Cardiology: Canine Dilated Cardiomyopathy Flashcards
What are the different primary cardiomyopathies?
- Dilated cardiomyopathy
- Arrhythmogenic right ventricular cardiomyopathy
- Hypertrophic cardiomyopathy
- Atrial myopathy (atrial standstill)
- Restrictive cardiomyopathy
- Unclassified cardiomyopathy
RCM and UCM very rare in dogs
What are the different primary cardiomyopathies?
- Dilated cardiomyopathy
- Arrhythmogenic right ventricular cardiomyopathy
- Hypertrophic cardiomyopathy
- Atrial myopathy (atrial standstill)
- Restrictive cardiomyopathy
- Unclassified cardiomyopathy
RCM and UCM very rare in dogs
What is the most common primary cardiomyopathy?
Dilated Cardiomyopathy
Idiopathic
What breeds are more commonly affected by ARVC?
Boxers and English bull dogs
What predisposes to HCM?
What breeds seem predisposed?
(hypertrophic cardiomyopathy)
- Secondary to aortic stenosis, systemic hypertension of infiltrative disease
- Terrier breeds, pointer dogs, golden retrievers
What breeds has atrial cardiomyopathy been described in?
ESS and labrodors
What are the different causes of secondary cardiomyopathies?
- Tachycardia induced cardiomyopathies
- Drugs/toxins
- Infiltrative
- Metabolic
- Nutritional
- Inflammatory
- Connective tissue disease
- What drugs/toxins can cause cardiomyopathies?
- What can be a infiltrative cardiomyopathy cause
- What metabolic/endocrine disorders can cause cardiomyopathy?
- What are nutritional causes of myopathy?
- Chemotherapeutic drugs, cyclophosphamide, heavy metals
- Neoplasia, glycogen storage disease, amyloidosis
- Hypo/hyperthyroidism, diabetes mellitus, acromegaly
- Taurine deficiency, L-carnitine
What are inflammatory causes of secondary cardiomyopathies are there?
(myocarditis)
Infectious:
* Canine distemper, Parvo (herpes, corona)
* Bartonella
* Borrelia, leptospira, leishmania
* Toxoplasma, trypanosoma cruzi
* Cryptococcus, histoplasmosis
* Aspergillus
Non-infectious:
* Viral- autoimmune
* Drug hypersensitivity
* Trauma
* Systemic inflammatory diseases
What is the definition of DCM?
Primary myocardial disorder characterised by a dilation of the four cardiac chambers and a reduction in contractility
What breeds and ages are more typically affected by DCM?
- Affects large and giant breed dogs- can be small
- Middle-ages/old
Poor prognosis
Describe the pathology of DCM?
- Dilation of any of the 4 chambers L>R
- Increased heart weight: BW ratio
- LV thickness : LV diameter reduced
- Valvular lesions: age related, mitral regurgitation
- Histological lesions- attenuated wavy fibres, fibrofatty degeneration
Describe the pathophysiology of DCM?
- Impaired systolic function
- Redcued cardiac output
- Activation of sympathetic and RAAS
- Vasoconstriction, increased HR and contractility
- Myocardial hypertrophy, chamber dilation
- Increased myocardial O2 demand
- Increased call stress CO and CP maintained
- Further myocardial death then fibrosis
- Impaired systolic function
How do the following breeds vary with DCM?
1. Dobermans
2. Great Danes
3. Irish wolf hounds
4. Newfoundlands
5. Cockerspaniels
6. Springerspaniels
6. Labradors
7. Dalmations
- Long occult phase, sudden death common
- Atrial fib with CHF, sudden death common
- can present with AF then progress to overt DCM
- Taurine defiency identified with improvement on supplement
- Reduced contract and enlarged cardiac dimensions
- reduced contract and enlarged dimensions- slow progression
- Predisposed to pathways resulting in SVT
- Associated with protein restricted diet
What is the definition of arrhythmogenic right ventricular cardiomyopathy?
ARVC usually involved the right ventricle with progressive loss of myocytes with faty of fibrofatty tissue replacement resulting in regional or global abnormalities
What are the three forms of ARVC?
- Asymptomatic- VPCs detected by holter monitoring
- Symptomatic- arrhythmias, normal systolic function
- Structural changes of the heart and arrythmias
What is the aetiology of arrythmogenic right ventricular cardiomyopathy?
- Fibrofatty tissue replacement particularly in the right ventricle- also LV/atria
- Fatty tissue or scarring may be seen grossly
- Possibly dilated heart
- How is DCM preclinical phase characterised?
