Thirteen studies (2,882 patients) were included in the review: one randomised controlled trial (RCT); eight prospective observational studies; and four retrospective observational studies. Follow-up ranged from three months to 68 months. Sample sizes in the studies ranged from 22 to 952 patients.
There were statistically significant higher levels of benefit after CRT observed for patients with a wide QRS interval compared with patients with QRS intervals less than 120ms for the six-minute walk test (pooled SMD 1.27, 95% CI 0.59 to 1.96; four studies) and for NYHA class improvement (pooled SMD 1.24, 95% CI 0.72 to 1.75; three studies). There were no significant differences between these groups for left ventricular ejection fraction or left ventricular end-systolic volume.
Patients with sinus rhythm achieved significantly greater benefits of treatment with CRT than patients with atrial fibrillation in the six-minute walk test (pooled SMD 1.67, 95% CI 0.55 to 2.79; three studies) and quality of life (pooled SMD 1.24, 95% CI 0.55 to 1.94; three studies). There were no differences between these groups for left ventricular ejection fraction or NYHA class improvement.
There were no significant differences between patients with NYHA Class II symptoms and patients with NYHA Class III/IV symptoms in left ventricular end-diastolic diameter or left ventricular end-systolic diameter after treatment with CRT (three studies).