RESUMO
The purpose of the study reported here was to determine baseline information of the electrocardiogram (ECG) and the influence of age on cardiac function in Taiwanese Lan-Yu (TLY) miniature pigs. Non-anesthetized TLY minipigs (from birth to 6 months of age) were placed on a webbed stanchion, simulating a standing position, for acquisition of an ECG, using six limb leads (I, II, III, aVR, aVL, and aVF), with each as a single-channel ECG recorder. The P and T waves obtained from leads I, III, and aVL were useful in determining the subtle cardiac changes during maturation of TLY minipigs. Interestingly, changes in the QT interval analyzed from all 6 leads were almost indistinguishable. Shortening of the QT interval was induced (p < 0.05) between days 1 and 7 of postnatal life. The QT interval lengthened to a steady state at day 60, and paralleled pigs' physical maturation. The longer QT interval was conversely correlated to heart rate as pigs matured. In the QRS complex interval, only lead aVR was significantly decreased at day 7 (p < 0.05). Further changes in the QRS interval from day 21 were not observed in any lead. Because the duration of the ventricular complex represents the period required for the excitation front to reach the terminals of the Purkinje fibers in the ventricular myocardium, the increase in QRS interval observed within 21 days of birth could be attributed to an increase in the thickness of ventricular myocardium. The data suggest that cardiac maturation was achieved at 60 days of age, although the body weight of minipigs continued to increase beyond 60 days of age. Because the body weight of these newly developed TLY minipigs can be maintained within 25 to 30 kg at one year of age and their major ECG findings did not significantly differ from those of domestic pigs and humans, they may be useful as a model for cardiovascular and pharmacologic research. The similarity of ECG profiles between pigs and humans also was evaluated.
