Alterations in cardiac rate and rhythm in miniature swine during simulated aerial combat maneuver +Gz stress.

Electrocardiograms (McFee-axial reference system) were recorded from 18 chronically instrumented, conscious, female miniature swine before, during, and after exposures to +Gz stress. The animals were exposed to five simulated aerial combat maneuver (SACM) type acceleration profiles which spanned approximately 106 s and included two 5-s +9Gz peaks. A 5-min rest period separated each SACM exposure. Maximum heart rates during +Gz decreased over the course of the 5 SACM's-241 +/- 4 b/m and 224 +/- 5 b/m for the first and last exposures, respectively. Resting heart rates obtained 5 min after each SACM exposure were steadily increased from a control of 86 +/- 5 b/m to a final of 129 +/- 8b/m. Of the 18 animals studied, 10 developed arrhythmias during +Gz, or within the first minute after +Gz exposure. Arrhythmias exhibited included premature atrial and ventricular contractions, intraventricular conduction defects, sinus arrhythmias, premature junctional contractions, atrial bigeminy, ectopic atrial and ventricular rhythms, complete A-V dissociation, left anterior arborization-block, and junctional rhythms with aberrant conduction. While arrhythmias were not uncommonly observed during +Gz, most occurred at the end of the SACM profile or immediately following the SACM.