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Ann Thorac Surg 2002;74:2022-2025
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Nineteen-millimeter prosthetic aortic valves allow normalization of left ventricular mass in elderly women

^a Sections of Cardiac Surgery and Cardiology, University of Manitoba, Winnipeg, Manitoba, Canada

Accepted for publication July 22, 2002.

* Address reprint requests to Dr Pascoe, Z3031, St. Boniface General Hospital, 409 Tache Ave, Winnipeg, MB, Canada R2H 2A6

	Abstract

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BACKGROUND: Implantation of small aortic valve prostheses has been reported to be associated with impaired left ventricular (LV) mass regression and incomplete resolution of symptoms although these data have been generated largely with male patients. Therefore we sought to determine the clinical and hemodynamic outcomes of female patients who received a 19-mm aortic valve.

METHODS: Between May 1995 and December 2000, 38 female patients (average age 73 years, range 42 to 89) underwent isolated aortic valve replacement (AVR; n = 22) or AVR plus coronary artery bypass graft surgery (CABG; n = 16) with a 19-mm aortic prosthesis. The average New York Heart Association (NYHA) class was 3.08 and of the 26 patients who had angina, 47.2% were in CCS class III or IV. Clinical and echocardiographic follow-up was done an average of 33.4 months (8 to 72) after surgery.

RESULTS: Operative mortality was 10.5%. Overall survival at an average of 33 months was 71.1%. The average NYHA class was 1.52 ± 0.34 postoperatively (p < 0.001 versus preoperative) and 95% had no anginal symptoms or were in Canadian Cardiovascular Society class I. The LV mass index showed significant regression (114 ± 11 g/m² to 89 ± 9 g/m², p = 0.001) despite an effective orifice area index (EOAI) of 0.64 ± 0.09 cm²/m².

CONCLUSIONS: Despite a very small EOAI, elderly female patients with 19-mm prosthetic aortic valves can experience a satisfactory improvement in symptoms and normalization of LV mass. This finding suggests that small prosthetic aortic valves continue to have an application in contemporary cardiac surgical practice. The current perception of patient-prosthesis mismatch may need to be reconsidered for select populations.

	Introduction

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Replacement with a prosthesis has become standard therapy for treating diseases of the aortic valve. The goal of surgery is to replace the valve with a competent, nonstenotic prosthesis that allows resolution of patient symptoms and normalization of hemodynamics. Although it is easy to define a competent prosthesis, defining what constitutes a nonstenotic prosthesis has been a challenge. The term "patient-prosthesis mismatch" has been coined to describe the situation in which "the effective prosthetic valve area, after insertion into the patient, is less than that of a normal human valve [1]." The most commonly used measure of patient-prosthesis matching has been the valve effective orifice area (EOA), indexed to body surface area (BSA). Some studies have shown decreased symptom resolution, poor regression of left ventricular (LV) mass, or decreased survival with an EOAI of less than 0.85 cm²/m² [2], while others have observed this phenomenon with an EOAI less than 0.80 cm²/m² [3] or 0.75 cm²/m² [4]. Using these numbers one can easily determine that only the smallest patients will have an appropriate match when a conventional 19-mm prosthesis is implanted.

Yet there have been conflicting reports: some authors demonstrate excellent outcomes after aortic valve replacement (AVR) with either mechanical or biological prostheses of small size whereas others demonstrate poor outcomes. Medalion and coworkers [5] demonstrated in 892 adult patients that survival is not impacted by small prosthetic valves unless the indexed valve internal orifice area is less than four standard deviations below normal. Rao and colleagues [4] found in 2,981 patients that an indexed effective orifice area less than 0.75 cm²/m² was associated with significantly higher early and late mortality after bioprosthetic AVR. Bech-Hanssen and coworkers [6] found that small aortic valves allowed symptom resolution and significant LV mass regression, whereas González-Juanatey and colleagues [7] demonstrated nonsignificant LV mass regression in patients with 19-mm valves. These studies were conducted without limitations on the study population and as a result discrepancies may be due to differences between the populations studied. Recognizing this we limited our study to a specific population. Elderly female patients were studied to determine clinical and hemodynamic outcomes after aortic valve replacement with a 19-mm mechanical or biological valve.

	Material and methods

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Study protocol
Female patients who received 19-mm aortic valve prostheses between May 1995 and December 2000 were identified from the local Society of Thoracic Surgeons database. The study was limited to patients who had undergone isolated AVR or AVR plus coronary artery bypass graft (CABG) surgery. The medical records of these patients were reviewed. Those patients who had not undergone echocardiographic and clinical evaluation more than 6 months after valve implantation were invited to return for investigation. A standardized history and physical examination and echocardiography were carried out for each patient. The study was conducted in accordance with standards set forth by the biomedical ethics research board of the University of Manitoba.

