Lecture 14- Canine Myocardial Diseases

Define cardiomyopathy

Heterogeneous myocardial diseases causing mechanical or electrical dysfunction → ventricular hypertrophy or dilation; often genetic; leads to weakness, exercise intolerance, syncope, CHF, sudden death.

Primary vs secondary cardiomyopathy

Primary = intrinsic myocardial disease, often genetic; Secondary = due to systemic disease (endocrine, amyloid, glycogen), ischemia, doxorubicin, diet-associated DCM.

Major types of cardiomyopathy

Dilated (systolic dysfunction), Hypertrophic (concentric hypertrophy, diastolic dysfunction), Restrictive (endocardial fibrosis, large LA), ARVC, nonspecific cardiomyopathy.

Clinical manifestations of cardiomyopathy

CHF, dyspnea, exercise intolerance, arrhythmias, syncope, thromboembolism, acute lameness, sudden death.

Define DCM

Primary myocardial disease with ventricular dilation, wall thinning, papillary muscle atrophy, systolic dysfunction; secondary MR/TR; neuroendocrine compensation.

Breeds predisposed to DCM

Large/giant breeds, Doberman, Boxer; nutritional forms in Goldens, Cockers, Newfoundlands.

Nutritional causes of DCM

Taurine deficiency, carnitine deficiency, grain-free diets high in peas/lentils/chickpeas/sweet potatoes.

DCM history findings

Cough, dyspnea (worse at night), syncope, weakness, collapse, anorexia, exercise intolerance, weight loss; often misdiagnosed as bronchitis.

DCM physical exam findings

Muffled heart sounds, soft systolic murmur, gallop, arrhythmia, weak pulses, pulse deficits, jugular distension, ascites, crackles.

ECG findings in DCM

A fib, VPCs, ventricular arrhythmias, APCs, LA/LV enlargement patterns, conduction disturbances.

Thoracic radiograph findings in DCM

Cardiomegaly (L-sided), pulmonary edema (L-CHF), pleural effusion/ascites (R-CHF).

Biomarkers in DCM

↑ NT-proBNP, ↑ cTnI; genetic testing for Doberman, Boxer, Schnauzer.

Pathology of DCM

Fibrosis, inflammation, lipid accumulation, myocyte degeneration, edema; varies by breed.

Echo findings in DCM

Dilated ventricles, thin walls, FS%

Diet-associated DCM features

Grain-free diets; may be reversible early; taurine/carnitine deficiency in small subset; LV function may take 2-3 yrs to recover; still risk of arrhythmias/sudden death.

Breeds predisposed to taurine deficiency

Golden Retrievers, Cocker Spaniels, Newfoundlands.

Breeds predisposed to carnitine deficiency

Boxers, Cocker Spaniels, Dobermans.

Key diagnostics for DCM

Echo, thoracic rads, ECG, NT-proBNP, chemistry, CBC/UA, HW test, taurine level, BP, cTnI, diet history.

Chronic management of DCM

CHF: furosemide, pimobendan, ACEi, spironolactone; AFib: digoxin + diltiazem; ventricular arrhythmias: sotalol/mexiletine/amiodarone; supplements: taurine/carnitine/CoQ10; diet change; exercise restriction.

Prognosis of DCM

Doberman CHF: poor (3-6 mo); early detection improves survival; pimobendan improves B2 survival (up to 15+ mo); high sudden death risk with VPCs.

Doberman DCM characteristics

Occult cardiomyopathy; ventricular arrhythmias; 45-63% affected; 40-50% sudden death; VF risk; cardiogenic shock; genetic tests available.

NT-proBNP in Dobermans

500-600 pmol/L threshold for occult DCM prediction; higher values → likely disease.

Doberman case (Max) diagnosis

DCM with AFib and early CHF; echo FS 15%, LA enlargement; VPCs; cardiomegaly; ↑ NT-proBNP, ↑ cTnI.

Doberman case (Max) treatment

Pimobendan, furosemide, enalapril, spironolactone, digoxin, taurine pending results.

Doberman case prognosis

Guarded; median survival 3-6 months; pimobendan improves preclinical survival.

Define ARVC (Boxer)

Arrhythmogenic Right Ventricular Cardiomyopathy: ventricular tachycardia (300-400 bpm), LBBB-pattern VPCs, low voltage ECG, RV fibrofatty replacement, sudden death risk.

Genetics of ARVC

Dysfunctional ryanodine receptor; second mutation under investigation.

Holter criteria for ARVC

>100 VPCs/24 hrs = likely affected.

ARVC treatment

Sotalol; sotalol + mexiletine; mexiletine + atenolol; amiodarone; activity restriction; Holter monitoring.

Boxer case (Bella) diagnosis

ARVC confirmed by Holter (>1000 VPCs, VT runs) + genetic test; mild RV dilation; mild ↑ troponin.

Boxer case (Bella) treatment

Sotalol 1-2 mg/kg BID; mexiletine/atenolol alternatives; activity restriction; Holter monitoring.

Boxer case prognosis

Variable; mild cases live years; severe arrhythmias → sudden death risk; genetic counseling recommended.

DCM in giant breeds

AFib common; sudden death possible; shorter survival if CHF; arrhythmia-only dogs may have prolonged survival.

Irish Wolfhound cardiomyopathy

LA enlargement + arrhythmias hallmark; chylous effusion possible; high prevalence of CV abnormalities; AFib common; some progress from lone AFib to DCM.

Cocker Spaniel cardiomyopathy

Age 6-10 yrs; equal sex ratio; ECG tall R wave/APCs; generalized cardiomegaly + pulmonary edema; low taurine common; taurine/carnitine supplementation improves some; pimobendan slows progression.

Newfoundland DCM

Middle-aged/older; FS 20-28% in some normals; AFib common; taurine deficiency with certain diets; refractory CHF common cause of death.

Juvenile DCM (PWD)

Age 5 wks-3-4 mo; sudden death/peracute CHF; typical DCM on necropsy; chromosome 8 mutation; arrhythmias infrequent; pulmonary edema/hepatomegaly; normal early echo may progress.

Doxorubicin toxicity

DCM-like syndrome; oxidant injury; arrhythmias; cumulative dose >240 mg/m² risk; lower dose risky in predisposed breeds; poor response to treatment.

Canine hypertrophic cardiomyopathy

Very uncommon; GSPs, GSDs, Shih Tzu; possible genetic basis; conduction abnormalities, 3rd-degree AV block, ventricular arrhythmias; CHF or sudden death.

Define myocarditis

Myocardial inflammation due to viral, bacterial, fungal, parasitic, immune causes; features: CHF, arrhythmias, thromboembolism; heart often a bystander.

Infectious causes of myocarditis

Parvo, FMD, Bluetongue, EMC virus, EVA, FIP, FIV, Lyme, fungal, protozoal (Toxoplasma, Leishmania).

Finnegan case phenotype

Young dog with R > L heart DCM phenotype; SVT with RBBB morphology; jugular distension, abdominal distension; CHF (R-sided).

Finnegan serology

Chagas IFA ≥1280 → Trypanosoma cruzi myocarditis.

Finnegan taurine panel

Plasma taurine high (187), WB normal (288); not taurine-deficient.

Finnegan differential

Dietary DCM, tachycardia-induced cardiomyopathy, myocarditis (Texas), juvenile DCM.

Finnegan treatment

Pimobendan, diuretics, amiodarone, taurine supplementation pending levels.

Trypanosomiasis (Chagas)

T. cruzi; kissing bug vector; severe myocarditis; RA/RV predominate; L or R CHF; treated with benznidazole (may not improve cardiac outcomes); manage CHF/arrhythmias.