Left ventricular kinetic energy as a marker of mechanical dyssynchrony in failing hearts with LBBB: a 4D flow CMR study

Background Left bundle branch block (LBBB) leads to dyssynchronous left ventricular (LV) contraction and relaxation which may contribute to LV dysfunction and ultimately heart failure. LBBB-related mechanical dyssynchrony often responds to cardiac resynchronization therapy (CRT). However, this therapy is expensive and the number of non-responders remains significant. Reliable functional markers of dyssynchronous LV pumping that can predict response to CRT have proved elusive. Almost all studies of LV mechanical dyssynchrony focus on wall motion properties rather than aspects of intraventricular flow. 4D flow CMR specific measures have recently emerged as markers of LV function in failing hearts. Reduced volume and kinetic energy (KE) of the portion of LV inflow which passes directly to outflow (Direct Flow) has been demonstrated in failing LVs compared to normal LVs. In this study we hypothesized that the volume and KE of Direct Flow would be further reduced in myopathic LVs with LBBB compared to similarly dysfunctional and remodeled LVs without LBBB.