Serial measurements of myocardial efficiency in patients with aortic valve stenosis: pathophysiological insights and prognostic information

Abstract

Abstract Background In patients with aortic valve stenosis (AS), the pathophysiological abnormalities involved in the transition to symptomatic heart failure are unclear. During progression of chronic heart failure, the coupling between myocardial stroke work and myocardial oxygen consumption, i.e. myocardial external efficiency (MEE), deteriorates. However, in AS patients it is unknown whether changes in MEE over time are involved in disease progression and whether MEE has prognostic information. Purpose In patients with AS, we 1) investigated changes in MEE over time and 2) studied if MEE was associated with long-term prognosis. Methods In a prospective design, we studied 10 healthy controls and 38 patients with moderate-severe, asymptomatic AS (aortic valve area 0.5±0.1 cm2/m2, mean gradient 31±12 mmHg) and left ventricular ejection fraction ≥50%. The patient group was evaluated by serial 11C-acetate positron emission tomography, cardiovascular magnetic resonance imaging and echocardiography with a median follow-up period of 2.8 years. Furthermore, we conducted an extended follow-up of patients for a median of 5.2 years to detect clinical events (defined as symptoms due to AS, aortic valve replacement, hospitalization due to heart failure or cardiovascular death) and related them to MEE changes. Results During follow-up AS patients mean aortic valve pressure gradients increased by 13 mmHg (9 to 17; p<0.001) (mean (95% confidence interval)) and aortic valve opening area declined by −0.15 cm2 (−0.20 to −0.09; p<0.001). Global longitudinal strain worsened by 2.6% (1.8 to 3.5; p<0.001) and N-terminal pro-B-type natriuretic peptide increased by 162 ng/L (28 to 296; p=0.02) whereas left ventricular ejection fraction and cardiac index did not change significantly. MEE increased during follow-up by 4.3% (1.9 to 6.8; p=0.001) from 25.2% (24.0 to 26.5) to 29.5% (27.3 to 31.8) and was higher compared to healthy volunteers 19.9% (18.1 to 21.8; p<0.001). The changes in MEE were positively correlated to changes in end-diastolic volume (r=0.58, p=0.005) and wall stress (r=0.54, p=0.01). There were no changes in MVO2 0.0 mL/min/100g (−0.8 to 0.8; p=0.98) during follow-up. As compared to event-free patients, patients who experienced a clinical event during long-term follow-up (n=24, 63%) had higher baseline MEE 26.5% (24.3 to 28.6) vs 23.8% (22.6 to 25.1) (p=0.04) and did not increase MEE during follow-up 1.9% (−1.8 to 5.6; p=0.28) vs 5.9% (2.6 to 9.2; p=0.002). Conclusion In asymptomatic AS patients, MEE increased over time in tandem with increasing transvalvular gradients and wall stress. Thus, the myocardium displayed an inherent capacity to improve the coupling between oxidative metabolism and contractile function in response to pressure overload. High baseline MEE and blunted MEE increase predicted a poor prognosis. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): Lundbeck FoundationArvid Nilssons Foundation