Myocardial Oxygen Consumption and Efficiency in Aortic Valve Stenosis Patients With and Without Heart Failure

Abstract

Background: Myocardial oxygen consumption (MVO₂) and its coupling to contractile work are fundamentals of cardiac function and may be involved causally in the transition from compensated left ventricular hypertrophy to failure. Nevertheless, these processes have not been studied previously in patients with aortic valve stenosis (AS).

Methods and results: Participants underwent ¹¹C-acetate positron emission tomography, cardiovascular magnetic resonance, and echocardiography to measure MVO₂ and myocardial external efficiency (MEE) defined as the ratio of left ventricular stroke work and the energy equivalent of MVO₂. We studied 10 healthy controls (group A), 37 asymptomatic AS patients with left ventricular ejection fraction ≥50% (group B), 12 symptomatic AS patients with left ventricular ejection fraction ≥50% (group C), and 9 symptomatic AS patients with left ventricular ejection fraction <50% (group D). MVO₂ did not differ among groups A, B, C, and D (0.105±0.02, 0.117±0.024, 0.129±0.032, and 0.104±0.026 mL/min per gram, respectively; P=0.07), whereas MEE was reduced in group D (21.0±1.6%, 22.3±3.3%, 22.1±4.2%, and 17.3±4.7%, respectively; P<0.05). Similarly, patients with global longitudinal strain greater than -12% and paradoxical low-flow, low-gradient AS had impaired MEE (P<0.05 versus controls). The ability to discriminate between symptomatic and asymptomatic patients was superior for global longitudinal strain compared with MVO₂ and MEE (area under the curve 0.98, 0.48, and 0.61, respectively; P<0.05).

Conclusions: AS patients display a persistent ability to maintain normal MVO₂ and MEE (ie, the ability to convert energy into stroke work); however, patients with left ventricular ejection fraction <50%; global longitudinal strain greater than -12%; or paradoxical low-flow, low-gradient AS demonstrate reduced MEE. These findings suggest that mitochondrial uncoupling contributes to the dismal prognosis in patients with reduced contractile function or paradoxical low-flow, low-gradient AS.

Keywords: aortic valve stenosis; myocardial external efficiency; myocardial metabolism; myocardial oxygen consumption; positron emission tomography.

Figure 1

MEE and oxygen consumption. MEE declined late, and MVO₂ was constant regardless of study group (A), despite deteriorating GLS (B), LVEF (C), or increasing NT‐proBNP (D). Values are mean±SD. *P<0.05 vs other groups (except for LVEF <50 vs 50–59 [P=0.20]). AsympEF ≥50 indicates asymptomatic aortic valve stenosis patients with left ventricular ejection fraction ≥50%; GLS, global longitudinal strain; LVEF, left ventricular ejection fraction; MEE, myocardial external efficiency; MVO₂, myocardial oxygen consumption; NT‐proBNP, N‐terminal pro‐B‐type natriuretic peptide; SympEF ≥50, symptomatic aortic valve stenosis patients with left ventricular ejection fraction ≥50%; SympEF <50, symptomatic aortic valve stenosis patients with left ventricular ejection fraction <50%.

Figure 2

Diagnostic accuracy to distinguish between asymptomatic and symptomatic aortic valve stenosis (AS) patients. Receiver operating characteristic curve analysis illustrating the diagnostic accuracy to distinguish between AS patients with and without symptoms. GLS vs MEE, GLS vs MVO₂, and GSL vs LVEF, all P<0.05. GLS vs NT‐proBNP, P=0.10. Values are AUC (95% CI). AUC indicates area under the receiver operating characteristic curve; GLS, global longitudinal strain; LVEF, left ventricular ejection fraction; MEE, myocardial external efficiency; MVO₂, myocardial oxygen consumption; NT‐proBNP, N‐terminal pro‐B‐type natriuretic peptide.

Figure 3

Reduced MEE and MVO₂ in patients with paradoxical low‐flow low‐gradient aortic valve stenosis (AS). Reduced MEE in patients with P‐LFLG compared with AS patients with NFHG and NFLG AS. Mean±SD. *P<0.05 compared with NFHG and NFLG. MEE indicates myocardial external efficiency; MVO₂, myocardial oxygen consumption; NFHG, normal‐flow, high‐gradient; NFLG, normal‐flow, low‐gradient; P‐LFLG, paradoxical low‐flow, low‐gradient aortic valve stenosis.