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Ann Thorac Surg 2002;73:37-43
© 2002 The Society of Thoracic Surgeons

Original article: cardiovascular

Clinical outcome in patients with 19-mm and 21-mm St. Jude aortic prostheses: comparison at long-term follow-up

Aldo D. Milano, MDa, Marco De Carlo, MDb, Gianclaudio Mecozzi, MDa, Alessandro D’Alfonso, MDa, Giovanni Scioti, MDa, Carmela Nardi, MDb, Uberto Bortolotti, MD*a

a Division of Cardiac Surgery, Cardio-Thoracic Department, University of Pisa Medical School, Pisa, Italy
b Division of Cardiology, Cardio-Thoracic Department, University of Pisa Medical School, Pisa, Italy

Accepted for publication August 31, 2001.

* Address reprint requests to Dr Bortolotti, U.O. Cardiochirurgia, Ospedale Cisanello, via Paradisa 2, 56124 Pisa, Italy
e-mail: u.bortolotti{at}cardchir.med.unipi.it


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 References
 
Background. Small-sized prostheses for aortic valve replacement may result in residual left ventricular outflow tract obstruction. Aim of the study was to verify whether implantation of 19-mm versus 21-mm St. Jude Medical standard prostheses (St. Jude Medical, Inc, St. Paul, MN) influences long-term clinical outcome.

Methods. Two hundred twenty-nine patients who underwent aortic valve replacement with 19 mm (group 1, 53 patients) or 21-mm St. Jude Medical standard prostheses (group 2, 176 patients) were included in the study. Mean follow-up of current survivors was 10 ± 4 years.

Results. Operative mortality was 7.5% in group 1 and 8.5% in group 2. At discharge, an important patient-prosthesis mismatch (effective orifice area index <= 0.60 cm2/m2) was present in 18% of group 1 versus 5% in group 2 (p = 0.004). Among patients with body surface area less than 1.70 m2, such mismatch was present in 15% of group 1 versus 2% of group 2 (p = 0.008). At last follow-up New York Heart Association (NYHA) functional class (p < 0.001), left ventricular mass reduction (p = 0.02), mean (p = 0.002) and peak transprosthetic gradients (p < 0.001), and effective orifice area index (p = 0.005) were significantly better in group 2. Freedom from sudden death (92% ± 5% vs 99% ± 1%, p = 0.01), valve-related death (84% ± 6% vs 90% ± 5%, p = 0.02), and cardiac events (56% ± 13% vs 86% ± 4%, p = 0.008), were significantly lower in group 1. Effective orifice area index was an independent predictor of late cardiac events.

Conclusions. Although long-term results after aortic valve replacement with small-sized St. Jude Medical standard prostheses are satisfactory, 19-mm valve recipients show a high prevalence of important patient-prosthesis mismatch with less evident functional improvement and higher rate of cardiac events, suggesting a very cautious use of this prosthesis.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 References
 
Aortic valve replacement (AVR) in patients with a small aortic annulus is often challenging for the surgeon in terms of prosthesis selection. Small-sized prostheses cause a residual obstruction to left ventricular outflow, thus maintaining left ventricular hypertrophy and limiting clinical improvement, and probably also affecting long-term survival [1–6]. It is well known that transprosthetic pressure gradients increase during exercise [7] and with decreasing valve size [4, 8].

The St. Jude Medical standard prosthesis (SJP) (St. Jude Medical, Inc, St. Paul, MN) has been in use for more than 20 years and represents a point of reference for newer prosthesis design [9], particularly since it is considered to have an excellent hemodynamic performance [10, 11]. However, mean transprosthetic gradients as high as 17 ± 3 mm Hg [12] for the 21-mm SJP, and as high as 22 ± 8 mm Hg [12] for the 19-mm SJP have been reported at rest. Thus the use of small-sized prostheses for AVR may determine a patient-prosthesis mismatch, depending both on the type and size of the valve substitute and on cardiac output [1, 5, 13].

