Background: Dogs with atrial fibrillation (AF) live longer with strict heart rate control (SHRC, 24-hour mean heart rate ≤125 beats/minute). Although amiodarone (AM) and diltiazem (DTZ) are used to lower ventricular response rate in dogs with AF, information about their relative efficacy for achieving SHRC is lacking.
Hypothesis/Objectives: Determine if therapy with AM, DTZ or a combination will achieve SHRC in dogs with AF.
Animals: Twelve client-owned dogs with newly-diagnosed AF were enrolled and returned for follow-up
Methods: Prospective, randomized, non-blinded clinical trial. Eligible dogs had AF with mean daily heart rate (MDHR) >125 beats/minute (baseline, 24-hour Holter) and were randomly assigned to receive AM or DTZ at standard doses. Repeat 24-hour Holter assessments were performed at 3, 6 and 9-21 weeks after starting treatment. If MDHR >125 beats/minute at any assessment, the second drug was added.
Results: Six dogs each received AM or DTZ first. MDHR decreased significantly after AM (P = 0.03) or DTZ (P = 0.05) initiation; 1 dog in each group achieved SHRC at 3 weeks. At last follow-up, 11/12 dogs were receiving combined AM/DTZ for median [range] 50 [20 –153] days with no difference based on which drug was initiated first (P = 0.87). Most dogs (7/11, 64%) had not achieved SHRC (139 [94 – 160]) beats/minute at standard doses (AM, 7.5 [6.2 – 9.3] mg/kg/day; DTZ, 7.3 [6.3 – 11.9] mg/kg/day).
Conclusions and clinical importance: Monotherapy with AM or DTZ or combination therapy of AM/DTZ does not achieve SHRC in most dogs with AF.
