Daily Heart Rate Variability in Dogs With Atrial Fibrillation.

Background: Daily variability of heart rate in 24-h Holter recordings in dogs with atrial fibrillation (AF) receiving antiarrhythmic drugs (AAD) is unknown and could influence medical decisions.

Hypothesis/objectives: Dogs with AF, Holter-derived mean heart rate (meanHRHolter) over 24 h is not significantly different from a subsequent, consecutive 24-h period.

Animals: Twenty-five dogs with AF.

Methods: Prospective, descriptive, multicenter study. MeanHRHolter rate and ventricular arrhythmias (VAs) were prospectively analyzed after starting AAD. Clinically relevant difference (defined as ≥ 10 bpm in the meanHRHolter), success of rate control (defined as meanHRHolter ≤ 125 bpm). A Bland-Altman analysis and intra-class correlation coefficient (ICC) were calculated to compare two consecutive 24-h Holter recordings. VAs percentage difference [(maximum daily value-minimum daily value)/maximum daily value × 100] and grading variability between recordings were also investigated.

Results: Small BIAS with ICC 0.98 (95% confidence interval [CI] 0.95-0.99) on meanHRHolter with no statistical difference between two consecutive 24-h Holter recordings (95% CI [-2.84-2.92], degree of freedom 24, p = 0.98). Only 2/25 dogs (8%; 95% CI [2%-25%]) had clinically significant variation, while 1/25 (4%; 95% CI [0%-20%]) dogs showed different classifications in the success of rate control between the consecutive recordings. The VAs percentage difference was 52%, with 7/25 (28%; 95% CI [14%-47%]) dogs showing a VAs grading difference of ≥ 2.

Conclusion And Clinical Importance: The daily heart rate variability in dogs with AF receiving AAD is low, suggesting that a single 24-h Holter recording is adequate to assess rate control. Daily variability might be an important consideration when assessing VAs in dogs with concomitant AF.