AS Flashcards
Supravalvular stenosis embryology
- ↑ development of Ao wall above sinus of Valsalva
o ↓/abn expression of elastin genes: ↓ elasticity, ↑media thickness, collagen deposition
Supravalvular stenosis lesions
- Discrete obstruction just distal to sinus of Valsalva
- CA are proximal to obstruction: ↑ pressure in systole
o Stenosis: ↓ flow
Supravalvular stenosis breeds
- Rare in dogs, least common form
- Described in cats
valvular stenosis lesions
Uncommon
Lesions
* Valvular malformations can include
o Bicuspid AoV: partial/complete fusion of 2 cusp
Most common in Hu
o Unicuspid valve
o Dysplatic AoV leaflets
* Stenosis is due to incomplete opening, doming of the valve → ↓ effective valve area
* Annular hypoplasia also possible, seen most often with concurrent congenital defects
Embryology SAS
- SAS 2nd to abn development of one LVOT component
LVOT formed by
o Conotruncal septum
o IVS
o MV septal leaflet
Etiology SAS
o Primary developmental fault of region btw conus and truncus
o Persistent embryonal tissue: retain proliferative capacity + chondrogenic potential after birth
o Abn flow pattern: shear stress in LVOT
Endothelial damage
Cell proliferation
Collagen deposition
Forms of SAS
o Fribrous membrane proximal to AoV: usually very thin and just below AoV
o Fibromuscular ridge: slightly lower, thicker
o Tunnel type obstructive lesion: muscular hypertrophy/narrowing of LVOT
Gross exam SAS: grades described in Newfoundland
o 1: Mildest form
Small, whitish slightly raised nodules on endocardial surface of IVS, below AoV
Thickened endocardium
Only identified from 3-12weeks
o 2: narrow ridge of whitish, thickened endocardium
Extending partially around LVOT from base of MV septal leaflet → IVS
o 3: Most severe form
Fibrous band, ridge or collar encircling LVOT below AoV
Raised above endocardium
Extend to/involve cranioventral leaflet of MV + base of AoV
Usually >6mo
Gross exam SAS associated lesions
o Concentric LVH: severity reflect PG
o LAE: from ↓LV compliance, myocardial failure, MR
o Dilation of ascending Ao and Ao arch: turbulent flow
o Abnormalities of MV can also be present: minor to severe MVD, attachments to septal leaflets
o Thickened AoV: from turbulent flow
Can result in AI
o Focal areas of myocardial fibrosis/infarction
o Intramural coronary arterial changes
Histology lesions
- Stenotic ring:
o Large, uni/multinucleated rounded connective → resemble chondrocytes
o Loosely arranged reticular fibers
o Mucopolysaccharide ground substance
o Elastic fibers - Advanced lesions: bundles of collagen + cartilage
- Intramural coronary artery pathology and remodeling (PG >35mmHg)
o Luminal narrowing
o Intimal proliferation of connective tissue/SM cell
o Medial degeneration and hypertrophy, SM cell disorganization
Cause of CA pathology
not known
↑LV systolic P
↑ systolic wall tension
Abnormal coronary blood flow
* ↓ baseline diastolic flow
* Reversal of coronary flow in systole
* Minimal coronary flow reserve
Pathophys SAS
LVOT obstruction: same for all level of obstruction → ↑ LV afterload
* ↑PG across stenotic region → ↑LV systolic P → ↑ wall stress → LVCH
o Wall stress is proportional to LVP and inversely proportional to wall thickness
o LVH: compensatory response to ↑ thickness → ↓ wall stress
Preserve SV and CO
* Persistent/chronic P overload → ventricular remodeling
o Hypertrophy → fibrosis → death
o LVH: ↑ ventricular stiffness → ↓ diastolic fct → ↓ ventricular relaxation → ↓diastolic filling
Proportional to degree of LVH
o Subendocardial ischemia:
2nd to ↑intracardiac compressive forces in systole and ↑ O2 consumption
Minimal coronary flow reserve: can’t keep up w/ exercise and ↑ HR (short diastole)
↓ coronary perfusion
Hu: ↑ prevalence of CA ostium obstruction may contribute
Wall stress equation
Wall stress = P x r/2th
Signalment: breeds SAS
o Most common in larger breeds: boxer, newfoundland, German shepherd, Golden retrievers, Bull Terrier, Rottweiler
Overrepresented: Samoyed, Great Dane
