Comparative study of atrial fibrillation and AV conduction in mammals.

This study compares atrial fibrillation, a common heart rhythm disorder, in humans, dogs, horses, and kangaroos to explore the pathophysiological mechanisms involved. The research found that larger animals had slower heart rates and that digitalis, a medication for heart conditions, reduced heart rate in all species and enforced regular heart rhythms in horses.

Overview of the Study

• The researchers conducted a comparative study on atrial fibrillation, which is one of the most common cardiac arrhythmias in humans and also prominent in dogs and horses. They hoped to contribute to the understanding of the underlying pathophysiological mechanisms involved.
• The study examined atrial fibrillation in several mammals including humans, dogs, horses, and a kangaroo using histograms and serial autocorrelograms of the ventricular rhythm, both with and without the medication digitalis.

Findings on Heart Rate and Rhythm

• The study found that as the animal size—and consequently heart size—increases, the heart rate (ventricular rate) decreases.
• While the ventricular rhythm was random in dogs, kangaroos, and humans, a level of regular rhythm was observed in horses.

Effect of Digitalis Medication

• Digitalis, a common medication used to treat heart conditions, was found to lower the heart rate in all species studied.
• Besides decreasing the heart rate, digitalis also enforced regularity in the heart rhythm of horses.

Insights on Cardiac Evolution

• The differences in atrial excitation, atrioventricular (AV) conduction, and ventricular behavior among the four species were minimal compared to the notable differences in heart size.
• Based on this, the researchers concluded that evolutionarily, the size and morphology of heart cells likely have greater importance than their function.