Does presence of left ventricular contractile reserve improve response to cardiac resynchronization therapy? An updated meta-analysis.

Background: Up to a third of patients undergoing cardiac resynchronization therapy (CRT) do not have a clinical or echocardiographic response. It is also unclear, whether contractile reserve (CR) could predict CRT response. This meta-analysis examines whether the presence of CR improves response to CRT and whether this is modulated by other clinical factors.

Methods: Search of PubMed/EMBASE/Cochrane databases for articles examining response to CRT stratified by the presence or not of CR. End-point classified as clinical or echocardiographic response. The analysis compared response to CRT (echocardiographic or clinical) between patients with or without CR.

Results: 824 patients in 12 studies were included. The presence of left ventricular CR was associated with a significant reduction in echocardiographic non-responders to CRT compared to patients without CR (OR: 0.16, 95% CI 0.08-0.33, p<0.00001). The presence of left ventricular CR was associated with a significant reduction in clinical non-responders to CRT compared to patients without CR (OR: 0.23, 95% CI 0.14-0.37, p<0.00001). Sensitivity analysis showed no difference in response when pooling studies using left ventricular ejection fraction (LVEF) or non-LVEF markers of CR. Meta-regression showed that CR was associated with lower rates of non-responders and this was more pronounced in patients with a narrower mean QRS complex.

Conclusions: Identification of CR is associated with improved response to CRT. Importantly, QRS width is a potential moderator variable which can explain part of the heterogeneity in echo response. The combination of CR and QRS width may modulate the response to CRT.