(Circulation. 1999;100:II-6.)
© 1999 American Heart Association, Inc.
Surgery for Valvular Heart Disease |
Prospectively Randomized Evaluation of Stentless Versus Conventional Biological Aortic Valves
Impact on Early Regression of Left Ventricular Hypertrophy
From University Leipzig, Heartcenter, Department of Cardiac Surgery, Leipzig, Germany.
Correspondence to Dr Thomas Walther, Universität Leipzig, Herzzentrum, Klinik für Herzchirurgie, Russenstrasse 19, 04289 Leipzig, Germany. E-mail walt{at}medizin.uni-leipzig.de
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Abstract |
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Background—The aim of this prospectively randomized study was to evaluate left ventricular hypertrophy and its regression after stentless versus conventional biological aortic valve replacement.
Methods and Results—From March 1996 through April 1998, 180 patients were prospectively selected; 106 patients received a stentless aortic valve (SAV), and 74 received a conventional stented bioprosthesis (CSB). Of these patients, 95% and 96%, respectively, had aortic stenosis. Their mean age was 72.3 and 74.8 years, and there were no significant differences in left ventricular function, preoperative pressure gradients, and NYHA functional status. Aortic annulus diameter indexes were comparable at 13.46 (SAV) versus 13.55 (CSB) mm (P=NS). Larger SAVs were implanted because of the oversizing technique. In-hospital mortality (n=3 and 1 for SAV and CSB) was not valve related. At follow-up, all patients were in NYHA class 1 or 2. Baseline end-diastolic left ventricular posterior wall thickness was 15.6 (SAV) and 14.8(CSB) mm (P=NS) and decreased to 11.8 (SAV) and 13.2 (CSB) mm (P<0.05) at 6 months. Left ventricular mass index was 213 and 202 g/m2 at baseline (P=NS), whereas after 6 months, it was 141 (SAV) and 170 (CSB) g/m2 (P<0.05).
Conclusions—Regression of left ventricular hypertrophy occurs in all patients after aortic valve replacement but is significantly enhanced after SAV implantation. This possibly is due to improved transvalvular hemodynamics.
Key Words: valves • echocardiography • hypertrophy • stentless bioprosthesis
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Introduction |
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In patients with aortic stenosis, left ventricular hypertrophy (LVH) develops as an adaptation to the increased pressure load. Being an independent cardiac risk factor, LVH is associated with a higher incidence of cardiovascular clinical events and death.1 Regression of LVH occurs after aortic valve replacement (AVR), but little is known about the impact of the type of prosthetic aortic valve implanted. None of the currently available artificial heart valves provides all functional properties of the native valve.2 3 Nevertheless, in addition to conventional stented bioprostheses (CSBs), stentless aortic valves (SAVs) have been used increasingly with good functional and hemodynamic results during the past 10 years.4 5 6 7 8 In longitudinal studies, early LVH regression after stentless valve implantation has been demonstrated.9 10 However, none of these trials was randomized. The aim of this prospectively randomized study was to evaluate the course of LVH regression after stentless versus conventional AVR.
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Methods |
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From March 1996 through April 1998, 180 patients with aortic valve disease were prospectively evaluated. The study was approved by the local ethics committee, and all patients gave informed consent after the study protocol was outlined in detail.
Patients amenable for bioprosthetic aortic valve implantation were randomized to receive an SAV, either Freestyle (Medtronic Inc) or Toronto SPV (St Jude Medical Inc), or a CSB, a Carpentier Edwards porcine valve (Baxter Healthcare Inc). Follow-up was performed at our outpatient clinic after 6 months. No patient was lost to follow-up. Because of longer distances to the hospital, 15% of the patients were followed up by their family physicians. At all visits, patients were assessed for functional state and quality of life through the specific activity questionnaire11 and had routine transthoracic echocardiography (TTE).
