Electrocardiogram of the humpback whale (Megaptera noaeangliae) with specific reference to atrioventricular transmission and ventricular excitation

Objectives. The objective of the study was to record the electrocardiogram (ECG) of a large whale to obtain crucial data for comparative electrophysiologic analysis. Background. The data were needed to establish the mismatch between heart size and PR interval and QRS duration in mammals. Methods. In the waters off the coast of Newfoundland, in two humpback whales (Megaptera novaeangliae) with an estimated weight of 30,000 kg a 1-lead ECG was recorded, enabling reliable assessment of P waves and QRS complexes. Results. It was found that both the PR interval (atrioventricular [AV] transmission time) and QRS duration (ventricular excitation) are extremely short for animals of this size. These findings are difficult, if not impossible, to explain on the basis of currently accepted electrophysiologic theories. However, the narrow QRS complex may be due to a very dense His-Purkinje network in the ventricular wall of whales. Alternative mechanisms that can explain the function of the mammalian AV node need to be considered and explored. Conclusions. The results of the study may be of value for the understanding of the ECG in humans.