CRT Response Prediction Index (QRS + Mechanical Dyssynchrony)
CRT Response Prediction Index (QRS + Mechanical Dyssynchrony): Explanation, Rationale and Clinical Context
This calculator provides a transparent composite index that combines electrical dyssynchrony (QRS duration on surface ECG) and a user-supplied mechanical dyssynchrony measure (for example: septal-to-lateral delay by tissue Doppler, interventricular mechanical delay, or an equivalent echo/TDI-derived delay in milliseconds). The index is not a replacement for guideline-based patient selection or comprehensive multimodality assessment; rather it is an evidence-informed aide that highlights the combined contribution of electrical and mechanical dyssynchrony to the probability of a favourable response to cardiac resynchronization therapy (CRT).
Rationale for the formula used here: (1) Numerous studies show that wider QRS duration-especially QRS ≥150 ms and typical left bundle branch block morphology-is strongly associated with higher CRT response rates; therefore electrical dyssynchrony is given greater relative weight in the composite score. (2) Echocardiographic/Imaging measures of mechanical dyssynchrony improve prediction in many cohorts and can identify patients with mechanical delay even when QRS is borderline; they are therefore included and weighted substantially. (3) Because no single universally validated numeric "CRT response index" combining QRS and a mechanical delay exists in major guidelines, this tool uses a transparent linear normalization and weighting (60% QRS, 40% mechanical dyssynchrony) so clinicians can see the inputs, scaling and interpretation and adapt thresholds in local practice or after multidisciplinary review.
How to use and interpret: enter the measured QRS duration (ms) and the measured mechanical dyssynchrony (ms) according to your local imaging method. The calculator normalizes QRS on an 80–160 ms linear scale and mechanical dyssynchrony on a 0–100 ms scale, computes a weighted composite, and reports a percentage likelihood with pragmatic interpretation tiers: <40% (low), 40–69% (intermediate), ≥70% (high). A high index reinforces standard indications (severe symptomatic HF, reduced LVEF, typical LBBB and QRS ≥150 ms) but should be considered alongside QRS morphology, scar burden (imaging or clinical suspicion), LV lead targetability, comorbidities, and guideline recommendations. This tool is intended for bedside or educational use and should not replace individualized clinical judgment or centre-specific selection algorithms.
References:
Abraham TP, et al. “QRS Width and Mechanical Dyssynchrony for Selection of Cardiac Resynchronization Therapy” - discusses the relationship between QRS duration and mechanical dyssynchrony and how prevalence of responders increases with QRS width.
Miyazaki C, et al. (Circulation: Heart Failure) - prospective analyses of echocardiographic dyssynchrony indices and CRT response.
Bax JJ, et al. “Echocardiography and Noninvasive Imaging in Cardiac Resynchronization Therapy” - imaging predictors and the role of mechanical dyssynchrony.
Aalen J, et al. “Imaging predictors of response to cardiac resynchronization therapy” (Eur Heart J, 2020) - modern imaging predictors and balanced view of electrical vs mechanical markers.
Review articles summarizing predictive value of combined electrical and mechanical measurements and the limits of single-parameter selection.