Influence of Pacing Site Characteristics on Response to Cardiac Resynchronization Therapy

Study Questions:

What is the impact of late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) and cardiac-gated computed tomography (CCT) on accurate geographic registration of myocardial scar and lead tip location for both the left ventricular (LV) and right ventricular (RV) pacing leads?


Sixty patients receiving cardiac resynchronization therapy (CRT) underwent preimplant LGE-MRI, postimplant cardiac CT, and serial echocardiography. Blinded segmental evaluations of mechanical delay, percent scar burden, and lead tip location were performed. Response to CRT was defined as a reduction in LV end-systolic volume ≥15% at 6 months. The authors constructed a multivariate logistic regression model to assess the incremental association of MRI and baseline clinical variables to predict occurrence of nonresponse to CRT using backward stepwise selection.


The mean age and LV ejection fraction were 64 ± 9 years and 25 ± 7%, respectively. Mean scar volume was higher among CRT nonresponders for both the LV (23 ± 23 vs. 8 ± 14%; p = 0.01) and RV pacing regions (40 ± 32 vs. 24 ± 30%; p = 0.04). Significant pacing region scar was identified in 13% of LV pacing regions and 37% of RV pacing regions. Absence of scar in both regions was associated with an 81% response rate, compared to 55%, 25%, and 0%, respectively, when the RV, LV, or both pacing regions contained scar. LV pacing region dysynchrony was not predictive of response.


The authors concluded that myocardial scar occupying the LV pacing region is associated with nonresponse to CRT.


This prospective, multimodality imaging study reported that while scar in the LV pacing region was observed in a minority of patients, it was associated with a low CRT response, and scar occupying the RV pacing region was seen more commonly, but was associated with intermediate CRT response. Presence of scar in both pacing regions was associated with no response, whereas absence of scar in these regions was associated with the highest response rate. These findings add justification for lead navigation approaches with strategies aimed at the selective placement of pacing leads in nonscarred myocardium.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Implantable Devices

Keywords: Cicatrix, Myocardium, Heart Ventricles, Cost of Illness, Multimodal Imaging, Cardiac Resynchronization Therapy

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