Few data are available on the direct comparison of 19-mm versus 21-mm prostheses, because these valve sizes are usually grouped together as "small-sized prostheses." Our aim was to verify whether the use of a 19-mm SJP versus a 21-mm SJP for AVR is associated with different 15-year clinical outcomes in terms of overall survival and freedom from valve-related complications and cardiac events.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 References
 
Patient profile
Between 1981 and 1995, 229 consecutive patients underwent AVR (isolated or with associated coronary artery bypass grafting [CABG]) for aortic stenosis with either a 19-mm SJP (53 patients, group 1) or a 21-mm SJP (176 patients, group 2). Patients with more than mild aortic regurgitation and patients undergoing concomitant mitral or tricuspid valve operations were excluded. The main preoperative characteristics of the patients are summarized in Table 1.


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  		Table 1. Preoperative Patient Profile

 
Surgical technique
All operations were performed with moderate systemic hypothermia and use of cold potassium cardioplegia and pericardial topical cooling. Prosthesis size was selected according to the size of the aortic annulus. Prostheses were usually implanted by means of multiple interrupted sutures reinforced with Teflon pledgets placed below the aortic annulus.

Data collection and follow-up
Preoperative and operative data were obtained by retrospective review of clinical and operative records, and pathology reports. A complete echocardiographic examination before discharge from the hospital was available for 205 patients (98% of the discharged patients), for 49 patients of group 1 (100%), and 156 of group 2 (97%). Based on the effective orifice area index (EOAi) of the prosthesis calculated at discharge, patients were divided into 3 groups, irrespective of prosthesis size [14]: (1) group A, 24 patients with EOAi less than or equal to 0.60 cm2/m2, (2) group B, 149 patients with EOAi more than 0.60 cm2/m2, and less than or equal to 0.90 cm2/m2, and group C, 32 patients with EOAi more than 0.90 cm2/m2.

Follow-up information on hospital survivors was collected during a 6-month interval ending in December 2000. Unsuccessful attempts to trace patients were followed by contact with a family member or with the referring physician. One hundred and nine patients were reevaluated at our outpatient clinic (103 patients underwent a complete echocardiographic study), 46 underwent telephone interviews, and 12 answered a standard follow-up questionnaire for prosthetic valve recipients. Follow-up of hospital survivors was 99% complete (208 of 210) at a mean follow-up time of 8 ± 5 years (range, 70 days to 19 years), for a total follow-up of 1,806 patient-years. For group 1 patients, total follow-up was 402 patient-years (mean, 8 ± 5 years), whereas for group 2 patients total follow-up was 1,404 patient-years (mean, 8 ± 5 years). Three patients in group 1 and 2 in group 2 were removed from follow-up at the time of reoperation on the aortic (4 patients) or mitral valve (1 patient). At last follow-up, there were 36 current survivors with a 19-mm SJP and 126 with a 21-mm SJP, with a mean follow-up time of 10 ± 4 years.

An analysis of the 15-year outcome was performed grouping patients according to prosthesis size. Hospital mortality (death before discharge from the hospital or within 30 days since AVR, or both), major postoperative complications, and prosthesis-related events were defined according to the recently revised guidelines [15]. Cardiac events were defined as new episodes of angina, myocardial infarction, congestive heart failure, and ventricular arrhythmia requiring hospitalization or leading to death. Sudden deaths, defined as unexpected or unexplained deaths of unknown cause, were analyzed both separately and together with valve-related deaths.

Doppler echocardiography
Standard M-mode dimensions were collected according to the American Society of Echocardiography criteria. All Doppler measurements were averaged more than 3 cycles in patients with sinus rhythm or more than 5 cycles in those with atrial fibrillation. From the data obtained with pulsed-wave and continuous-wave Doppler recordings, we calculated the peak and mean gradient across the prosthesis (from the long form of the modified Bernoulli equation), the EOAi, and the left ventricular mass index from Devereux and Reichek’s formula [16].

Statistical analysis
Data are presented as mean plus or minus standard deviation and as simple percentages. Linearized rates were compared between the two groups using a likelihood ratio test. Overall survival and freedom from valve-related complications and cardiac events were determined by Kaplan-Meier actuarial analysis and expressed as percentage of patients who were event free plus or minus standard error. Differences in actuarial freedom between groups of patients were determined using the log-rank test. The linearized rate of postoperative complications was expressed as percent per year plus or minus the standard error.

