Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB032

Poster Communications

The electrocardiogram of vertebrates: evolutionary changes from ectothermy to endothermy

B. JD Boukens1, R. Filogonio2, D. Crossley3, T. Wang4, B. Jensen1

1. Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands. 2. Department of Physiological Sciences, Federal University of São Carlos (UFSCar), São Carlos, Brazil. 3. University of North Texas, Denton, Texas, United States. 4. Bioscience, Aarhus University, Aarhus, Denmark.

The electrocardiogram (ECG) reveals that heart chamber activation and repolarization are much faster processes in mammals and birds compared to ectothermic vertebrates of similar size. Temperature, however, affects electrophysiology of the heart and most data from ectotherms are determined at body temperatures below those of mammals and birds. We reviewed the effects of temperature on intervals in the ECG of ectothermic and endothermic vertebrates. Data gaps were covered by novel data on the ECG of reptiles that were raised to mammalian body temperatures (Iguana iguana, N=4; Python regius, N=5; Alligator mississippiensis, N=4). We compared animals of approximately 1kg to minimize the influence of heart mass. Compared to mammals and birds, the reptiles at 35-37 °C had 4 times lower heart rates, 2 times slower atrial and ventricular conduction (longer P- and QRS-wave duration), and 4 times longer PR interval (atrioventricular delay) and QT intervals (total ventricular repolarization). In this study, we conclude that the faster chamber activation in endotherms cannot be explained by temperature alone. Based on histology, we show that endotherms have a more compact tissue architecture. In mammals, disorganization of the compact wall by fibrosis associates with conduction slowing and we suggest the compact tissue architecture allows for faster chamber activation. The short cardiac cycle and high heart rates that characterizes mammals and birds, however, is predominantly accommodated by shortening of the atrioventricular delay and the QT interval, which is so long in a 1kg iguana that it compares to that of an elephant.

Where applicable, experiments conform with Society ethical requirements