Clinical predictors of defibrillation threshold in patients with implantable cardioverter-defibrillators

Abstract

Background: Safety of patients with malignant ventricular arrhythmias, treated with implantable cardioverterdefibrillators (ICD), depends on the possibility of immediate and effective intracardiac defibrillation. It is especially important in those patients in whom there is a risk of increased defibrillation threshold (DFT) of ventricular fibrillation (VF). Thus, it is important to know whether some clinical parameters may predict a high DFT.
Aim: To assess the relationship between DFT and clinical, demographic and antropometric parameters, type and progression of underlying disease as well as antiarrhyhmic therapy used in ICD recipients.
Methods: The study group consisted of 168 patients (47 females, 121 males, mean age 55±15 years, range 15-82 years) who were selected to receive an ICD. DFT was systematically tested during ICD implantation in all patients. Various clinical, demographic, antropometric and echocardiographic parameters were analysed as the function of DFT value, examining their accuracy in predicting a high (≥15 J) or a low (<15 J) DFT, using logistic regression model.
Results: Univariate analysis revealed that DFT value was significantly related to the following parameters: idiopathic VF, dilated cardiomyopathy, amiodarone therapy and the use of beta blockers. There was a significant correlation between DFT and LVEDD, height, LVEF and impedance of defibrillating system. Multivariate analysis showed that amiodarone therapy, height, impedance of defibrillating system and LVEDD were independently related to the DFT value. Parameters which predicted a high (≥15 J) DFT, consisted of amiodarone therapy (p=0.005), height (p=0.01), LVEDD (p=0.01), LVEF (p=0.03), dilated cardiomyopathy (p=0.01) and body surface area (p=0.049). Amiodarone therapy occurred to be the only parameter which independently predicted a high DFT (odds ratio 2.78; 95% confidence interval 1.19-6.5).
Conclusions: Tall stature, enhanced LVEDD, decreased LVEF and amiodarone therapy increase the risk of a high DFT in ICD recipients. Chronic amiodarone therapy increases three times the risk of elevated DFT. In patients with already implanted ICD in whom amiodarone is started, reassessment of DFT following administration of a loading dose of the drug is required.