Canine Myocardial Disease Flashcards
What can cause primary myocardial disease in the dog?
–Dilated cardiomyopathy (DCM) is the most common thing we see
–Arrhythmogenic right ventricular cardiomyopathy (ARVC)
•Occurs more so in boxers
–Hypertrophic cardiomyopathy (rare)
What can cause secondary myocardial disease in the dog?
–Infective myocarditis
•Usually present as dogs with an explain sudden onset dysrhythmia and may go on to develop a DCM
–Deficiency diseases
•Identified in 80’s and 90’s – tend to be things that aren’t seen as much anymore as we are better at having things and not being deficient
–Toxic causes
What is dilated cardiomyopathy characterised by?
Characterised by impaired myocardial contractility with dilation of LV (+/-RV) – cannot reverse myocardial failure as we do not know what causes it
What kind of arrhythmia is common with dilated cardiomyopathy?
•Tachyarrhythmias are common
–Supraventricular and/or ventricular
What is the end stage of many cardiac diseases?
•DCM is an end stage of many cardiac diseases, primary DCM is a diagnosis of exclusion
–Animal suffers with some sort of myocardial insult and by the time we see it, we have this end stage heart
Which heart is affected with a cardiomyopathy here?
Both from great Danes:
Left – got hit by a car and died suddenly
Right – DCM, eccentric hypertrophy, external diameter has increased
What is the pathophysiology of dilated cardiomyopathy?
- Eccentric hypertrophy of the LV
- Systolic failure
–‘forward failure’
•Diastolic failure
–‘backward failure’ – congestion
- LA dilation and increased LAP
- Right side can also be affected
What is the histopathology of cardiomyopathy?
•Two distinct types of HP are reported these are thought to relate to the underlying mechanism of the disease:
–Narrow (attenuated) myocardial cells with a wavy appearance (Newfoundlands)
–Myofibre degeneration, myocyte atropy and lysis, fatty infiltration and fibrosis (Boxers, some Dobermans)
•Otherwise often non-specific and include:
–Scattered areas of myocardial necrosis
- Myocardial degeneration and fibrosis
- Inflammatory cell infiltrates are inconsistent but an active myocarditis is rare
With histopathology of cardiomyopathy, which type is most common in Newfoundlands?
Narrow (attenuated) myocardial cells with a wavy appearance (Newfoundlands)
With histopathology of cardiomyopathy, which type is most common in Boxers and some dobermans?
Myofibre degeneration, myocyte atropy and lysis, fatty infiltration and fibrosis (Boxers, some Dobermans)
What are some non-specific histopathology signs with cardiomyopathy?
•Otherwise often non-specific and include:
–Scattered areas of myocardial necrosis
- Myocardial degeneration and fibrosis
- Inflammatory cell infiltrates are inconsistent but an active myocarditis is rare
What is the pathophysiology of the OCCULT phase of cardiomyopathy?
Occult phase - no clinical signs
–CO falls
–Sympathetic, hormonal and renal compensatory mechanisms activated therefore
–These maintain CO by increasing HR, peripheral vasoconstriction and volume expansion
–Chronic NH activation also contributes to progressive myocardial damage and CHF
–Underlying myocardial disease, often will compensate for years but as time goes by, CO continues to fall and increasing levels of compensation and RAAS system etc. and as a consequence, we are asking the sick ventricle to work even harder, output falls, body vasoconstricts and retains fluid and then the ventricle has to deal with even more fluid and eject blood into a higher pressure system – contributing to the progression of the disease
What are the breed dispositions for cardiomyopathy?
•Breed predispositions – genetic basis
–Doberman, Newfoundland, IWH, St Bernards, Labradors, Great Dane, Cocker spaniels, Boxers (ARVC), GSD
•Most common breeds, presentation and progression is different in the different breeds.
–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
What age, size and sex of dogs is most likely to be affected with cardiomyopathy?
- 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 and they also tend to be affected earlier than females
What are the 2 phases of DCM?
–Occult phase – may go on for years!
•no clinical signs usually
–Symptomatic phase
- usually CHF, typically LHS sometimes biventricular heart failure
- Syncope – as a result of a poor output (fainting)
- Weight loss – as a first clinical sign sometimes
- Sudden death – can occur in some breeds
What are some screen programmes you can use to identify the occult phase of DCM?
–24 hour Holter monitor
•>50VPCs /24 hr abnormal but no clear exact number and depends on the morphology whether couplets / triplets
–Echocardiography
What are the clinical signs like for overt DCM?
•Onset of clinical signs can be sudden
–Weakness
–Lethargy
–Syncope
–Dyspnoea
–Exercise intolerance
–Cough
–Anorexia
–Ascites
–Cardiac cachexia
What would you find on clinical exam of a dog with DCM?
- Variable depending on the degree of myocardial dysfunction
- Pale mucous membranes
- Sluggish CRT
- Cool extremities
- Tachycardia +/- arrhythmias – AF, VPCs, VT
- Variable pulses +/- pulse deficits
- Pulsus alternans
- Signs of LCHF / RCHF
- S3 gallop sound – if sinus rhythm
–Animals with dysrhythmias will not gallop
–Sinus tachcardia
•Soft MR / TR murmurs
–As heart is dilating, pulling valves apart so tricuspid and bicuspid valves leak, so a less hard murmur is heart
What investigations would you potentially use for the investiagion of DCM?
- History
- Clinical examination
- Echocardiography
–Can confirm presence of DCM
- Clinical pathology
- Radiography
- ECG
- Blood pressure
–Increasingly interested in this, most interested in this one we have started treating them. BP should be reasonably normal, systemic arterial BP will be normal as that is why there are compensatory mechanisms.
•24hr Holter monitor
–To see what is going on when they are at home as in the clinic, there will be some impact of the sympathetic nervous system on rate and rhythm, want to know what this is like at home
Right parasternal short axis view
What is going on?
Eccentric dilation
Right Parasternal short axis view at the level of the aorta
Is the LA enlarged?
Aorta in the middle
LA enlargement – slug like left auricular appendange
Zeus Dalton 6 mth Great dane
Which side of the heart does he have changes to?
What else can be seen?
- Big LHS, tall cardiac. Also very wide, lots of RHS change
- DCM could be PDA
- Generalised cardiomegaly
- Left atrial enlargement
- Alveolar pattern
What is enlarged on this radiograph?
What else can be seen?
- Generalised cardiomegaly
- Left atrial enlargement
- Interstitial pattern
What is wrong with this ECG?
Tachycardia induced cardiomyopathy
