CANINE CARDIOMYOPATHIES Flashcards
respiratory signs patient - what diagnostic tests to prioritize?
- thoracic radiographs > most important to rule out many things
- ECG > we hear tachyarrhythmia, but need to know more about rhythm diagnosis
- CBC/biochem > may need to treat with diuretics, want to know kidney function
- BP > weak femoral pulses; identify if hypotensive
if a patient presents and we have a suspicion of heart failure, what a good first step?
if congestive heart failure is anywhere in my Ddx, will probably benefit from furosemide to get fluid off their lungs
> will not be bad if eg. pneumonia anyways
Atrial fibrillation - typical ECG appearance
- Absence of P waves
- Irregular rhythm
- Usually tachycardic
- (+/- f waves)
- Typically narrow QRS complexes (supraventricular origin)
Atrial fibrillation (AF)
- prevalence in dogs and cats
- most common cause in small animals?
- Most common clinically relevant arrhythmia in dogs (esp. large/giant breeds)
- Rare in cats > as their small atria cant easily attain critical mass
- Requires critical atrial mass to
initiate and sustain AF - Pathologic atrial dilation is most common cause in small animals
> E.g. 2° to DCM, MVD - Primary (“Lone”) AF
> Giant breeds (Irish wolfhounds, Great Dane)
Consequences of AF
- No atrial contribution to filling
- Tachycardia (↓ diastolic filling time)
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Resulting in: - ↓ cardiac output
- ↑ filling pressures
- ↑ myocardial oxygen demand
- Worsening of CHF
thoracic radiographs for DCM
- Left atrial enlargement
- Left ventricular enlargement
- Pulmonary venous distension
- Diffuse bronchointerstitial pulmonary pattern > Worse caudodorsally
<><><><> - Radiographic diagnosis: left-sided cardiomegaly & cardiogenic pulmonary edema
Development of pulmonary edema, pathogenesis (related to left sided congestive heart failure)
- Left atrial enlargement
- Pulmonary Venous Distention
- pulmonary capillary hypertension
- interstitial pulmonary edema
- alveolar pulmonary edema
echocardiogram observation for DCM
- rounded, dilated ventricle and decreased systolic function
- reduced contractility
- this test gives us a definitive diagnosis of DCM
Dilated Cardiomyopathy (DCM) Phenotype, prevalence? what dogs get it more commonly?
- Dilation of left +/- right ventricle
- Decreased contractility
- Second most common canine acquired cardiac disease (second to degenerative mitral valve disease)
- More common in large/giant breeds
DCM etiologies
Primary
* genetic > doberman
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Secondary
* Nutritional
* Tachycardia-induced
* Toxicity > E.g. doxorubicin
* Infectious
> Trypanosoma cruzi (Chagas dz)
> Viral (e.g. parvovirus)
nutritional DCM - may be related to what? who may be predisposed?
Taurine deficiency
* Impaired energy metabolism
* Cocker spaniels, Golden Retrievers
* Cats
Progression of Canine DCM
NORMAL Stage A
- Normal heart and Free of clinical signs
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PRECLINICAL Stage B
- Abnormal heart and Free of clinical signs
- usually lasts 2-4 years
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CLINICAL/CHF Stage C and D
- stage C: onset of CHF, possible sudden death
- More abnormal heart and With clinical signs
- stage D: Development of refractory heart failure
- can have CHF death, sudden death, CHF euthanasia
- usually lasts 4-6 months in dobermans, or ~1 year for others
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- A: at risk
- B and on: Development of evidence of heart disease/cardiomegaly
- C and on: Development of signs of heart failure
- D: Development of refractory heart failure
Determinants of myocardial performance:
- Preload
- Afterload
- Contractility
> these 3 all contribute to stroke volume
<><><><> - Distensibility
<><><><> - Heart rate
<><><><> - stroke volume and heart rate determine cardiac output
Determinants of myocardial performance: how they change with DCM
- Preload up
- Afterload up
- Contractility down
- Distensibility down
- Heart rate up
Therapeutic plan for DCM
- Preload: high > Furosemide, ACEi
- Furosemide most important!
- reduce preload, get fluid out of the lungs
<><><><> - Afterload: high > ACEi, Pimobendan
- has some vasodilatory effects, can help decrease afterload
<><><><> - Contractility: low > Pimobendan
<><><><> - Distensibility: low
> ACEi (?)
> Spironolactone (?)
<><><><> - Heart Rate: high
> Treat if pathologic tachyarrhythmia
Treatment of stage B (preclinical) DCM in dogs:
- pimobendan has shown benefit
- benazepril (ACE inhibitor) seems to lengthen time to clinical signs
> these studies both done in dobermans, but we use these for other breeds too
ARRHYTHMOGENIC RIGHT VENTRICULAR CARDIOMYOPATHY
- breed?
- boxers, but also reported in other breeds
ARVC - pathogenesis and result
- Progressive fibrofatty replacement of the right, and to some degree the left, ventricular myocardium
- Manifests as right ventricular (RV) origin arrhythmias (may see LV origin as well)
ARVC clinical presentation
- age?
- types?
- ECG and signs?
- Any age (commonly 6-10yrs)
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3 subtypes: - Asymptomatic
> Incidental detection of arrhythmia - Exercise intolerance or syncope
> Associated with ventricular arrhythmia - Systolic dysfunction and CHF
> Rare (10% of ARVC cases)
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Vast majority of cases show arrhythmia only with NORMAL echo
How to best diagnose ARVC?
- ECG
- Holter (24 hour ambulatory ECG)
- +/- Echocardiogram
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Gold standard: myocardial biopsy… but high risk of complications
possible ECG findings for ARVC?
important considerations for diagnosis?
- isolated VPCs or doublets / triplets
- runs of ventricular tachycardia
<><> - Rule out other causes of ventricular arrhythmias! use other tests
ARVC Treatment
* When to treat? how?
* Goals of treatment?
* caveat?
When to treat?
* Symptomatic due to
ventricular arrhythmia
* If asymptomatic, if arrhythmia severe in frequency/complexity
How:
* Sotalol
* Mexiletine
* Combo
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Goals of treatment:
* Reduce frequency & complexity of ventricular arrhythmias, reduce symptoms
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* No treatment has been proven to prevent sudden death, which can be unpredictable
