Acquired Valvular Disease Flashcards
describe a normal valve
3 layers
- atrialis: elastic and collagen fibers
- spongiosa: ECM rich in proteoglycans and occasional interstitial cells
- fibrosa: tightly packed collagen fibers
describe a myxomatous valve
- non-inflammatory progressive disarray of the valve structures
-interstitial cells are activated
-excessive disposition of ECM
-fragmentation and disorganizing of elastic and collagen fibers
-damage to endothelial lining
- valves become progressive thicker and irregular but NOT due to an inflammatory condition (usually due to age)
describe myxomatous valve disease in dogs
- most common cause of heart disease in dogs
-more common in small to medium breed dogs
-more common in males than females - disease prevalence and severity increases with age
- high risk breed:
-cavalier king charles spaniel
-others: dachshunds, cocker spanials, beagles, toy mini poodles, etc.
-tiny decrepit - approx 30% of dogs with MMVD will develop congestive heart failure
describe valve involvement of MMVD in dogs
- less than 2% just have tricuspid valve alone
- 30% mitral and tricuspid valve
- 50-60% mitral valve alone!!
so with 80-90%, mitral valve is involved
describe a normal mitral valve
- separates LA and LV, acts as a one way valve
-open during diastole, closed during systole - apparatus consists of:
-annulus
-leaflets: thin, translucent, smooth
-chordae tendineae
-papillary muscles
describe a myxomatous mitral valve
- disarray of valve structure
- thickened, nodular leaflets
- thickened chordae tendinae
- valve prolapse +/- fail
- +/- chordal rupture
describe pathophysiology of MMVD
- myxomatous degeneration of mitral valve
-abnormal valve motion, chordae tendinae changes/rupture - causes mitral regurgitation
- results in volume overload
- results in LA enlargement and LV ECCENTRIC hypertrophy
- leads to mitral annular dilation, causing more mitral regurgitation in a cycle
- body can compensate for some time but will eventually lead to an increase in LA pressure
- which increases pulmonary venous and capillary hydrostatic pressure and eventually to left sided CHF +/- secondary pulmonary hypertension
describe physical exam/murmur of MMVD
- grade/intensity: usually increases with progression of disease
- PMI: cardiac apex
left (mitral valve)
right (if tricuspid valve involved) - timing: systolic: (between S1-S2)
-regurgitation through AV valve when it is supposed to be closed causes a large pressure difference between atrium and ventricle
describe clinical signs of MMVD
- range from none to severe! may be asymptomatic
- 30% present in congestive heart failure
-tachypnea, hyperpnea, dyspnea, orthopnea
-crackles on lung auscultation
-coughing
-weakness, syncope
-arrhythmias
describe MMVD diagnostics
- echocardiogram! most definitive diagnosis
- thoracic radiographs
- electrocardiogram
- other: bloodwork, systolic blood pressure
describe echocardiogram of MMVD
- the ONLY antemortem definitive diagnostic
- will see thickened and irregular mitral valve leaflets
- systolic mitral regurgitation
- with increasing severity:
-left atrial enlargement (LA:Ao ratio)
–normal <1.3-1.5
-left ventricular dilation:
–left ventricular internal dimension in diastole, normalized/adjusted to body weight (LVIDdN), normally <1.6
–looks like a mushroom normally, if not looking like a perfect mario kart mushroom may be a bit dilated
describe thoracic rads of MMVD
- evaluate cardiac silhouette size via vertebral heart score
- monitor for progressive disease
- determine if clinical signs due to cardiac or respiratory pathology
- MMVD pattern on lateral views:
-left ventricular enlargement: increased CS height, dorsal deviation of trachea (follows spine instead of sternum)
-left atrial enlargement: backpack bulge, straightening/loss of caudal cardiac waist, dorsal deviation/narrowing of left mainstem (top) bronchus)
- on VD/DV views:
-left ventricular enlargement: tall/long heart, rounded apex
-left atrial enlargement: left atrial body has increased/double opacity at caudal heart base, tracheal bow legged cowboy sign, bulge at 2-3 o clock if left auricle also enlarged
- MMVD with CHF
-cardiomegaly characterized by LEFT atrial and ventricular enlargement
-interstitial to alveolar pattern: typically caudodorsal/perihilar
-pulmonary venous distension
describe electrocardiography with MMVD
- varies from normal to arrhythmias
- secondary to atrial stretch:
-atrial premature complexes
-atrial tachycardia
-atrial fibrillation - LA enlargement pattern: p mitrale (looks like an M)
- LV enlargement pattern: tall R waves
- sinus tachycardia
describe other diagnostics for MMVD
- blood pressure:
-higher BP can increase afterload on heart, worsening mitral regurg
-MMVD does NOT cause an increase in BP - NTproBNP
-cardiac biomarker
-serial monitoring can demonstrate increases associated with progressive disease - clinical lab tests:
-CBC/chem/UA: recommended prior to initiating therapy - 24hr Holter monitor or event monitor:
-evaluate arrhythmias occurring outside the hospital
describe ACVIM classification for MMVD
- stage A:
-dogs breeds at high risk of developing MMVD, but no disease yet - stage B1: mild, B2: moderate
-MMVD present but not CHF yet
-B!: thickened leaflets and evidence of regurg but no signs of enlargement yet, so will just monitor with echos
-B2: have developed secondary changes to heart from chronic volume overload from MMVD and associated mitral regurg (LA and LV enlargement)
–in this stage we initiate pimobendan to delay onset of CHF by approx 1 year
–pimobendan = inodilator: positive inotrope that enhances systolic function and balanced vasodilator that reduces preload and afterload
-if no echo, can use VHS and murmur grade to tell progression
- stage C: have had or currently have CHF
-treat with standard therapy (furosemide, pimobendan, RAAS inhibition) - stage D: refractory to normal therapy
