(Circulation. 1999;100:II-1.)
© 1999 American Heart Association, Inc.
Surgery for Valvular Heart Disease |
Valve Replacement for Aortic Stenosis in Patients With Poor Left Ventricular Function
Comparison of Early Changes With Stented and Stentless Valves
From the Clinical Trials and Evaluation Unit (J.C., M.F.), the Department of Echocardiography (M.H., D.G.G.), and the Department of Cardiac Surgery (J.R.P.), Royal Brompton Hospital and National Heart and Lung Institute, London, UK.
Correspondence to Julian Collinson, Clinical Trials and Evaluation Unit, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK. E-mail j.collinson{at}rbh.nthames.nhs.uk
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Abstract |
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Background—Long-standing aortic stenosis causes significant left ventricular (LV) dysfunction, which may progress irreversibly. In many cases, LV function can be salvaged by aortic valve surgery, although debate exists regarding the best valve prosthesis to use.
Methods and Results—We studied 33 patients retrospectively who had significant aortic stenosis and impaired LV systolic function, as assessed by transthoracic Doppler echocardiography. Patients were assessed preoperatively and before discharge from the hospital. A total of 20 patients received a stentless (homograft or Toronto) valve, and 13, a stented valve. No patient had significant aortic regurgitation or other valvular disease. Preoperatively, fractional shortening was 18.8±5.5% in the stentless group and 18.6±3.8% in the stented group. Postoperatively, it was 25.6±6.9% (P<0.001 compared with baseline) and 17.0±2.8%, respectively (P<0.001 compared with stentless group). Fractional shortening improved because of a reduction in LV end-systolic and end-diastolic dimensions in the stentless group. Systolic long axis function at the LV free wall also recovered, with an increase in systolic excursion and both peak shortening and lengthening rates. No change was noted in mitral valve Doppler patterns.
Conclusions—Patients who received a stentless valve demonstrated a significantly greater early improvement in LV systolic function compared with those who received a stented valve.
Key Words: echocardiography • valves • stenosis • surgery
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Introduction |
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Increased left ventricular wall tension due to aortic stenosis may lead to left ventricular dilatation and heart failure1 ; the prognosis for such patients is extremely poor if valve replacement is not performed.2 3 Severe ventricular impairment is not in itself a contraindication to surgery, despite the increased intraoperative mortality, because the outcome of survivors is greatly improved.4 5 Echocardiography is used to measure the transvalvular pressure drop, but in patients with a failing ventricle, the measured gradient alone may underestimate the severity of the stenosis6 7 ; measurements based on the continuity equation may be more useful in estimating severity in these cases.
For patients with heart failure and aortic stenosis, valve replacement can result in rapid clinical improvement.8 However, the increased pressure drop across stented valves, both metallic valves and tissue, and the concomitant increase in ventricular wall stress may delay improvement in ventricular function after replacement.
Our hypothesis was that stentless biological valves (homograft and the Toronto stentless porcine valve), with a lower pressure drop, may allow more rapid improvement in ventricular function, which may be of clinical importance in the early postoperative period.
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Methods |
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We retrospectively compared early changes in echocardiographic measurements of left ventricular function in patients who received stented valves and those who received stentless valves. Patients who underwent aortic valve replacement for aortic stenosis between January 1, 1992, and December 31, 1997, were eligible for inclusion in the study.
The other inclusion criteria were as follows:
1. Isolated aortic valve surgery required for significant valve stenosis, as assessed by Doppler echocardiography
2. Poor left ventricular systolic function, with an end-diastolic dimension >60 mm and fractional shortening <25%
3. Availability of complete pre- and postoperative echocardiographic studies
Patients were excluded if they were undergoing a reoperation for aortic valve surgery or any additional procedure (ie, coronary artery bypass grafting, other valvular interventions). At the time of examination, all patients were in sinus rhythm. Patient results were compared with those from 21 normal subjects (mean age, 58±11 years) who had no evidence of cardiac, pulmonary, or systemic disease.
All patients had calcific aortic stenosis. Thus, we do not know whether individual patients had a bicuspid valve. Patients underwent postoperative echocardiography at a median of 5 days after the operation (range, 3 to 7 days). At this time, patients were mobile and were on no intravenous medication (other than heparin).
All patients underwent preoperative and predischarge transthoracic echocardiography to assess peak transvalvular gradients, left ventricular end-systolic and end-diastolic dimensions, and fractional shortening. A subgroup of the patients had left ventricular free wall and septal long axis function assessed.
