BIV pacing in moderate-to-severe HF
For patients with moderate-to-severe HF (NYHA class III– IV), CRT has been shown in 4 trials (MUSTIC SR, MIRACLE, CONTAK-CD, MIRACLEICD1,2,22,23) to provide improvements in NYHA functional class, exercise capacity (measured by the 6-minute hall walk distance) and peak oxygen consumption and quality of life.
The CARE-HF study randomized patients to either CRT plus optimal medical therapy or CRT alone. It was the first trial showing that CRT without an ICD prolonged survival and reduced both morbidity and mortality, with the effect sustained over 37 months of follow up24. Similarly, in the COMPANION trial, Bristow et al have shown that BiVP decreased the combined risk of death from any cause or first hospitalization and, when combined with an implantable cardioverted defibrillator (ICD), significantly reduces mortality7. A meta-analysis of 6 randomized, controlled trials of CRT for more severe, chronic, symptomatic LV systolic dysfunction found that CRT was associated with a 28% reduction in all-cause mortality and a 37% reduction in new hospitalizations for exacerbation of HF25.
In the COMPANION trial, patients with advanced heart failure (NYHA III or IV) due to ischemic or nonischemic cardiomyopathies and a QRS interval of at least 120 msec were randomly assigned to receive optimal pharmacologic therapy alone or in combination with CRT with either a pacemaker or a pacemaker–defibrillator. The primary composite end point was the time to death from or hospitalization for any cause. As compared with optimal pharmacologic therapy alone, CRT with a pacemaker or a defibrillator significantly decreased the risk of the primary end point. The risk of the combined end point of death from or hospitalization for heart failure was also significantly reduced in the pacemaker and the defibrillator groups7. The CARE-HR trial enrolled patients with NYHA class III or IV heart failure due to left ventricular systolic dysfunction and cardiac dyssynchrony to receive standard pharmacologic therapy alone or with cardiac resynchronization. The primary end point was the time to death from any cause or an unplanned hospitalization for a major cardiovascular event. The principal secondary end point was death from any cause. As compared with medical therapy alone, CRT significantly decreased the risk of the primary endpoints. Also, CRT significantly reduced the interventricular mechanical delay, the end-systolic volume index, and the area of the mitral regurgitant jet; increased the left ventricular ejection fraction; and improved symptoms and the quality of life8.