QRS vs. QRSd in Echocardiographic Response to CRT

A study published on July 11 in the Journal of the American College of Cardiology (JACC) found that "QRS morphology is a more important baseline electrocardiographic determinant of cardiac resynchronization therapy (CRT) response than QRS duration (QRSd)."


CRT has been shown to improve cardiac function and heart failure symptoms, but it is unclear why at least one-third of all patients with CRT fail to benefit. The authors aimed to "shed more light on the interaction between QRS morphology and QRSd and to determine echocardiographic response and outcome after CRT implantation as stratified according to both baseline electrocardiographic characteristics."

The authors retrospectively assessed baseline characteristics, clinical and echocardiographic response, and outcomes of all patients who received CRT at the Cleveland Clinic between December 2003 and July 2007. A total of 496 patients were included in the study, who were divided into four groups according to their baseline QRS morphology and QRSd.

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Findings include:


  1. "Non-left bundle branch block (LBBB), as the baseline electrocardiogram morphology before CRT implantation, is much more prevalent in real-world practice than in randomized clinical trials;"
  2. "Echocardiographic and clinical response to CRT is determined by baseline QRS morphology in the first place and to a lesser degree by QRSd," and those with LBBB had better response rates than non-LBBB; and
  3. "Event-free survival (from death, heart transplantation or left ventricular assist device) is better in CRT-treated patients with baseline LBBB and QRS ≥150ms. However, this difference is not significant after adjusting for baseline characteristics."

The authors conclude that "by comparing CRS morphology and QRSd as baseline characteristics, they identified QRS morphology as the most important predictor of response to CRT." However, they note that "due to the lack of sufficiently powered trials in these subgroups, guideline committees have the difficult task of using this and similar studies to refine patient selection for CRT."

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