Standardization of Dolphin Cardiac Auscultation and Characterization of Heart Murmurs in Managed and Free-Ranging Bottlenose Dolphins (Tursiops truncatus)

Abstract

Cardiac auscultation is an important, albeit underutilized tool in aquatic animal medicine due to the many challenges associated with in-water examinations. The aims of this prospective study were to (1) establish an efficient and repeatable in-water cardiac auscultation technique in bottlenose dolphins ( Tursiops truncatus ), (2) describe the presence and characterization of heart murmurs detected in free-ranging and managed dolphins, and (3) characterize heart murmur etiology through echocardiography in free-ranging dolphins. For technique development, 65 dolphins cared for by the Navy Marine Mammal Program (Navy) were auscultated. The techniques were then applied to two free-ranging dolphin populations during capture-release health assessments: Sarasota Bay, Florida (SB), a reference population, and Barataria Bay, LA (BB), a well-studied population of dolphins impacted by the Deepwater Horizon oil spill. Systolic heart murmurs were detected at a frequent and similar prevalence in all dolphin populations examined (Navy 92%, SB 89%, and BB 88%), and characterized as fixed or dynamic. In all three populations, sternal cranial and left cranial were the most common locations for murmur point of maximal intensity (PMI). An in-water transthoracic echocardiogram technique was refined on a subset of Navy dolphins, and full echocardiographic exams were performed on 17 SB dolphins and 29 BB dolphins, of which, 40 had murmurs. Spectral Doppler was used to measure flow velocities across the outflow tracts, and almost all dolphins with audible murmurs had peak outflow velocities ≥1.6 m/s (95%, 38/40); three dolphins also had medium mitral regurgitation which could be the source of their murmurs. The presence of audible murmurs in most of the free-ranging dolphins (88%) was attributed to high velocity blood flow as seen on echocardiography, similar to a phenomenon described in other athletic species. These innocent murmurs were generally characterized as Grade I-III systolic murmurs with PMI in the left or sternal cranial region. This study is the first to describe an efficient technique for in-water dolphin cardiac auscultation, and to present evidence that heart murmurs are common in bottlenose dolphins.

Cardiac assessments of bottlenose dolphins (Tursiops truncatus) in the Northern Gulf of Mexico following exposure to Deepwater Horizon oil

“…Cardiac auscultation was systematically performed as previously described with Navy and free-ranging dolphins [ 1 ]. All auscultations were performed in seawater with the 3M™ Littman® Veterinary Master Classic II 32” (3M™ Littman®, St. Paul, MN, USA).…”

“…Nineteen dolphins were auscultated in SB and 34 in BB by a cardiologist (AH or SMH) in addition to other marine mammal veterinarians (BKL, FMG, CRS) according to standard procedure [ 1 ]. Murmurs were graded by intensity using the conventional Grade I-VI scale [ 45 – 47 ].…”

“…To comprehensively assess the cardiac health of dolphins living within the DWH oil spill footprint, techniques for in-water cardiac evaluation were refined with dolphins cared for by the U.S. Navy Marine Mammal Program in 2018 and applied to free-ranging bottlenose dolphins in BB ( n = 34) and Sarasota Bay, Florida (SB) ( n = 19), a non-oiled reference population. Cardiac auscultation detected systolic murmurs in the majority of dolphins from both sites (88% BB, 89% SB) and echocardiography showed most of the murmurs were innocent flow murmurs attributed to elevated blood flow velocity [ 1 ]. Telemetric six-lead electrocardiography detected arrhythmias in BB dolphins (43%) and SB dolphins (31%), all of which were considered low to moderate risk for adverse cardiac events.…”

A review of the toxicology of oil in vertebrates: what we have learned following the Deepwater Horizon oil spill

“…Although there were no published studies of the cardiovascular system in marine mammals exposed to DWH oil at the time of the workshop, a few studies have been completed in the last year. Linnehan et al (2020) found that marine mammals (managed in San Diego) and wild common bottlenose dolphins (in Sarasota, Florida and Barataria Bay, Louisiana) displayed a similarly high prevalence (approximately 90%) of systolic heart murmurs, with maximal intensity typically in the sternal cranial and left cranial areas of the heart. However, three dolphins in Barataria Bay also exhibited medium mitral regurgitation and moderate to severe lung disease; veterinarians gave all three individuals a guarded to poor prognosis based upon all of the health assessment data available.…”

High site-fidelity in common bottlenose dolphins despite low salinity exposure and associated indicators of compromised health

“…This is consistent with extensive photographic-identification and telemetry research documenting that bay, sound, and estuarine dolphins in the Southeastern U.S. typically stay in relatively small usage areas [e.g., 24 , 26 – 33 ], often despite acute or chronic environmental stressors such as low salinity [ 10 , 19 , 34 ], tropical disturbances [ 21 , 35 ], oil spills and other anthropogenic contaminants [ 10 , 34 , 36 – 38 ], and harmful algal blooms [ 35 , 39 – 42 ]. Due to their high site fidelity, BBES dolphins were exposed to DWH oil in their heavily contaminated habitat and subsequently suffered numerous adverse health effects from oil toxicity (e.g., lung disease, impaired stress response and adrenal dysfunction, immune dysfunction, and poor overall health prognoses), leading to drastic and prolonged elevated reproductive failure rates and mortality rates following the oil spill [ 43 – 53 ]. NOAA declared a UME related to the effects of DWH oiling on cetaceans throughout the nGOMx, including dolphins in the Barataria Basin [ 51 , 54 ].…”