Acquired valve disease Flashcards
Aetiology of myxomatous mitral valve disease (MMVD)
Cause unknown
Inherited component in some breeds (CKCS, Dachshund)
Presumed to be familial in other breeds
Pathology of myxomatous mitral valve disease (MMVD)
Nodular thickening of the mitral valve leaflets
Abnormalities in collagen content and alignment and expansion of the spongiosa due to accumulation of proteoglycans
Prolapse of the mitral valve into the left atrium is commonly seen
Progressive deformation of the valve apparatus leads to ineffective coaptation and consequent regurgitation
Grossly seen as deformed, thickened valve leaflets and elongation of the chordae tendinae
Jet lesions (impact lesions) may be seen on the mitral endocardium secondary to severe mitral regurgitation
Pathophhysiology of myxomatous mitral valve disease (MMVD)
Chronic left-sided volume overload
Mitral regurg results in an increase in preload and the compensatory response - eccentric hypertrophy of the left ventricle
progressive increase in left ventricular and atrial size
Severe disease can lead to pulmonary oedema
Concentric hypertrophy
Reduced ventricular volume
Thickened walls
Eccentric hypertrophy
Increased ventricular volume
Also with thickened walls
Sequelae of myxomatous mitral valve disease (MMVD)
Left sided congestive heart failure (pulmonary oedema)
Arrhythmias - especially atrial fibrillation (may result in right sided CHF)
Left atrial tears/acquired septal defects
Pulmonary hypertension
Stages of myxomatous mitral valve disease (MMVD)
A: predisposed/at risk
B: pre-clinical disease
B1: MR but no/minimal secondary remodelling
B2: LA and LV dilation
C: CHF
D: refractory CHF
Stage A myxomatous mitral valve disease (MMVD)
Dogs considered at increased risk but without apparent structural abnormalities
E.g. CKCS
Stage B myxomatous mitral valve disease (MMVD)
Dogs with structural heart disease but no evidence of CHF i.e. pre-clinical MMVD
Stage B1 myxomatous mitral valve disease (MMVD)
Asymptomatic MMVD but with no radiographic or echocardiographic evidence of cardiac remodelling
Stage B2 myxomatous mitral valve disease (MMVD)
Asymptomatic MMVD which is haemodynamically severe enough, and present for long enough to induce cardiac remodelling (left atrial and ventricular dilation) identified on radiographs +/- echocardiography
Murmur at least grade 3
Stage C myxomatous mitral valve disease (MMVD)
DOgs with MMVD and CHF (either controlled or current decompensated)
Stage D myxomatous mitral valve disease (MMVD)
Dogs with end-stage MMVD with CHF refractory to standard treatment
Signalment of myxomatous mitral valve disease (MMVD)
Middle aged to older dogs
Small breed dogs typically under 20kg
Can develop in any breed and may progress quicker in large breed dogs
History of pre-clinical (stage B) myxomatous mitral valve disease (MMVD)
Most will be asymptomatic
If advanced (B2) left atrial dilation may cause compression of the caudal mainstem bronchi and consequent chronic cough
History of clinical disease (stage C; CHF) myxomatous mitral valve disease (MMVD)
Chronic murmur
Elevated resp rate or effort
Cough
Reduced exercise capacity
Weight loss, muscle loss, reduced appetite, lethargy
Abdominal distension if right sided CHF
Collapse/syncope (less common)
Physical examination of pre-clinical (stage B) myxomatous mitral valve disease (MMVD)
Left apical systolic murmur
Concurrent right apical murmurs
Physical examination of clinical (stage C) myxomatous mitral valve disease (MMVD)
Left apical systolic murmur and concurrent right apical murmur
Tachypnoea +/- dyspnoea
Pulmonary crackles
Tachycardia, tachyarrhythmias
Signs of right-sided CHF less common
Signs of right sided heart failure
Jugular distension
Positive hepatojugular reflux
Abdominal distension with fluid thrill
Echocardiography of stage B1 myxomatous mitral valve disease (MMVD)
Mitral valve leaflets are abnormal
Evidence of mitral regurgitation
Left atrium and left ventricle are normal (or near normal) in size
Echocardiography of stage B2 myxomatous mitral valve disease (MMVD)
Abnormal mitral valve leaflets with mitral regurg and secondary dilation of the left atrium AND left ventricle
Echocardiography of stage C myxomatous mitral valve disease (MMVD)
As B2 but more severe mitral regurg and left sided dilation
Evidence of elevated pressures within the left atrium
B lines may be seen
Look for evidence of atrial tears and right sided CHF (less common)
Assessment of left atrial size on echo
Right parasternal short axis view of the heart base
Left atrial diameter is normalised to the aorta (LA:Ao)
Cut off is 1.6 or more
Assessment of left ventricular size
Several different measurements including both linear dimensions and volumes
Diagnosis of B2 MMVD a left ventricular internal diameter measured from a short axis M-mode, more than or equal to 1.7 is used as a cut off
What are thoracic radiographs used for in assessment of myxomatous mitral valve disease (MMVD)
Cardiac remodelling
Pulmonary oedema
Concurrent respiratory disease
Point of future comparison
Assessment of cardiac remodelling on thoracic radiograph
Vertebral heart score general breed >=11.5 for general breed
Vertebral left atrial size >= 3
Likely consistent with B2
Cardiac biomarkers
N-terminal pro brain natriutetic (NT-proBNP)
Cardiac troponin I
Limited use as standalone test
N-terminal pro brain natriuretic peptide (NT-proBNP)
Released by ventricular stretch
Increases in volume with increasing severity of volume overload of the left heart
A normal or near normal NT-proBNP in a patient with signs of CHF (coughm dyspnoea etc) is unlikely to have CHF
External lab so not useful for emergency
Cardiac troponin I
Marker for myocardial cell damage
Prognostic value
Elevated in renal disease due to reduced elimination
ECG for myxomatous mitral valve disease (MMVD)
Low sensitivity for detection of cardiac remodelling
Sinus arrhythmia indicates predominance of parasympathetic system making decompensated CHF unlikely
Sinus tachycardia indicates sympathetic elevation - may be stress or decompensated disease
Advanced MMVD may see supraventricular and ventricular arrhythmias
Atrial fibrillation can be seen secondary to severe left atrial dilation
Clinical pathology for myxomatous mitral valve disease (MMVD)
Usually middle aged - older dogs should be screened for co-morbidities if treatment for CHF is anticipated
Systolic blood pressure for myxomatous mitral valve disease (MMVD)
Advisable to rule out concurrent systemic hypertension
Which SNAP antibody test should be used in the work up for a dog with cough, tachypnoea and/or exercise intolerance?
