Comparative electrocardiogram in two anesthetized pinnipeds, the South American fur seal (Arctocephalus australis) and the Southern sea lion (Otaria byronia), with analysis of ECG parameters allometry

Abstract

The mammalian heart has been described as a highly evolutionarily conserved structure and the cardiovascular system allometry has been fully studied among many mammalian species, but few of these studies have been focused on marine mammals. Previously reported electrocardiogram (ECG) of anesthetized Southern sea lions (SSL; n=13) and South American fur seals (SAFS; n=19) females were compared, and linear models were used to examine variations of ECG parameters with body mass (BM) and heart rate (HR). Electrocardiograms resulted in qualitatively similar characteristics (rhythm, polarity patterns, mean electrical axes orientation, and waves/complex forms), but there were significant quantitative differences in HR and all ECG parameters. With few exceptions, duration and amplitude parameters were significantly higher in the SSL, whereas the SAFS had a significantly higher HR. Allometric scaling was verified for most duration variables (P, T, QRS, and PR interval) and P wave amplitude, which resulted all significantly and positively associated with BM, with no significant effect of HR. Results suggest that the cardiac conduction system is highly conserved, and allometry occurs for these species even in anesthetized subjects, particularly in atrial contraction and atrioventricular conduction, which was proposed as potentially related to optimal atrioventricular activation sequence and high hemodynamic efficiency.