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(Circulation. 2001;103:1492.)
© 2001 American Heart Association, Inc.
Brief Rapid Communications |
From the Department of Medicine, Section of Cardiology, Baylor College of Medicine, Houston, Tex.
Correspondence and reprint requests to Sherif F. Nagueh, MD, Section of Cardiology, 6550 Fannin St, SM-1246, Houston, TX 77030-2717. E-mail sherifn{at}bcm.tmc.edu
| Abstract |
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Methods and ResultsThe LV size, function, and outflow tract gradient of 26 HOCM patients (53±15 years old) who underwent NSRT were assessed by echocardiography at baseline and 1 and 2 years after the procedure. LVH was evaluated by wall thickness of individual myocardial segments, planimetered myocardial area, and mass. The outflow gradient decreased from 36±6 mm Hg before NSRT to 0±3 mm Hg at 2 years (P<0.001), with patients experiencing symptomatic improvement (P<0.05). LV end-diastolic and end-systolic dimensions increased significantly at both 1 and 2 years (P<0.001). All parameters of LVH showed evidence of regression. LV mass decreased (301±78 g at baseline, 223±5 g at 1 year, and 190±58 g at 2 years; P<0.01), with the 2-year reduction in mass related to infarct size and the acute reduction in outflow tract gradient (r=0.48, P<0.05 and r=0.63, P<0.01, respectively).
ConclusionsNSRT results in LV remodeling that is characterized by an increase in LV size and a decrease in the extent of LVH.
Key Words: hypertrophy cardiomyopathy remodeling
| Introduction |
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| Methods |
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40 mm Hg at rest or
60 mm Hg on
dobutamine provocation: mean dose 15±3 µg ·
kg-1 ·
min-1) who underwent NSRT, as previously
described,10 and completed a
2-year follow-up composed the study cohort. The group had a mean age of
53±15 years (9 of 26 women). All patients had a septal wall thickness
1.5 cm with a
1.3 ratio of septum to posterior wall thickness. All
had dyspnea, 17 had angina, and 12 suffered from
presyncope/syncope. Patients completed an NYHA classification questionnaire as well as a Bruce protocol stress test at baseline and 1 and 2 years after the NSRT procedure. Creatine kinase (CK) levels were determined before and every 6 hours during the 24-hour period after NSRT.
Echocardiographic
Studies
Echocardiograms were performed with an HP or Acuson
ultrasound imaging system equipped with 2.5-, 3.5-, and 5-MHz
transducers. Standard parasternal and apical views were obtained.
Short-axis tomograms were acquired at 3 levels: mitral valve, papillary
muscle, and apex.
Color-guided continuous-wave Doppler was applied in the apical views to determine the peak LVOT gradient, with care taken to avoid contamination with the mitral regurgitation jet.11 Studies were stored for later analysis.
Echocardiographic
Analysis
Using a computerized reading station offline, a
single observer blinded to the patients identity, clinical data, and
study sequence performed all measurements at baseline and 1 and 2 years
after NSRT.
LV minor and major dimensions at end diastole and end systole, wall thickness, end-diastolic volume (EDV), and ejection fraction (EF) were measured according to American Society of Echocardiography recommendations.12 Left atrial volume was derived with the multiple-disks method.13
LVH was assessed according to previously published criteria.12 14 First, the wall thickness of each of the following myocardial segments was measured at both the mitral valve and the papillary muscle levels in the short-axis view14 : anterior septum, anterior lateral, inferior lateral, and inferior septum. Subsequently, the total wall thickness score was calculated at both levels.14 Second, end-diastolic myocardial areas at the mitral, papillary muscle, and apical levels recorded in the parasternal short-axis views were planimetered. Third, LV mass and mass indexed to body surface area were calculated.12 The end-diastolic myocardial area at the papillary muscle level was used to derive mass.
Because NSRT results in an infarction limited to the anterior septum basal segment that does not extend to the papillary muscle level, this approach would tend to underestimate the overall extent of regression in LVH. A good correlation was present between total myocardial area and mass at baseline and at 1 and 2 years (r=0.8, 0.86, and 0.89, respectively, all P<0.01).
Reproducibility
For intraobserver variability (12 patients
analyzed), the 95% interval of agreement was -5% to 7% for
segmental wall thickness, -8% to 10% for total thickness score,
-11% to 14% for myocardial area, and -12% to 14% for
mass.
SPECT Myocardial
Scintigraphy
Stress single photon emission CT (SPECT) imaging 6
weeks after NSRT was used to determine infarct size and was performed
by previously reported
methods,10 with images
reconstructed and reoriented in standard views. Experienced nuclear
cardiologists, blinded to all other data and using raw polar maps
statistically compared with a corresponding normal data bank,
determined the SPECT defect size.
