title: Pacing threshold changes after transvenous catheter countershock.
abstract: The serial changes in pacing threshold and R-wave amplitude were examined after insertion of a countershock catheter in 12 patients referred for management of recurrent ventricular tachyarrhythmias. In 6 patients, values before and immediately after catheter countershock were monitored. Pacing threshold increased (from 1.4 +/- 0.2 to 2.4 +/- 0.5 V, mean +/- standard error of the mean, p less than 0.05) while the R-wave amplitude decreased (bipolar R wave from 5.9 +/- 1.1 to 3.4 +/- 0.7 mV, p less than 0.01; unipolar R wave recorded from the distal ventricular electrode from 8.9 +/- 1.8 to 4.6 +/- 1.2 mV, p less than 0.01; and proximal ventricular electrode from 7.7 +/- 1.5 to 5.0 +/- 1.0 mV, p less than 0.01). A return to control values occurred within 10 minutes. In all patients, pacing threshold increased by 154 +/- 30% (p less than 0.001) during the first 7 days that the catheter was in place. It is concluded that catheter countershock causes an acute increase in pacing threshold and decrease in R-wave amplitude. A catheter used for countershock may not be acceptable as a backup pacing catheter.
mesh_terms: D000328:Adult; D000368:Aged; D006328:Cardiac Catheterization / Q000295:instrumentation; D002304:Cardiac Pacing, Artificial; D004554:Electric Countershock / Q000295:instrumentation; D004562:Electrocardiography; D006801:Humans; D008297:Male; D008875:Middle Aged; D013610:Tachycardia / Q000628:therapy*; D014693:Ventricular Fibrillation / Q000628:therapy*