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Eur J Cardiothorac Surg 2002;22:922-926
© 2002 Elsevier Science NL

Multivariate analysis of risk factors for hospital mortality in valvular reoperations for prosthetic valve dysfunction

InCor – Heart Institute, University of São Paulo Medical School, São Paulo, Brazil

Received 6 June 2002; received in revised form 26 August 2002; accepted 6 September 2002.

* Corresponding author. Heart Institute, Av. Dr. Enéas de Carvalho Aguiar, 44, Cerqueira César, CEP: 05403-000, São Paulo, SP, Brazil. Tel.: +55-11-30695638; fax: +55-11-30695415
e-mail: carlos.brandao{at}incor.usp.br

	Abstract

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
Objectives: The purpose of the study was to analyze risk factors for hospital mortality in patients undergoing valvular reoperations for prosthetic valve dysfunction. Methods: We performed a prospective analysis of 146 patients who underwent valvular reoperations for prosthetic valve dysfunction between July 1995 and June 1999 at the Heart Institute of the University of São Paulo Medical School. Multivariate statistical analysis with logistic regression was used to analyze preoperative and intraoperative variables to determine risk factors for hospital mortality. Results: The overall hospital mortality was 10.9% (16 patients). Univariate analysis showed that the following variables were associated with higher mortality rates: advanced New York Heart Association (NYHA) functional class, increased creatinine level, prolonged extracorporeal circulation time and treatment of annular abscess. Logistic multivariate analysis identified advanced NYHA functional class and a creatinine level higher than 1.5 mg/dl as independent predictors of hospital mortality. Conclusions: Advanced NYHA functional class and higher creatinine levels were independent predictors of hospital mortality in patients submitted for valvular reoperations for prosthetic valve dysfunction.

Key Words: Prosthesis • Reoperation • Surgery • Hospital mortality • Risk factors

	1. Introduction

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
Reoperations on cardiac valves have become increasingly frequent in recent years. This trend reflects many factors, such as the increased life expectancy of the population, the decreased overall mortality associated with valvular surgery, and the large use of bioprostheses in our population [1], which have limited durability because of structural dysfunction. Patients undergoing valvular reoperations are a very heterogeneous group; they present with a large variety of clinical conditions including structural dysfunction of bioprostheses, native valve restenosis, prosthetic valve endocarditis, mechanical valve thrombosis, and paravalvular leaks. The purpose of this study was to identify risk factors for hospital mortality in patients submitted for valvular reoperations for prosthetic valve dysfunction at the Heart Institute of the University of São Paulo Medical School.

	2. Materials and methods

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
We performed a prospective analysis of 146 consecutive patients submitted for valvular reoperations for prosthetic valve dysfunction between July 1995 and June 1999. Patient ages ranged between 6 and 83 years, with an average age of 47.5 years and a standard deviation of 16.8 years. Ninety (61.6%) patients were female and 56 (38.4%) were male.

Patients with prosthetic valve dysfunction and without coronary artery disease were included in the study. The operations were performed by one surgical team, with a standard operative technique. All patients provided informed consent, and our institutional human research committee approved our study protocol.

The etiology of the primary valve lesion was rheumatic fever in 106 patients (72.6%), degenerative disease in 18 (12.3%), endocarditis in 13 (8.9%) and congenital disorder in nine (6.2%). Thirteen patients (8.9%) were in New York Heart Association (NYHA) functional class (FC) II, 73 (50%) were in FC III and 60 (41.1%) were in FC IV.

The indications for reoperation were primary tissue failure of bioprosthesis in 121 (82.9%) patients, prosthetic valve endocarditis in 12 (8.2%), paravalvular leak in 12 (8.2%) and thrombosis (mechanical) in one (0.7%) patient. The interval between the operations ranged between 1 month and 20 years, with a mean interval of 7.2±3.9 years. One hundred and thirty-six (93.2%) patients had biological prostheses and ten (6.8%) had mechanical prostheses.

