Lateral QRS amplitude is independently associated with outcome after cardiac resynchronization therapy: Advancing patient selection?

Background: Cardiac resynchronization therapy (CRT) is a cornerstone in the treatment of selected heart failure patients. However, a relevant proportion of patients do not show beneficial response. Identification of simple, additive, and outcome-relevant selection criteria may improve selection of patients.

Objective: We sought to determine whether baseline QRS amplitude is associated with outcome in CRT.

Methods: Quantification of intrinsic, pre-CRT implantation QRS amplitude was performed in an observational multinational 2-center retrospective cohort analysis (derivation cohort Zurich, n = 178, 2000-2015; validation cohort Leuven, n = 183, 1999-2016) with a composite end point of all-cause mortality, ventricular assist device implantation, or heart transplantation at 5 years.

Results: Higher baseline to peak amplitude in lateral leads (lead I and V₆) was associated with a lower risk of reaching the composite end point (lead I: hazard ratio, 0.86 [95% confidence interval, 0.78-0.95] per millivolt, P = .002; lead V₆: hazard ratio, 0.94 [95% confidence interval, 0.88-1.00] per millivolt, P = .043). Concordance index-based comparison of quartile, spline, and receiver operating characteristic curve analysis suggested cutoff values of 6 mV for lead I and 3 mV for V₆ for optimal discrimination of outcome. External validation confirmed the cutoff of 3 mV in lead V₆ as a highly significant discriminator of outcome (P < .001) associated with a risk reduction of 65%.

Conclusion: Low QRS amplitude in lateral electrocardiogram leads is associated with higher risk of poor outcome in CRT patients. A cutoff of 3 mV in lead V₆ proved highly discriminative. Further studies need to confirm the additive value of QRS amplitude in selection of patients for CRT and to assess whether CRT may be made available to more patients.