The beneficial effects of cardiac resynchronization therapy (CRT) on symptoms, hospitalizations and mortality are well established in patients with left ventricular systolic dysfunction and QRS. 120 ms. Majority of studies about CRT have included patients with left bundle branch block (LBBB). However, in some subgroups of patients with heart failure and electrical disorders such as right bundle branch block (RBBB) or induced LBBB by permanent pacing, the benefit of CRT remains uncertain.
Right ventricle apex (RVA) pacing cause electrical and mechanical dyssynchrony, which could worsen the left ventricular ejection fraction and remodel left ventricle. Some trials, as DAVID or MOST, have suggested a possible harmful role of RVA pacing. In patients with left ventricular dysfunction and need of pacing, CRT could be considered as an alternative. Several trials, as HOBIPACE and RD-CHF, support CRT in patients with left ventricular disfunction who need pacing. Therefore, current clinical practice guidelines recommend the use of CRT in heart failure patients with depressed systolic function who need permanent pacing.
In other hand, RBBB also causes electrical disorders like interventricular and intraleft ventricular dyssynchrony. And this has been identified as a predictor of HF worsening. CRT might also have some hemodynamic benefits in patients with RBBB and intraleft ventricular dyssynchrony. Nowadays, recommendations for CRT in the guidelines do not specify QRS morphology although emphasize that there is not yet sufficient evidence to provide specific recommendations for patients with RBBB.