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Atrial Fibrillation 95

VetBooks.ir Diseases and Disorders

ATRIAL FIBRILLATION A, Lead II ECG showing atrial fibrillation with a rapid ventricular response rate (290-
300 bpm) in a dog with CHF. Note the narrow QRS complexes and irregular R-R intervals (often less apparent at rapid
ventricular rates). 25 mm/sec. B, Lead II ECG showing atrial fibrillation in the same dog 2 weeks after appropriate
treatment for CHF, including diltiazem and digoxin. The ventricular response rate is 120-130 bpm, and the irregularity
of the R-R intervals and lack of P waves can be seen easily. 25 mm/sec.

elevated HR, a 24-hour ambulatory ECG ○ Simultaneously treat CHF, if present, ○ Cat: 0.03125 mg (one quarter of 0.125-
(Holter) recording in the home environment because cardiac decompensation contrib- mg tablet)/CAT PO q 48-72h
is recommended (p. 1120). utes to high sympathetic tone and fast • In patients with AF and significant concur-
ventricular response (p. 408). rent ventricular arrhythmias, sotalol (1-2 mg/
TREATMENT • For acute onset of vagally mediated AF (e.g., kg PO q 12h) may be used cautiously for
under anesthesia/opioid administration) rate control and suppression of ventricular
Treatment Overview attempt cardioversion using IV lidocaine as arrhythmias. Sotalol can also be combined
Goal of treatment of AF is to reduce long-term a rapid bolus at 2-3 mg/kg over 5 seconds. with digoxin.
effects of uncontrolled tachycardia on myocar- Repeat up to 3 times, not to exceed 8 mg/kg. • Cats with AF usually have structural heart
dial function. Aims are either • Electrical cardioversion or pharmacologic disease and require anticoagulation (p. 505);
• Restore and maintain sinus rhythm with cardioversion (with amiodarone) may be dogs typically do not require anticoagulation.
electric or pharmacologic cardioversion attempted by a cardiologist. There is limited
(rhythm control). Most dogs fail pharma- success in restoring normal sinus rhythm Drug Interactions
cologic cardioversion or do not maintain long term with these techniques in veterinary • Simultaneous administration of digoxin with
sinus rhythm for very long after electric patients. amiodarone or quinidine can increase digoxin
cardioversion because of advanced myocardial serum concentrations and potentially cause
pathology. Chronic Treatment digoxin toxicosis.
• Control the ventricular rate by slowing For rate control, CCB, digoxin, and beta-blockers • CCB should not be combined with beta-
conduction across the AV node with antiar- are used alone or in combination. Combination blockers for rate control because excessive
rhythmic drugs (rate control), allowing AF therapy of diltiazem with digoxin controls ven- AV block, hypotension, and reduced cardiac
to persist but at a reduced HR. Target HR tricular rate better than monotherapy. contractility may ensue.
on an in-hospital ECG with rate control • Diltiazem extended-release (Dilacor-XR,
therapy should be less than 150 beats/min, Cardizem-CD): 2.5-3.5 mg/kg PO q 12h Possible Complications
or on Holter, a 24-hour mean HR should (dog), 30-60 mg/dose PO q 12-24h (cat) • CCB
be less than 125 beats/min. or diltiazem modified release: diltiazem CD ○ Overdose causes excessive AV block
2-3 mg/kg PO q 8h (dog). Effect on HR (pauses); clinical signs include weakness,
Acute General Treatment occurs within a few hours of oral dosing. lethargy, or fainting.
• For unstable dogs (overt weakness, syncope, or Only mild effects on contractility when given ○ Without clinical signs (listed above),
CHF) with HR > 250 beats/min, consider the at prescribed doses pauses noted during sleep on a 24-hour
calcium channel blocker (CCB) diltiazem IV • Atenolol: 0.5-2 mg/kg q 12-24h; start at a Holter should not be a reason to lower
bolus (0.1-0.25 mg/kg IV up to 3 times) and/ low dose and titrate up as needed; use caution the dose of rate control medication.
or constant rate infusion (2-6 mcg/kg/min). in dogs with poor systolic function or in heart ○ Intravenous CCB may cause transient
○ If impaired systolic function is suspected failure hypotension and reduced contractility;
(e.g., DCM), monitor blood pressure • Digoxin start with very low dose and monitor
during infusion of CCB because of the ○ Dog: 0.003-0.004 mg/kg PO q 12h (or arterial blood pressure. Titrate to
2
negative inotropic effects (choose lowest 0.11 mg/m q 12 h). Not to exceed effect. Stop infusion if hypotension is
dose and titrate upward based on response). 0.25 mg q 12h evident.
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