Patient Population
We included 180 patients in the study from March 1996 through
April 1998. Of these, 74 patients received CSBs and 106 patients
received SAVs (Freestyle, n=49; Toronto, n=57). The patients
were randomized after preoperative echocardiographic
examination. Severe calcification of the aortic sinuses diagnosed
intraoperatively, very low coronary ostia in relation to the
annulus, and atypical insertion of the coronary ostia made it
impossible to implant stentless valves. These patients were excluded,
which explains the differences in group sizes.
Patient age was 74.8±4 (CSB) and 72.3±7 (SAV) years (P<0.05). Roughly half of the patients (54% receiving CSBs and 50% receiving SAVs) were female. The preoperative NYHA class was 2.6±0.6 (CSB) versus 2.6±0.6 (SAV) (P=NS).
The predominant aortic valve lesion was stenosis in 96% and 95% for CSB and SAV, and left ventricular ejection fraction assessed by angiography was 57±15% and 59±16% (P=NS). Maximum preoperative transaortic pressure gradients were 81±25 and 76±25 mm Hg (P=NS). Preoperative body surface area was 1.74±0.2 (CSB) and 1.82±0.2 m2 (SAV) (P<0.05).
Surgery
All operations were performed with the use of complete or
partial median sternotomy and standard extracorporeal circulation with
hypothermic cardioplegic arrest (Bretschneider HTK solution,
Köhler Chemie).
For further comparison, aortic annulus diameter was measured intraoperatively by use of a standard set of sizers before the new valve was implanted.12 This was performed after excision of the diseased aortic valve and after complete decalcification. Annulus diameter was divided by body surface area to obtain the annulus index as a baseline value.
Aortic valve implantation was performed according to standard techniques as described previously.8 SAV implantation was performed with single 4-0 Tevdek stitches at the annulus without pledgets and a continuous 4-0 Prolene suture line at the commissures. CSBs were implanted in a supra-annular position with 2-0 Tevdek Teflon armed U stitches.
Echocardiography
The System Five (Sonotron Vingmed) was used by 2 experienced
echocardiographers at standard views. Cardiac morphology
(chamber and wall sizes, wall motion, valve structure) and function
(fractional shortening, ejection fraction with the Simpson method) and
transvalvular hemodynamics with Doppler and
color Doppler were assessed. Intraoperative TEE was applied to
confirm the underlying pathology and to control postoperative valve and
ventricular function.
All hemodynamic measurements were performed with patients in stable conditions. Aortic valve flow velocities were assessed by use of continuous-wave Doppler. Transvalvular pressure gradients were calculated using the Bernoulli equation with correction for left ventricular outflow tract velocities.13 End-diastolic left ventricular posterior wall thickness >12 mm was considered hypertrophied; left ventricular mass was calculated with a standard formula.14 Aortic valve incompetence was judged as transvalvular or paravalvular and graded according to the regurgitant jet area in relation to left ventricle as mild (<20%), moderate (20% to 40%), or severe (>40%).
Statistical Analysis
Absolute and relative frequencies were calculated. Results are
given as mean±SD. After tests for normal distribution, Student’s
t test for matched pairs or independent samples was applied.
A value of P<0.05 was considered significant. The
2 test was used for comparison of outcome
variables. Postoperative valve-related morbidity and mortality were
evaluated according to standard guidelines.15
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Results |
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After decalcification, the annulus diameter was 24.4±2.2 (SAV) and 23.5±2 (CSB) mm. Consequently, the aortic annulus index was 13.46±1.3 (SAV) and 13.55±1.6 (CSB) mm (P=NS). Larger SAVs than CSBs were implanted; mean valve diameters were 25±2 and 23.2±2 mm (P<0.05). For implantation of stentless valves, longer aortic cross-clamp time was required, 75±19 and 55±13 minutes (P<0.05).
