Canine dilated cardiomyopathy and other myocardial diseases Flashcards
What is a cardiomyopathy?
Myocardial disorder in which the heart muscle is structurally and functionally abnormal
Which cells make up heart muscle?
Cardiomyocytes
Name the most common cardiomyopathy in dogs
Dilated cardiomyopathy
List the 4 primary cardiomyopathies in dogs
- Dilated cardiomyopathy (DCM)
- Arrhythmogenic right ventricular cardiomyopathy (ARVC)
- Hypertrophic cardiomyopathy (HCM)
- Atrial cardiomyopathy (can also be called atrial standstill)
List some causes of a secondary cardiomyopathy
- Tachycardia induced
- Systemic hypertension
- Drugs/toxins
- Infiltrative disease e.g. neoplasia
- Metabolic/endocrine disease
- Nutritional
- Inflammatory: myocarditis
What is the most common cause of nutritional cardiomyopathies?
Taurine deficiency
Define dilated cardiomyopathy
Primary myocardial disorder characterised by a dilation of the four cardiac chambers (especially the left chambers) and a reduction in contractility
Which animals are typically affected by dilated cardiomyopathy?
- Generally affects large and giant breeds
- Middle aged/old dogs
- No sex predisposition
- Guarded/poor prognosis
The prevalence of DCM is highest in which dog breed?
Dobermann
Describe the gross pathology of a dog with DCM
- Dilatation of any of the 4 cardiac chambers (L>R): eccentric hypertrophy
- Increased heart weight: BW ratio
- LV thickness : LV diameter reduced
- Valvular lesions: age related, due to mitral regurgitation caused by valvular annulus stretching
How does DCM appear on histology?
- Attenuated fibers (atrophied): Myocytes thin, degeneration, fibrosis
- Fibro-fatty infiltration: Myocyte lysis, vacuolation, fibrosis, fatty infiltration
In DCM what happens once there is damage to the cardiomyocytes?
- Damaged cells no longer function effectively as a syncytium
- Cell death and fatty or fibrous replacement (as per histopathology)
-> IMPAIRED SYSTOLIC FUNCTION
What are the consequences of impaired systolic function?
-> Reduced cardiac output -> activation of symp NS and RAAS -> vasoconstriction, increased HR + contractility, myocardial hypertrophy, chamber dilation -> increased myocardial oxygen demand, wall stress -> further myocardial cell death, myocardial fibrosis -> FURTHER impaired systolic function -> (round in a loop)
Name 3 similarities of DCM and mitral degenerative valve disease
- Enlargement of left ventricle (+/- right)
- Enlargement of left atrium
- Mitral regurgitation
Name some differences of DCM and mitral degenerative valve disease
DCM:
- Mild mitral regurgitation
- Reduced systolic function
- Decreased wall contractility
- LV>LA
MDVD:
- Lots of mitral regurgitation
- Normal (?)/hyperdynamic systolic function
- Normal wall contractility
- LA>LV
Describe DCM in Dobermanns (breed variation)
- High prevalence (approx. 60%)
- Slowly progressive, inherited
- Long asymptomatic preclinical phase
- Ventricular arrhythmias (♀)
- Sudden death
- Cardiomegaly less obvious
- Annual screening, short survival after CHF
ARVC stands for?
Arrhythmogenic right ventricular cardiomyopathy
What is Arrhythmogenic right ventricular cardiomyopathy?
Involves predominantly the right ventricle with progressive loss of myocytes and fatty or fibrofatty tissue replacement, resulting in regional (segmental) or global abnormalities.
Arrhythmogenic right ventricular cardiomyopathy is most commonly seen in which breed?
Boxers
Describe the three forms of Arrhythmogenic right ventricular cardiomyopathy
- Asymptomatic – VPCs detected by Holter monitoring
- Symptomatic (syncopal) – arrhythmias (VPCs), normal systolic function
- Structural changes of the heart (ventricular dilation) + arrhythmias
Describe the gross pathology of arrhythmogenic right ventricular cardiomyopathy
- Fatty tissue or scarring may be seen grossly
- Possibly dilated heart: right ventricle
- Wall thinning
Describe the histopathology of arrhythmogenic right ventricular cardiomyopathy
Loss of myocytes with fatty/fibrofatty replacement
Describe the features of atrial cardiomyopathy
- Thinning atrial walls
- Atrial standstill on ECG: no P wave, escape rhythm
- LA»_space;»> LV on echo
Describe the features of hypertrophic cardiomyopathy
- Rare, similar to feline HCM
- Terrier breeds, Pointer dogs, Golden Retriever
Describe a likely clinical presentation of a patient with DCM
Adult dogs
Large-giant breeds
Exercise intolerance
Most dogs are in CHF at presentation
- DCM is characterized by a preclinical/occult phase, where no clinical signs are evident, but ventricular
arrhythmias are frequently present and sudden death can occur
Upon clinical exam what may you find if you have a dog with DCM?
