Leadless Pacemaker Implant Location as a Predictor of Pacing Induced Cardiomyopathy.

BACKGROUND: Leadless pacemakers (LPs) avoid the lead- and pocket-related complications of transvenous systems, but they pace exclusively from the right ventricle (RV), and chronic RV pacing carries a recognized risk of pacing-induced cardiomyopathy (PICM). Whether implant location within the RV, a potentially modifiable factor, contributes to this risk has not been established. METHODS: Patients undergoing LP implantation with ≥50% RV pacing, pre-and post-procedural echocardiograms, and post-implant 3-dimensional radiographic imaging were included. All implants targeted the RV septum per manufacturer recommendation. PICM was defined as ≥10% decline in left ventricular ejection fraction (LVEF) to <50% without alternative cause. RESULTS: PICM developed in 20/81 patients (24.7%), with LVEF declining from 61±8% to 37±9%. Post-implant 3-dimensional radiographic imaging demonstrated inadvertent free wall implantation in 15/20 patients who developed PICM (75%) compared with 8/61 patients who did not (13%; P <0.001). Paced QRS duration was wider in patients with PICM than in those without (186±19 vs 155±13 ms, P <0.001) and discriminated free wall from non-free wall implantation with an area under the receiver operating characteristic curve (AUC) of 0.85; a QRS duration of 172 ms provided optimal discrimination. Baseline LVEF, baseline QRS duration, and comorbidity burden did not differ between groups. CONCLUSIONS: Inadvertent free wall LP implantation is strongly associated with the subsequent development of PICM. Paced QRS duration is a readily available surrogate for implant location, and targeting a paced QRS duration below approximately 172 ms at the time of implant may serve as a practical, non-invasive check on appropriate septal placement.