- How does this progress?
- No clinical signs, ventricular arryhtmias frequently present and sudden death can occur
- Signs of CHF and forward failure, left- right and biventricular CHF
What may be found on physical examination of a dog with DCM?
- Cardia cachexia ‘muscle wasting’
- Pale MMS, Sluggish CRT
- Tachypnoea/dyspnoea
- Weak femoral pulses
- Jugular distension, abdominal effusion, positive hepatojugular reflex
Auscultation
* Lungs- increased respiratory sounds, crackles, tachypnoea/dyspnoea (pulmonary oedema)
* Heart- tachycardia, arrhythmias, soft systolic murmur, left apex- mitral regurgitation
* Gallop sound (S3)- rapid ventricle filling
What clinical pathology might be different with DCM?
- Pre-renal azotaemia common
- Mild increases of liver enzymes (hepatic congestion)
- Albumin low if effusions
- Rule out hypothyroidism- TT4,TSH
- Cardiac markers:
Troponin- myocardial cell damage, not specific for cardiac disease
NT-proBNP- marker for heart stretch
- What arrythmias are common with DCM?
- What evidence of chamber enlargment can an ECG show?
- AF and VPCs
- Ventricular enlargment patterns: tall R waves, prolonged QRS duration, ST segment changes
Atrial enlargment patterns: wide, tall P waves, prolonged QRS
How can a DV and right lateral radiograph show signs of DCM?
- Cardiomegaly- lateral view
- Left atrial enlargment
- Pulmonary vasculature- distended lobar pulmonary veins
- Lung patterns
interstitial- early pulmonary oedema
alveolar- advanced pulmonary oedema - Check abdomen for abdominal effusion
- How does DCM present in simple terms with echo?
- What specific changes are there for chambers?
- What specifically changes about contractility?
- Rounded, dilated, poor contractility
- Increase M mode of LV, increased LA/Ao ratio (>1.5), increased E point to septal separation, usually mild MR
- Decreased FS%, decreased EF%, decreased LV ESV, increased systolic time intervals, asynchronus contraction of LV
Diagnosis is exclusion
What is holter monitoring useful for with DCM?
- Permits diagnosis in preclinical phase (arrythmias without chamber dilation/systolic dysfunction)
- Assesment of arryhtmias- needed for treatment
- Assessment of response to treatment
- What does AF mean on a holter?
- What do VPCs, VT cause?
- HR <140 bpm
- Reduced number of ventricular ectopic beats, reduced malignancy of ectopic complexes
How is preclinical disease of DCM treated?
Pimobendan
What are the different targets of congestive heart failure?
- Reduce preload
- Inotropic support
- Reduce afterload
- Control of arrhythmias
How is preload reduced with CHF from DCM?
Diuretics and Venodilators
* Furosemide- essential in CHF (loop diuretic)
* Torasemide- more potent then furosemide
* Spinonolactone- anti-remodelling, weak diuetic
* Thiazide- in progression, if ascites present and furosemide insufficient
* Glyceryl trinitrate- percutaneous venodilator- acute pulmonary oedema
What inotropic support can be given for CHF?
- Pimobenden- positive inotrope and vasodilator
calcium sensitizer, phosphodiesterase III inhibitor - Dobutamine
Sympathomimetic
In emergency situations
Can be pro-arrythmic
What inotropic support can be given for CHF?
- Pimobenden- positive inotrope and vasodilator
calcium sensitizer, phosphodiesterase III inhibitor - Dobutamine
Sympathomimetic
In emergency situations
Can be pro-arrythmic
How is afterload reduced?
What drugs are used?
Vasodilators
* ACE inhibitors- benazepril, enalapril, ramipril, imidapril
What drugs can be used for atrial fibrillation?
- Calcium channel blockers- diltiazem
- Digoxin- reduce dose if renal failure/overweight
Check K+ levels - Beta-blockers- less safe- more negative inotropic and chronotropic
Do not use in heart failure
What drugs can be given for ventricular arrythmias?
- Lidocaine- emergency treatment
- Sotalol- for oral treatment
- Mexiletine- requires a VMD import license but same vaughn-williams class as lidocaine
- Amiodarone
What is the prognosis for DCM?
Very variable
* Some breeds have extremely short MST
* English cockers >2y
* Occult disease in dobermans quickly progresses
* Negative prognostic indicators- young age, ascites, dyspnoea, atrial fibrillation
