Objective:

To evaluate non-linear RR interval metrics in dogs with atrial fibrillation (AF) and their correlation with 24-hour average heart rate (meanHR).

Approach:

• Study Population: Fifty client-owned dogs with confirmed AF underwent 24-h Holter monitoring to assess ten non-linear RR metrics.
• Metrics Evaluated: Metrics included CVRR, Poincaré SD1, SD2, SD1/SD2 ratio, |ΔRR|, turning-point ratio, DFA-α, sample entropy, and multiscale entropy.
• Statistical Analysis: Spearman correlation and within-quintile IQR ratio were used to assess rate dependence.

Key Findings:

• Metrics were categorized into rate-coupled (CVRR, SD1, SD2, |ΔRR|, DFA-α) and rate-independent (SD1/SD2 ratio, turning-point ratio, MScEn) classes.
• All dogs exhibited a negative Jensen gap (mean -13.4 bpm), indicating a relationship with CVRR.
• Five dogs were reclassified as non-rate-controlled based on medianHR.
• Rate-independent metrics differed significantly between pre- and post-drug groups.

Interpretation:

The study highlights the limitations of using meanHR alone for assessing rate control in canine AF.

Limitations:

• The study is retrospective and based on a specific population of dogs, which may limit the generalizability of the findings.
• The 125-bpm threshold may oversimplify the continuous nature of RR interval distributions, potentially affecting the assessment of rate control.

Conclusion:

Future studies should integrate rate-independent metrics alongside meanHR for a more comprehensive assessment of rate control.