Rare in cats
Particularity of lesion development SAS
o Not present at birth → develop in 1st 3-8 weeks of life
Gradient can ↑ in rapidly growing giant breed dogs
Mechanism for ↑ severity: uncertain
* Fibrocartilagenous ring of SAS derived from embryonal endocardial tissue w proliferative capacity and chondrogenic potential after birth
* ↑ body size and LVH may contribute to progression
Genetic SAS
Inherited in Newfie: polygenic, autosomal dominant w/ gene modification
Heritable in other breeds
C/s SAS
asymptomatic or
o Exertional syncope: exercise induced ↑ LVP → activation of ventricular mechanoR → bradycardia + vasodilation
o Sudden death (arrhythmias)
o L CHF: myocardial failure, ↑ ventricular stiffness, MR, Afib
Rare since LVH keep normal SV
Usually 2nd to complicating factor: myocardial infarct, MR, AI
PE SAS
o Hypokinetic, late rising arterial pulse → obstruction to ejection
Pulsus parvus et tardus
Normal pulse pressure
o Murmur
Systolic ejection L basilar murmur → high velocity and turbulent flow across lesion
* Can radiate in carotid artery
To and fro murmur: if concurrent AI present
Paradoxical split S2: delayed AoV closure from ↑ET
S3-S4 gallop
ECG SAS
- Often normal
- LVH and myocardial ischemia responsible for changes in QRS and ST segment
o ↑ R wave amplitude
o L axis deviation - VPCs in dogs with severe PG
- ST segment deviation: slurred, depressed, elevated
o ST segment depression: LVH or myocardial ischemia
o Exercise induced ST segment deviation + VPCs → suspect ischemia/abnormal coronary blood flow
CTX SAS
- Post stenotic dilation of Ao (ascending, arch + brachiocephalic trunk)
o Widening of mediastinum on VD
o Lost of cranial waist on lateral - Cardiomegaly: LVH + LAE
Echo 2D SAS
o LVH: moderate to severe PG
o Subvalvular fibrous ring:
Narrowing btw IVS and base of anterior MV leaflet
* Can involve MV
Proximal to AoV on LAX views
Discrete membranous/fibromuscular ridge
o Post stenotic dilation of Ao
Secondary thickening of AoV cusps
Mid systolic partial closure of AoV
o LA hypertrophy/enlargement: ↑LAP to fill stiff, hypertrophied LV
o Bright, hyperechoic regions in LV → severe focal replacement fibrosis
LV papillary muscles and endocardium
Echo M-Mode SAS
o Mid systolic partial AoV closure
o Diastolic MV valve fluttering (AI)
o ↓ mitral E-F slope
Doppler echo SAS
o Pressure gradient present across LVOT
Mild: 2.2 – 2.5m/s is equivocal
Fixed obstruction pattern
o E/A reversal if diastolic dysfct
o MR
Concurrent MVD
Involvement of anterior MV leaflet in subaortic ridge
Geometric changes in LV
SAM may be present → dynamic LVOTO
* Some dogs will have isolated DLVOTO → Golden retreivers
o Diastolic dysfunction: reversal of E and A waves
From LVH or myocardial ischemia
AI
Causes of AI w/ SAS
o Involvement of valve leaflets w fibrous ring → thickening of leaflets
o Jet lesions leading to thickening of leaflets
o Dilation of ascending Ao
o Bacterial endocarditis
Cardiac KT SAS pressure study
o Localization of obstruction by withdrawing KT from LV → LVOT → AoV → Ao
o Systolic PG across obstruction
↓ by anesthesia by 40-50%
Dynamic obstruction: PG will diverge later in systole
Fixed obstruction: PG will diverge early
o ↑ LV end diastolic P
Cardiac KT angio SAS
o LV ventriculogram:
Small LV cavity + LVCH
Subvalvular obstruction
MR
Post stenotic dilation
o Supravalvular Ao injection: r/o or assess AI
Prominent LCA and major extramural branches
* ↑ myocardial O2 demand
Natural hx: when do CHF develop
- CHF most likely if
o AI
o Concurrent MV abnormalities
Natural hx: risks
- Sudden death
o ↑ risk with severe SAS in first 3y of life (70%) - ↑ risk for bacterial endocarditis
Natural hx mild SAS
o Mild LVH, mild PG (<75mmHg)
o Not use for breeding
Natural hx SAS: who develops c/s
30% of severe cases
Treatment to reduce c/s
- Restrict exercise if moderate to severe gradient
Embryology Ao Coarct: 2 theories
- Hypothesized to occur from ectopic ductal tissue or abnormal ductal flow