Echocardiography
Preoperative and postoperative two-dimensional and M-mode echocardiographic data were collected using the Sonos 1000 (Hewlett Packard, Andover, MA) using a 2.5 MHz transducer with fundamental imaging, Vingmed System V (General Electrical Medical Systems, West Milwaukee, WI) with 1.5 to 1.7 MHz transducer with harmonic imaging or Acuson XP 128 (Acuson, Mountain View, CA) with 2.5 MHz transducer with fundamental imaging. Standard parasternal, apical, subcostal, and suprasternal views were utilized. Hemodynamic variables were calculated using standard formulas (Table 1): Transvalvular pressure gradients (TPG) were determined using the modified Bernoulli equation [8], valve area (AVA) and effective orifice area (EOA) were calculated by the continuity equation [8], and left ventricular mass (LVM) was calculated by the Devereux formula [9]. Two investigators reviewed all echocardiograms; if they were in disagreement a third opinion was obtained and the final decision was reached by consensus.

	Results

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Patient characteristics
Of 595 aortic valve replacements between May 1995 and December 2000, 38 female patients received a size 19-mm aortic valve. Perioperative follow-up was complete for all patients although 3 patients were unavailable to undergo postoperative echocardiographic assessment. The average patient age was 73 ± 4 years. The average New York Heart Association (NYHA) functional class was 3.2 ± 0.3. Twenty-six patients (68%) had angina with an average Canadian Cardiovascular Society (CCS) angina class of 2.9 ± 0.4. The average body surface area (BSA) was 1.70 ± 0.06 m². Preoperative clinical and hemodynamic characteristics are summarized in Tables 2 and 3.

Clinical outcomes
The 30-day mortality was 10.5% (n = 4) and the cause of death was cardiac (lethal arrhythmia or low output state) in 3 patients. The median intensive care unit length of stay was 1 day (mean 4.8 ± 3.9) and the median hospital length of stay was 10 days (mean 18 ± 9). Three patients suffered a perioperative myocardial infarction (8%), 4 patients had a cerebrovascular accident (11%), and 3 patients had a permanent deficit. Atrial fibrillation developed postoperatively in 53% of patients and 11% were discharged with the arrhythmia. Acute renal failure developed in 16% of patients and 1 patient required dialysis. At an average of 33.4 ± 7.9 months (range 8 to 72) of follow-up, 71.1% of patients were alive. The average NYHA functional class was 1.52 ± 0.34, which was significantly reduced from the preoperative class of 3.08 ± 0.36 (p < 0.001). Ninety-five percent (n = 22) of patients had no angina or were in CCS class I. None of the patients have had a recurrence of heart failure or syncope since valve replacement.

Hemodynamics
Overall the patients experienced an improvement in hemodynamic variables as measured by pressure gradients and valve area (Table 3). Interestingly there was a significant (p = 0.001 preoperative versus postoperative) decrease in left ventricular mass (Fig 1) and LV mass index (Fig 2), despite a mean EOA of 1.08 ± 0.14 cm² and an EOAI of 0.64 ± 0.09 cm²/m². The average postoperative LV mass was 154 ± 17 g, which is normal for women [6], and the average LVMI was 89 ± 9 g/m².

View larger version (26K): [in this window] [in a new window]   Fig 1. Effect of 19-mm aortic valve prosthesis on left ventricular (LV) mass. ( = mean.)

View larger version (26K): [in this window] [in a new window]   Fig 2. Effect of 19-mm aortic valve prosthesis on left ventricular (LV) mass index. ( = mean.)

	Comment

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In contrast to other published series utilizing a 19-mm aortic valve [7, 17] our patients experienced a significant improvement in symptoms and a significant reduction in left ventricular mass. These observations may be the result of our population being made up largely of elderly women who have a relatively sedentary lifestyle whereas others have reported their experience with a more diverse population [7, 17]. At follow-up none of our patients exhibited clinical evidence of significant mismatch yet echocardiographic assessment revealed an average EOAI of 0.64 ± 0.09 cm²/m². Therefore most of our patients had patient-prosthesis mismatch by current definitions [2–4] yet overall they experienced a significant reduction in symptom class and normalization of left ventricular mass. We did not perform stress echocardiography to determine if gradients and orifice area would change with an increase in cardiac output but in this sedentary population the information obtained may not be clinically relevant.

A paper presented at a recent thoracic surgery conference demonstrated by multivariate analysis that severe preoperative hypertrophy was the only predictor of incomplete LV mass regression after aortic valve replacement [18]. Our patients had less advanced left ventricular hypertrophy preoperatively and this factor may have contributed to complete regression of hypertrophy after valve replacement. Any improvement in EOA is beneficial and in our population the EOAI of 19-mm valves was sufficient to affect a favorable outcome. Using EOAI as a measure the point at which patient-prosthesis mismatch becomes significant may need to be reconsidered for select patient populations.

We have shown in our population of primarily small, elderly women with mild LVH that symptomatic and hemodynamic benefit and LV mass regression arise from aortic valve replacement with conventional 19-mm prostheses. This finding suggests that small prosthetic valves continue to have a place in the treatment of aortic valve disease and should not be abandoned in favor of more complex procedures.

Limitations
It is important to recognize that the data presented are from a very specific population subgroup. This paper describes a very select population of patients who have not been compared with similar patients receiving larger valves. As such we cannot comment on the impact of valve size or patient-prosthesis mismatch on operative mortality, long-term survival, and LV mass regression. Moreover the patients were brought back at nonstandardized times, which may influence variability in observed hemodynamic changes. The results presented should not be extrapolated to a general population of patients undergoing aortic valve replacement.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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