Electrocardiograms of bottlenose dolphins (Tursiops truncatus) out of water: habituated collection versus wild postcapture animals.

Electrocardiography (ECG) was performed on captured free-ranging bottlenose dolphins (Tursiops truncatus) during a health assessment exercise and compared with that of a Navy collection of dolphins habituated to handling out of water in order to assess possible cardiovascular impacts of capture and handling. Six-lead recordings (I, II, III, aVr, aVl, and aVf) in the frontal plane and direct thorax leads were collected from both groups, with a modified base-apex lead additionally employed with the Navy collection dolphins. Measured and calculated parameters included amplitudes of P, R, S, and T waves and total QRS complex; T:S and T:QRS ratios; heart rate; durations of P wave; QRS complex, PR, QT, and RR intervals; maximum minus minimum RR interval; ST segment elevation-depression; and mean electrical axis (MEA). Physiologically minor but statistically significant differences were detected in S wave amplitude, PR interval, QRS duration, and MEA. The PR interval, QRS duration, and S wave amplitude were slightly greater and the MEA oriented slightly rightward in wild postcapture dolphins compared to Navy collection dolphins. There were no differences in heart rate or maximum minus minimum RR interval, which serves as a proxy for the expected sinus arrhythmia of dolphins. The base-apex lead resulted in greater QRS amplitude than lead II, as expected for the category B ventricular activation of dolphins. The left-side direct thorax lead was more consistent than that of the right side. Clinically, ECG was a useful adjunct to auscultation and thoracic palpation for monitoring heart rate and rhythm and generated a record for archiving. Safe capture and handling protocols in place, under which dolphins are immediately returned to the water at progressive signs of distress, may make cardiovascular decompensation less likely to be detected by ECG. It appears that the dolphin cardiovascular system compensates suitably well to capture, as measured by ECG under the conditions of this study.