Echocardiographic Technique
Doppler echocardiographic examination was
performed using a Hewlett-Packard echograph, model 77020 A Sonos 1500,
interfaced to a 2.5-MHz phased-array transducer. Two-dimensional guided
M-modes were obtained while the patient was lying in the semilateral
position; simultaneous ECG and phonocardiogram were also
obtained. Standard M-mode echograms of the left ventricular
minor axis were obtained with the cursor by the tips of the mitral
valve leaflets. From the apical 4-chamber view, we also recorded
M-modes of the ventricular long axes,
represented by mitral ring motion.9 The cursor
was positioned at the left and septal sites of the ring. Transmitral
forward flow velocities were obtained using the same transducer in the
pulsed-wave Doppler mode, with the sample volume at the tips of the
mitral valve leaflets, from the apical 4 chamber view.
M-modes of the left ventricular minor and long axes and Doppler traces were recorded separately on a strip-chart recorder at a paper speed of 100 mm. All M-mode traces were digitized and analyzed using a dedicated computer program.10
Minor Axis
Left ventricular end-diastolic
dimensions were measured using leading-edge methodology at the onset of
the Q wave of the ECG and the end-systolic dimension at the
onset of the first high-frequency component of the second heart sound
of the phonocardiogram (A2). Fractional shortening was calculated as
the percentage of systolic decrease in the minor axis divided
by end-diastolic dimension. Ejection fraction was
calculated using the "cubed" formula: [(end-diastolic
dimension)3/(end-systolic
dimension)3]/(end-diastolic
dimension)3. Left ventricular mass
was calculated using the Penn convention method: left
ventricular mass=1.04x[(end-diastolic
dimension+posterior wall thickness in
diastole+interventricular septal thickness in
diastole)3-(end-diastolic
dimension)3]-13.6 g. From the digitized
traces, we measured the peak rates of minor axis shortening and
lengthening.
Long Axis
Two long axis sites were measured: the left
ventricular free wall and septum. Systolic
long axis excursion was taken as the amplitude of ring movement between
the outermost point at the time of the Q wave (end
diastole) to the innermost point at A2 (end systole). Peak
shortening and lengthening rates were measured from the digitized
traces.
Operative Technique
Under general anesthesia, cardiopulmonary
bypass was routinely established through a medial sternal approach.
Stentless porcine valves and aortic homografts were implanted through
an oblique aortotomy, using a free-sewn technique and double suture
lines. Mechanical or stented valves were selected at the choice of the
operating surgeon and implanted by an interrupted single suture
line.
Statistical Analysis
Values are expressed as mean±SD. Measurements in patients were
compared with those in controls using the unpaired Student’s
t test. Pre- and postoperative values within the patient
groups were compared using a paired t test. A 5%
probability was considered significant.
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Results |
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Patients
A total of 332 aortic valve replacements for aortic stenosis were performed at our institution during this time; 33 (10%) of them (20 stentless and 13 stented) fulfilled the eligibility criteria of the study. Exclusion criteria were as follows: left ventricle fractional shortening >25% or left ventricle not dilated (n=281), atrial fibrillation occurred when assessed (n=12), and no postoperative echocardiogram was available (n=6). The mean age of the patients was 63.5±11 years; 29 (88%) were male. None of the patients had a history of coronary artery disease. No perioperative deaths, myocardial infarctions, or other significant perioperative events occurred in either group of patients. The type of valve substitute used was determined by the operating surgeon; details are shown in Table 1
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Clinical Data
The mean age of the stentless group was 63.5±10.9 years; in the
stented group, it was 66.5±13.9 years. A total of 12 patients (92%)
in the stented group and 17 (85%) in the stentless group were male. No
patient in either group had more than mild aortic
regurgitation. Preoperative aortic pressure drop was
not different in the 2 groups; it was 72±19 and 67±14 mm Hg in
the stentless and stented groups, respectively. Postoperatively, the
aortic gradient was 12±6 mm Hg in the stentless group and
38±10 mm Hg in the stented group (P<0.001 for
difference between groups). No differences in cardiac medications taken
by the patients existed preoperatively. Postoperatively, those
receiving a mechanical valve took anticoagulants. No patient was taking
an angiotensin-converting enzyme (ACE)
inhibitor at the time of either assessment.
