Asian Cardiovasc Thorac Ann 2008;16:208-211
© 2008 Asia Publishing EXchange Ltd
Echocardiographic Follow-Up after Implanting 17-mm Regent Mechanical Prostheses
Giovanni Casali, MD,
Giampaolo Luzi, MD,
Mariano Vicchio, MD,
Paola Lilla della Monica, MD,
Giovanni Minardi, MD,
Francesco Musumeci, MD
Department of Cardiology and Cardiovascular Surgery, S. Camillo-Forlanini Hospital, Rome, Italy
For reprint information contact: Mariano Vicchio, MD Tel: 39 347 335 9845 Fax: 39 347 335 9845 Email: marianovicchio{at}libero.it, Via Cassano 150, 80144, Naples, Italy.
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ABSTRACT
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The aim of this study was to evaluate midterm echocardiographic results and changes in quality of life after aortic valve replacement with 17-mm St. Jude Medical Regent mechanical prostheses in patients with aortic valve stenosis. The study population was 34 women and 2 men, aged 31–83 years. Echocardiographic follow-up was 100% complete at 4.1 ± 1.8 years. Hospital mortality was 5.6%. Actuarial 5-year survival was 88.5% ± 0.067%. Postoperative echocardiography showed significant regression of left ventricular mass index and significant reductions of peak gradient, mean gradient and mean effective orifice area index. All survivors were interviewed using the 36-item Short Form Health Survey questionnaire. Scores obtained in 7 of the 8 domains of the test were significantly higher than preoperative values. In our experience, implantation of this prosthesis allowed regression of left ventricular mass index and improved the perceived quality of life.
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INTRODUCTION
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Aortic valve replacement (AVR) is a successful therapeutic strategy in patients with aortic valve disease, allowing improved survival, left ventricular (LV) mass regression and better quality of life (QOL). However, AVR in patients with small aortic roots is still a challenge for the cardiac surgeon with regard to operative technique and selection of prosthesis. Since the introduction by Rahimtoola1 of the concept of prosthesis-patient mismatch, implantation of small prostheses in the aortic position has been blamed for residual gradients responsible for poor left ventricular mass regression, increased long-term mortality and more valve-related complications.2,3 Various strategies to increase the effective orifice area (EOA) of the implanted valve have been described, such as aortic root enlargement or replacement with a larger prosthesis, a stentless bioprosthesis or a new-generation supraannular mechanical prosthesis. Some of these techniques are more difficult, require longer cross clamp times, and are associated with higher hospital mortality rates than isolated AVR, with no increase in long-term survival.4–6 The aim of this study was to investigate the early and midterm results and quality of life in patients who underwent AVR for isolated aortic valve stenosis with a 17-mm Regent mechanical prosthesis (St. Jude Medical, Inc., St. Paul, MN, USA).
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PATIENTS AND METHODS
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Between February 2000 and January 2006, 36 patients with isolated aortic valve stenosis received a 17-mm Regent prosthesis in our hospital. The characteristics of these patients are given in Table 1
. The cause of aortic stenosis was degenerative in 22 (61.1%) patients, congenital in 4 (11.1%) and rheumatic in 10 (27.8%). All patients underwent preoperative echocardiographic and angiographic evaluation.
All operations were performed through a median sternotomy. Cardiopulmonary bypass methods were uniform throughout the study, using moderate systemic hypothermia with crystalloid hyperkaliemic cardioplegia infusion into the aortic root and continuous topical cooling with cold saline for myocardial protection. Aortic prostheses were inserted in the supraannular position, using non-pledgeted simple interrupted Tevdek 2/0 stitches. The prosthesis was implanted with the axis perpendicular to the interventricular septum, after complete removal of calcium from the annulus. Prosthesis size was selected according to the size of the aortic annulus, which was determined using the manufacturer’s sizer. All patients included in this study had a severely calcified annulus.
