Heart Rate and Survival in Dogs With Atrial Fibrillation

Atrial fibrillation is a clinically significant arrhythmia that develops in the presence of existing heart disease. In dogs with congestive heart failure (CHF), the presence of atrial fibrillation is a poor prognostic indicator.

Treatment of atrial fibrillation in dogs is aimed at heart rate control. Traditionally, maintenance of higher rates has been recommended, but these recommendations are not evidence-based.

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Researchers from the United Kingdom and United States recently performed a retrospective evaluation of the effect of heart rate on survival in dogs with atrial fibrillation.

Study Design

Medical records from the University of Liverpool and the University of Pennsylvania from 2008 to 2016 were evaluated. Dogs with a diagnosis of atrial fibrillation and at least 1 Holter recording obtained in the home environment were included. Patients were excluded if they had been treated with doxorubicin, had serious concurrent systemic disease (eg, neoplasia), experienced a change in rhythm to sinus or atrial flutter, or required a pacemaker.

Patient signalment, cardiovascular and rhythm diagnosis, medical treatments during the Holter recording, and patient outcome were recorded.

The following data points were analyzed from the Holter recordings:

• Mean heart rate, averaged over 24 hours
• Minimum heart rate, averaged over 1 minute
• Maximum heart rate, averaged over 1 minute

The primary study endpoint was all-cause mortality. A secondary endpoint of death due to cardiac disease was included. Cardiac deaths included euthanasia due to progression of CHF and sudden death.

Results

Forty-six dogs were included in the study (3 intact females, 8 spayed females, 17 intact males, 18 neutered males). Patients represented multiple breeds and ages (median, 7 years; range, 1-14 years). Thirty-one patients were under medical management for CHF. Forty-four patients were on 1 or more medications for rate control with digoxin, diltiazem, amiodarone, and/or sotalol.

Sex, neutering status, age, weight, study site, and cardiac diagnosis were not significantly associated with either all-cause or cardiac mortality. The presence or absence of CHF at the time of diagnosis of atrial fibrillation was not significantly associated with all-cause mortality.

While all heart rate parameters correlated with both all-cause and cardiac mortality, only mean heart rate was associated independently with survival. The median mean heart rate was 125 bpm (range, 62-203 bpm).

Kaplan-Meier survival curves were analyzed for dogs split into 2 cohorts based on the median mean heart rate of 125 bpm. Median survival time for dogs with mean heart rate less than 125 bpm (1037 days) was significantly longer than those with mean heart rate of 125 or higher (105 days).

Take-home Message

The results of this study show that patients with atrial fibrillation live longer with lower heart rates. This study suggests a therapeutic target of 125 bpm based on Holter recordings for patients with atrial fibrillation. Prospective studies are needed to further explore treatment targets in patients with atrial fibrillation as well as compare the medications used for rate control.

Dr. Boatright, a 2013 graduate of the University of Pennsylvania School of Veterinary Medicine, works as a general practitioner and emergency veterinarian in western Pennsylvania. She is active in her state and local veterinary medical associations and is a former national officer of the Veterinary Business Management Association.