Atrial fibrillation in DCM: Holter heart-rate target
7-year-old Great Dane with dilated cardiomyopathy and atrial fibrillation, admitted 3 weeks ago with pulmonary oedema. He is now stable at home on furosemide, pimobendan, benazepril and extended-release diltiazem. In the clinic, the auscultated heart rate is 170 bpm. 24-hour Holter at home:
| Parameter | Result | Reference |
|---|---|---|
| 24-h mean heart rate | 158 bpm | — |
| Maximum heart rate | 265 bpm (on walks) | — |
| Minimum heart rate | 98 bpm (at night) | — |
| Rhythm | Persistent atrial fibrillation | — |
| Ventricular premature complexes | 140/24 h, isolated | — |
What is the most appropriate course of action?
chevron_right Show answer and explanation
A. Keep the regimen: a mean of 150–160 bpm is acceptable in a giant-breed dog with AF
A mean home heart rate of 158 bpm indicates inadequate control. In dogs with AF, a mean Holter heart rate below about 125 bpm has been associated with longer survival; breed size does not change that target.
B. Add digoxin to the diltiazem and repeat the Holter aiming for a mean below 125 bpm
Correct. Combining diltiazem and digoxin slows the ventricular response more than either drug alone. The practical target is a mean Holter heart rate below about 125 bpm, which is associated with longer survival. Monitor serum digoxin and renal function.
C. Electrical cardioversion to restore sinus rhythm and then withdraw the diltiazem
With DCM and a markedly dilated left atrium, AF almost always recurs after cardioversion. In AF with structural heart disease and heart failure, the usual strategy is rate control, not rhythm control.
D. Replace the diltiazem with sotalol to control both the rate and the ventricular ectopy
Sotalol has beta-blocking and negative inotropic effects, poorly tolerated in DCM that has just decompensated, and is not a first choice for rate control. The isolated ventricular ectopics on the Holter do not justify the switch.
lightbulb Key takeaway
AF rate should be judged on a home Holter, not by auscultation: clinic rates over- or underestimate it depending on stress, and the pulse deficit makes femoral counts unreliable. Titrate treatment to a mean rate below about 125 bpm and repeat the Holter after each change.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.