Impact of myocardial scar distribution and electrical remodeling on response to cardiac resynchronization therapy

Background Cardiac resynchronisation therapy (CRT) improves outcomes in selected patients with heart failure and electrical dyssynchrony. Cardiac magnetic resonance (CMR) enables detailed scar assessment, which may influence response. Purpose To evaluate combined clinical, electrical and CMR predictors of CRT response in routine clinical practice. Methods Nineteen patients (mean age 69.2 ± 7.1 years; 78.9% male) who underwent CRT implantation were retrospectively analysed. Most had non-ischaemic cardiomyopathy (68.4%) and left bundle branch block (89.5%). Implants were predominantly for primary prevention (94.7%). Clinical, echocardiographic and device parameters were assessed at baseline and at three months. CRT response was defined as an increase in left ventricular ejection fraction (LVEF) ≥5% or a reduction in left ventricular end-diastolic volume (LVEDV) ≥15%. All patients underwent pre-implant CMR for scar assessment. Results Mean LVEF increased from 33.8 ± 8.3% to 44.6 ± 10.1% (p < 0.001). QRS duration decreased from 161 ± 17 ms to 123.5 ± 8.9 ms (p < 0.001). Mean NYHA class improved from 3.0 ± 0.3 to 1.7 ± 0.5 (p < 0.001), with 89% improving by ≥1 class. All patients met response criteria. No deaths, heart failure hospitalisations or major procedural complications occurred. Scar was present in 63% of patients; 80% were mild and 20% transmural. Among those with evaluable CMR data, septal and anteroseptal scars were more frequent in non-responders, while inferior and inferolateral scars were associated with greater functional improvement. Conclusion CRT was associated with significant improvement in symptoms, electrical synchrony and left ventricular function. Pre-implant CMR scar pattern appeared to influence response, with septal or anterior scarring potentially predicting reduced benefit. Combining imaging and electrical evaluation may optimise patient selection and CRT outcomes. As left bundle branch area pacing increasingly targets the interventricular septum, pre-procedural scar assessment may have future implications for predicting response to conduction system pacing and warrants further evaluation.