Angiostrongylus vasorum
Treatment of stage A myxomatous mitral valve disease (MMVD)
No treatment indicated
SHould undergo yearly auscultation and may elect for annual cardiac screening
Treatment of stage B1 myxomatous mitral valve disease (MMVD)
No treatment indicated
Repeat echocardiography advised in 6-12mo
Treatment for Stage B2 myxomatous mitral valve disease (MMVD)
Pimobendan
Pimobendan
Phosphodiesterase III inhibitor
Calcium sensitisation
Positive inotrope
Arterial and venous dilator
In dogs: proven benefit in both MMVD and DCM
Contraindications: fixed outflow tract obstruction
Treatment of stage C and D myxomatous mitral valve disease (MMVD) with acute CHF
Oxygen
Furosemide IV (CRI after inital bolus)
Pimobendan PO (hopefully already started)
Sedation/anti-anxiety (butorphanol)
maybe also:
- vasodilators
- further inotropic support
- mechanical ventilation
Treatment of stage C and D myxomatous mitral valve disease (MMVD) with chronic CHF
Pimobendan PO
Diuretics
- Furosemide PO
- Torasemide PO
ACE-i
- Benazepril
Spironolactone
Surgery for myxomatous mitral valve disease (MMVD)
Surgical valve repair performed under cardiac bypass surgery for stage C dogs
- Very expensive and few places do it
Hybrid surgical interventions not requiring bypass becoming more widely used/available
Management of atrial fibrillation with MMVD
Digoxin
Dilitiazem
Prognosis of myxomatous mitral valve disease (MMVD)
Usually a long course of disease with slow progression
Once in CHF, median survival times are typically 9-12mo
Large breed dogs may be more likely to develop myocardial failure and/or arrhythmias and deteriorate more quickly
Infective endocarditis
Uncommon in small animals
Caused by bacterial infection of the endocardial surfaces - most likely on the mitral or aortic valves
Should be suspected in cases of pyrexia of unknown origin
Murmur is not always present
Requirements for development of infective endocarditis
Transient or persistent bacteraemia
Damaged endothelium
Ability of bacteria to adhere and evade host defences
Often a hypercoagulable state
Reported aetiological agents of infective endocarditis
Staphylococcus spp
Streptococcus spp
E. coli
Pseudomonas aeruginosa
Bartonella
Pathology of infective endocarditis
Vegetations on the endocardial surface of the valve leaflets
Vegetations range from small nodules to large coalescing lesions
Made up of platelets, RBC, bacteria, fibrin
Mature lesions may have dense fibrous tissue and calcification
Pathophysiology of infective endocarditis
Bacteraemia leads to activation of a systemic inflammatory response
High risk of thromboembolic events
Stimulation of humoral/cellular immune system results in immune complex deposition and subsequent clotting abnormalities
Diagnosis of infective endocarditis
Blood culture
Clin path
Echocardiography
ECG
Presentation of infective endocarditis
Medium to large breed dogs over-represented
Concurrent pathology creates risk factor
Pyrexia of unknown origin, systemic embolisation, or activation of the immune system
Cardiac clinical signs may be:
- new or changed murmur
- arrhythmias
- CHF
Blood culture for infective endocarditis
Prior to antibiosis
Aseptic technique
Frequently negative
Possible false positives
Clin path for infective endocarditis
Neutrophilia +/- left shift
Thrombocytopaenia (risk DIC
Renal or hepatic abnormalities associated with thromboembolic disease
Echocardiography for infective endocarditis
Presence of valvular vegetations
Regurgitation across affected valve
May result in systolic dysfuntion and CHF
ECG for infective endocarditis
Due to the risk of arrhythmias
Major criteria in the diagnosis of infective endocarditis
Positive echocardiography - vegetative, oscillating lesions
New valvular insufficiency
Positive blood vultire
- at least 2 positive cultures
- at least 3 positive cultures if possible skin contaminant
Minor criteria for the diagnosis of infective endocarditis
Fever (>39.4)
Medium/large breed
Subaortic stenosis
Thromboembolic disease
Immune mediated disease
- polyarthritis
- glolmerulonephritis
Positive blood culture
High Bartonella serology
How many of the criteria must a patient meet for a diagnosis of infective endocarditis to be made?
Definitive: 2 major OR 1 major + 2 minor OR 5 minor
Presumed: 1 major + 1 minor OR 3 minor
Treatment of infective endocarditis
Bactericidal antibiotics
- fluoroquinolone + potentiated amoxicillin + metronidazole
- initially IV
- minimum course 6 weeks
Antithrombotics
Prognosis of infective endocarditis
Guarded
- risk of recurrence
- complications
- irreversible valve damage
