Valvular Heart Diseases Flashcards
Name the most common cardiac disease in dogs
Myxomatous degenerative valve disease
Describe the pathogenesis of myxomatous degenerative valve disease
Idiopathic
Slow progression over several years
Risk of sudden death low
Small breeds
Mitral valve and tricuspid valve most commonly affected
What changes occur in the heart is myxomatous valvular degeneration?
- Nodular thickening of the valve leaflets: proteoglycan accumulation
- Lengthened or ruptured chordae
Describe the aetiology and predispositions for myxomatous degenerative valve disease
Idiopathic condition – multiple hypotheses:
- Abnormalities in collagen and extracellular matrix formation
- Abnormalities of serotonin signalling
- Mechanical stress
Predisposition in Cavalier King Charles Spaniel
Middle aged/older dogs
How does the gross pathology of the heart change in myxomatous degenerative valve disease?
- LA and LV dilatation: eccentric hypertrophy due to chronic volume overload
- Elongation chordae tendinae
- Thickened, deformed leaflets
- Jet lesions: damage to the left atrial wall
Describe the microscopic changes in the heart if myxomatous degenerative valve disease
Accumulation of glycosaminoglycans (pink sedimentary material) within the valve leaflets and a disrupted collagen matrix
If there are valve leaks, what happens next?
- Leakage of blood back into atria (left most likely)
- Reduction in forward stroke volume = blood leaving the heart in each pump cycle
- If there is a leaky valve some blood goes back into the atrium when it should normally all go out of the ventricles through the aorta
- Increase in volume of blood entering left ventricle in next diastole = volume overload
What commonly occurs secondary to chronically elevated left atrial pressure and can be seen secondary to concurrent respiratory/lung pathology as seen in small breeds?
Pulmonary hypertension
Define afterload
The work of the heart to pump blood
Define preload
The volume of the left ventricle at the end of diastole
A volume overload due to a constant increased preload causes?
Eccentric hypertrophy
How do valve leaks affect preload and afterload?
- Decreased afterload as there is less blood to pump out of the heart as it goes back into the atria (which is easier than out of the aorta)
- Increased preload as the volume in the LV at the end of diastole is increased
How do valve leaks affect cardiac output?
Reduced cardiac output as there is a decreased stroke volume
What are the consequences of decreased cardiac output?
Activation of sympathetic NS -> increased HR and contractility
Activation of RAAS
What are the consequences of RAAS activation?
Retention of Na and fluid
Vasoconstriction to increase afterload
Increased circulating volume to increase preload
What are the consequences of increased afterload and preload?
Chamber dilation
-> Mitral regurgitation
Describe the different stages of myxomatous degenerative valvular disease
A = at risk
B1 = murmur and no enlargement
B2 = murmur and enlargement
C1 = CHF, hospitalised
C2 = CHF, at home
D1 = refractory, hospitalised
D2 = refractory, at home
How might a dog with myxomatous degenerative valve disease present in the consult room/on clinical exam
- Small breeds predisposed
- Adult/older dogs
- Loud harsh heart murmur, left apical systolic
- Dyspnoea, tachypnoea, crackles
- Exercise intolerance
- Cough
- Possibly no clinical signs
Once the clinical exam has been performed on a dog with suspected MDVD, what are the next steps?
- Thorough auscultation to locate and describe the murmur: this will give you your diagnosis!!
- Blood pressure
- Clinical pathology: Biomarkers (NTProBNP)
- Radiography
- ECG
- Echocardiography
- Ambulatory ECG
List the clinical signs of right sided CHF
Ascites
Hepatomegaly
Jugular pulsation
How can blood pressure be used to investigate myxomatous degenerative valvular disease?
- Often normal
- Hypertension → increased afterload → worse regurgitant fraction = BAD!
- More blood is pushed back into the atrium
- Hypotension if forward (systolic) failure
How can blood tests and biomarkers be used to investigate myxomatous degenerative valvular disease?
- Prerenal azotaemia, particularly on diuretics
- Assess electrolytes, particularly on diuretics
- Biomarkers:
NT-proBNP - helpful to differentiate respiratory/cardiac cause of cough. Marker for HF.
Troponin I - marker for myocardial cell damage
How can thoracic radiographs be used to investigate myxomatous degenerative valvular disease?
- DV + right lateral
- Cardiac size: Tracheal elevation, Bulges?
- Pulmonary vessels
- Lung infiltrate
- Effusions?
What are some common arrythmias seen with myxomatous degenerative valve disease?
- Prolonged P wave = left atrial enlargement
- Tall R wave = left ventricular enlargement
In advanced cases: - Supraventricular premature complexes
- Atrial fibrillation
- Ventricular premature complexes
If a patient with suspected myxomatous degenerative valve disease has sinus arrhythmia, what does this mean?
NOT in congestive heart failure - preclinical disease
What is the best diagnostic method to confirm suspicions of MDVD?
