Optimization of superior vena cava coil position and usage for transvenous defibrillation

Prior studies of active pectoral implantable defibrillator (ICD) lead systems demonstrated a lowering of defibrillation thresholds (DFTs) with the addition of a superior vena cava (SVC) coil. These studies were done on fixed-tilt waveforms where a large reduction in impedance leads to large phase duration changes.

The present study was designed to evaluate the SVC coil benefit and intercoil spacing on DFTs with a "tuned" waveform.

This prospective, multicenter study included 113 patients randomized at implant to a 17-cm and a 21-cm intercoil spacing ICD lead. DFTs were measured with SVC coil turned ON versus OFF in a random order, using an optimized binary search method.

DFT voltage (423 +/- 120 vs. 438 +/- 118 V; P = .042) and stored energy (9.8 +/- 5.6 vs. 10.2 +/- 5.8 J; P = .043) were significantly reduced with the SVC coil ON. However, intercoil distance had no significant effect on DFT voltage (437.3 +/- 115.1 vs. 407.7 +/- 123.8 V; P = .19) or stored energy (10.3 +/- 5.4 vs. 9.2 +/- 5.8 J; P = .31). Subgroup analyses showed that the dual-coil leads were most effective when placed in the high position (innominate vein-SVC junction) or when the single-coil shock impedance was > or =58 Omega, regardless of intercoil spacing.

With a tuned waveform, the addition of an SVC coil to the shocking pathway reduces DFTs, although this difference was smaller than reported previously. Intercoil distance had no significant effect on the defibrillation parameters.