Statistics
Repeated measures of ANOVA or ANOVA on ranks were
applied to evaluate changes in clinical and
echocardiographic parameters at the 3 time
points. Bonferroni t or
Student-Newman-Keuls tests were used for all paired comparisons. The
relation between changes in mass, infarct size, and acute reduction in
LVOT gradient was evaluated by simple linear regression
analysis. The study had >80% power to detect a 20% change in
LVH. Statistical significance was declared if
P
0.05.
| Results |
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Changes in LV Size and EF
Although the long-axis dimension was unchanged, LV
end-diastolic dimensions (anteroposterior and mediolateral)
increased significantly after NSRT
(Table 1
). Likewise, the minor-axis end-systolic
dimensions increased (P<0.01),
leading to significant increases in EDV
(Figure 1A
) and end-systolic volumes
(P<0.01). LVEF was relatively
unchanged; however, EF at year 2 was statistically lower
(P<0.05).
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Regression of LVH
Septal thickness at the infarction site decreased from
20 mm before to 12 mm at 1 year
(P<0.01) and 10 mm at 2
years (P<0.01 versus baseline,
P>0.05 versus 1 year), and all
parameters of LVH showed evidence of regression. The
anterior septum thickness (distal to infarction site), inferolateral
wall, inferior septum, and anterolateral wall at both the
mitral valve and papillary muscle levels were significantly less both 1
and 2 years after NSRT
(Table 2
). A number of segments became significantly
thinner, and the total wall thickness score at both levels continued to
decrease
(Figure 1B
and 1C
) up to 2 years after NSRT.
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Similarly, the myocardial area at the mitral, papillary muscle, and apical levels was significantly smaller after NSRT (P<0.01).
LV mass also continued to decrease through the 2-year
follow-up
(Figure 1D
); likewise, mass corrected for body surface area
decreased significantly
(P<0.001). This latter change
was greater in year 1 than in year 2 (median values 38 versus 11
g/m2;
P<0.05). The incidence of
complete heart block was distributed equally between patients having
LVH regression
20% or <20%.
Determinants of LVH Regression
Significant but weak correlations were present
between the reduction in LV mass at 2 years and the infarct size as
assessed by both CK (r=0.48,
P=0.05) and SPECT imaging
(r=0.4,
P=0.05). This weak correlation
was due to several large infarcts and big gradient reductions when we
initially performed the procedure and to our later ability to reach
successful hemodynamic results despite smaller infarcts
by targeting ethanol delivery to the culprit septal segments using
myocardial contrast echocardiography. The strongest
relation was evident with the acute reduction of LVOT gradient at the
time of the procedure (r=0.63,
P=0.01;
Figure 2
).
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On multiple regression analysis, CK leak and the acute reduction in gradient accounted for 52% of the variance in LV mass reduction (r=0.72, R2=0.52, P<0.001).
| Discussion |
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Implications for the Pathogenesis of
HOCM
LVH in HOCM is believed to be a compensatory process
secondary to the decreased contractility induced by the
mutation that leads to increased ventricular pressure and
stress, which induces
hypertrophy,16
which is further enhanced by
obstruction.17 Results of
the present study show the association of LVH regression with the
elimination of obstruction, confirming the notion that
hypertrophy may be a secondary
phenomenon.
Implications for Treatment
In our study cohort, NSRT essentially eliminated the
LVOT gradient and was associated with marked reduction in symptoms and
improved exercise tolerance. These long-term beneficial results are
similar to those achieved with
surgery.5 6 NSRT
also resulted in regression of LVH, which may be another beneficial
effect, given that the frequency of sudden death in HOCM patients
increases with increased
LVH.4 Regression of LVH may
also contribute to symptomatic improvement and is probably
related to the fact that the increasing hypertrophy in
patients with obstruction contributes to a decrease in LV compliance
and impaired exercise tolerance. The resultant septal infarction of
NSRT, however, may predispose patients to ventricular
dysrhythmias and potentially offset the benefit of LVH regression.
Clearly, more prospective data are needed, because the number of
patients followed up, despite no occurrence of sudden death over 2
years, is too small to determine the impact of NSRT on
ventricular dysrhythmias. Also, when counseling HOCM
patients regarding this procedure, serious complications of NSRT noted
by others and ourselves should be considered. Side effects observed in
our later experience, but not in the present group, include left
anterior descending coronary artery dissection (6 patients,
3.2%), death (3 patients, 1.6%), and sustained
ventricular tachycardia (1 patient, 0.5%, not
on ß-blockers).
Although complete heart block developed in 7 patients (27%), including 4 with CK >2500 U/L, after we modified our technique, the incidence of heart block in the subsequent 162 HOCM patients decreased to 8.6%. Our modifications included injecting ethanol at a slower rate (1 to 1.5 mL/min instead of bolus) and using intracoronary myocardial contrast echocardiography to help target ethanol to the culprit septal segments. This latter incidence (8.6%) of complete heart block after NSRT is close to the 5% to 7% rate reported after surgery.
| Acknowledgments |
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| Footnotes |
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Received December 31, 2000; revision received January 18, 2001; accepted January 18, 2001.
| References |
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