The positions of the valves operated on were as follows: mitral valve in 52 patients (35.6%); aortic valve in 36 (24.6%); mitral and aortic valves in 24 (16.4%); mitral, aortic and tricuspid valves in 16 (10.9%); mitral and tricuspid valves in 15 (10.3%); tricuspid valve in two (1.5%); and aortic and tricuspid valves in one (0.7%) patient. Six (4.1%) patients were submitted for associated treatment of annular abscess.

2.1. Operative technique
The standard approach was through a median sternotomy. The sternum was divided with an oscillating saw. After complete division of the sternum, its two halves were lifted upward with rakes and its adhesions to the underlying tissues were cut until wide mobilization was obtained. The left pleural space was systematically opened and further dissection was carried out to expose the aorta and the right atrium for cannulation.

Cardiopulmonary bypass was performed by cannulating the ascending aorta and both venae cavae through the right atrium. Myocardial protection was performed by mild hypothermia at 28 °C and anterograde cold crystalloid cardioplegic solution. Prostheses were removed using an annular preserving technique. Epsilo-aminocaproic acid was used in all of our patients to reduce perioperative bleeding.

2.2. Variables
The following preoperative variables were analyzed in this study: sex, age, NYHA FC, indication for reoperation, type of prosthesis, number of previous operation(s), cardiac rhythm, urgency of operation, diabetes, cerebrovascular accident, creatinine level, left ventricular ejection fraction (LVEF), left ventricular diastolic diameter (LVDD), left ventricular systolic diameter (LVSD) and right ventricular systolic pressure (RVSP).

The intraoperative variables analyzed were extracorporeal circulation (ECC) time, aortic cross-clamp time, number and position of valves and associated procedures.

2.3. Statistical analysis
Univariate analysis was performed using the chi-square test or the Fisher exact test, when appropriate. Variables associated with P<0.05 on univariate analysis were included in the multivariate analysis.

The multivariate analysis was performed using a logistic regression model, with a stepwise backward elimination procedure. Validation of the logistic regression model was performed by the ‘goodness-of-fit’ test [2]. Statistical Analysis Software (SAS Institute, Cary, NC) [3] was used for all analyses. The independent risk factors included in the final model are presented as odds ratios, including 95% confidence intervals.

Hospital mortality was defined as death within any time interval after the operation if the patient had not been discharged from the hospital or within 30 days of the operation [4].

	3. Results

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
The hospital mortality was 10.9% (16 patients). The main cause of death was low cardiac output, which occurred in six patients. Other causes of death were multiorgan failure in five patients, sepsis in three, adult respiratory distress syndrome in one and coagulation disturbance in one patient.

Univariate analysis revealed that the preoperative variables FC IV and creatinine level higher than 1.5 mg/dl were associated with increased hospital mortality (Table 1). The intraoperative variables associated with higher hospital mortality were ECC time longer than 120 min and treatment of annular abscess (Table 2).

	4. Discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

The NYHA FC is one of the most important predictors of hospital mortality [8–10]. Husebye et al. [11] identified FC as a predictor of mortality and suggested that patients with structural dysfunction of bioprostheses may be operated on, even if oligosymptomatic, to decrease hospital mortality rates and improve long-term survival. Other authors recommend earlier surgery in patients with all forms of valve dysfunction [12], even in asymptomatic patients with prosthetic structural problems [13,14].

Renal function was another important predictor of hospital mortality in this study. Biglioli et al. [15] showed similar results with univariate analysis. In addition, Akins et al. [12] and Piehler et al. [9] identified renal insufficiency as an independent predictor of morbidity and mortality in patients submitted for valvular reoperations.

ECC time was associated with a higher mortality rate in the univariate analysis. This important risk factor has been described by many authors [15,16]. Longer ECC times were associated with other factors, such as lengthy operations, multivalvular procedures, associated procedures, or patients with ventricular dysfunction that needed prolonged circulatory assistance. A prolonged aortic cross-clamp time was also associated with higher mortality in this series, as has been reported by other authors such as Biglioli et al. [15] and Pansisi et al. [8]. This variable is directly related to the complexity of the procedure.

