FAILURE OF 3RD-GENERATION IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS TO ABORT SHOCK THERAPY FOR NONSUSTAINED VENTRICULAR-TACHYCARDIA DUE TO SHORTCOMINGS OF THE VF CONFIRMATION ALGORITHM

Unnecessary shocks by ICDs for rhythms other than sustained VT or VF h ave been described as the most frequent adverse event in ICD patients. To avoid unnecessary shocks for self-terminating arrhythmias, the thi rd-generation Jewel PCD defibrillators 7202, 7219, and 7220 Plus use a specially designed VF confirmation algorithm after charge end. The pu rpose of this study was to determine the ability of this VF confirmati on algorithm to recognize nonsustained VT, and to analyze the reasons for failure of the PCD device to abort shock therapy for nonsustained VT despite use of this VF confirmation algorithm. Analysis of stored e lectrograms of electrical events triggering high voltage capacitor cha rging in the programmed VF zone of the device showed 36 spontaneous ep isodes of nonsustained VT (227 +/- 21 beats/min) during 18 +/- 7 month s follow-up in 15 patients who had a Jewel PCD implanted at our hospit al. Intracardiac electrogram recordings and simultaneously retrieved m arker channels demonstrated that the ICD shock was appropriately abort ed according to the VF confirmation algorithm in 24 (67%) of 36 episod es of nonsustained VT. Twelve episodes (33%) of nonsustained VT, howev er, were follow ed by a spontaneous ICD shock in 6 (40%) of the 15 stu dy patients. The only reason for all 12 shocks for nonsustained VT was the inability of the device to recognize the absence of VT after char ge end due to shortcomings of the VF confirmation algorithm: 11 of the 12 shocks for nonsustained VT were triggered by the occurrence of pac ed beats during the VF confirmation period and 1 shock for nonsustaine d VT was triggered by the occurrence of 2 premature beats after charge end. Thus, better VF confirmation algorithms need to be incorporated in future PCD devices to avoid unnecessary shocks for nonsustained VT.