Low voltage direct current delivered through unipolar transvenous leads: an alternate method for the induction of ventricular fibrillation.
The induction of VF during testing of an ICD may not always be possible using either burst pacing or high energy T wave shocks. The purpose of this study was to evaluate the effectiveness of low energy DC stimulation for inducing VF in a porcine model. The VFT was measured using constant voltage stimuli and a step-up method in ten anesthetized pigs (25-30 kg). Stimuli of different durations (0.5, 1.0, 2.0 s) were delivered (unsynchronized) between a right ventricular apical coil and a subcutaneous test can. Current was measured from the voltage drop across a series resistor (10 omega). With anodal stimulation, VF required 6.4 +/- 0.2 V compared to 13.8 +/- 0.6 V with cathodal stimulation (P < 0.001). The current required to induce VF (measured 10 ms after the stimulus onset) was 58.3 +/- 2.2 mA with anodal stimulation and 119.3 +/- 4.7 mA with cathodal stimulation (P < 0.001). Stimulus duration did not significantly influence the voltage or current required for VF induction. In 6 of the 10 pigs, synchronizing a 0.5-second stimulus to the R wave did not significantly alter the VFT compared to same stimulus synchronized to mid-upslope of the T wave. The results indicate that VF can be consistently induced through transvenous electrodes by passing unsynchronized DC for 0.5-2 seconds. The induction of VF required about 50% less current and voltage with anodal stimulation. It should be possible to induce VF with the DC voltage available from the internal battery source of an ICD.
Angeion Corporation Minneapolis, Minnesota, USA.
D E
DE
Euler
T A
TA
Whitman
P R
PR
Roberts
M J
MJ
Kallok
D000818:Animals; D002304:Cardiac Pacing, Artificial; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D004566:Electrodes; D019544:Equipment Failure Analysis; D005260:Female; D006352:Heart Ventricles / Q000503:physiopathology; D008297:Male; D013552:Swine; D014693:Ventricular Fibrillation / Q000503:physiopathology*