Valve replacement in aortic stenosis with preoperative mean gradient <50 mmHg: Hemodynamic outcome

Background and aims of the study: No prior studies have defined pre- versus postoperative hemodynamics of large numbers of patients with low mean transvalvular gradients. This was our objective. Methods: Retrospective analysis was undertaken of preoperative and postoperative echo/Doppler data in 294 patients who underwent aortic valve replacement (AVR) for aortic stenosis (AS). Some 136 patients had a preoperative mean gradient of <50 mmHg. The relationship of preoperative to pre- minus postoperative (Δ) mean gradient (GRAD), peak valvular velocity (V₂), left ventricular outflow tract velocity (V₁), V₁/V₂ratio, V_-V₁, and aortic valve area (AVA) were plotted and analyzed such that a'zero-benefit threshold' from surgery could be estimated. Results: Strong relationships (r >0.80) were noted for GRAD to ΔGRAD, V₂ to ΔV₂, and (V₂-V₁) to Δ(V₂-V₁) with zero-benefit thresholds of 16 mmHg for GRAD, 2.6 m/s for V₂ and 1.7 m/s for V₂-V1. These thresholds were lower in patients who received homografts (11 mmHg, 2.2 m/s, and 1.1 m/s respectively), p<0.02. The relationship of pre operative V₁/V₂ to ΔV₁/V₂, and AVA-ΔAVA were weaker (r = 0.52 and 0.33 respectively) with zero-benefit thresholds of 0.41 and 2.0 cm². Among patients with depressed preoperative fractional shortening, improvement was confined to those without coexistent coronary artery disease. Conclusion: This analysis of thresholds of mean gradient benefit suggests that most patients with low gradient AS improve hemodynamically from AVR. The hemodynamic 'break-even' point averages a mean gradient of 16 mmHg.