Atrial fibrillation

From Dog
Atrial fibrillation corrected by electrical cardioversion[1]

Atrial fibrillation (AF) is a common heart disease characterized by a sustained supraventricular tachycardia.

Atrial fibrillation, which appears more commonly in large-breed dogs, appears electrocardiographically as a disorganized, rapid atrial electrical activity resulting in loss of atrial contribution to ventricular filling as well as an irregular and typically rapid ventricular response rate[2]. The physiologic consequences of AF include a reduction in cardiac output and development or worsening of clinical signs of congestive heart failure[3]

Cause of AF include:

Although most dogs with AF exhibit characteristic clinical signs, those with lone AF may have no demonstrable signs at the time of diagnosis.

Clinical presentation is affected by the severity of underlying cardiovascular disease and the presence of pericarditis or congestive heart failure, and signs may be exacerbated by exercise. Dogs often have a history of lethargy, weakness, and exercise intolerance[14]. Other reported abnormalities at presentation include syncope, cough, dyspnea, ascites, and anorexia.

A definitive diagnosis requires electrocardiographc analysis (usually a 24-hour Holter), which reveals a unique lack of identifiable P waves and an irregular ventricular rate characterized by a variable R-to-R interval. In most cases, the QRS complexes are narrow and predominately upright in lead II.

The use of a 24-hour Holter analysis provides a better overall estimate of heart rate in the clinical setting and home environment. The ideal ventricular rate during therapeutic management of AF has not been adequately established, although the target rate for large- and giant-breed dogs is considered to be lower than for small-breed dogs.

Additional diagnostic tests—including echocardiography, thoracic radiography, blood pressure measurement and routine blood tests including assessment of cardiotropin. This condition should be distinguished from Wolff-Parkinson-White syndrome where there is ventricular tachycardia and normal heart rhythm, but widened QRS complexes, often with slurring or notching of the upstroke R wave (delta wave).

Treatment is aimed at achieving a heart rate that allows the dog to remain free of clinical signs[15].

Amiodarone, diltiazem, quinidine and verapamil have been reported to restore sinus rhythm in a few dogs[16][17].

Intravenous procainamide or diltiazem may be considered for initial, acute therapy[18].

Digoxin has mild positive inotropic effects that may be beneficial for dogs with concurrent systolic dysfunction. Because of its parasympathomimetic effects, digoxin can result in vagally mediated GI disturbance and may not be as effective in patients with heart failure and increased sympathetic tone. Co-administration of digoxin and diltiazem provides better heart rate control than digoxin alone, and this combination is often used for initial therapy of AF[19].

Commonly used α-blockers include atenolol and carvedilol. In addition to its α-blocking effects, carvedilol has antioxidant and α-blocking mediated vasodilatory effects that are of potential benefit when treating dogs with heart failure.

For dogs that can tolerate anesthesia, biphasic transthoracic electrical cardioversion may be valuable for immediate conversion to sinus rhythm[20]. More than one shock is often necessary for conversion[21].

A moderately sodium-restricted diet, and high-sodium foods should be avoided. Ideally, follow-up evaluations are performed at least every 3 to 4 months to monitor drug therapy and cardiovascular disease progression.

Prognosis depends on the presence and severity of the underlying disease process.


  1. Estrada AH et al (2009) Avoiding medical error during electrical cardioversion of atrial fibrillation: prevention of unsynchronized shock delivery. J Vet Cardiol 11(2):137-139
  2. Westling J, Westling W, Pyle RL. (2008) Epidemiology of atrial fibrillation in the dog. Intern J Appl Res Vet Med 6(3):151-154
  3. Patterson DF, Detweiler DK, Hubben K, et al (1961) Spontaneous abnormal cardiac arrhythmias and conduction disturbances in the dog. A clinical and pathologic study of 3,000 dogs. Am J Vet Res 22:355-369
  4. Westling J, Westling W, Pyle RL. (2008) Epidemiology of atrial fibrillation in the dog. Intern J Appl Res Vet Med 6(3):151-154
  5. Bonagura JD, Ware WA. (1986) Atrial fibrillation in the dog: clinical findings in 81 cases. JAAHA 22:111-120
  6. Moe GK, Rheinboldt WC, Abildskov JA. (1964) A computer model of atrial fibrillation. Am Heart J 67:200-220
  7. Tidholm A, Svensson H, Sylven C. (1997) Survival and prognostic factors in 189 dogs with dilated cardiomyopathy. JAAHA 33(4):364-368
  8. Tidholm A, Haggstrom J, Borgarelli M, et al (2001) Canine idiopathic dilated cardiomyopathy. Part I: aetiology, clinical characteristics, epidemiology and pathology. Vet J 162(2):92-107
  9. Rensma PL, Allessie MA, Lammers WJ, et al (1988) Length of excitation wave and susceptibility to reentrant atrial arrhythmias in normal conscious dogs. Circ Res 62(2):395-410
  10. Sharifov OF, Fedorov VV, Beloshapko GG, et al (2004) Roles of adrenergic and cholinergic stimulation in spontaneous atrial fibrillation in dogs. J Am Coll Cardiol 43(3):483-490
  11. Menaut P, Belanger MC, Beauchamp G, et al (2005) Atrial fibrillation in dogs with and without structural or functional cardiac disease: a retrospective study of 109 cases. J Vet Cardiol 7(2):75-83
  12. Saffitz JE, Schuessler RB. (2004) Altered atrial structure begets atrial fibrillation, but how? J Cardiovasc Electrophysiol 15(10):1175-117
  13. Dilaveris P, Giannopoulos G, Synetos A, et al (2005) The role of renin angiotensin system blockade in the treatment of atrial fibrillation. Curr Drug Targets Cardiovasc Haematol Disord 5(5):387-403
  14. Manohar M, Smetzer DL. (1992) Atrial fibrillation. Compend Contin Educ Pract Vet 14(10):1327-1333
  15. Gelzer ARM, Kraus M. (2004) Management of atrial fibrillation. Vet Clin North Am 34:1127-1144
  16. Johnson JT. (1985) Conversion of atrial fibrillation in two dogs using verapamil and supportive therapy. JAAHA 21:429-434
  17. Oyama MA, Prosek R. (2006) Acute conversion of atrial fibrillation in two dogs by intravenous amiodarone administration. J Vet Intern Med 20(5):1224-1227
  18. Moise NS, Pariaut R, Gelzer ARM, et al (2005) Cardioversion with lidocaine of vagally associated atrial fibrillation in two dogs. J Vet Cardiol 7(2):143-148
  19. Heist EK, Ruskin JN. (2006) Atrial fibrillation and congestive heart failure: risk factors, mechanisms, and treatment. Prog Cardiovasc Dis 48(4):256-269
  20. Bright JM, Martin JM, Mama K. (2005) A retrospective evaluation of transthoracic biphasic electrical cardioversion for atrial fibrillation in dogs. J Vet Cardiol 7(2):85-96
  21. Bright JM, zumBrunnen J. (2008) Chronicity of atrial fibrillation affects duration of sinus rhythm and transthoracic cardioversion of dogs with naturally occurring atrial fibrillation. J Vet Intern Med 22(1):114-119