Canine Cardiomyopathies (TV4101, Lecture 4 Notes)

Discuss dilated cardiomyopathy

- Hereditary in large breed dogs (especially Dobermans and Great Danes)

- Common in older, male dogs

- Multifactorial disease

Describe the pathogenesis of dilated cardiomyopathy

- Myocardial necrosis, apoptosis, degeneration and fibrosis > decreased contractility > systolic dysfunction > progressive eccentric hypertrophy > increased end diastolic pressure > congestion

- Secondary poor apposition of AV values > regurgitation (and murmur) > poor coronary flow > ischaemia > arrhythmias

Discuss the clinical signs of dilated cardiomyopathy

- Long occult phase with early signs of lethargy

- Sudden onset of collapse, syncope or death

- Weakness and exercise intolerance

- Weight loss and cachexia

- Tachypnoea, dyspnoea and cough (LCHF)

- Increased sympathetic tone (e.g. tachycardia, peripheral vasoconstriction)

- Jugular distension/pulses, ascites, muffled heart sounds and hepatosplenomegaly (RCHF)

- S3 gallop, mitral/tricupsid murmur or arrhythmias

Discuss the diagnosis of dilated cardiomyopathy

- Radiography, assess for generalised cardiomegaly (especially LA), cardiogenic pulmonary oedema, distended pulmonary veins +/- CVC distension and effusion (RCHF)

- Echocardiography, assess for systolic dysfunction, poor systolic wall motion, decreased wall thickness, chamber dilation, reduced fractional shortening and AV valve regurgitation

- Occult DCM

Discuss treatment of dilated cardiomyopathy

Stage B

- Administer Pimobendan (delays progression, improves prognosis)

- Antiarrhythmics

- Continued monitoring

Stage C

- Control CHF sings

- Administer Pimobendan and frusemide

- Reduce heart rate and enhance ventricular filling

- ACE inhibitors

*MST = 4-6m

List the negative prognostic indicators of dilated cardiomyopathy

- Pleural effusion

- Severe LV systolic dysfunction

- Arrhythmias

- High biomarkers

Discuss arrhythmogenic right ventricular cardiomyopathy (ARVC)

- Inherited, acquired heart disease of Boxers

- Fibrous/fatty infiltration of myocardium > myofiber atrophy, necrosis and MNC infiltration

List the forms of ARVC

Occult - ventricular arrhythmias (no clinical signs).

Overt - weakness or syncope with paroxysmal or sustained ventricular tachycardia despite normal LV function and heart size.

ARVC with DCM = poor myocardial function progresses to DCM unless sudden death from arrhythmias occurs first with biventricular CHF.

Discuss the clinical signs of ARVC

- Syncope due to arrhythmia or reflex vagal hypotension and bradycardia

- PE normal unless CHF occurs

- Sudden death

Discuss the diagnosis of ARVC

- ECG (i.e. 24hr Holter monitor)

- Echocardiography with DCM or CHF

Discuss the treatment of ARVC

- Antiarrhythmic (e.g. sotolol or mexiletine), if clinical signs from tachycardia

- DCM and CHF treatment

- Annual Holter screening

Discuss hypertrophic cardiomyopathy

- Uncommon in young-middle aged, male dogs

- Excessive concentric hypertrophy > increased ventricular stiffness> impaired filling and diastolic failure

- Dynamic outflow obstruction due to SAM and mitral regurgitation

Discuss the diagnosis of hypertrophic cardiomyopathy

- Echocardiography, assess for LV concentric hypertrophy and LA enlargement +/- mitral regurgitation and SAM

- Radiography, assess for LA/LV enlargement and CHF

- ECG, assess for arrhythmias

Discuss the treatment of hypertrophic cardiomyopathy

- Beta blocker

- ACE inhibitors or frusemide for CHF

- Pimobendan if dynamic outflow obstruction

- Exercise restriction

*Variable prognosis

List causes for myocardial disease

Metabolic

- Oxidative stress (i.e. due to abdominal vascular compromise such as GDV or splenic entrapment)

- Endocrine (e.g. hyperthyroidism in cats)

- Storage diseases

Nutritional (uncommon with formulated diets)

- L-carnitine deficiency

- Taurine deficiency

Toxic

- Doxorubicin

- Alcohol, plants or heavy metals

Ischaemia

- Coronary thromboembolism resulting infarction (rare, i.e. heart attack)

- Infarction secondary to myocardial disease

Inflammation

- Parvovirus, Distemper or Herpesvirus

- Bacteraemia

- Lyme disease

- Toxoplasma or Neospora

- Fungal (rare)