Atrial fibrillation (AF) is the most common pathologic arrhythmia in dogs. Three dogs with AF and a complicating thromboembolism were described. A 13-year-old spayed, mixed-breed dog was referred for additional treatment of congestive heart failure (CHF) from degenerative valve disease and severe mitral regurgitation. Despite attempts to stabilize the patient, it died 12 hours after discharge.

A 5-year-old, neutered Bernese mountain dog was referred for lethargy, decreased appetite, and vomiting. Key findings for both included AF and an echo-dense spherical atrial mass consistent with a thrombus. Treatment with warfarin, aspirin, and other drugs was initiated. Echocardiogram 6 weeks postpresentation showed no evidence of the mass; sinus rhythm was restored with direct current cardioversion under anesthesia.

A 7-year-old male Shetland sheepdog was referred for treatment of CHF. During evaluation and treatment, the dog rapidly deteriorated and developed apparent severe left leg pain. The limb was cool with blanched skin. Color Doppler results suggested absence of blood flow in the left femoral artery. The dog was euthanized, and a large, firm, white thromboembolus was found in the aorta occluding the left external iliac artery.

The multifactorial causes of thrombosis (Virchow’s triad) affects the ability to predict dogs at increased risk for this complication. Diagnostic screening of the left atrial chamber at the onset of AF is feasible and noninvasive; echocardiography can be performed with newly diagnosed AF and should be encouraged if signs consistent with aortic thromboembolism develop. Prophylactic anticoagulant intervention (not routine) should be implemented when a thrombus or consistent signs are observed. Although warfarin and aspirin were referenced in this article, there is no consensus on the best anticoagulant for these cases. Clopidogrel is an alternative to aspirin for inhibition of primary hemostasis. Warfarin, unfractionated heparin, and low molecular weight heparin block secondary hemostasis. Multiple factors, including clinician familiarity, cost, owner preference, and ability to monitor efficacy, may determine therapy.—Lydia Soydan, DVM

Thrombotic complications associated with atrial defibrillation in three dogs. Usechak PJ, Bright JM, Day TK. J VET CARDIOL 14:453-458, 2012.