Ventricular pump function and pacing: physiological and clinical integration.

Optimal cardiac pump function depends on ordered mechanical events that are orchestrated by electrical timing. This electromechanical coupling occurs at multiple anatomic levels: within atria, between atria and ventricles, between ventricles, and especially within the left ventricle (LV). Such disruptions to proper electrical timing result in disordered mechanical events (desynchronization, or “dyssynchrony”), can occur spontaneously or be induced in isolation or in various combinations at any level, and degrade cardiac pump function. These disruptions to normal mechanical ordering occur because of fixed or functional conduction blocks and can be generated by myocardial disease or can be induced by cardiac pacing. The adverse effects of disruption of proper electromechanical coupling at all levels with particular attention to the effects of ventricular conduction delay due to conventional (usually right ventricular apical, RVA) pacing and left bundle-branch block (LBBB) are discussed later. Subsequently, remedies for prevention or treatment are discussed along the same lines.