Abstract: Objective To investigate the differential impact of right versus left ventricular ectopic excitation on the short-term cardiac memory. Methods Surface electrocardiogram (ECG) (Lead Ⅱ) was recorded and bipolar electrode pacing was performed on the left ventricular (LV) and right ventricular (RV) anterior free walls at an open-chest condition in normal adult rabbits. Within 20 min after pacing, T wave morphology and T wave electrical axis were analyzed and compared with that of the same ventricles before pacing. Results After LV pacing, the T wave morphology was basically normal and the deflection of T axis was within normal range (14??22?). However, RV pacing resulted in significant T wave inversion and counter-clockwise deflection of T axis (maximal deflection ?127.9?) (P<0.05 vs. that of the same site before pacing, respectively). Conclusion The influence of RV ectopic excitation on short-term cardiac memory is much greater than that of LV ectopic excitation: RV ectopic excitation induces serious T wave inversion and T axis counter-clockwise deflection, while LV ectopic excitation has no significant influence on T wave morphology and T axis.

Key words: cardiac memory, T wave, cardiac pacing, ectopic excitation, cardiac electrical axis