BackgroundBefore subcutaneous implantable cardioverter defibrillator (S-ICD) implantation, the adequacy of sensing is required to be verified through surface ECG screening. Our objective was to determine whether S-ICD can be considered as a supplementary therapy in patients who are receiving biventricular (BIV) pacing.MethodsWe evaluated 48 patients with BIV devices to determine S-ICD candidacy during BIV, left ventricular (LV), right ventricular (RV) pacing, and intrinsic conduction (left bundle branch blockLBBB) by using an automated screening tool. Eligibility was defined by the presence of at least one appropriate vector in the supine and standing positions.ResultsEligibility was verified during BIV pacing in 34 (71%) patients. In patients screened-out, QRS duration was longer (p=0.035) and ischemic cardiomyopathy was more frequent (p=0.027). LV-only pacing was associated with a lower passing rate (46%) (p0.001 versus BIV). The LBBB QRS morphology during inhibited ventricular pacing was acceptable in 51% of patients. The QRS generated by RV pacing was acceptable in 25% of patients. In patients who passed the screening test during BIV, the QRS was not acceptable in 76% during RV pacing (i.e., accidental loss of LV capture). The concomitant adequacy during inhibited ventricular pacing (i.e., possible intrinsic conduction) was not assessed in 40% of patients.ConclusionsS-ICD may be a supplemental therapy in the majority of CRT patients. Standard BIV pacing should be preferred to the LV-only pacing mode, as it is more frequently associated with adequacy of S-ICD sensing. Spontaneous LBBB and RV-paced QRS morphologies are frequently inadequate. Therefore, in patients selected for concomitant S-ICD and CRT implantation, accidental loss of LV capture or possible intrinsic conduction must be prevented.
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