Cardiovascular changes in horses with atrial fibrillation and high thyroid hormone concentration: a case-control study.

The research studied whether high thyroid hormone concentration causes cardiovascular changes and recurrence in horses with atrial fibrillation. It found that 60% of horses with this condition also had elevated thyroid hormone levels and showed symptomatic cardiovascular effects.

Research Objective

The research had three objectives:

• Determine whether high thyroid hormone concentrations were present in horses with atrial fibrillation.
• Investigate whether other cardiovascular effects were observed in horses with high thyroid hormone concentrations and atrial fibrillation.
• Analyze whether thyroid hormone status impacted the recurrence rate of atrial fibrillation in horses.

Research Methods

The study followed a prospective case-control clinical study setup and encompassed twenty-three horses found with naturally occurring atrial fibrillation.

• Thyroid hormone concentrations were measured and documented.
• Other clinical work data such as heart rate, ECG report, blood pressure, and echocardiogram results of all the horses were also recorded.
• The recurrence rate was ascertained through owner/veterinarian follow-ups.

Research Results

The research found that:

• 60% of horses with atrial fibrillation had high thyroid hormone concentration.
• Horses in this category also registered higher heart rate, systolic blood pressure, left ventricular free wall thickness, and relative wall thickness.
• These horses were also seen to have more periods of atrial fibrillation with rapid ventricular response rate.
• All horses, regardless of the thyroid hormone status, were converted successfully to normal sinus rhythm without incidence of recurrence between the groups.

Research Conclusion

The study found strong evidence supporting the presence of high thyroid hormone concentration in horses suffering from atrial fibrillation. The study also found similar cardiovascular symptoms in these horses as found in other species with the same condition. Therefore, the study recommends measuring thyroid hormone concentrations in horses presenting with atrial fibrillation, especially those with a history of thyroid or iodine supplementation.

More importantly, the study cautions against the use of thyroid hormone or iodine supplementation in healthy performance horses, possibly because of the correlation found between these supplements and atrial fibrillation.