All variables listed in Table 1 were investigated for association with hospital death, overall death, valve-related complications, sudden death, and cardiac events at univariate analysis. Student’s t test or Wilcoxon test for continuous data and {chi}2 or Fisher’s test for discrete variables were used, as appropriate. All variables with a p value of less than 0.10 at univariate analysis were entered in the multivariate analysis. Predictors of hospital mortality were identified by means of a logistic regression with forward selection and with a selection cut off set at 0.05. Predictors of events during follow-up were identified by means of Cox’s proportional hazards regression with Z-value cut off set at 2.0. Cut-off points for age were determined with the help of receiver operating characteristic curves, choosing the value with the highest likelihood ratio. Data analysis was performed with the NCSS 2000 software (Statistical Solutions Ltd, Cork, Ireland).


   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 References
 
Early results
Overall hospital mortality was 7.5% (4 of 53) in group 1 and 8.5% (15 of 176) in group 2 (p > 0.2). The majority of deaths were caused by postoperative low cardiac output (3 patients in group 1 and 10 in group 2); 1 patient of each group died because of perioperative myocardial infarction, whereas 4 patients in group 2 died because of ventricular fibrillation, hemorrhage, respiratory insufficiency, and acute renal failure, respectively. Variables significantly correlating with hospital mortality at univariate and multivariate analysis are summarized in Table 2. From multivariate analysis, significant predictors of hospital mortality were higher New York Heart Association (NYHA) functional class (p < 0.001), associated CABG (p < 0.001; odds ratio, 5.3, confidence interval, 95%,1.5–19.2), and larger body surface area (BSA) (p = 0.02).


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  		Table 2. Predictors of Hospital Death, Late Death, Overall Death, and Cardiac Events at Univariate and Multivariate Analysis

 
Echocardiographic data before discharge from the hospital are summarized in Table 3. Patients with a 19-mm valve showed a significantly higher peak and mean transprosthetic gradient (p < 0.001), and a lower EOAi (p = 0.002) compared with 21-mm valve recipients. An important patient prosthesis mismatch with EOAi less than or equal to 0.60 cm2/m2 was found in 18% of group 1 patients versus 5% of group 2 patients (p = 0.004). Among patients with a small BSA (< 1.70 m2), an important patient prosthesis mismatch was present in 15% of 19-mm valve recipients (6 of 41) versus 2% of 21-mm valve recipients (2 of 113) (p = 0.008).


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  		Table 3. Echocardiographic Data

 
Late results
During follow-up there were 41 late deaths, 10 in group 1 and 31 in group 2. The causes of late deaths are listed in Table 4. The linearized rate of overall death, including hospital deaths, was 3.5% ± 0.9% per year in group 1 and 3.3% ± 0.5% per year in group 2 (p > 0.2; Table 4). Differences in actuarial survival at 5, 10, and 15 years between the two groups could be due to chance (p > 0.2; Fig 1). Considering grouping based on EOAi at discharge from the hospital, actuarial survival was 79% ± 12% for group A, 64% ± 8% for group B, and 79% ± 9% for group C (p > 0.2). From multivariate analysis, independent predictors of overall death were older age (p < 0.001) and CABG associated with AVR (p < 0.001; odds ratio, 3.1; confidence interval, 95%, 1.6–5.8; Table 2). The cut-off point for age identified by means of ROC curves was more than 75 years old.


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  		Table 4. Linearized Rate of Valve-Related Complications, Cardiac Events, and Death From Different Causes During Follow-up

 


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  		Fig 1. Actuarial estimate of overall survival in patients with a standard 19-mm or 21-mm St. Jude Medical aortic prosthesis. Numbers on the horizontal axis represent patients at risk. (n.s. = not significant.)