Effective orifice area was derived from the continuity equation, using the area of the LV outflow tract (LVOT) and the time-velocity integrals of the LVOT (TVI1) and the prosthesis (TVI2): EOA = (LVOT cross-sectional area x 0.785 x TVI1)/TVI2. The mean gradient was measured using continuous-wave Doppler echocardiography and the simplified Bernoulli equation. LV mass index was calculated from Reichek’s formula, and body surface area was calculated using the Dubois formula. Preoperative echocardiographic data are given in Table 2. In May 2007, all survivors underwent late postoperative echocardiography. Echocardiographic follow-up was 100% complete (mean, 4.4 ± 1.8 years; median, 4.8 years; range, 14 months–7.25 years). An electronic database was created to collect pre and postoperative echocardiographic data and record all complications. Complications were classified according to the guidelines of the Society of Thoracic Surgeons.7 All survivors were interviewed using Medical Outcomes Trust Short Form 36-Item Health Survey (SF-36) tool that has an established validity and reliability in the assessment of perceived quality of life after cardiac surgery.8 SF-36 consists of 36 questions grouped into 8 multi-item domains, which measure functioning in different aspects of daily life. They include physical and social functioning, usual role activities, pain, vitality, and general evaluations of mental, emotional and physical health. The scores for each domain range between 0 and 100, with 0 coded the worst and 100 the best possible health status.
Data were analyzed with SPSS version 13.0 software (SPSS, Chicago, IL, USA). Continuous variables are expressed as mean ± standard deviation. Categorical variables are expressed as counts and percentages. The preoperative and postoperative echocardiographic parameters and SF-36 test results were compared using the paired Student t test. The cumulative probability of freedom from an event and the actuarial survival were calculated by the Kaplan-Maier method and expressed as percentage ± standard error.
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RESULTS
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Hospital mortality was 5.6% (2 patients). One patient died soon after the operation because of low cardiac output syndrome, and the other died of sepsis. Actuarial 5-year survival was 88.5% ± 0.067%. During follow-up, 2 patients died; one from lung cancer, and the other from progressive degeneration of Alzheimer’s disease. Freedom from reoperation was 100%. No valve-related or anticoagulation-related complications were observed during follow-up. The postoperative echocardiographic data are given in Table 2
. Peak and mean gradients were significantly reduced, and mean EOA index (EOAI) was significantly increased. A significant regression of LV mass index was found. New York Heart Association functional class improved significantly postoperatively (Figure 1). On echocardiographic follow-up, 2 (5.9%) survivors showed mild prosthesis-patient mismatch (EOAI > 0.9 cm2·m–2), 26 (76.5%) had a moderate mismatch (EOAI 0.6–0.9 cm2·m–2), and 6 (17.6%) had a severe mismatch (EOAI < 0.6 cm2·m–2). All survivors were interviewed using the SF-36 questionnaire. The scores obtained in the 8 domains of the test are illustrated in Figure 2. Compared to the preoperative scores, significantly higher scores were reached on follow-up, with p < 0.001 in all domains except bodily pain.