Surgical Outcome, Morbidity, and Mortality
All patients were safely transferred to ICU. Rethoracotomy for
bleeding had to be performed in a total of 5 patients, 3 after SAV and
2 after CSB implantation (P=NS). One of these patients
required prolonged mechanical ventilation; all others had an uneventful
recovery. Extubation was performed after a median of 9 and 10 hours,
respectively. Reintubation for respiratory failure had to be performed
in 3 patients, all on the first postoperative day. Severe
ventricular arrhythmias requiring
intravenous antiarrhythmic therapy occurred in 2 patients
each. New-onset AV block was seen in 11 (SAV) and 7 (CSB) patients
postoperatively (P=NS). In 7 and 4 patients, regular
conduction was completely restored after a maximum of 5 days as
documented by 24-hour ECG. The remaining 4 (SAV) and 3 (CSB) patients
required permanent pacemaker implantation before discharge. These
patients had heavily calcified aortic annuli requiring extensive
decalcification. Transient confusion was observed in 3 and 2 patients;
it had resolved until the third postoperative day in all of them.
There were 4 in-hospital deaths, 3 after SAV, all not valve related. Causes of death were respiratory failure requiring prolonged mechanical ventilation and subsequent pneumonia in 1, prolonged ICU stay because of low cardiac output syndrome complicated by multiple organ failure in 2, and intraoperative stroke with severe progressive neurological deficit in 1 patient. At early follow-up, 2 patients had died (1 after SAV, 1 after CSB), both because of malignancies. Thus far, no thromboembolic or hemorrhagic events or endocarditis occurred. At 6 months, 1 patient in each group presented with new-onset moderate to severe paravalvular incompetence. On reoperation, torn sutures were found in both patients at sites where the aortic annulus had significant calcification.
Postoperative Hospital Stay and Follow-Up
All other patients were discharged from the hospital in time
according to the German standards of postoperative cardiac care. Wound
healing was uneventful in all patients. After stentless valve
implantation, permanent anticoagulation with warfarin was prescribed
only if additional atrial fibrillation was present. Patients in the
conventional group received a 3-month course of warfarin. Because there
have been no problems regarding thromboembolic events, this protocol
was recently changed. Currently, no patient receives systemic
anticoagulation therapy. At discharge, 84% (SAV) and 79% (CSB) were
in stable sinus rhythm. At follow-up, all patients had clinically
improved and tolerated more physical activities at no or only little
dyspnea. NYHA functional class was 1.1±0.4 (SAV) and 1.1±0.3 (CSB)
(P=NS). The specific activity questionnaire had improved in
all patients, to 5.5±1 (SAV) and 5±1 (CSB).
Echocardiography
Intraoperatively perfect SAV function with central valve closure
was seen in all patients. Trivial transvalvular incompetence
(closing volume) was present in 7%. The typical laminar
systolic transvalvular flow profile after SAV compared
CSB implantation is demonstrated in the
Figure
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Postoperative TTE was performed on the fifth to seventh day. Good views were obtained in 85% (SAV) and 84% (CSB) of the patients, and moderately good views were obtained in 12% and 11%. In 3% and 5%, only part of the measurements could be performed because of imperfect visualization. TTE revealed normal aortic valve function in all patients postoperatively.
Maximum transaortic blood flow velocities were 2.33±0.5 (SAV) and 2.47±0.5 (CSB) m/s (P=NS) postoperatively. At follow-up, they had decreased to 2.23±0.4 and 2.43±0.4 m/s (P<0.05). Postoperative maximum transvalvular pressure gradients were lower after stentless valve implantation without reaching significance at that time (18.1±9 and 20.8±9 mm Hg). At 6 months, maximum transvalvular pressure gradients were 16.7±7.7 (SAV) and 20.1±7.3 (CSB) mm Hg (P<0.05). Calculated cardiac indexes were 2.6±1 (SAV) and 2.8±1 (CSB) L · min-1 · m-2 postoperatively (P=NS); after 6 months, they were 3.2±1 and 3.0±1 L · min-1 · m-2 (P=NS).
Measurements of end-diastolic left ventricular
posterior wall diameter are given in Table 1. There was a significant
difference in favor of SAVs after 6 months, reaching almost normal
diameters. In Table 2, left
ventricular mass indexes are shown. No relevant difference
was seen postoperatively, whereas left ventricular mass
index was significantly lower after SAV implantation at follow-up.
