Impact of Body Mass Index on Safety and Efficacy of the Subcutaneous Implantable Cardioverter-Defibrillator

Objectives: This study determined whether obesity increased the risk of failed shocks and complications among subcutaneous implantable cardioverter-defibrillator (S-ICD) recipients.

Background: The S-ICD is an established treatment for patients at high risk for ventricular arrhythmias. Obesity may increase the transvenous defibrillation threshold and the rate of complications.

Methods: We analyzed data from the 321 patients enrolled in the S-ICD Investigational Device Exemption (IDE) study. They were categorized into 3 body mass index (BMI) groups: <25 kg/m² (underweight and normal), 25 to 30 kg/m² (overweight), and >30 kg/m² (obese). Patients underwent implantation followed by defibrillation testing at 65 J. Chronic defibrillation testing was repeated >150 days post implantation in a subset of patients.

Results: Seventy-nine patients had BMI <25 kg/m², 105 had BMI 25 to 30 kg/m², and 137 had BMI >30 kg/m². A failed first shock of any kind occurred in 52 patients, including 41 patients during implant defibrillation testing, 11 patients during chronic defibrillation testing, and 5 patients during spontaneous ventricular arrhythmias. The rate of failed first shocks during implant defibrillation testing increased across BMI categories (5.1% among underweight and normal patients, 13.3% among overweight patients, and 16.9% among obese patients; p = 0.04). Among obese patients, shock impedance was higher during failed first shocks than successful first shocks (103.5 ohms vs. 84.6 ohms; p = 0.001). The rate of failed first shocks during chronic defibrillation testing and spontaneous ventricular arrhythmias did not significantly differ among BMI groups, nor did the rate of complications. Of the 8 underweight patients, there were no failed shocks or complications.

Conclusions: Obese patients are at increased risk of failed first S-ICD shocks during defibrillation testing. Whether this can be overcome by optimal implantation techniques remains unknown. Rates of complications were not increased among obese patients.