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Bipolar or unipolar epicardial and intraseptum electrograms were recorded from the in situ rat hearts with spontaneous sinus rhythm or myocardial electrical stimulation of 400 bpm in order to investigate the sequence and duration of cardiac activation in the rat. The ventricular epicardial isochronous maps in the rat showed the activation sequence comparable to those in humans and dogs, although the activation time (6 to 13 msec) of epicardium was approximately one-third of those of such species. The delay of activation between septum and ventricular surface in the rat was 5 to 8 msec, which was also shorter as compared with those in humans and dogs. However, the conduction velocity of the ventricular epicardium in the rat was approximately 40 cm/sec, mostly equal to that of humans. These findings might be accounted for by the possible presence of the bundle branch-purkinje system, at least functionally, similar to humans. The local QT interval in the septum were relatively longer (69 to 123 msec), compared with that of the ventricular surface (50 to 98 msec), and such durations of ventricular epicardium and septum were considerably less than those of dogs and humans. These results are consistent with the configuration of QRS-T on the limb lead ECG.
Suzuki et al. (Wed,) studied this question.