- Abn development of 4th and 6th Ao arch
o Ductal tissue theory: migration of SM from ductus into Ao → constriction
o Hemodynamic theory: ↓LV outflow leads to coarctation
Gross exam Ao Coarct
- Narrowing of the aorta
o Distal to subclavian artery, adjacent to ductus arteriosus
Jct of the arch and descending Ao
o Discrete narrowing of Ao in area of DA insertion → juxtaductal
Vs tubular hypoplasia
o Ridge like thickening of the media of Ao wall
Protrude into lumen from posterior and lateral wall - Ascending/descending Ao can be abn
- Collaterals may develop: ↑ perfusion of caudal body
Histo Ao Coarct
- Disorganized intimal medial hyperplasia
o Thick intimal and medial ridge protrude in Ao lumen - Posterior infolding extending around circumference of Ao
- Dissection/aneurysm of distal portion can occur
Pathophys Ao Coarct
- Form of aortic stenosis: ↑LV systolic P → LVH
o When lumen ↓ >45-55% of CSA - Depend on stenosis severity
o Associated lesions: PDA, VSD, AS, MS
o Rapid development: sudden DA constriction after birth
CHF: no time for LVH to develop - PDA can remain patent and provide blood flow to caudal body
Signalment Ao Coarct
o Rare in dogs, not reported in cats
PE Ao Coarct
o Inequality of pulse pressure = HALLMARK of dz
Proximal Ao: ↑systolic > diastolic pressure → ↑ pulse pressure in forelimbs
Distal to obstruction: ↓systolic < diastolic pressure → ↓ pulse pressure in hindlimbs
o Weak/absent femoral pulses
o Pelvic limb weakness
Differential perfusion
* Poor perfusion of caudal limbs
* Hypertension of cranial limbs
o Murmur loudest in systole, can last into mid diastole
From defect itself
Systolic ejection HM
Continuous if well developed collaterals
o Gallop sound
ECG Ao Coarct
- LVH: ↑ R wave amplitude
CTX Ao Coarct
- Indentations/notching of ribs (Hu): enlarged intercostal arteries
o Caused by the erosion of the inferior surfaces of the posterior ribs by dilated and tortuous intercostal collateral vessels
o Internal mammary and spinal arteries also enlarge to provide collateral flow - Indentation of the Ao at the site of coarctation (“3 sign”)
- Post stenotic dilation of the descending aorta may be seen
Echo Ao Coarct
- LVH
o ↑ systolic pressure - In Hu: detailed 2D and Doppler studies of Ao
o Narrowing visualized
o PG across defect
Cardiac KT pressure study Ao Coarct
o ↑ systolic pressure in ascending Ao
o ↓ systolic pressure distal to obstruction
Cardiac KT angio Ao coarct
confirm diagnosis
Natural hx Ao Coarct
- Px variable depending on
o Degree of Ao narrowing
Treatment Ao Coarct
- Treatments include surgical repair (anastomosis of Ao segments), balloon angioplasty, endovascular stents
o Maintain DA patency until repair: PGE
Tubular hypoplasia or interruption of the aorta
- Ascending and descending Ao do not communicate
o Rare in dogs
o Most die 1st day/weeks of life
o 2 reports: life maintained by PDA and marked collateral flow
Tubular hypoplasia or interruption of the aorta Hu classification
o Type A: distal to L subclavian artery
o Type B: btw L subclavian and carotid arteries
o Type C: btw L and R carotid arteries
Gross exam dextrocardia
- Heart is positioned in R hemithorax
o Apex pointing toward the R
o R/L asymmetry remains present - Situs inversus → all organs are mirror image of normal
o Usually no other cardiac abnormalities - Situs solitus → associated with major intracardiac abnormalities in Hu
o AV discordance
o TGA - Atrial situs: can be solitus, inversus or ambiguous
Etiology dextrocardia
o Primary congenital abnormality
Congenital developmental malposition
o Secondary to fluid, tissue, air pushing the heart to the R = cardiac DEXTROPOSITION
Associated lesions/dz dextrocardia
- Respiratory abnormalities: if situs inversus
o Bronchitis, sinusitis, bronchiectasis
ECG dextrocardia
- Inverted voltage of atrial and ventricular depolarization (negative P and QRS)
- P wave axis: to the R and inferiorly
CTX dextrocardia
- Apex of the heart is directed to the R
