Incidence and clinical predictors of low defibrillation safety margin at time of implantable defibrillator implantation.

BACKGROUND

Determination of the defibrillation safety margin (DSM) is the most common method of testing device effectiveness at the time of implantation of implantable cardioverter defibrillator (ICD) or cardiac resynchronization therapy defibrillator (CRTD). Low DSM remains a problem in clinical practice.

OBJECTIVE

The purpose of this study is to ascertain the incidence and clinical predictors of low DSM and the treatment strategies for low DSM in ICD or CRTD recipients.

METHODS

Selected ICD or CRTD recipients from January 2006 to May 2008 who underwent DSM test at the time of implantation were included. Low DSM patients were defined as patients who had a DSM within 10 J of the maximum delivered energy of the device. These patients were compared to patients who had DSM > 10 J.

RESULTS

This study included 243 patients. Of these, 13 (5.3%) patients had low DSM, and 230 patients had adequate DSM. Patients with low DSM had a high prevalence of amiodarone use (69% vs 13%, p < 0.01), secondary prevention indications (69% vs 30%, p < 0.01), and a trend toward younger age (51 ± 18 vs 58 ± 15 years, p = 0.08). After adjustment for age and sex, amiodarone use was significantly associated with low DSM. All low DSM patients except one obtained adequate DSM after taking additional steps, including discontinuing amiodarone and starting sotalol, RV lead repositioning, adding a subcutaneous array or shock coil, changing single-coil to dual-coil lead, and upgrading to a high output device.

CONCLUSION

The incidence of low DSM patients is low with high-energy devices. Amiodarone use is associated with low DSM, and its discontinuation or substitution with sotalol is one of a variety of available options for low DSM patients.