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96 Atrial Premature Complexes and Atrial Tachycardia

• Beta-blocker: same as CCB starting digoxin therapy at trough levels (6-8 difficult to resolve while the other is present
○ Not recommended in dogs with acute hours after pilling). Ideal trough level should (rapid HR and CHF).
VetBooks.ir ○ When discontinuing chronic beta-blocker PROGNOSIS & OUTCOME Prevention
decompensated CHF
be 0.5-1.0 ng/mL.
Dogs with AF from breeds with a known genetic
therapy, taper over several days to avoid risk
of catecholamine-mediated arrhythmias.
from breeding programs, even if no overt
• Digoxin CHF is a major risk factor for development predisposition (e.g., IWH) should be excluded
○ Signs of digoxin toxicity include lethargy, of AF and vice versa. The combination of AF structural heart disease is identified.
inappetance, vomiting/diarrhea. Occasionally, and CHF carries a worse prognosis than either
proarrhythmic effects are seen (first-degree AV alone. Mortality of dogs with AF is associated Technician Tips
block, ventricular arrhythmias). Elimination with the HR. Median survival of dogs under Counting the HR by auscultation is usually
half-life in dog: 14-56 hours; if digoxin rate control therapy achieving a mean 24-hour inaccurate in AF when the rate is > 180 beats/
toxicity is suspected, stop digoxin for average HR < 125 beats/min was 2.8 years, but min. Obtain an ECG to confirm the diagnosis
several days, and then start up again at a for dogs with a mean 24-hour HR ≥ 125 beats/ and to get an accurate HR assessment.
lower dose. Consider reducing the dose of min, it was only 3.75 months. Dogs without
digoxin in the presence of cachexia, ascites underlying disease have a better prognosis; SUGGESTED READING
or obesity, hypoproteinemia, hypokalemia, median survival for lone AF is 3.3 years. Pedro B, et al: Retrospective evaluation of the effect of
hypothyroidism, renal dysfunction. heart rate on survival in dogs with atrial fibrillation.
PEARLS & CONSIDERATIONS J Vet Intern Med 32(1):86-92, 2018.
Recommended Monitoring
• To determine efficacy of pharmacologic rate Comments AUTHOR: Anna R. M. Gelzer, DMV, PhD, DACVIM,
DECVIM
control therapy, repeat ECG or ideally a If AF and acute decompensated CHF (especially EDITOR: Meg M. Sleeper, VMD, DACVIM
24-hour Holter in the home environment pulmonary edema) are present simultaneously,
5-7 days after starting oral medications. treatment of CHF (e.g., diuretics, pimobendan)
• To avoid toxicity, digoxin serum concentra- must be instituted at the same time as rate
tions should be measured 5-7 days after control therapy. Either abnormality is very

Atrial Premature Complexes and Atrial Tachycardia

BASIC INFORMATION RISK FACTORS • Syncope or weakness are possible with rapid
Cardiac diseases, especially those causing atrial tachycardias
Definition enlargement: • Patient may have dyspnea related to conges-
• Atrial premature complex (APC): a premature • Chronic myxomatous/degenerative valvular tive heart failure (CHF).
beat originating from ectopic focus in the heart disease • SVTs may rarely precipitate sudden death
atria • Dilated, hypertrophic, or restrictive if resultant myocardial ischemia leads to
• Atrial tachycardia (AT): a rapid, regular cardiomyopathy ventricular tachycardia or fibrillation or if
rhythm originating from a focus in the • Congenital heart disease antiarrhythmic medications used in treatment
atria other than the sinus node (three or • Atrial tumors such as hemangiosarcoma have a proarrhythmic effect.
more consecutive APCs are considered Noncardiac disease:
AT) • Increased sympathetic tone PHYSICAL EXAM FINDINGS
• Supraventricular tachycardia (SVT): origi- • Hyperthyroidism • An irregular heart rhythm is ausculted with
nates from the atria or the atrioventricular • Sepsis early beats.
(AV) junction (includes AT and AV junc- • Electrolyte and acid-base abnormalities (i.e., ○ When beats are very premature, pulse
tional tachycardia) hypokalemia) deficits are also noted.
○ This definition may also be considered to • Hypoxemia ○ It is not possible to determine whether a
include atrial fibrillation and atrial flutter, • Anemia premature beat is an APC or a ventricular
which are discussed in a separate section Drugs: premature complex (VPC) on physical
(p. 94). • Digoxin toxicity (may produce AT with AV examination alone.
block) • A burst or bursts of a rapid, regular rhythm
Synonyms • Sympathomimetic agents can be ausculted with paroxysmal AT/SVT
Premature atrial or supraventricular complex, • Anesthetic agents or can be sustained with continuous AT/
contraction, or impulse Ventricular pre-excitation: SVT.
• Wolff-Parkinson-White syndrome
Epidemiology Etiology and Pathophysiology
SPECIES, AGE, SEX Clinical Presentation • Hemodynamic effects of atrial tachyar-
Occasional APCs can be a normal occurrence DISEASE FORMS/SUBTYPES rhythmias depend on the underlying disease,
in very old dogs. • Isolated APCs ventricular rate, and whether the patient is
• AT, SVT: paroxysmal (noncontinuous bursts at rest or exercising.
GENETICS, BREED PREDISPOSITION of at least three APCs in a row) or sustained ○ Excessively rapid ventricular rates reduce
An orthodromic reciprocating tachycardia (continuous) cardiac output, systemic blood pressure,
(antegrade conduction through the AV and coronary artery perfusion secondary
node and retrograde back to the atria by a HISTORY, CHIEF COMPLAINT to the shortened diastolic interval.
bypass tract) has been identified in Labrador • May be an incidental finding in a patient • Sustained or frequently recurrent ATs may
retrievers. without clinical signs lead to tachycardia-induced cardiomyopathy,

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