Right pectoral implantable cardioverter defibrillators: role of the proximal (SVC) coil

Introduction: Increased defibrillation thresholds (DFTs) with right active pectoral implantable cardioverter defibrillators (ICDs) and/or right proximal coils (SVC) ore attributed to poorer vector. However, SVC affects impedance, current flow, and shock waveform phase duration (PD), which exert independent DFT effects. Objective: Compare DFTs and shock characteristics in SVC On with SVC Off in right ICDs. Methods and Results: DFT+ testing (n = 42, 62% males, 62 +/- 15 years, left ventricular ejection fraction (LVEF) 26 +/- 11 %, ischemic cardiomyopathy 65%, amiodarone 26%) revealed > 20% incidence of high DFT (> 20J). Dilated cardiomyopathy and amiodarone increased DFT Individual impedance variability (25-74 Omega) generated a wide PD range (2.6-8.7 ms). Overall, SVC On reduced impedance by 33% (from 54 +/- 10 to 35 +/- 5 Omega, P < 0.0001), and shortened PD (from 5.45 +/- 1.20 to 3.67 +/- 0.74 ms, P < 0.01). SVC On affected DFTs in 19/42 (45%) patients. SVC On was beneficial in 12/19. PD shortened but current flow remained unaltered. (In these, SVC Off impedance was > 45 Omega and PD > 5 ms.) SVC On was detrimental in 7/19 despite increasing current flow. In these, PD shortened excessively (median 2.9 ms) because impedance was low (31 +/- 4 Omega). In 3/6 cases with DFTs > 20 J in both SVC On and Off, PD optimization reduced DFT Overall, selection of best SVC configuration or deliberate PD programming yielded DFTs <= 20 J in > 90% patients, reducing need for system modification to < 7%. Conclusions: Right pectoral active ICDs have high DFTs. The SVC coil may be detrimental when pulse waveform excessively shortens. Noninvasive maneuvers, for example, SVC and waveform optimization, may improve DFT.