abstract
The classic and definitive electrocardiography (ECG) studies of dolphins and pinnipeds were conducted in the early 1970s,2,3 but the technique has rarely been used in marine mammal fieldwork until recently with development of small portable ECG units.1,4 Our aim was to determine if changes in ECGs of wild bottlenose dolphins (Tursiops truncatus) could be useful in assessing condition and cardiovascular impacts of capture during a field study in St. Joseph Bay, Florida. Captures of free-ranging bottlenose dolphins are conducted periodically to collect biological data, and minimizing capture impacts is a high priority for researchers and outside monitors. As a comparison population we used working dolphins from the U.S. Navy Marine Mammal Program that are accustomed to out-of-water handling. We hypothesized that when using identical equipment and procedures out of water, 1) some ECG characteristics would differ between free-ranging dolphins immediately post-capture and habituated dolphins, and 2) the amplitude of the T-wave (or T/QRS or T/S ratio) would increase with increasing serum K or blood lactate, or decreasing blood pH that might occur with capture. ECGs were recorded from bottlenose dolphins in Florida immediately following capture during sampling and tagging procedures. Although a base-apex lead configuration would provide maximum QRS amplitude because of their category B ventricular activation,2 these lead placements would not have been practical under field conditions. Therefore, ECGs were recorded in the frontal plane. Good quality 6-lead recordings were obtained from seven dolphins, plus an additional three dolphins that were recorded using only direct thorax lead placement of the portable ECG unit. Six-lead, base apex, and direct thorax lead recordings were obtained from 19 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). The PR interval, QRS duration and S wave amplitude were slightly but significantly greater, and the MEA oriented slightly further right, in the wild post-capture dolphins than in the collection dolphins. T wave amplitude (and T/QRS and T/S ratios) did not correlate with K, lactate or pH. Blood lactate trended (nonsignificantly) higher in wild post-capture dolphins, but their blood pH was unexpectedly significantly higher than the collection animals, associated with a presumed respiratory alkalosis (i.e., significantly lower pCO2). Functional significance of the detected ECG differences is likely minor, and the slight ECG differences identified in this analysis would not be readily apparent under field conditions. Clinically, ECG was a useful adjunct to auscultation and thoracic palpation for monitoring heart rate and rhythm. Safe capture and handling protocols in place under which dolphins are immediately returned to the water at the first 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.
acknowledgements
Electrocardiography equipment was obtained with funding from NOAA Fisheries John H. Prescott Marine Mammal Rescue Assistance Grant program (NA 06NMF4390265).
References
1. Falabella V, Campagna C, Lewis M. 1999. Electrocardiography of southern elephant seal (Mirounga leonina) weanlings. J Zoo Wildl Med 30: 526-531.
2. Hamlin RL, Jackson RF, Himes JA, Pipers FS, Townsend AC. 1970. Electrocardiogram of bottle-nosed dolphin (Tursiops truncatus). Am J Vet Res 31: 501-505.
3. Hamlin RL, Ridgway SH, Gilmartin WG. 1972. Electrocardiogram of pinnipeds. Am J Vet Res 33: 867-875.
4. Siegal-Willott J, Estrada A, Bonde R, Wong A, Estrada DJ, Harr K. 2006. Electrocardiography in two subspecies of manatee (Trichechus manatus latirostris and T. m. manatus). J Zoo Wildlife Medicine 37: 447-453.