Metabolic flexibility and reverse remodelling of the failing human heart.

BACKGROUND AND AIMS: Cardiac resynchronization therapy (CRT) produces long-term reverse remodelling which requires greater adenosine triphosphate delivery to the contractile machinery. Whilst the heart retains some metabolic flexibility in non-ischaemic cardiomyopathy, whether this correlates with reverse remodelling is unknown. This study investigated whether CRT acutely changes cardiac substrate uptake, and whether this translates to favourable reverse remodelling. METHODS: The effect of CRT on cardiac substrate uptake was assessed via direct coronary flow and arteriovenous measurements, with metabolomic/lipidomic analysis on infusions of insulin/glucose and intralipid. Cardiac function was assessed with left ventricular pressure-volume loops during implantation, and cardiac magnetic resonance before and 6 months following CRT, with and without biventricular pacing. RESULTS: Regardless of substrate infusion, CRT acutely improved stroke work without increasing O2 uptake on both insulin/glucose (by 34%, P = .05) and intralipid (by 36%, P = .03). This was followed by increased fatty acid (FA) uptake on insulin/glucose (R = 0.89, P = .03) and increased β-hydroxybutyrate uptake (R = 0.81, P = .05) during intralipid infusion. After 6 months, there was a 48% (P < .001) reduction in left ventricular end diastolic volume, beyond that achievable by acutely shortening or lengthening QRS duration. Reverse remodelling significantly correlated with increased FA uptake with CRT on insulin/glucose (R = 0.71, P = .05) driven by long and medium chain uptake, and increased ketone uptake with CRT on intralipid (R = 0.79, P = .05). CONCLUSIONS: CRT acutely alters the metabolic phenotype of non-ischaemic cardiomyopathy towards a more physiological picture of FA uptake which correlates with reverse remodelling. Retained metabolic flexibility may therefore be critical for subsequent reverse remodelling.