Introduction:Increased defibrillation thresholds (DFTs) with right active pectoral implantable cardioverter defibrillators (ICDs) and/or right proximal coils (SVC) are 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 Ω) generated a wide PD range (2.6–8.7 ms). Overall, SVC On reduced impedance by 33% (from 54 ± 10 to 35 ± 5Ω, 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 >45Ω 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 ± 4Ω). 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.