Canine Cardiomyopathy

Chapter 38 Canine Cardiomyopathy



Robert Prošek, DVM, MS, DACVIM (Cardiology)



KEY POINTS



• Primary cardiomyopathies, by definition, are idiopathic diseases that are not the result of an identifiable systemic disorder or any type of congenital or acquired heart disease.

• Myocardial diseases resulting from a well-defined disease process are appropriately referred to as secondary myocardial diseases, and these need to be considered before the diagnosis of a primary cardiomyopathy.

• Dilated (congestive) cardiomyopathy (DCM) is the most common form of primary myocardial disease in dogs and is characterized by chamber dilation and decreased contractility.

• Large and medium sized dogs are typically affected by DCM.

• Atrial fibrillation is common and often is one of the first abnormalities detected in giant breeds with DCM such as Great Danes, Irish Wolfhounds, and Newfoundlands.

• Breed variations in canine DCM should be considered in Cocker Spaniels, Dalmatians, Boxers, Doberman Pinschers, Portuguese Water Dogs, and the giant breeds.

• Boxers with arrhythmogenic right ventricular cardiomyopathy often have syncope and, as the name states, arrhythmias (ventricular).

• Myocardial failure that leads to congestion is an emergency that requires a low-stress environment, oxygen, diuretics, vasodilators, and inotropic support.


INTRODUCTION


Primary myocardial diseases, or “true” cardiomyopathies, are those conditions that predominately affect the heart muscle, that are not the result of other congenital or acquired valvular, pericardial, vascular, or systemic diseases, and whose causes are unknown. The most common form of myocardial disease in the dog is dilated cardiomyopathy (DCM), but arrhythmogenic right ventricular cardiomyopathy (ARVC) (in Boxers) and hypertrophic cardiomyopathy (HCM) are also reported. There is increasing breed-specific information about canine DCM, especially in Doberman Pinschers, Dalmatians, Portuguese Water Dogs, Cocker Spaniels, and the giant breeds, which should be considered in diagnosis and treatment. Secondary myocardial diseases resulting from well-defined disease processes are listed in Box 38-1 and should be considered before making the diagnosis of a primary cardiomyopathy. Diagnostic and treatment techniques often are tailored to each patient and breed, with emphasis on control of a stable rhythm, prevention of congestive heart failure (CHF), and improvement in quality and length of life.



Box 38-1 Classification of Secondary Myocardial Diseases of Dogs*



Drugs and Toxins



Anthracyclines (doxorubicin*)

Catecholamines

Ionophores

Canine X-Linked Muscular Dystrophy (Duchenne)*



Infiltrative



Glycogen storage diseases

Mucopolysaccharidosis

Neoplastic


Ischemic



Metabolic



Acromegaly

Diabetes mellitus (Chapter 68, Hyperglycemic Hyperosmolar Syndrome)

Hyperthyroidism (Chapter 73, Myxedema Coma)

Systemic hypertension (Chapter 42, Hypertensive Crisis)


• Idiopathic

• Renal disease


Nutritional



L-Carnitine deficiency*

Taurine deficiency*

Vitamin E, selenium deficiency


Inflammatory



Myocarditis (Chapter 48, Myocarditis)


Infectious



Viral, bacterial, fungal, protozoal


• Parvovirus, distemper

• Lyme disease, trypanosomiasis


* Conditions discussed in this chapter.



DILATED CARDIOMYOPATHY


DCM is characterized by chamber dilation and impaired systolic and often diastolic function of one or both ventricles. It is an adult-onset disease, with the exception of the Portuguese Water Dog in which the young are affected (2 to 32 weeks old). Generally, it is a disease of large and medium-sized dogs with increased incidence in the Doberman Pinscher, Great Dane, Irish Wolfhound, and American Cocker Spaniel in North American surveys, but European studies show an increased incidence in the Airedale Terrier, Newfoundland, English Cocker Spaniel, and Doberman Pinscher.1



Physical Examination


Often a soft grade 1 to 3 of 6 systolic left or right apical murmur is noted and is a result of either mitral or tricuspid valve insufficiency, respectively. Auscultation may also reveal a chaotic rhythm of atrial fibrillation or an irregular rhythm due to atrial or ventricular premature beats. With right-sided CHF the following may be noted: jugular pulses or distention or both, muffled heart and ventral lung sounds with pleural effusion (pleural fluid line), and hepatomegaly due to congestion with or without ascites. With left-sided CHF, examination will often reveal pulmonary crackles or rales, hypokinetic femoral pulses, pulse deficits with ventricular premature beats, or atrial fibrillation. Peripheral edema is rare. Finally, albeit rare, cardiogenic shock may be present as a result of decreased arterial blood pressure (usually blood pressure is normal as a result of vasoconstriction and neurohormonal activation).



Thoracic Radiography


Thoracic radiographs should be examined for generalized cardiomegaly and signs of CHF. Signs of left-sided heart failure include interstitial or alveolar pulmonary edema and moderate to severe left atrial enlargement. Right-sided failure results in pleural effusion, enlarged caudal vena cava, hepatomegaly, and ascites (Figure 38-1).


image

Figure 38-1 Lateral radiographs of a Doberman Pinscher with dilated cardiomyopathy. A, On presentation. B, Same patient after 36 hours of aggressive treatment of congestive heart failure (furosemide, O2, nitroprusside, dobutamine).



Electrocardiography


The electrocardiogram (ECG) should be examined for sinus tachycardia, possibly with atrial or ventricular premature beats, atrial fibrillation, and ventricular tachycardia, especially in Boxers and Doberman Pinschers. Prolonged or increased voltage QRS complexes suggestive of left ventricular enlargement or low-voltage QRS complexes with pleural effusion may be noted.



Routine Blood Tests


Routine blood work findings are usually normal unless severe heart disease is present. Prerenal azotemia, high alanine aminotransferase levels, and electrolyte abnormalities may be evident in cases of severe heart disease. Hyponatremia and hypochloremia, if noted with CHF, are associated with a poorer prognosis. Hypokalemia, metabolic alkalosis, and prerenal azotemia may also be the result of diuretic therapy for heart disease.



Effusion Analysis


Peritoneal or pleural effusion in dogs with DCM is usually a modified transudate (nucleated cell count <2500/ml, total protein <4.0 g/dl), but on occasion a chylous effusion is found.



Echocardiography


Ventricular and atrial dilation are common with reduced myocardial systolic function (reduced left ventricular fractional shortening percentage [FS%] and ejection fraction). Increased E-point septal separation is also common with ventricular dilation.2 Doppler studies confirm evidence of mitral and tricuspid regurgitation, low-velocity transaortic flow, diastolic ventricular dysfunction, and possible pulmonary hypertension (due to severe left-sided heart failure). Pleural effusion can also be noted along with mild pericardial effusion due to CHF. Remember, most DCM cases with CHF should have moderate to severe atrial enlargement, and low FS% is not pathognomonic for DCM; many normal hearts contract more in apical-to-basilar direction, and this motion is not accounted for by the FS% (Figure 38-2).


image

Figure 38-2 A, Example of a normal dog M-mode and (B) an M-mode from a dog with dilated cardiomyopathy. Dog in B would have a decreased fractional shortening percentage based on left ventricular internal dimension in diastole − left ventricular internal dimension in systole divided by left ventricular internal dimension in diastole = LVIDd−LVIDs/LVIDd.

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Canine Cardiomyopathy

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