Effects of shock polarity reversal on defibrillation threshold in an implantable cardioverter-defibrillator.

BACKGROUND An increased defibrillation threshold (DFT) may limit the efficacy of an implantable cardioverter-defibrillator (ICD) in termination of life-threatening ventricular arrhythmias. A search for methods of decreasing DFT has been ongoing since the introduction of ICD into clinical practice. AIM To assess the effects of various shock polarities on DFT. METHODS The study group consisted of 19 patients (8 females and 11 males, mean age 52+/-17 years) who received devices (Biotronik, Germany) with a single-coil defibrillation lead. In all patients the value of DFT was assessed using a normal shock polarity as well as using a reversed polarity shock, starting from the energy lower than that measured during normal DFT testing. The impedance of the defibrillation system using two different polarities was also measured. The effects of demographic and clinical parameters on defibrillation parameters were also examined. RESULTS When using normal shock polarity, the mean DFT value was 12+/-5 J (range 3.1-20 J) and impedance was 64+/-12 Omega. When shock polarity was reversed, the mean DFT value was 9.2+/-5.0 J (range 2-20 J) and impedance was 67+/-11 Omega. In 11 (58%) patients the polarity change caused a marked (by 37%) decrease in the mean DFT value - from 11.5+/-5.1 J to 7.2+/-3.8 J. In 5 patients DFT reduction was > or = 5 J. There was no relationship between demographic or clinical parameters and defibrillation efficacy using the two tested shock polarities. CONCLUSIONS The reversal of shock polarity reduces DFT in more than half of patients. In patients with a high DFT the use of reversed polarity of defibrillating impulse may reduce DFT, which widens the safety margin and makes implantation of additional leads unnecessary. Because clinical parameters have no value in predicting the effects of polarity changes on DFT, the efficacy of reversed polarity shock has to be assessed individually in each patient.