 
Details on valve-related complications are provided in Table 4. Actuarial freedom from valve-related complications at 15 years was 50% ± 16% and 58% ± 6%, respectively (p > 0.2; Fig 2). Considering grouping based on EOAi at discharge from the hospital, actuarial freedom from valve-related complications was 50% ± 21% for group A, 53% ± 7% for group B, and 69% ± 11% for group C (p = 0.10). Multivariate analysis did not identify any independent predictor of the occurrence of valve-related complications.



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  		Fig 2. Actuarial freedom from valve-related complications in patients with a standard 19-mm or 21-mm St. Jude Medical aortic prosthesis. (n.s. = not significant.)

 
Linearized rate of valve-related deaths and actuarial freedom from valve-related deaths at 5-year, 10-year, and 15-year follow-ups between patients with a 19-mm SJP and a 21-mm SJP are listed in Table 4 and Figure 3, respectively.



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  		Fig 3. Actuarial freedom from valve-related death including sudden death in patients with a standard 19-mm or 21-mm St. Jude Medical aortic prosthesis.

 
Details on the causes of valve-related deaths are reported in Table 4. Including sudden deaths among valve-related deaths, patients with a 19-mm valve had a higher linearized rate of valve-related death (p = 0.03), and a lower 15-year actuarial freedom (84% ± 6% versus 90% ± 5%; p = 0.02; Fig 3). With respect to EOAi grouping, actuarial freedom from valve-related deaths including sudden death was 90% ± 7% for group A, 87% ± 5% for group B, and 90% ± 7% for group C (p > 0.2). From multivariate analysis, independent predictors of valve-related death including sudden death were implantation of a 19-mm versus a 21-mm valve (p = 0.02; odds ratio, 3.7; confidence interval, 95%, 1.2–11.4), male sex (p = 0.04; odds ratio, 3.4; confidence interval, 95%, 1.1–10.8), and older age (p = 0.05; Table 2).

Fifteen-year freedom from sudden death was lower for group 1 patients (92% ± 5% vs 99% ± 1%; p = 0.01). With respect to EOAi grouping, actuarial freedom from sudden death was 94% ± 5% for group A, 98% ± 1% for group B, and 96% ± 4% for group C (p > 0.2). From multivariate analysis, older age was the only independent predictor of sudden death (p = 0.03), whereas implantation of a 19-mm versus 21-mm SJP, although associated with the occurrence of sudden death, did not reach statistical significance, probably because of the small number of events observed (p = 0.13; odds ratio, 6.0; confidence interval, 95%, 0.6–60; Table 2).

Functional status and cardiac events
Mean NYHA functional classes at last follow-up were 1.8 ± 0.8 in group 1 versus 1.3 ± 0.5 in group 2 (p < 0.001). Eight patients (22%) in group 1 and 4 patients (3%) in group 2 were in NYHA functional class III (p = 0.01). Details on cardiac events are provided in Table 4. Cardiac events were mainly episodes of congestive heart failure requiring hospitalization, being observed in 10 patients of group 1 (2.5% ± 0.8% per year) and in 7 of group 2 (0.5% ± 0.2% per year; p = 0.002). The linearized incidence of adverse cardiac events in group 1 was similar between patients with a BSA greater than or equal to 1.70 m2 (3.0% ± 2.1% per year) and patients with a smaller BSA (2.4% ± 0.8% per year) (p > 0.2). Actuarial freedom from cardiac events at 15 years was 56% ± 13% and 86% ± 4%, respectively (p = 0.008; Fig 4). Considering EOAi at discharge from the hospital, actuarial freedom from cardiac events was 56% ± 15% for group A, 80% ± 5% for group B, and 94% ± 4% for group C (p = 0.03; Fig 5). The difference between groups B and C could be due to chance (p > 0.2), whereas both groups had a significantly higher freedom from cardiac events compared with group A (p = 0.04 and p = 0.02, respectively). Multivariate analysis indicated that the EOAi at discharge from the hospital (p = 0.007) and CABG associated with AVR (p = 0.05; odds ratio, 2.6; confidence interval, 95%, 1.0 –7.1; Table 2) were independent predictors of cardiac events during follow-up.



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  		Fig 4. Actuarial freedom from cardiac events in patients with a standard 19-mm or 21-mm St. Jude Medical aortic prosthesis.

