Chronophysiologic aspects of ECG changes during a systemic asphyxic episode and subsequent reoxygenation in an experimental rat model.

The aim of the study was to evaluate the effect of ventilatory manoeuvres on some ECG parameters as a function of the light-dark (LD) cycle in in vivo conditions. The PQ and QT intervals were measured in ketamine/xylazine-anaesthetized female Wistar rats (100 mg/15 mg/kg, i.m.) after adaptation to an LD cycle (12:12 h). The animals were exposed to a 2 min apneic episode and subsequent 20 min period of reoxygenation. Significant LD differences were found in the duration of the PQ interval (p < 0.001) after 30 and 60 sec., and in the QT interval after 90 (p < 0.01) and 120 sec. (p < 0.001), apneic episode. Reoxygenation restored the PQ and QT intervals with the preservation of LD differences from the pre-asphyxic period. It is concluded that although long-term asphyxia probably minimized LD differences in the duration of the PQ interval, the dispersion of refractory periods increases by the manner depending on LD cycle. Reoxygenation did not act proarrhythmogenicly and the followed parameters were recovered to the pre-asphyxic level (Fig. 5, Ref. 43).