Comparative Electrocardiography of the Squamata

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Abstract
Electrocardiograms (ecgs) of 422 specimens representing 50 species of the order Squamata were examined. The Einthoven lead system was followed. The study showed that the mean heart rate of lizards is significantly higher at each temperature in the temperature range in this study than that of snakes. The relation of this phenomenon to either body mass or surface area is unclear. The sinus venosus (SV) wave is reported for the first time in the Squamatan ecg. The average length of the SV-P interval is 0.19 sec. in lizards and 0.29 sec. in snakes. The SV-PR-R ratio is .33 in lizards and .27 in snakes. The mean P-R interval is 0.16 sec. and 0.26 sec. for lizards and snakes, respectively, while the mean Q-T intervals are 0.35 sec. and 0.61 sec. for lizards and snakes. The Q-T:R-R ratio is identical in both lizards and snakes. Other intervals measured include the QRS, P and T. The frontal plane directions of the QRS, P and T were also determined. Direction of depolarization of the atria proceeded from the region of the sinoatrlal node to the left and somewhat caudally. Ventricular depolarization and repolarlzatlon both proceed in a base to apex direction.