 


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  		Fig 5. Actuarial freedom from cardiac events in patients with different prosthetic effective orifice area index assessed before discharge from hospital. (EOAi = effective orifice area index.)

 
Echocardiographic data at follow-up
Twenty-eight patients in group 1 (78% of current survivors) and 75 in group 2 (60% of survivors) underwent two-dimensional transthoracic echocardiography during their follow-up visit at our center. Results are summarized in Table 3. Peak and mean transprosthetic pressure gradients were significantly higher in patients with a 19-mm valve (p < 0.001 and p = 0.002, respectively), with a lower EOAi (p = 0.01). Eighteen percent of group 1 patients showed an EOAi less than or equal to 0.60 cm2/m2 versus 4% of group 2 (p = 0.03). On the other hand, 11% in group 1 versus 17% had an EOAi more than 0.90 cm2/m2 (p > 0.2).

Although left ventricular mass index was still abnormal at last follow-up in both groups of patients (148 ± 23 g/m2 vs 138 ± 24 g/m2, p = 0.08), the regression of left ventricular hypertrophy was significantly higher in patients with a 21-mm prosthesis than in patients with a 19-mm valve (22% ± 9% vs 18% ± 9%, p = 0.02). A trend to a linear correlation between EOAi at discharge and percent reduction in left ventricular mass was observed (r = 0.201; p = 0.07).


   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
References
 
Despite continuing improvement in valve design and prosthestic orifice area, currently available small-sized prostheses for AVR still determine a certain degree of obstruction to left ventricular outflow and generate residual transprosthetic gradients. When considering small-sized prostheses, 19-mm and 21-mm valves are usually grouped together and compared with prostheses of larger size [6, 17]. However, the actual orifice area reported for the 19-mm SJP is 21% smaller than that of the 21-mm SJP, being 1.63 cm2 versus 2.06 cm2 [8]. Our aim was to verify whether such difference in valve area has an impact on clinical outcome in terms of overall mortality, valve-related complications and cardiac events.

In the present series, hospital mortality was about 8% in both groups and was mainly influenced by preoperative NYHA functional class (p < 0.001), associated CABG (p = 0.004), and BSA (p = 0.01). In the same time period hospital mortality calculated for all patients who underwent AVR with or without associated CABG, regardless of prosthesis size, was 4.9%, quite lower than that observed in the present series. Overall survival of patients with a 19-mm or 21-mm SJP was similar at 5, 10, and 15 years, comparing favorably with previous reports [17, 18]. Older age (p < 0.001) and CABG associated with AVR (p < 0.001) were independent predictors of overall death. The presence of coronary artery disease requiring revascularization at the time of AVR appears to be a very important risk factor in patients receiving a small-sized SJP. In agreement with previous reports [3, 19–21], and also in our experience, CABG was found to be an independent predictor of hospital and overall death.

Our findings indicate that BSA is an independent risk factor for hospital mortality but not for overall death and sudden death, as observed by others. In particular, Kratz and colleagues [3] identified a BSA of more than 1.90 m2 as an independent risk factor for sudden deaths after AVR with small-sized valves, whereas He and coworkers [20] indicated a BSA of more than 1.70 m2 as a predictor of late death. Moreover, on the basis of the hemodynamic performance, it has been suggested to limit the use of the 21-mm SJP only to patients with a BSA less than or equal to 1.70 m2 [19, 22]. In contrast, other studies reported no clinically relevant problems with the use of small-sized St. Jude and Carbomedics (Sulzer Carbomedics, Inc, Austin, TX) prostheses, even in patients with a BSA of more than 1.70 m2 [11, 23–25].