In regard to patient sex, our results were similar to those described by Cohn et al. [5], with no apparent effect of gender on hospital mortality. In contrast, Lytle et al. [17] found women to be at increased risk of death for aortic reoperations, but not mitral procedures, in a series of 1000 patients. Although age has been described as an independent predictor of mortality in patients undergoing valvular reoperations [9,17], it did not influence hospital mortality in our series.

The indication for reoperation did not significantly affect hospital mortality, although the mortality rate was higher in the prosthetic valve endocarditis group. This complication is still associated with a high operative risk [6,7,16], and early surgery for removal of the infected prosthesis is indicated. The presence of advanced disease with involvement of the periannular tissues presented significantly higher mortality in the univariate analysis. Lytle et al. [18] have previously demonstrated that endocarditis with an annular abscess is a condition associated with high morbidity and mortality.

The type of prosthesis requiring reintervention did not significantly influence hospital mortality, and there was no mortality associated with the mechanical prosthesis. We think that this is not related to the type of prostheses itself, but to the characteristics of the patients, as we preferentially do not use mechanical prostheses in patients of an older age, with a decreased ejection fraction or in patients with endocarditis. Also, the number of patients in this group was low, as we use more bioprostheses in our population [1]. Bortolotti et al. [16] identified the type of prosthesis as a risk factor for hospital mortality. McGrath et al. [19], in patients with failed mechanical and bioprosthetic valves, with no difference between the two groups in the FC, showed 13.2% operative mortality for the bioprosthesis patients and 12.4% for the mechanical valve patients.

Diabetes and cerebrovascular accident are risk factors present in some series in the literature [17,20]. In our series, patients with diabetes presented higher mortality, although this was not statistically significant. Cerebrovascular accident also did not influence hospital mortality.

Our univariate analysis revealed that left ventricular function, analyzed via the LVEF, was not associated with higher hospital mortality. Turina and Turina [21] have reported similar results. However, in the series of Bortolotti et al. [16], LVEF significantly influenced the mortality. The LVDD and LVSD did not influence hospital mortality, as previously shown by Biglioli et al. [15]. The RVSP, which reflects the pulmonary artery pressure, did not influence operative mortality in our patients. Biglioli et al. [15] and Akins et al. [12] showed no influence of median and systolic pulmonary artery pressures on hospital mortality. According to Carabello et al. [22], the only independent echocardiographic predictor of poor evolution in valve surgery is the systolic volume index.

Although the mortality rate appeared to be higher for first reoperations than second or third reoperations, this difference was not significant. Piehler et al. [9] identified the number of previous valve operations as an independent predictor of hospital mortality. In our opinion, the higher mortality associated with the first reoperations may be due to other variables that influence mortality, such as ventricular function, renal insufficiency, and others.

Atrial fibrillation has been identified as a risk factor for mortality and morbidity associated with valve surgery [23], as it may cause low cardiac output during the postoperative period or predispose to thromboembolic events. In our series, atrial fibrillation was not identified as a risk factor for hospital mortality, as reported by Andrade et al. [24].

Several series in the literature have identified emergency status as an independent predictor of mortality associated with valvular reoperations [8,10–12,15,16]. In our series, no hospital mortality occurred in the emergency group, although there were only four patients in this group.

The number of valves was not a risk factor for hospital mortality in our study, although it has been identified as an important predictor in other reported series [8,10]. Although mortality was higher for patients who underwent reoperations involving the aortic position, valve position also was not a risk factor for hospital mortality. Rossiter et al. [25] have suggested that the higher rates of mortality associated with reoperations involving the aortic position may be due to the higher incidence of endocarditis in aortic prostheses.

In summary, advanced NYHA FC and higher creatinine levels are independent predictors of hospital mortality in patients submitted for valvular reoperations for prosthetic valve dysfunction.

	References

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 

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