Minor Axis
Left ventricular minor axis dimensions at
end-diastole and end-systole were increased at baseline,
and fractional shortening was reduced when patients were compared with
controls. These values did not differ between the groups (Table 2). Postoperatively, patients receiving a
stentless valve showed a significant decrease in mean
end-systolic dimension, from 53±6 to 41±7 mm
(P<0.001), and in end-diastolic dimension, from
65±7 to 55±6 mm (P<0.001). Fractional shortening
increased from 19±6% to 26±7% in this group of patients (Figure 1); at 5 days, it did not differ
significantly from controls. In contrast, no statistically significant
change was seen in left ventricular dimensions or
fractional shortening in the stented group (preoperative and
postoperative values for fractional shortening were 19±4% and
17±3%, respectively). Postoperatively, fractional shortening was
significantly higher in the stentless group than the stented group
(P<0.001 for the comparison). The improvement in fractional
shortening was reflected in the calculated ejection fraction; in the
stentless group, it increased from 45±10% to 57±12%
(P<0.001). No significant change occurred in the stented
group. Left ventricular mass fell from 338±72 to 265±64 g
(P<0.001) in the stentless group, but no significant change
occurred in the stented group (329±51 g preoperatively and 304±68 g
postoperatively). No significant difference in mitral Doppler was
seen in either early (E) or late (A) diastolic filling
velocities or the E/A ratio.
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Long Axis
Pre- and postoperative assessments were performed in 9 patients in
the stentless group and 10 in the stented group. Preoperative left
ventricular free wall and septal excursion, peak
shortening, and peak lengthening were reduced compared with normal
values (Table 3). Postoperatively, no
change occurred in septal values for either group, but left
ventricular free wall excursion and shortening and
lengthening velocities all increased toward normal only in the
stentless group (Figure 2). No
significant changes occurred in any of the long axis values in the
group receiving stented valves.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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We studied a group of patients with aortic stenosis and severely impaired systolic function in the absence of coronary artery disease. These patients represent
10% of all operations for aortic stenosis. Despite similar
preoperative values, left ventricular dimensions had
decreased after an average of 5 days postoperatively, but only in
patients receiving a stentless valve. A corresponding increase occurred
in left ventricular systolic fractional shortening
and ejection fraction to values approximating the normal range. E/A
ratio and transmitral flow velocities in early and late
diastole did not alter.
Left ventricular dilatation and dysfunction are often the
result of long-term aortic stenosis. Aortic valve
replacement can result in an improvement in ventricular
function, even in patients with severe heart failure,11 12
despite a rate of operative mortality of 
10%.13 14
Stentless valves have a beneficial early effect on
hemodynamic indices because of their low
profile.15 More recently, a 6-month follow-up of patients
(with either preoperative aortic stenosis or
regurgitation) receiving the stentless Toronto
valve demonstrated an improvement in fractional shortening that was not
seen in patients with stented valves.16 Whether these
results reflect any changes in clinical outcome is unclear.
A marked reversibility of preoperative left ventricular dysfunction was seen in our study. Therefore, it seems that there may be a subgroup of patients for whom left ventricular dilatation and dysfunction may be rapidly reversible. Improved recovery of function in patients receiving stentless valves compared with those receiving stented valves may occur because ventricular function in these patients is particularly sensitive to even mild obstructive gradients. Thus, a pressure drop of just 30 mm Hg developed by normally functioning mechanical valves (or stented valves) may be enough to delay recovery. The lower afterload associated with stentless valves reduces wall stress, allowing recovery of ventricular function. In our other studies, seemingly long-term deterioration in ventricular function could be reversed by altering the afterload with ACE inhibitors or successful peripheral vascular reconstruction.17 18 ACE inhibitors cause a decrease in afterload that is associated with recovery of left ventricular dimensions and symptomatic improvement.
The left ventricular dysfunction seen in our patients contained a component that promptly reverted toward normal after aortic valve replacement with a stentless valve. The short time interval involved suggests that this change was the direct effect of a reduction in outflow tract resistance rather than remodeling. The extent of this early change will likely correlate with the degree to which resistance falls, and it is thus greater with a stentless prosthesis. We conclude that the left ventricle, although poorly functioning, can still rapidly improve in function shortly after alleviating outflow tract resistance in patients with aortic stenosis.
The present study is limited by being retrospective, nonrandomized, and having a relatively small sample size. A few patients with poor left ventricular function were excluded because a postoperative echocardiogram was not available.
We hypothesized that the use of stentless valves in patients with aortic stenosis and markedly reduced ventricular function may result in more rapid recovery of function compared with similar patients receiving a stentless valve. Larger prospective studies with longer term follow-up are required to determine whether these early changes improve clinical outcomes.
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