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Discussion |
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Despite good clinical results, the obstructive nature of a stent has a negative impact on biological valve performance.16 SAVs were reintroduced in 1997 to yield a more ideal prosthesis, and encouraging results have been reported.6 7 8 10 17 18 In combination with effective anticalcification treatments, SAVs may become the first choice in future.19 20
Aortic Stenosis and LVH
LVH as present in aortic stenosis correlates with
overall cardiovascular morbidity and mortality,
especially that caused by congestive heart failure, sudden death,
myocardial infarction, and stroke.1 21 22 Regression of
LVH has been reported after conventional stented AVR.23
Nevertheless, incomplete regression of LVH was shown to be associated
with decreased survival.24 Incomplete regression of LVH
may be related to the obstruction caused by the stent or to the
nonflexible annulus. By enhancing LVH regression, stentless valves may
lead to a decreased postoperative risk and thus improved long-term
outcome for patients.25 26 Our own initial results
compared with stented mechanical and biological valves were in favor of
stentless bioprostheses.27 In the present study, SAVs
and CSBs were compared for the first time in a prospectively randomized
fashion.
Evaluation of Results
Comparison of the SAV and CSB groups was possible and justified
because there were no differences in annulus index. It has been
previously shown that exact sizing of the patient’s annulus after
complete decalcification is crucial for further comparison of different
valves.12 Furthermore, the importance of indexing results
after valve replacement for body surface areas has been
emphasized.28 Thus, the concept of indexing aortic annulus
diameters before further comparison of different implanted valves is
helpful and is gaining increasing acceptance. This prevents
differences in outcome that are related to preexisting patient-related
variables rather than type of prosthetic valve. In the
present study, larger SAVs than CSBs were implanted. This can be
explained by 2 factors. First, the oversizing technique is used for SAV
selection.6 8 Second, patients in the stentless group had
slightly larger body surface areas, requiring larger implants.
The hemodynamic results are intentionally given as continuous-wave Doppler recordings of transvalvular blood flow velocities. All further data were calculated from these initial baseline measurements. In this study, postoperative instead of preoperative data were compared with follow-up results. The difference between these 2 sets of data reveals the true changes that can be attributed to the implanted valve over time.
Hemodynamic results were in favor of stentless valves. This can be easily explained by the larger effective orifice areas resulting from the lack of an obstructing stent and larger valve size selection at a given annulus diameter. From an echocardiographic perspective, stentless valves resemble native aortic valve function and can be considered close to an ideal artificial heart valve. Paravalvular leakage was not a major issue in this series and should not occur in the presence of 2 suture lines.
There were no relevant differences between the 2 groups in overall clinical outcome. Intraoperative aortic cross-clamp time was longer in the stentless group, but the overall duration was acceptable because it did not result in any excess morbidity. The operative mortality was low and not valve related.
Regression of LVH was seen in all patients after AVR. In this prospectively randomized trial, it also has been proved that use of SAVs leads to significant enhancement of LVH regression. The increase in LVH regression can be explained by better hemodynamics and the flexible design compared with conventional valves. As such, the stentless valve design allows more physiological blood flow and a larger effective orifice area at any given aortic annulus diameter. LVH was assessed with routine TTE.14 Nevertheless, 3-dimensional echocardiography or ultrafast MRI may result in even more exact measurements in the future.
Further follow-up must be performed to prove long-term outcome and the benefit of early LVH regression after SAV implantation.
Conclusions
This is the first prospectively randomized trial comparing LVH
regression after stentless versus conventional biological AVR. The
indexed aortic annulus diameter is essential for objective comparison
of different valves. At a 6-month follow-up,
hemodynamic and left ventricular
morphological measurements were in favor of stentless valves. Enhanced
regression of LVH after stentless AVR may be of clinical benefit for
patients. When combined with effective anticalcification treatments,
SAVs that resemble native valve function will be the prostheses of
choice in the future.
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Acknowledgments |
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We acknowledge the statistical advice of Dr Rer Nat Thomas Rauch.
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