Determinants of trans-prosthetic gradients after isolated surgical aortic valve replacement and effect on survival

Abstract

Abstract Background Surgical aortic valve replacement (sAVR) remains the primary therapeutic approach for severe symptomatic aortic stenosis. Patient-prosthetic mismatch (PPM) occurs when the implanted valve is too small for the patient and is characterized by a small orifice area and elevated trans-valvular pressure gradient identified on post-operative transthoracic echocardiography (TTE). PPM is thought to be associated with adverse clinical outcomes, especially when severe, however data is conflicting. Purpose We sought to determine the impact of patient- and prosthesis-related parameters on post-operative trans-valvular pressure gradient, as a surrogate of PPM, and identify its influence on survival in a large single centre study. Methods This was a retrospective study of patients who underwent isolated sAVR between June 2003 and February 2017 at our tertiary cardiothoracic centre. Patients were excluded if their clinical and surgical records were incomplete, they hadn’t attended post-operative follow up or they had undergone valve replacement with anything other than a conventional stented tissue or mechanical prosthesis. All patients underwent postoperative follow up at eight weeks, six months and annually thereafter in keeping with local guidelines. TTE was performed between six and 12 months after surgery. Peak trans-valvular gradient was calculated using the continuity equation based upon continuous wave doppler assessment through the aortic valve. The highest value obtained from multiple views was recorded. Independent predictors of post-operative gradient were determined using a cox-proportional hazards model. Survival analysis was evaluated by Kaplein-Meier curves and log-rank test. Results One thousand seven hundred and ninety patients underwent isolated SAVR during the study period, of which 604 patients satisfied the inclusion and exclusion criteria. Mean age was 69.5 (±11.4) years and 346 (59%) were male. Mean peak pressure gradient was 29.96 (±12.4) mmHg. Independent predictors of increased post-operative gradients were: smaller valve size, postoperative diuretic use, age, gender and operating surgeon (p<0.001) (Table 1). Seventy-two patients (12%) died during follow-up. Mean survival was 12.1 years. After adjusting for confounders, post-operative pressure gradient was identified as a significant predictor of mortality (HR 1.02, p=0.001), alongside age (HR 1.06, p=0.001) and diabetes mellitus (HR 2.18, p=0.007) (Figure 1). Conclusion In a large cohort of patients undergoing sAVR at a single centre in the UK, valve size was the biggest determinant of postoperative pressure gradient alongside sex, diabetes, diuretic use and operating surgeon. Postoperative pressure gradient was a significant predictor of all-cause mortality. Accordingly, implanting the largest possible valve size should be considered the single most effective way of reducing the post-operative gradient and long-term mortality in patients undergoing sAVR.Table 1:Multivariate linear regressionFigure 1:K-M curve