Horses with atrial fibrillation (AF, disorganized electrical conduction and pumping of the atria) can have a difficult time with exercise. Scientists have shown that the condition influences the properties and blood flow in horses during treadmill exercise, which could explain this exercise intolerance. They published their findings in the August issue of Research in Veterinary Science.

Atrial fibrillation is the most common cardiovascular cause of poor performance in horses because the cardiac impulse becomes confused at the level of the sinoatrial node (the impulse-generating tissue located in the right atrium of the heart). This confusion results in the atria never relaxing or contracting properly, so the heart cannot pump as efficiently as it should.

Researchers at Hanover University’s College of Veterinary Medicine in Germany studied the affects of treadmill exercise on equine heart rate and pulmonary artery wedge pressure (PWP); the latter provides an accurate assessment of blood flow status, cardiac function, and venous oxygen saturation. The scientists measured rates in 10 healthy Warmblood horses and in six horses affected with AF. While heart rate and PWP should naturally increase with exercise, the increase in heart rate and PWP was significantly higher in horses with AF than in normal horses.

The findings led researchers to conclude that general performance–not just strenuous, high-levels of performance–can be affected by AF