Aortic valve replacement with stentless bioprostheses : prospective long-term studies of the Biocor and the Toronto SPV

Abstract

Background: Aortic valve disease is increasing among the elderly and aortic valve replacement is the most common cardiac surgical valve procedure in adults. Aortic stenosis (AS) is often associated with left ventricular hypertrophy (LVH) in an unexplained pattern. Traditionally, younger patients receive mechanical valves and patients older than 70 years receive bioprostheses. Stentless bioprostheses have physiologically attractive hemodynamic properties. There is hope that stentless bioprostheses will improve long-term survival and that a reduced risk of valve-related complications will allow its use in younger patients than those receiving bioprostheses today.

Patients and methods: These studies comprise 367 patients operated with the Biocor stentless (BS, n= 112) or the Toronto stentless porcine valve (T-SPV, n=255) bioprostheses in two different patient populations (mean age; 78.5 vs. 63.3 years and female; 66% vs. 29%, respectively). Early and late clinical results were evaluated for both patient populations. Long-term survival for the BS population was compared to expected survival for an age- and gender-matched comparison population and relative survival rates were calculated. Hemodynamic results were investigated by echocardiography for both valves at early and late follow-up, and in addition, the BS valve was evaluated during exercise. Regression of left ventricular mass index (LVMI) was studied in both populations after the use of stentless bioprostheses. The angiotensin-converting enzyme (ACE) gene insertion (1) / deletion (D) polymorphism was studied and subsequently related to LVMI in patients with AS operated with stentless valves.

Results: Early mortality was 7% (81112) and 1% (21255) for the BS and the T-SPV valve groups, respectively, and long-term actuarial survival at 7 years was 59%±6% and 90%±2%. There was no difference in survival between the BS valve patients and the expected survival for the age- and gender- matched comparison population supplied by Statistics Sweden, and the annual relative survival rates indicated a normalized survival pattern for those patients. Valve-related complications were few for both stentless valves under study. Early and late hemodynamic function was similar and at seven years the mean pressure difference across the aortic valve was 5.4±2.0 and 3.6±2.0 mm Hg for the BS and the T-SPV valves, respectively. Coronary artery disease and hypertension were associated with a higher LVMI over time in patients with the T-SPV and most patients had a normal LVMI at five years of follow-up. Patients with the DD genotype of the ACE gene had a higher LVMI (197±47g/m2) preoperatively than those with ID (175±41g/m2) or H (155±43 g/m2) genotypes (p=0.01). The left ventricular mass index decreased in DD (p<0.001) and ID (p<0.001) genotypes but not in the H genotype during follow-up. There was a significant difference in regression of LVMI over time between genotypes (p=0.0056) with no significant difference between genotypes at follow-up.

Conclusions: Early and long-term hemodynamic function is excellent for both stentless bioprostheses and they both confer good long-term survival. The BS patient population could be regarded as "cured" from valve disease since the observed survival did not differ from the expected survival for an age- and gender-matched Swedish comparison population, a conclusion that is also supported by a constant relative survival after the first postoperative year. Coronary artery disease and hypertension influenced the degree of LVH and its regression over time and most patients with the T-SPV valve had no LVH at long-term follow-up. Furthermore, I/D polymorphism of the ACE gene is one determinant for the hypertrophic response in patients with severe AS.