Does mechanical dyssynchrony in addition to QRS area ensure sustained response to cardiac resynchronization therapy?

Aims Judicious patient selection for cardiac resynchronization therapy (CRT) may further enhance treatment response. Progress has been made by using improved markers of electrical dyssynchrony and mechanical discoordination, using QRS _AREA, and systolic rebound stretch of the septum (SRSsept) or systolic stretch index (SSI), respectively. To date, the relation between these measurements has not yet been investigated. Methods and results A total of 240 CRT patients were prospectively enrolled from six centres. Patients underwent standard 12-lead electrocardiography, and echocardiography, at baseline, 6-month, and 12-month follow-up. QRS _AREA was derived using vectorcardiography, and SRSsept and SSI were measured using strain-analysis. Reverse remodelling was measured as the relative decrease in left ventricular end-systolic volume, indexed to body surface area (DLVESVi). Sustained response was defined as >_15% decrease in LVESVi, at both 6- and 12-month follow-up. QRS _AREA and SRSsept were both strong, multivariable adjusted, variables associated with reverse remodelling. SRSsept was associated with response, but only in patients with QRS _AREA >_ 120 lVs (AUC = 0.727 vs. 0.443). Combined presence of SRSsept >_ 2.5% and QRS _AREA >_ 120 lVs significantly increased reverse remodelling compared with high QRS _AREA alone (DLVESVi 38 ± 21% vs. 22 ± 21%). As a result, 92% of left bundle branch block (LBBB)-patients with combined electrical and mechanical dysfunction were ‘sustained’ volumetric responders, as opposed to 51% with high QRS _AREA alone. Conclusion Parameters of mechanical dyssynchrony are better associated with response in the presence of a clear underlying electrical substrate. Combined presence of high SRSsept and QRS _AREA, but not high QRS _AREA alone, ensures a sustained response after CRT in LBBB patients.