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94 Atrial Fibrillation

Atrial Fibrillation Bonus Material Client Education
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VetBooks.ir BASIC INFORMATION typically accompanied by pulse deficits.

DISEASE FORMS/SUBTYPES
Definition Clinical Presentation An electrocardiogram (ECG) confirms the
diagnosis.
Atrial fibrillation is a supraventricular arrhyth- • Chronic AF: associated with atrial dilation
mia characterized by a rapid, irregular and structural heart disease Differential Diagnosis
rhythm. • Paroxysmal AF: may terminate when underly- On the ECG, AF should be differentiated from
ing systemic disease is corrected • Baseline artifact (poor grounding, purring,
Synonym • Primary (lone) AF: occurs without an identifi- shivering movement): ventricular rate is not
A fib able cause or structural heart disease in giant irregularly irregular, P waves appear if
breeds interference is corrected.
Epidemiology • Atrial flutter: atrial activity shows regular
SPECIES, AGE, SEX HISTORY, CHIEF COMPLAINT sawtooth pattern instead of irregular F waves.
• Atrial fibrillation (AF) is the most common • AF may be an incidental finding. R-R intervals may show regularity, even if
clinically significant arrhythmia in dogs, but • Weakness, exercise intolerance, anorexia are variable conduction across AV node (e.g.,
cats are rarely affected. common 2 : 1, 3 : 1, 4 : 1)
• Incidence low in dogs < 2 years old, increases • May show signs of congestive heart failure • Atrial tachycardia: has distinct P′ waves at
with age (CHF): dyspnea, ascites, cough PP intervals of up to 300 beats/min. If P′
• Giant breed dogs develop AF earlier in life, • Syncope (rare) waves are hiding in preceding T waves, try
small breeds later in life. vagal maneuver to slow down rate.
• Males are overrepresented (60%-75%); PHYSICAL EXAM FINDINGS • Wide QRS tachycardia: can be true ven-
females have later onset with longer survival. • Irregularly irregular rhythm (as opposed to tricular tachycardia; rhythm may be irregular,
a regularly irregular rhythm, as in sinus similar to AF, but QRS is wide and bizarre,
GENETICS, BREED PREDISPOSITION arrhythmia) sometimes polymorphic versus AF with a
AF is most common in giant and large-breed • Heart rate (HR) is usually rapid (up to 250 ventricular conduction disturbance (bundle
dogs; small-breed dogs have a low susceptibility beats/min), particularly if structural heart branch block), which can mimic ventricular
to AF. disease is present. tachycardia
• Highest predisposition in Irish wolfhound • Variable pulse strength with pulse deficits • Atrial standstill: the R-R intervals are usually
(IWH), Great Dane, Newfoundland, mastiff, • Signs associated with underlying heart disease regular, and rate is slow (escape rhythm)
St. Bernard, Doberman, and Bouvier des or concurrent CHF: murmur, dyspnea, versus AF with low-voltage or invisible
Flandres pulmonary crackles, and/or ascites F-wave oscillations may appear as if there is
• In IWHs, multiple genetic loci are responsible absence of atrial activation.
for inherited dilated cardiomyopathy (DCM) Etiology and Pathophysiology
(affecting 9.5%) and AF (affecting 80.5% • Atrial pathology and/or increased atrial size Initial Database
of those with DCM). predisposes to AF ECG is the gold standard for diagnosis. Aus-
• In Dobermans, mutation in PDK4 (NCSU • Atrial stretch, fibrosis, or altered autonomic cultation raises suspicion of AF but is not a
DCM1) and NCSU DCM2 can lead to tone, as occurs during CHF, predisposes to definitive test. ECG features of AF:
DCM; AF is often associated with end-stage atrial premature contractions (APCs) • An irregularly irregular ventricular rhythm
DCM. ○ Atrial stretch is associated with increased (irregular RR intervals with no predictable
dispersion of refractoriness and altered pattern)
RISK FACTORS electrical propagation. ○ At very fast rates, the irregularity is harder
• Structural heart disease resulting in atrial ○ APCs originating from abnormal atrial to appreciate.
fibrosis and atrial enlargement predisposes tissue or from pulmonary veins can trigger • The ventricular rate is typically fast but may
to AF. onset of reentry arrhythmias. be normal.
○ DCM ○ Multiple, simultaneous reentrant wavelets • Narrow QRS complexes (but QRS complexes
○ Chronic atrioventricular (AV) valvular create continuous chaotic electrical activity. may appear wide due to concurrent ven-
heart disease • The atrial activity in AF is irregular and tricular conduction disturbance [bundle
○ Congenital heart diseases (e.g., left-to-right usually exceeds 400 beats/min. branch block])
shunting patent ductus arteriosus) ○ The AV node filters many of these • No distinct P waves (in any leads)
○ Infiltrative disease (e.g., cardiac neoplasia) impulses, resulting in an irregular, rapid • +/− F waves (low-voltage oscillations of
• Gastrointestinal disease ventricular response. various amplitudes) visible during diastolic
• Hypothyroidism • Hemodynamic compromise may occur as interval
• Hypoadrenocorticism the result of loss of the atrial kick. • Vagal maneuver may decrease the ventricular
• Mechanical irritation of the myocardium ○ Suboptimal ventricular filling, especially rate and aid in the diagnosis of AF by
(e.g., pericardiocentesis, cardiac catheteriza- at high rates, can decrease cardiac output revealing definitive lack of P waves
tion) up to 30%. • Thoracic radiography and echocardiography
• Drugs (especially anesthetic drugs, opiates) ○ AF can trigger onset or recurrence of CHF aid in diagnosing underlying cardiac disease
• Inherently large hearts in giant-breed dogs by decreased cardiac output and tachycardia. and CHF.
predispose to AF, even when no overt
structural cardiac disease is present (lone DIAGNOSIS Advanced or Confirmatory Testing
fibrillation). Ventricular rate during AF is influenced by
• Cats with hypertrophic, restrictive, or dilated Diagnostic Overview autonomic tone; stressful situations such as
cardiomyopathy and secondary atrial enlarge- AF is suspected based on auscultation of a hospital visits typically elevate the ventricular
ment are predisposed. rapid, irregularly irregular heart rhythm that is rate excessively. To verify if a dog has chronically

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