Mitral Regurgitation in Cardiac Resynchronization

Abstract

ardiac resynchronization (CRT) has emerged as a highly beneficial alternative to patients with heart failure (HF), providing symptomatic improvement, reversing remodeling, and reducing mortality rates. 1,2 Mitral regurgitation (MR) is an important pathological feature in cardiomyopathy, occurring in a fair proportion of patients with advanced HF and probably inducing additional adverse ventricular remodeling through volume overload. 3 Thus, MR may be an important factor influencing the final benefits a patient receives after CRT. Early reports of the effects of CRT on MR were mixed, with a majority of reports suggesting a reduction in MR after CRT. 4 In this emerging tale, the missing narrative was a thoughtful investigation of how CRT may influence MR. Such insights would help us to better understand the evolution of MR after CRT and potentially suggest means of optimizing MR reduction after CRT. Hence, the work by Solis et al 5 examining the potential mechanisms underlying the improvement of MR after CRT is highly instructive. This group of investigators is best positioned to tease out the intricacies of the anatomic and functional factors influencing post-CRT MR, having done pioneering work in animal and clinical models of MR over the last decade, using 2D and 3D echocardiography. Their work has resulted in paradigmshifting insights into mechanisms of MR in various etiologic settings. 6 Article see p 444In the current report, they apply the same systematic approach and address 2 key factors underlying functional MR, namely, the anatomic tethering forces and closing pressure. Ventricular remodeling causes leaflet tethering and incomplete coaptation. Ventricular dysfunction results in inadequate pressure generation and therefore lowers closing forces, again causing inadequate leaflet coaptation. Despite some conflicting theories, it is generally agreed that CRT mediates its benefits through mechanical resynchronization of the heart with modest increments in left ventricular (LV) systolic function. Either or both of these CRT effects could have salutary or adverse effects on MR after CRT. Solis et al examined changes in valve tethering and closing forces in 34 patients with HF who underwent CRT for classic indications. They used noninvasive indices validated in their laboratory. Patients were symptomatically better and had better exercise tolerance after CRT as evidenced by improvements in New York Heart Association class and increase in the 6-minute walk. This was accompanied by a significant reduction in MR regurgitant volume and LV volumes and an increase in ejection fraction. There were changes in mitral valve geometry after CRT, with a decrease in mitral annular area, leaflet closing area, and tenting volume. Similarly, there was an increase in the closing pressure ratio after CRT. Overall, MR decreased significantly in more than half the subjects.There are several findings in this study that lend themselves to deeper discussion. The LV volumes decreased after CRT in those with and those without decrease in...