Anti- and pro-arrhythmic effects of cardiac resynchronization therapy: point of view.

Cardiac resynchronization therapy (CRT) in patients with heart failure and bundle branch block (BBB) improves regional muscle mechanics and mechanical pump function of the heart. In addition, modulation of wall motion timing and contraction can exert an antiarrhythmic effect, reducing the potential of sudden cardiac death. This effect of CRT could also be attributed to the improvement in excitation-contraction coupling, mechanical synchronization, and improved myocardial perfusion. However, it can be hypothesized that the BBB results in a concealed reentry, in which a delayed depolarization wave re-enters during phase two of the action potential. This concealed phase 2 reentry can lead to early after depolarizations and cardiac arrhythmias. By synchronizing the two ventricles, CRT eliminates the reentry substrate and the resulting arrhythmias. This hypothesis and the potential arrhythmogenic effects of CRT are discussed with regard to ventricular remodeling and mechano-electrical feedback in this setting.