Echocardiography
What is echocardiography used for in MDVD?
To assess severity, progression of disease and response to treatment
How will a heart with MDVD appear on echocardiography?
- Thickened atrioventricular leaflets, may see prolapse
- Presence of MR on colour Doppler – size of jet depends on severity
- LA enlargement: LA/Ao ratio, LA major
- LV enlargement: Eccentric hypertrophy with rounded LV – especially increased internal diameter in diastole (LVIDd, from increased preload)
- Hyperdynamic systolic function
- Tricuspid regurgitation
- Pulmonary hypertension
How does the left side of the heart normally appear on echo?
Bullet shaped left ventricle, square shaped left atrium
How should the size of the left atrium compare to the size of the aorta in a normal animal?
The atrium should be no more than 1.5x the size of the aorta
What is a holter/ambulatory ECG?
24h ECG
Quantification of arrhythmias
Atrial fibrillation: response to treatment
Describe the treatment of myxomatous degenerative valve disease based on the stage
A – none indicated, monitor at routine appointments
B1 – none indicated, murmur will be present, HAMLET APP
B2 – PIMOBENDAN, HAMLET APP
C – CHF therapy as standard
D – as for C with increasing doses and additional therapies e.g. sequential nephron blockade
Name the 4 drugs used in the therapy of CHF - in the correct order
Furosemide
Pimobendan
ACEi
Spironolactone
Why is Pimobendan given in the B2 stage of MDVD?
Delays the onset of heart failure
Name two drugs given to patients with supraventricular arrythmias
Diltiazem
Digoxin
Name 1 drug given to patients with ventricular arrythmias
Solatol - do not use if heart failure is confirmed or suspected
Name a drug given to patients with pulmonary hypertension
Sildenafil
When should cough suppressants be used?
Should only use if it is a genuine heart failure cough as an animal is usually coughing for a reason
Describe the prognosis of MDVD
- Very variable - Some asymptomatic dogs never develop CHF
- Breed? CKCS better prognosis (earlier onset)
- Once signs of CHF appear prognosis worse but timeline variable
- Large breed dogs can show myocardial failure and deteriorate more rapidly
What is endocarditis?
Very rare!
Infection of 1 or more endocardial surfaces (valves/leaflets)
Which valves are most affected by endocarditis?
Aortic or mitral
List some possible agents that can cause bacterial endocarditis
Streptococcus spp
Staphylococcus spp
E. Coli
Pseudomonas
Describe the aetiology of bacterial endocarditis
- Transient, persistent bacteraemia → occult infection (GI, dental, oropharynx), IV catheter, recent surgery
- Damaged valvular endothelium: high velocities, turbulent blood flow
- Bacteria ability to adhere through various mechanisms
- Hypercoagulable states
Describe the pathology of bacterial endocarditis
- Vegetations on the endocardial surface of the valve leaflets: small nodules to polypoid
- Affected valves usually deformed, can be perforated, haemorrhagic
- Septic/sterile arterial embolisation (kidney, heart, lung, brain)
Describe the microscopic pathological findings in bacterial endocarditis
Platelets, RBC, WBC, bacteria, fibrin
Fibrous tissue, calcification
Bacteria within vegetation
List the diagnostic methods for bacterial endocarditis
- Blood culture
- Echocardiography
- ECG
- Clinical pathology
Describe blood culture as a diagnostic method for bacterial endocarditis
- Prior to antibiosis, ideally if pyrexia present
- Aseptic technique
- 3 samples from different puncture sites, 10 mL per sample (total of 20-30mL increase the chance of positive result)
- Frequently negative
- False +ve due to skin contamination
Describe echocardiography as a diagnostic method for bacterial endocarditis
- Valvular vegetations
- Size -> risk of embolisation
- Regurgitation = MURMUR!
- Systolic dysfunction
Which criteria is used for diagnosis of bacterial endocarditis?
Modified Dukes criteria
Describe how the modified Dukes criteria is used to diagnosed bacterial endocarditis
Based on major and minor clinical signs
Definitive =
- 2 major OR
- 5 minor OR
- 1 major + 3 minor
List the major criteria in the modified Dukes criteria
- Positive echocardiogram
- New valvular insufficency
- Positive blood culture
List the minor criteria in the modified Dukes criteria
- Fever
- Medium/large breed
- Subaortic stenosis
- Thromboembolic disease
- Immune mediated disease
- Positive blood culture not meeting major criteria
How is bacterial endocarditis treated?
Bactericidal antibiotics – ideally based on culture and sensitivity: Fluoroquinolone + potentiated amoxicillin + metronidazole whilst awaiting culture
- Intravenously for at least 7 days
- Minimum course of 6 weeks, might need much longer course
Describe the prognosis of bacterial endocarditis
- Guarded
- Recurrence and complications possible
- Long term valvular damage
