Study finds alligator hearts keep beating no matter what

February 15, 2021

Mammals and cold-blooded alligators share a common four-chamber heart structure - unique among reptiles - but that's where the similarities end. Unlike humans and other mammals, whose hearts can fibrillate under stress, alligators have built-in antiarrhythmic protection. The findings from new research were reported Jan. 27 in the journal Integrative Organismal Biology.

"Alligator hearts don't fibrillate - no matter what we do. They're very resilient," said Flavio Fenton, a professor in the School of Physics at the Georgia Institute of Technology, researcher in the Petit Institute for Bioengineering and Bioscience, and the report's corresponding author. Fibrillation is one of the most dangerous arrhythmias, leading to blood clots and stroke when occurring in the atria and to death within minutes when it happens in the ventricles.

The study looked at the action potential wavelengths of rabbit and young alligator hearts. Both species have four-chambered hearts of similar size (about 3 cm); however, while rabbits maintain a constant heart temperature of 38 degrees Celsius, the body temperature of active, wild alligators ranges from 10 to 37 degrees Celsius. Heart pumping is controlled by an electrical wave that tells the muscle cells to contract. An electrical signal drives this wave, which must occur in the same pattern to keep blood pumping normally. In a deadly arrhythmia, this electrical signal is no longer coherent.

"An arrhythmia can happen for many reasons, including temperature dropping. For example, if someone falls into cold water and gets hypothermia, very often this person will develop an arrythmia and then drown," Fenton said.

During the study, the researchers recorded changes in the heart wave patterns at 38 C and 23 C. "The excitation wave in the rabbit heart reduced by more than half during temperature extremes while the alligator heart showed changes of only about 10% at most," said Conner Herndon, a co-author and a graduate research assistant in the School of Physics. "We found that when the spatial wavelength reaches the size of the heart, the rabbit can undergo spontaneous fibrillation, but the alligator would always maintain this wavelength within a safe regime," he added.

While alligators can function over a large temperature range without risk of heart trauma, their built-in safeguard has a drawback: it limits their maximum heart rate, making them unable to expend extra energy in an emergency.

Rabbits and other warm-blooded mammals, on the other hand, can accommodate higher heart rates necessary to sustain an active, endothermic metabolism but they face increased risk of cardiac arrhythmia and critical vulnerability to temperature changes.

The physicists from Georgia Tech collaborated with two biologists on the study, including former Georgia Tech postdoctoral fellow Henry Astley, now assistant professor in the Biomimicry Research and Innovation Center at the University of Akron's Department of Biology.

"I was a little surprised by how massive the difference was - the sheer resilience of the crocodilian heart and the fragility of the rabbit heart. I had not expected the rabbit heart to come apart at the seams as easily as it did," noted Astley.

Lower temperatures are one cause of cardiac electrophysiological arrhythmias, where fast-rotating electrical waves can cause the heart to beat faster and faster, leading to compromised cardiac function and potentially sudden cardiac death. Lowering the temperature of the body - frequently done for patients before certain surgeries - also can induce an arrhythmia.

The researchers agree that this study could help better understand how the heart works and what can cause a deadly arrhythmia - which fundamentally happens when the heart doesn't pump blood correctly any longer.

The authors also consider the research a promising step toward better understanding of heart electrophysiology and how to help minimize fibrillation risk. Until December 2020, when Covid-19 took the top spot, heart disease was the leading cause of death in the United States and in most industrialized countries, with more people dying of heart disease than the next two causes of death combined.

Astley said the research provides a deeper understanding of the natural world and insight into the different coping mechanisms of cold- and warm-blooded animals.

Co-author Tomasz Owerkowicz, associate professor in the Department of Biology at California State University, San Bernardino, considers the findings "another piece of the puzzle that helps us realize how really cool non-human animals are and how many different tricks they have up their sleeves."

He expressed hope that more researchers will follow their example and use a non-traditional animal model in future research.

"Everyone studies mammals, fruit flies, and zebrafish. There's such a huge wealth of resources among the wild animals that have not been brought to the laboratory setting that have such neat physiologies, that are waiting to be uncovered. All we have to do is look," he said.
-end-
CITATION: C. Herndon, et al., "Defibrillate you Later, Alligator; Q10 Scaling and Refractoriness Keeps Alligators from Fibrillation." (Integrative Organismal Biology, 2021) https://academic.oup.com/iob/advance-article/doi/10.1093/iob/obaa047/6120966?login=true

Georgia Institute of Technology

Related Heart Disease Articles from Brightsurf:

Cellular pathway of genetic heart disease similar to neurodegenerative disease
Research on a genetic heart disease has uncovered a new and unexpected mechanism for heart failure.

Mechanism linking gum disease to heart disease, other inflammatory conditions discovered
The link between periodontal (gum) disease and other inflammatory conditions such as heart disease and diabetes has long been established, but the mechanism behind that association has, until now, remained a mystery.

New 'atlas' of human heart cells first step toward precision treatments for heart disease
Scientists have for the first time documented all of the different cell types and genes expressed in the healthy human heart, in research published in the journal Nature.

With a heavy heart: How men and women develop heart disease differently
A new study by researchers from McGill University has uncovered that minerals causing aortic heart valve blockage in men and women are different, a discovery that could change how heart disease is diagnosed and treated.

Heart-healthy diets are naturally low in dietary cholesterol and can help to reduce the risk of heart disease and stroke
Eating a heart-healthy dietary pattern rich in vegetables, fruits, whole grains, low-fat dairy products, poultry, fish, legumes, vegetable oils and nuts, which is also limits salt, red and processed meats, refined-carbohydrates and added sugars, is relatively low in dietary cholesterol and supports healthy levels of artery-clogging LDL cholesterol.

Pacemakers can improve heart function in patients with chemotherapy-induced heart disease
Research has shown that treating chemotherapy-induced cardiomyopathy with commercially available cardiac resynchronization therapy (CRT) delivered through a surgically implanted defibrillator or pacemaker can significantly improve patient outcomes.

Arsenic in drinking water may change heart structure raising risk of heart disease
Drinking water that is contaminated with arsenic may lead to thickening of the heart's main pumping chamber in young adults, according to a new study by researchers at Columbia University Mailman School of Public Health.

New health calculator can help predict heart disease risk, estimate heart age
A new online health calculator can help people determine their risk of heart disease, as well as their heart age, accounting for sociodemographic factors such as ethnicity, sense of belonging and education, as well as health status and lifestyle behaviors.

Wide variation in rate of death between VA hospitals for patients with heart disease, heart failure
Death rates for veterans with ischemic heart disease and chronic heart failure varied widely across the Veterans Affairs (VA) health care system from 2010 to 2014, which could suggest differences in the quality of cardiovascular health care provided by VA medical centers.

Heart failure: The Alzheimer's disease of the heart?
Similar to how protein clumps build up in the brain in people with some neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, protein clumps appear to accumulate in the diseased hearts of mice and people with heart failure, according to a team led by Johns Hopkins University researchers.

Read More: Heart Disease News and Heart Disease Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.