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DISCUSSION
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We found AVR with a 17-mm Regent mechanical prosthesis showed good midterm survival, and echocardiography revealed satisfactory hemodynamic performance of the implanted prostheses. Despite an EOAI < 0.85 cm2·m–2, there was significant reduction in LV mass index and peak and mean gradients at follow-up. All patients were in New York Heart Association functional class I or II, and the perceived quality of life improved postoperatively. Other studies have shown similar results with mechanical prostheses in small aortic roots. A good 10-year survival rate after implanting 19-mm St. Jude mechanical prostheses was reported by Sawant and colleagues.9 Moreover, they did not find prosthesis-patient mismatch to be an independent predictor of long-term mortality. Severe prosthesis-patient mismatch following AVR has been associated with decreased long-term survival, thought to be due to the persistence of LV hypertrophy in patients with small aortic prostheses.2 However, those with prosthesis-patient mismatch had increased valve-related mortality, while the overall survival was similar.2 This valve-related mortality may have included deaths due to embolic stroke, endocarditis, valve failure and reoperation, unrelated to prosthesis-patient mismatch. Medalion and colleagues10 demonstrated in a large series that outcomes after AVR might be related to patient risk factors, but not negatively influenced by moderate prosthesis-patient mismatch. In patients undergoing AVR with mechanical and biological valves for severe aortic stenosis, Bech-Hanssen and colleagues11 described improvements in functional status, systolic and diastolic LV function and a reduction in LV mass index, irrespective of prosthesis size and type. They noted that mechanical valves were less obstructive than stented bioprostheses of the same size. Several reports have proposed implantation of stentless valves as an alternative in patients presenting with a small aortic annulus, to avoid prosthesis-patient mismatch.12 However, stentless valve implantation can be technically more demanding, and there is no proof that this will lead to better early and long-term survival.5
Many studies evaluating the performance of different aortic valve prostheses have emphasized that successful AVR should achieve an EOAI > 0.85 cm2·m–2 to minimize prosthetic gradients and obtain postoperative LV mass regression.13 Several investigators have suggested that prosthesis-patient mismatch induces poor LV mass regression, but this theory has not been clearly proven. Hanayama and colleagues14 showed that patients with postoperative echocardiographic evidence of severe prosthesis-patient mismatch (EOAI < 0.6 cm2·m–2) had long-term survival similar to those without a mismatch. Furthermore, studies have demonstrated that preoperative LV hypertrophy and postoperative hypertension adversely influence the reduction of LV mass index, showing that LV mass regression following AVR does not depend on prosthesis size or type.15 Incomplete regression of hypertrophy after AVR may be explained by potentially irreversible changes in the hypertrophied myocytes and interstitium, which may occur as a consequence of long-standing disease. In a large series, Blais and colleagues16 reported that prosthesis-patient mismatch increased 30-day postoperative mortality, evidenced by low-output syndrome as the most prevalent cause of death. In contrast, Howell and colleagues17 evaluated the impact of EOAI < 0.60 cm2·m–2 on 1,481 consecutive patients who underwent AVR, and demonstrated that it did not affect hospital mortality or midterm survival. Hospital mortality in our study was acceptable considering the mean age of the patients and their preoperative EuroSCORE.
Beyond survival analysis and echocardiographic performance, our study focused on late perception of QOL. Several studies have reported improved QOL after a cardiac surgical procedure, compared with the patients’ preoperative values or with a general population norm.18 A recent study has shown that patients report improvements in functional QOL after AVR, which are not influenced by prosthesis-patient mismatch.19 Our results agree with this, and show that small-sized bileaflet prostheses do not affect the patient’s perceived QOL. Numerous methods exist for evaluating QOL, and the SF-36 questionnaire has been widely validated. It enables assessment of any limitation of physical, psychological or social functioning. We obtained significantly higher scores postoperatively in 7 domains of the test. When interpreting this result, it should be considered that more than 50% of patients were in functional class III or IV before the operation, so a high percentage had experienced moderate to severe limitation of daily activity for various periods of time. Symptom relief and return to previous lifestyle will probably increase the patient’s perception of health status. Several studies compared pre and postoperative scores in heart surgery patients; all reported better perception of QOL at 3 months after the operation when patients had complete surgical resolution and a lifestyle similar to that before the onset of disease.
Limitations of this study include the lack of evaluation of the impact of prosthesis-patient mismatch on survival, because of the small number of patients enrolled. A comparative analysis of survival between the 26 patients with moderate prosthesis-patient mismatch the 6 with severe mismatch would not have statistical relevance. Although we have midterm follow-up data, we are awaiting long-term results of patients with small-sized prostheses. However, it was concluded that implantation of a 17-mm St. Jude Medical Regent mechanical prosthesis resulted in significant regression of LV mass and significant improvement in the perceived quality of life.
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REFERENCES
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ABSTRACT
INTRODUCTION
