Effects of CRT on myocardial innervation, perfusion and metabolism.

Heart failure leads to specific changes in cardiac perfusion, metabolism, and innervation. Typically, in the early phase of heart failure, left ventricular (LV) efficiency of forward work is compromised and right ventricular oxidative metabolism increased while resting myocardial perfusion is normal. With advancing disease, LV perfusion and especially the perfusion reserve and oxidative metabolism also become compromised. In addition to the abnormalities linked with the heart failure itself, commonly co-existing left bundle branch block leads to striking, mainly regional imbalance in these parameters. Recent studies have documented that cardiac resynchronization therapy (CRT) has prominent effects on myocardial perfusion, metabolism, and innervation. Cardiac resynchronization therapy normalizes many of these parameters and these changes can be considered to be the signs of successful resynchronization. In contrast, a significant number of patients do not respond to CRT. Some of the metabolic parameters, such as existing glucose metabolism as a marker of viability as well as those related to right ventricle function, may also be linked to the response to CRT.