ECG analysis of golden hamsters exposed to long-term -Gz conditions: ordinary and pathological findings

Changes of ECG due to long and intense -Gz acceleration was investigated in anesthetized Syrian golden hamsters. The R-R interval decreased (heart rate increased) slightly at the very initial phase of steady -Gz load. However, the R-R interval increased during the rest of the whole steady -Gz period. The P-R interval increased with a smaller -Gz load (-4 and -6 Gz), but it decreased with a larger -Gz (-8 and -10 Gz). The size of the QRS complex was measured as R amplitude. It decreased in all -Gz conditions. Effects were a little different for smaller and larger -Gz, as was observed in the case of P-R changes. Pathological ECGs were frequently observed. They were: (1) Arrhythmia of heart rate with or without atrio-ventricular blocks. (2) Abnormal P wave; e.g., splitting, flattening, or abolition of P wave. (3) Alteration of the QRS complex in amplitude or contour. (4) Changes in ST-T components. In spite of all these changes, however, it should be noted that several Syrian golden hamsters could tolerate up to -10 Gz for as long as 1,000 s.