Frank orthogonal vectorcardiograms in humans during and after exposure to +Gz acceleration stress

Frank orthogonal vectorcardiograms (VCGs) were recorded from 10 subjects prior to, during, and for 15 min after exposures to +3Gz , +5Gz, and +7Gz. The order of acceleration exposure was randomized, with the individual exposures separated by at least 1 week. Standard USAF anti-G suits were worn by all subjects. Detailed analysis of the scalar lead electrocardiograms revealed no abnormalities. There were no consistent signs of conduction disturbances or ischemic ST-T segment changes. The QRS axis of the VCG demonstrated posterior rotation in the sagittal plane and counterclockwise rotation in the transverse plane during +Gz stress. The changes in the VCGs recorded during +Gz stress appeared to be related to rotational changes of the heart due to mechanical stress and/or motion within the thorax. There were no ECG or VCG changes indicative of myocardial ischemia and/or damage during or after +Gz stress.