Dilated Cardiomyopathy and Atrial Fibrillation in a Labrador Retriever
VETERINARIAN SPECIALTY CASE STUDY
An EKG showed a supra ventricular tachycardia with irregular R-R intervals known as atrial fibrillation.
Colt is a 9 year old male, castrated lab that presented to Animal Specialty Group’s Emergency and Critical Care Service for evaluation of a dry, hacking cough of 1 day duration. He had been otherwise healthy with a good appetite and energy level.
Physical exam revealed a heart rate of 180 with an irregularly, irregular rhythm and weak pulses. The rest of his exam was unremarkable.
An EKG showed a supra ventricular tachycardia with irregular R-R intervals known as atrial fibrillation. The heart chambers appeared subjectively dilated on tFAST. Thoracic radiographs revealed severe left-sided cardiomegaly with dilated pulmonary veins and perihilar edema consistent with early congestive heart failure. Colt’s blood pressure and venous blood gas were within normal limits. CBC, chemistry, T4, and urinalysis revealed 1+ proteinuria, but were otherwise unremarkable.
Colt was admitted to the hospital for treatment of congestive heart failure with furosemide 2mg/kg q 6 and pimobendan 0.2mg/kg q 12. He was also placed on a continuous EKG and started on diltiazem XR 2mg/kg q 12 for control of his atrial fibrillation.
5. Cardiology Consultation
The following day Colt was evaluated by Dr Fred Brewer, DVM, DACVIM (Cardiology) who performed an echocardiogram. The echo revealed a severely dilated left ventricle with impaired systolic function and moderate – severe left atrial enlargement. The right heart appeared normal. Based on these findings Colt was diagnosed with dilated cardiomyopathy (DCM). Colt’s EKG revealed atrial fibrillation with a heart rate of 240. Recheck radiographs revealed improvement in the pulmonary edema.
Dr Brewer increased Colt’s ditiazem XR to 3.9mg/kg q 12 to try to decrease Colt’s heart rate. He also added in spironolactone 1mg/kg q 12 ad benazepril 0.32mg/kg q 24. The pimobendan was also increased to 0.32mg/kg q 12 to help improve systolic function.
Dilated cardiomyopathy (DCM) is a progressive disease of the heart muscle that leads to severe chamber enlargement and systolic dysfunction. The cause of DCM is not completely understood, but genetics appears to play an important role. Breeds that have a high incidence of DCM include Doberman Pinchers, Great Danes, Cocker Spaniels, Portuguese Water Dogs, Boxers, Newfoundlands, and Irish Wolfhounds. Nutritional deficiencies such at taurine deficiency have been shown to cause DCM in cats and some Spaniels and Retrievers.
DCM can lead to congestive heart failure, arrhythmias, syncope, and sudden death. Treatment involves controlling any associated arrhythmias and preventing the recurrence of heart failure with diuretics and ace inhibitors. Systolic function may also be increased with the use of pimobendan.ii DCM generally carries a guarded prognosis.
Colt was discharged from the hospital and was doing well at his 1 week recheck. His radiographs revealed improvement, but not full resolution of his pulmonary edema so his furosemide dose was increased by 25%. His renal values were within normal limits. At Colt’s 3 week recheck he was lethargic and inappetent for 24 hours and radiographs revealed recurrence of congestive heart failure. Colt’s atrial fibrillation was not well controlled at this time. He received IV furosemide therapy throughout the day and his maintenance dose was increased to 3mg/kg twice daily. Digoxin therapy was also added to help achieve heart rate control. DCM can be challenging to treat, but we are hopeful that Colt will have some quality time left with his owner.
 Tidholm A, Häggström J, et al. Canine idiopathic dilated cardiomyopathy. Part I: Aetiology, clinical characteristics, epidemiology and pathology. Vet J. 2001 Sep;162(2):92-107.  Prosek, R. Dilated Cardiomyopathy. Clinical Veterinary Advisory, 2nd Ed. 2011;309-312.