Cardiac resynchronization therapy in NYHA class IV heart failure.

Clinical practice guidelines recommend cardiac resynchronization therapy (CRT) for ambulatory New York Heart Association (NYHA) class IV patients with a QRS duration >or= 120 ms and a left ventricular ejection fraction <or= 35%. Only two prospective, randomized trials have compared outcomes after CRT in NYHA class III and IV patients. CRT improved mortality, exercise capacity, and quality of life in class IV patients, but the 1-year mortality remained high. Patients in these trials were in sinus rhythm at randomization and most patients had a left bundle branch block. Less data are available for NYHA class IV patients with atrial fibrillation, right bundle branch block, and previous ventricular pacing. No prospective randomized data are available for the use of CRT as rescue therapy in inotrope-dependent patients, but several case series have reported promising results. It is likely that "rescue therapy" with CRT will be most beneficial when patients improve enough with CRT to allow reinstitution of angiotensin-converting enzyme inhibitors and beta blockers.