Canine Cardiomyopathies Flashcards
Is dilated cardiomyopathy an example of eccentric or concentric hypertophy?
Eccentric
What happens during the occult phase of DCM?
No clinical sings
CO falls
Sympathetic, hormonal and renal compensatory mechanisms activated to maintain CO by increasing HR, peripheral vasoconstriction and volume expansion
What is the pathophysiology of DCM?
•Eccentric hypertrophy of the LV
•Systolic failure- ‘Forward failure’- Ventricle doesn’t eject blood effectively so cardiac output falls
•Diastolic failure- ‘Backward failure’- Congestion as a consequence of fall in CO
•LA dilation and increased LAP
•Right side can also be affected (But usually just left)
•Increased ventricular diastolic pressure
•Compromised coronary perfusion (myocardium only effectively perfused during ventricular diastole because the musculature constricts the vessels during systole)
–> myocardial dysfunction arrhythmias
What two distinct types of histopathology can be seen with DCM?
Narrow (attenuated) myocardial cells with a wavy appearance (Newfoundlands)
Myofiber degeneration, myocyte atrophy and lysis, fatty infiltration and fibrosis (Boxers, some Dobermans)
What might be seen with histopathology of DCM which does not show the two distinct types?
non-specific
scattered areas of myocardial necrosis –> myocardial degeneration and fibrosis
inflammatory cell infiltrates are inconsistent but an active myocarditis is rare
Describe the signalment of DCM
Breed predispositions – genetic basis
- Doberman, Newfoundland, IWH, St Bernards, Labradors, Great Dane, Cocker spaniels, Boxers (ARVC), GSD
- Boxers autosomal dominance inheritance pattern
- But different breeds have very different prognosis with the same disease
- Cocker spaniels – 2yrs with appropriate treatment
- Doberman – often a few weeks
Usually middle-aged dogs (has been reported in puppies as young as 6m)
Usually dogs >12kg
Males tend to be more severely affected but no gender predilection
Describe the typical history of DCM
Occult phase may go on for years with no clinical signs (screening programmes identify this phase of disease- 24h Holter, echocardiography)
Symptomatic phase:
- usually CHF
- syncope
- weight loss
- sudden death (particularly in certain breeds such as Dobermans)
What may be found on clinical exam of a dog with DCM? (Varies depending on degree of myocardial dysfunction)
- pale mm
- sluggish CRT
- cool extremities
- tachycardia +/- arrrhythmias (AF, VPCs, VT)
- variable pulses +/- pulse deficits
- pulsus alternans
- sighs of LCHF/RCHF
- S3 gallop sound (if sinus rhythm)
- soft MR/TR murmurs
What is typically found on echocardiography of a dog with DCM?
Large, round, poor contractile LV Poor systolic function Diastolic dysfunction Dilated, round LA +/- MR small/moderate due to annulus dilation +/- right sided changes
What might be seen on routine biochemistry in a dog with DCM?
Pre-renal azotaemia is common
Elevation in liver enzymes esp. ALP not uncommon due to hepatic venous congestion
Hypoproteinaemia in CHF
Hypoproteinaemia in CHF
Electrolyte disturbances
What might be seen on an ECG of a dog with DCM?
Findings are very variable:
- Normal
- Wide +/- tall complexes (occasionally small complexes)
Many DCM dogs have ventricular arrhythmias
Many dogs will present with atrial fibrillation
Describe the blood pressure of a dog with DCM
- Should be relatively normal because compensatory mechanisms to keep this up
- Can be reduced with medications we give
- This is frequently very low with systolic pressure <100mmHg
- Rule out hypertension
- Important to monitor with therapy
- Aim to maintain BP >100mmHg
How would you treat DCM?
- Treat the LCHF
- Treat immediate life-threatening arrhythmias- haemodynamically significant
- If treat LCHF many arrhythmias resolve or do not require treatment
- Rate control of AF- digoxin/ diltiazem/ BB (only if not in heart failure)
What are the 3 stages of arrhythmogenic right ventricular cardiomyopathy (Boxer Cardiomyopathy)?
- Asymptomatic with ventricular arrhythmias
- Symptomatic- normal heart size and LV function but dogs are syncopal/ weak from ventricular arrhythmias
- CHF- poor myocardial function, CHF and ventricular arrhythmias
What are the clinical signs of arrhythmogenic right ventricular cardiomyopathy?
- Can appear any age, mean age 8 years
- Ventricular arrhythmias
- Supra-ventricular arrhythmias
- > 500 VPCs/ 24 hours
- But spontaneous variation of up to 80%
- Syncope
- Sudden death
How would you investigate arrhythmogenic right ventricular cardiomyopathy?
24h Holter monitor is necessary
May need further physiological monitoring
Ideally consider referring these cases as they can be complex
How would you treat arrhythmogenic right ventricular cardiomyopathy?
- Treat any underlying causes
- Treat LCHF as necessary
- Anti-arrhythmic medication often used (Sotalol BID orally)
Describe hypertrophic cardiomyopathy in dogs (aka dynamic obstruction of the left ventricular outflow tract / dynamic subvalvular aortic stenosis)
- Rare in the dog
- Cause unknown- genetic basis suspected
- Diastolic failure
- Young to middle-aged large breed dogs
- Male predisposition
- Syncope/ sudden death
- CHF
- S4 heard in some dogs
What are the typical features of hypertrophic cardiomyopathy in dogs?
Symmetric hypertrophy
No myofiber disarray - histology shows hypertrophied myocardial fibres
LVOT obstruction (obstructive form)
Abnormal mitral valve apparatus
• Elongated anterior leaflet
• Abnormally orientated papillary muscles
What diseases may result in dynamic LVOTO?
Congenital aortic stenosis and mitral dysplasia
Primary hypertrophic obstructive cardiomyopathy
The relationship between LVH, aortic stenosis and mitral dysplasia in dogs is uncertain
What is the aetiology of HCM in dogs?
Uncertain aetiology- genetic basis?
- Polygenic or autosomal recessive pattern of inheritance
- Several genes have been identified in humans (beta-myosin heavy chain the most important)
- Cardiac myosin binding protein C in Maine Coon cats
What other causes should you rule out before diagnosing HCM?
- Hypertension
- Aortic stenosis
- Renal disease
- Pseudohypertrophy secondary to dehydration, hypovolaemia, etc.–> ensure patient is sufficiently volaemic before diagnosing concentric hypertrophy
- Hyperthyroidism
- Other systemic disease
Name some causes of secondary myocardial disease
- Viral aetiology- rarely associated with DCM in dogs (may be that they had viral myocarditis a long time in the past and DCM is a consequence of that)
- Doxorubicin- acute and chronic cardiotoxicity
- Metabolic/ nutritional deficiencies (e.g. L-carnitine, taurine)
- Ischaemic heart disease
- Tachycardia induced cardiomyopathy
- Infective myocarditis
- Non-infective myocarditis
How can doxorubicin cause myocardial disease?
- Acute toxicity- arrhythmias, anaphylaxis
- Chronic cardiotoxicity–> DCM
- Histamine, catecholamine release and free radical production are suggested to be involved
- To reduce risk- close monitoring when administering drug and echocardiography prior to first treatment and then repeat echo serially during treatment period