- Arrhythmia
- Quiet, soft heart murmur, left apical systolic (if you don’t look for it you won’t find it!!)
- Dyspnoea, tachypnoea, crackles (if in left sided heart failure)
- Ascites, jugular distention (if in right sided heart failure)
- Collapse?
- Possibly no clinical signs
Describe the likely history of a dog with DCM
Exercise intolerance
Cough
Increased respiratory rate and effort
Compare the clinical presentation of DCM with MVDV
DCM:
- Large breeds
- Quiet heart murmur
- Adult dogs
- Collapse more common
- Once in CHF typical symptoms present: exercise intolerance, cough, etc
- Sudden death risk!
MVDV:
- Small breeds
- Loud heart murmur
- Adult dogs
- Collapse less common
- Once in CHF typical symptoms present: exercise intolerance, cough, etc
What diagnostic investigations would you carry out with a dog presenting with a suspected DCM?
- History + physical examination
- Blood pressure
- Clinical pathology: Biomarkers – troponin as the myocytes are being damaged
- ECG
- Radiography
- Echocardiography
- Ambulatory ECG
Why is blood pressure used as a diagnostic tool in DCM?
- Reflects compensatory mechanisms
- Rule out hypertension
- If in heart failure, assess for hypotension
What does systolic hypotension indicate?
Low if forward failure = systolic dysfunction (heart not contracting as well as it should do)
Compare the ECGs of DCM and MDVD
DCM:
- Atrial fibrillation
- VPCs
- SVPCs
- Ventricular tachycardia
MDVD:
- Supraventricular premature complexes
- Atrial fibrillation
- Ventricular premature complexes
In DCM how is evidence of atrial and ventricular chamber enlargement seen on an ECG?
Ventricular enlargement patterns: tall R waves, prolonged QRS duration, ST segment changes
Atrial enlargement patterns: wide, tall P waves, prolonged QRS duration
How are thoracic radiographs used to diagnosed DCM?
- Sedation
- DV + (right) lateral
- Cardiac size: Tracheal elevation, Bulges?
- Pulmonary vessels
- Lung infiltrate
- Effusions?
What is the best diagnostic method to confirm DCM?
Echocardiography
List the 3 main features seen on echocardiography which indicated DCM
Rounded
Dilated
Poor contractility
Compare the echocardiography of DCM and MVDV
DCM:
- Enlarged left ventricle and atrium but LV>LA
- Dilated and rounded left ventricle
- Thin walls
- Reduced systolic function
- Decreased contractility
- Mild/moderate MR
MDVD:
- Enlarged left ventricle and atrium but LA>LV
- Dilated and rounded left ventricle
- Hyperdynamic systolic function
- Lots of MR
Describe the uses of ambulatory ECG Holter monitoring for diagnosis of DCM
- Permits diagnosis of DCM in preclinical/occult phase (arrhythmias without chamber dilation and/or systolic dysfunction), especially in Dobermann and Boxer with ARVC
- Assessment of arrhythmias – quantification, complexity; need for treatment
- Assessment of response to treatment
What would be seen on a Holter monitoring ECG which would indicate DCM
High numbers of VPCs
300-100 = likley affected
Name 2 drugs that can be used for DCM therapy in the pre-clinical phase
Pimobendan
ACE-inhibitor
Once DCM progresses into heart failure how is CHF treated?
- Furosemide: keeps the animals alive when they are in failure so this is the top priority + other diuretics?
- Pimobendan
- ACE-inhibitors
- Spironolactone
Which drugs are used in the treatment of arrythmias related to DCM
Supraventricular = Diltiazem, Digoxin
Ventricular = Sotalol
Describe the prognosis of DCM
- In general guarded-poor, depending on response to treatment
- Monitoring of response important
- 6-12m (less in certain breeds)
List 4 negative prognostic indicators for DCM
Young age
Ascites
Dyspnoea
Atrial fibrillation
