Echocardiographic parameters to predict inadequate defibrillation safety margin in patients receiving implantable cardioverter defibrillators for primary prevention
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Implantable cardioverter defibrillators (ICDs) have become an important part of the management of patients with congestive heart failure. At the time of ICD implantation, ventricular fibrillation (VF) is induced to assess adequate energy required for defibrillation. There are multiple parameters which influence the defibrillation safety margin (DSM); however, these factors are not well-established when ICDs are implanted for the primary prevention of sudden cardiac death (SCD) in patients with severe systolic dysfunction. We evaluated multiple clinical and echocardiographic parameters as predictors of adequate DSM in patients referred for ICD implantation for the primary prevention of SCD.
We prospectively enrolled 41 patients for ICD implantation with clinical indications for the primary prevention of SCD. Two blinded independent readers evaluated the prespecified echocardiographic parameters. These included left ventricular (LV) mass, indices of right ventricular and LV systolic and diastolic functions, and LV geometric dimensions. Basic clinical demographics, including age, gender, comorbidities, and etiology of cardiomyopathy, were also evaluated. DSM was established using our standard protocol for defibrillation testing which includes VF with successful first shock terminating VF at a value at least 10 J below the maximum output of the implanted device. High defibrillation thresholds (DFT) were defined as >21 J.
The mean age is 61.8 ± 14.7 years, with men comprising the majority of the patients (73 %). The only clinical variables which predicted the high DFT were age (in years) (54.5 ± 17.5 vs. 65.7 ± 11.3, p = 0.044), QRS duration (in milliseconds) (116.0 ± 29.5 vs. 110.5 ± 21.8, p = 0.03), LV mass (in grams) (241.0 ± 77.9 vs. 181.9 ± 52.3, p = 0.006), and LV mass index (in grams per square meter) (111.1 ± 38.2 vs. 86.4 ± 21.1, p = 0.02). On multivariate logistic regression analysis, LV mass was the only independent predictor of low DFT (≤22 J) in patients with ICD implanted for the primary prevention of SCD.
LV mass may help predict an adequate DSM in patients who are referred for ICD implantation for the primary prevention of SCD. These results may help distinguish the patients who may require high-energy devices prior to the implantation procedure. These results may help distinguish patients requiring high-energy devices, coils, or advanced programming prior to implantation and appropriate referral to electrophysiologists.