Study Question: Does cardiac resynchronization reduce mortality in patients with advanced heart failure?
Setting: Specialty (inpatient with outpatient follow-up)
Study Design: Meta-analysis of randomized controlled trials
Synopsis: Synchronized activation of the ventricles enhances cardiac function, leading to improved exercise capacity and quality of life. The effect of cardiac resynchronization on mortality is uncertain. The authors performed a thorough search of multiple databases, including MEDLINE, EMBASE, the Cochrane Register, as well as abstracts from international scientific sessions and bibliographies of recent reviews. Eligible studies were randomized controlled trials of cardiac resynchronization for the treatment of symptomatic left ventricular dysfunction.
From an initial 6,883 studies identified, only 11 reports of four separate trials were included in the meta-analysis. Individual trials were reviewed independently in a nonblinded manner by two investigators. A sensitivity analysis was performed to assess the effect of differences in disease severity at baseline and missing data.
Baseline patient characteristics were similar in the four trials. Mean ages of patients ranged from 63 to 66 years, mean left ventricular ejection fraction ranged from 21 to 23 percent (New York Heart Association functional class III and IV), and most, if not all, patients had a prolonged QRS interval, usually left bundle branch block. These characteristics are typical of only approximately 10 percent of patients with heart failure. Baseline treatment with angiotensin-converting enzyme inhibitors ranged from 87 to 96 percent, while baseline beta-blocker use ranged from 28 to 60 percent. Patients with conventional indications for a pacemaker were excluded.
None of the individual trials reported methods of allocation assignment, and it was unclear whether allocation was concealed. Follow-up ranged from three to six months. Compared with patients in the control group, patients undergoing cardiac resynchronization had significantly reduced heart failure–related death (3.5 versus 1.7 percent; number needed to treat [NNT] = 55 for three to six months) and hospitalization (17.4 versus 13 percent; NNT = 23 for three to six months). There was a nonsignificant trend in reducing all-cause mortality (6.3 percent in control patients versus 4.9 percent in treated patients).
Bottom Line: Cardiac resynchronization reduces heart failure–related mortality and morbidity in patients with moderate-to-severe left ventricular dysfunction and prolonged QRS interval. It remains uncertain if the rate of all-cause mortality is reduced. (Level of Evidence: 1a)