Six RCTs trials with a total of 3,108 participants were included. The authors did not discuss study quality although it was noted that longer follow-up periods would have been desirable.
Only one of the six trials included reported a significant reduction in all cause mortality. Overall, the meta-analysis showed that mortality was reduced significantly with cardiac resynchronisation therapy (hazard ratio 0.72, 95% CI: 0.60, 0.86). In patients without an implantable cardiac defibrillator device, mortality was significantly reduced, with a hazard ratio of 0.70 (95% CI: 0.58, 0.85). In patients with an implantable cardiac defibrillator device, there was a non-significant reduction in mortality with cardiac resynchronisation compared to implantable cardiac defibrillators only (hazard ratio 0.80, 95% CI: 0.48, 1.32).
Overall, cardiac resynchronisation therapy reduced hospitalisation for worsening heart failure significantly by 37% (hazard ratio 0.63, 95% CI: 0.44, 0.91, p=0.02). There was significant heterogeneity which disappeared when considering patients with or without implantable cardiac defibrillator devices separately. In patients without implantable cardiac defibrillator devices, hospitalisation was reduced by 53% (hazard ratio 0.47, 95% CI: 0.37, 0.61), whereas there was no significant reduction in hospitalisations comparing cardiac resynchronisation in implantable cardiac defibrillator patients versus implantable cardiac defibrillator only (hazard ratio 0.92, 95% CI: 0.68, 1.25).
In the meta-regression analysis, the main effect was seen for implantable cardiac defibrillator versus no implantable cardiac defibrillator treatment; implantable cardiac defibrillator studies also had a higher percentage of ischaemic patients (69% versus 43%, p=0.000). The meta-regression analysis suggested that benefits of cardiac resynchronisation therapy decreased with an increase of the proportion of ischaemic patients (p=0.001). The highest hospitalisation rate was seen in patients without cardiac resynchronisation and without implantable cardiac defibrillator (26.7%). The rates in the other groups (implantable cardiac defibrillator only, implantable cardiac defibrillator plus cardiac resynchronisation, cardiac resynchronisation only) were similar. The meta-regression analysis showed no effect of β-blocker therapy.