dealing with fewer
patients than this one
have identified patients with abnormal
intraventricular flow dynamics early after valve
replacement for aortic stenosis. These AFVs frequently were
found during the first postoperative week, especially between 3 and 7
days after surgery.20 Laurent et al18 showed
that these high intraventricular velocities can be
induced by left ventricular unloading. It was suggested
that the presence of these velocities is related to some preoperative
characteristics of left ventricular geometry and to
hemodynamic changes induced by valve
replacement.18 19 20 Several studies have
reported on the
association between the presence of these high velocities and severe
hypotension despite adequate left ventricular filling
pressure and normal systolic
function.18 19 21 22
Moreover, in the study of Aurigemma et al,19 5 of 13
patients with such a flow pattern died between the 9th and 94th
postoperative day.
Mechanisms of AFV After Valve Replacement for Aortic
Stenosis
The mechanism of dynamic intraventricular
pressure gradient in the presence of a hypertrophied left ventricle may
include systolic cavity obliteration or outflow tract
obstruction caused by systolic anterior motion of the mitral
valve.2 4 26 30 31 32 33 34
Confirming previous
reports,18 19 20 the present data
emphasize the role of
cavity squeezing rather than systolic anterior motion of the
mitral valve as the fundamental mechanism of AFV after valve
replacement for aortic stenosis. Fig 5
summarizes the presumed mechanisms leading to abnormal flow pattern
after the operation. In patients with aortic stenosis,
afterload is increased and the ventricle is often small and
hypertrophied. Valve replacement induces a dramatic decrease in
afterload that may further decrease left ventricular
volume35 36 and increase fiber
shortening.37 38 The combination of these factors may
lead
to cavity squeezing, which in turn will increase systolic flow
velocities. Inotropic stimulation by increasing myocardial
contractility and vasodilators by further unloading the
left ventricle may worsen these AFVs. These mechanisms appear to be
similar to that seen in hypertensive hypertrophic
cardiomyopathy in the elderly.3 4 In
some patients, especially those with an abnormal mitral
apparatus with elongated chordae, redundant mitral
apparatus, or calcified mitral
annulus,39 40 41 a
systolic anterior motion of the mitral valve
apparatus may contribute to the genesis of AFV. These
morphological abnormalities will cause the protrusion of leaflets into
the outflow tract and their exposure to the drag force of the
flow.42
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Flow Velocities or Pressure Gradient
There is still
considerable debate about the accuracy of
Doppler-derived pressure gradients in streamline or tunnel-like
stenoses compared with catheter-measured
gradients.43 44 45 46 47 48
In an in vitro study, Teirstein et
al43 suggested that Doppler gradients might
significantly underestimate manometer gradients in tunnel-like
stenoses because resistance and acceleration are not taken into
account in the simplified Bernoulli equation. In contrast, in patients
with obstructive cardiomyopathy, Stewart et
al44 found an overestimation of Doppler-derived
pressure gradient compared with invasively measured gradient. Finally,
others reported an excellent correlation between
simultaneously recorded Doppler- and
catheter-measured gradients.45 46 Recent experimental
data suggested that velocities >1 m/s proximal to stenosis
together with pressure recovery distal to the stenosis might
also explain the discrepancy between Doppler-derived and
catheter-measured gradients.47 48
Poststenotic pressure recovery increases in
stenoses with gradually tapered outlets and
inlets.48 In such stenoses, energy losses are less
pronounced because high kinetic energy present in the
stenosis may transform into potential energy.48
Because the Doppler beam determines the maximal velocity in the
vena contracta, ie, at the point at which kinetic energy is the
highest, and manometers assess pressure distal to the stenosis,
the Doppler technique may substantially overestimate net pressure
drop across a gradually tapered stenosis. In the present
study, systolic cavity obliteration observed in most patients
with abnormal flow dynamics creates a gradually tapered rather than an
abrupt stenosis. Thus, high
intraventricular velocities do not necessarily
reflect a pressure drop as calculated by the simplified Bernoulli
equation. Therefore, the term "abnormal flow velocity" appears to
describe this abnormal ventricular dynamic more
accurately than the term "intraventricular
pressure gradient."
