Cardiac resynchronization therapy into the nextdecade: from the past to morbidity/mortality trials

In selected patients, biventricular pacing leads to improvement in left ventricular (LV) performance, especially in the presence of pre-existing marked asynchrony of LV contraction. Improvements are sustained in the great majority of cases, and are accompanied by reduced symptoms, increased walking distance and reduced need for hospitalization. The degree of asynchrony of LV contraction and the amount of myocardial scarring are important parameters that determine the response to cardiac resynchronization therapy (CRT). Improvements in haemodynamics are due not to a positive inotropic effect of pacing but rather to elimination of an unsynchronized energy-wasting contraction pattern. Mortality trials are in progress to assess the effect of CRT on total mortality, arrhythmic mortality and mortality from heart failure.