Valve-related complications and deaths in the present series were comparable with those previously reported for AVR with larger valves in our experience [26] and were not significantly different between 19-mm and 21-mm valve recipients, unless sudden deaths were included among valve-related deaths. From multivariate analysis, independent predictors of valve-related death, including sudden death, were implantation of a 19-mm valve versus a 21-mm valve, male sex, and older age (> 75 years). The rate of sudden death was significantly higher in patients of group 1 than group 2; however, at multivariate analysis only older age (> 75 years) was found to be an independent risk factor for sudden death. Neither BSA, as reported by Kratz and colleagues [3], nor preoperative left ventricular ejection fraction and coronary artery disease, as reported by Debetaz and colleagues [21], were found to be independent predictors of sudden death. It can be hypothesized that sudden death may be related to the high degree of residual left ventricular hypertrophy observed in patients with 19-mm SJP. In fact, percent reduction in left ventricular mass index at last follow-up was significantly lower in patients with a 19-mm valve (p = 0.02).

A significant difference between patients with a 19-mm SJP and those with a 21-mm SJP was found in terms of 15-year freedom from cardiac events (56% ± 13% vs 86% ± 4%, p = 0.008), congestive heart failure being significantly more frequent in the former group (p = 0.002). Indeed, at last follow-up 22% of group 1 patients were in NYHA functional class III compared with only 3% of group 2 (p = 0.01). Preoperative NYHA functional class III–IV was found to be an independent risk factor for hospital death but not for cardiac events during follow-up, at variance with the findings of Kratz and coworkers [3]. Multivariate analysis indicated CABG associated with AVR and EOAi at discharge as the only independent predictors of cardiac events during follow-up. Implantation of a small-sized valve in a patient with a large BSA originates a patient-prosthesis mismatch, usually defined with EOAi less than or equal to 0.90 cm2/m2 [1, 13]. In the present study, EOAi was rather low for both valve sizes and was significantly lower in 19 mm-valve recipients than in 21-mm valve recipients, with 18% versus 5% of patients with EOAi less than or equal to 0.60 cm2/m2 at discharge (p = 0.004), which would be considered a severe aortic stenosis for a native valve [14]. Thus, a size 19-mm valve leads to a higher degree of patient–prosthesis mismatch, not only in patients with a large BSA. In fact, in the present series an important patient–prosthesis mismatch was present in 15% of 19-mm valve recipients with a small BSA (< 1.70 m2). Such patient–prosthesis mismatch has negative implications on effort tolerance and possibly on survival [22]. Although prosthesis size was also associated with the occurrence of cardiac events at univariate analysis, at multivariate analysis only EOAi appeared to have an independent prognostic role, thus showing that the hemodynamic performance of the valve rather than valve size alone influences the occurrence of late cardiac events, particularly from congestive heart failure. The mechanism by which valve hemodynamic performance affects late prognosis may be related to the degree of regression of left ventricular hypertrophy, which is a well-known risk factor for the development of congestive heart failure and anginal symptoms. In fact, a trend to a linear correlation between EOAi at discharge from the hospital and percent of left ventricular mass reduction at last follow-up was observed (p = 0.07). The degree of regression of left ventricular hypertrophy was also associated with prosthesis size, being significantly higher in 21-mm valve recipients than in patients with a 19-mm valve (p = 0.02).

Importantly, in the present series we did not observe a complete regression of left ventricular hypertrophy in either group of patients, as also reported by others [2, 4, 27]. Concordantly, peak and mean transprosthetic pressure gradients were relatively high, although comparable to those previously reported for small-sized St. Jude Medical aortic valves [4, 8, 11].

The present study has the limitations of a retrospective study where follow-up is carried out at only one point and analyzes a relatively small population, particularly concerning 19-mm valve recipients. However, very few data are available in the literature comparing 2 small-sized prostheses with each other. Such comparison is quite relevant to the surgeon who often faces the difficult choice between small-sized valves when operating on a small aortic annulus.

Breifly, in conclusion, our study shows satisfactory long-term results after AVR with both 19-mm and 21-mm SJP. However, a less evident regression of left ventricular hypertrophy and a higher rate of cardiac events are observed after AVR with 19-mm SJP. In patients who are candidates for AVR with a mechanical prosthesis, and in whom an active lifestyle is expected, it is our current policy to avoid the use of a 19-mm prosthesis, even in the presence of a small BSA, and to consider alternative surgical approaches when a larger prosthesis cannot be directly implanted.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 

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