Abstract
Cardiac resynchronization therapy (CRT) is an important adjunct to medical therapy
of heart failure. Necessary preconditions for a successful application of CRT are
mechanical and electrical dyssynchrony of the left ventricle. Small clinical studies
with a short follow-up time in patients with advanced systolic heart failure, structural
heart disease, low LV ejection fraction (< 35 %) and a wide QRS complex (> 150 ms)
demonstrated the beneficial effect of bi-ventricular pacing showing improvement of
cardiac function and reduction of heart failure symptoms within a few weeks or months
after initiation of CRT.
Large randomized trials (COMPANION and CARE-HF) in patients with advanced heart failure
showed a decrease of overall mortality and less heart failure hospitalizations besides
improvement of NYHA class. ICD backup in CRT devices proved to be important to reduce
sudden arrhythmic death. Since the benefit of decreased overall mortality is limited
in severe heart failure, three important trials (REVERSE, MADIT-CRT and RAFT) were
launched in order to test the effect of CRT in patients with mild or asymptomatic
heart failure (NYHA class I and II). The results of these trials with different study
designs, follow-up time and primary endpoints demonstrated that significant „reverse
remodeling“, reduction of overall mortality and decrease of heart failure hospitalization
can be best achieved in patients with left bundle branch block (LBBB) configuration,
a broad QRS complex ≥ 130 ms, sinus rhythm, female gender and non-ischemic cardiomyopathy.
Therefore, prevention of heart failure progression is easier to achieve at an early
stage of heart failure by using bi-ventricular pacing with ICD backup. The long-term
benefit of CRT in patients that fulfill the effectiveness criteria of CRT is more
pronounced in patients with mild- instead of advanced heart failure.