Prognostic Significance of
Intraventricular AFVs
The present study confirms that the in-hospital
course of
patients with AFV at rest after valve replacement is characterized by
higher morbidity and longer hospital stays.17 18 In
contrast to the study by Aurigemma et al,19 we did not
observe a higher in-hospital mortality. Furthermore, in patients
developing AFV only during pharmacological provocation, neither
morbidity nor mortality was found to be different than in patients
without AFV. Although they have higher in-hospital morbidity,
patients with AFV at rest have an excellent long-term prognosis.
Similar abnormal flow dynamics were reported recently in patients with
small aortic prostheses in the late postoperative
period.49 A late systolic increase in velocity of
the flow toward the apex in the isovolumic relaxation period associated
with dagger-shaped systolic Doppler spectrum was seen
in 56% of 25 patients during exercise.49 However, these
patients were not different from others with respect to symptomatology
or exercise capacity. The authors suggested that such flow dynamics
late after surgery are probably a marker of impaired
diastolic function.
Predictive Factors of Postoperative AFVs
The present study
confirms in a large number of consecutive
patients with aortic stenosis that the occurrence of
postoperative AFV can be predicted with a high degree of accuracy from
simple measurements of left ventricular geometry and
function.18 19 An inverse correlation was found
between
the occurrence of AFV and preoperative left ventricular
end-diastolic diameter (Fig 4
). A direct relationship
was found between the occurrence of AFV and the preoperative
intraventricular velocity, the septal to posterior
wall thickness ratio, the ejection fraction, the
transvalvular pressure gradient, and an index combining the
three echocardiographic parameters. These
data suggest that small, hyperdynamic, and asymmetrically hypertrophied
left ventricles are prone to develop AFV after the dramatic afterload
reduction induced by aortic valve replacement. More relevant from a
clinical viewpoint, these data identify the values of these risk
factors that almost certainly predict the occurrence of postoperative
AFV. In patients with aortic stenosis, these values can be used
preoperatively to predict those patients at risk for
hemodynamic compromise after aortic valve
replacement.
All patients with AFV at rest were older than 60 years of age, and the vast majority were women. Multivariate analysis, however, did not show female sex to be a risk factor for AFV at rest. Nevertheless, the strong univariate association of female sex with AFV supports a recent report on the sex difference in left ventricular function and hypertrophy in response to pressure overload caused by aortic stenosis in elderly patients.50 In contrast to men, women showed supernormal ejection performance and small, thick-walled left ventricles.51 In addition, a lower survival rate has been reported in women with such left ventricular pattern after valve replacement than in men with similar findings.51
Clinical Implications
The present study has several potential
clinical implications.
First, in the early postoperative days after aortic valve replacement
for aortic stenosis, the presence of risk factors for
postoperative AFV should encourage the physician to maintain volume
loading as high as possible and to avoid inotropic agents or systemic
vasodilators to force the ventricle to work at a high level of its
Starling curve and to maintain stroke volume without cavity squeezing.
Second, because AFV occurs most often at midcavity level rather than in
the left ventricular outflow tract, septal myectomy should
not be proposed even in the case of risk factors for developing
postoperative AFV. In a previous study by Aurigemma et
al,19 3 patients underwent myectomy in addition to valve
replacement. Nevertheless, they all showed AFV after surgery. Two of
them died, and one had a complicated in-hospital course. Third, the
presence of AFV should be strongly considered after aortic valve
replacement when a low cardiac output state occurs in a patient with a
preoperative normal left ventricular function and marked
hypertrophy. Careful Doppler
echocardiographic examination should be carried out,
with special attention paid to turbulent flow in the midcavity or left
ventricular outflow tract. Because image quality in the
postoperative phase is often poor, a transesophageal
approach could be helpful. Volume loading and administration of
ß-blockers should be considered in the case of AFV with
hemodynamic consequences.
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Acknowledgments |
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Dr Bartunek was a recipient of a fellowship from the European Communities (Programme for Scientific Cooperation With Central and East European Countries). We are grateful to Josefa Cano for her excellent secretarial help.
Received July 5, 1995; revision received September 13, 1995; accepted September 25, 1995.
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