TOF Flashcards
What are conotruncal defects
malformations of ventricular outflow region
o VSD
o Tetralogy of Fallot
o Persistent truncus arteriosus
Etiology
lesion specific genetic factors
o ↑ frequency in certain breeds
What did keeshond family studies showed
o Close relatives frequently have type I (subarterial) VSD → associated w failure of fusion of conal cushions
Attributed to varying degrees of maldevelopment of conotruncal septum
o Small group of Keeshond w TOF and VSDs was studied to determine spectrum of lesions
Confirmed that lesions were associated with hypoplasia of conotruncal cushions → abnormal septation of conal and truncal outflow portions
Patterson et al. grade 1 lesions
subclinical anomalies of crista supraventricularis
80 dogs → 22.7%
* Mild hypoplasia of conus cushions
o Delayed fusion of conotruncal septum at proximal border (upstream)
* Persistence of conus septal fusion line
o Fibrous raphe found at location of conus septal fusion
o Commissure btw R and L Ao cusp → PV
* Absence of papillary muscle of conus
o Always present in normal dogs
o Derived from sinistro-ventral conus swelling
* Aneurysm of IVS
o From RVOT, at proximal portion of crista supraventricularis, at location of pap of conus
o From LVOT, depression below R coronary cusp of AoV
*SUBCLINICAL = NO INTRACARDIAC SHUNTING PRESENT
Patterson et al. grade 2 lesions
similar + VSD or PS
62 dogs → 17.6%
* Lesions of grade 1 defect always present +
* Moderate to severe hypoplasia of conus cushions
o Failure of fusion at proximal border
* VSD: located at same site as anerusyms
o Endocardial tissue surrounding defect
Newborn: Grey/translucent appearance, soft friable consistency
Older: opaque, white and though
o Large defects: crista supraventricularis displaced anteriorly
Ao override IVS
* PS: thickening, fusion or hypoplasia of PV cusps
o Fusion/hypoplasia involved R and L posterior cusps
o Sometimes 3 dysplastic cusps
o No VSD but anomalous crista supraventricularis
o No subvalvular PS present
Patterson et al. grade 3 lesions mild form
similar + pulmonary stenosis/atresia + VSD
47 dogs → 13.4%
* Lesions of grade 1 defect always present
* Severe dysplasia of truncus cushions
* Mild form: small VSD w little/no overriding Ao + mild PS
o PS: similar to grade 2 lesions
o Surviving animals: small L to R shunt
Patterson et al. grade 3 lesions moderate form
large VSD + overriding Ao + anterior displacement/hypoplasia of crista supraventricularis
o PS: valvular + subvalvular
Often bicuspid PV → fusion/hypoplasia of R or L cusps
Hypoplastic PA
o Dilated/tortuous ascending Ao arch
o Similar to TOF
o C/s: cyanotic, exercise intolerance
Patterson et al. grade 3 lesions severe form
large VSD + dextroposition of Ao + PV atresia and extreme PA hypoplasia
o Blood reached pulmonary circulation from enlarged bronchial arteries
o No ductus in some cases
How might pulmonary atresia or truncus arteriosus communis fit into this scheme?
PA atresia: extreme form of TOF
Truncus arteriosus: in the spectrum of conotruncal abn = complete absence of PA
Features of VSD and type
- Large, malaligned VSD
o Roofed by AoV → subarterial
o From anteriocranial deviation of outlet septum
o Most commonly:
Fibrous continuity of TV → AoV = perimembranous
Large and non restrictive - If restrictive: from accessory/redundant TV tissue
Features of overriding Ao
over the septal defect
o Normal heart: R Ao sinus normally overlaps IVS
o TOF: accentuated w/ malaligned VSD
Dilation of Ao from conal malseptation + rotational changes
Overriding Ao vs DORV
absence of AoV-MV continuity + bilateral conus = DIFFERENT DZ
>50% Ao override
What additional abnormalities are found in the RVOT of dogs with tetralogy of Fallot?
Anterior and cranial deviation of the outlet (infundibular) septum → muscular, subvalvular narrowing
* Deviation leads to large perimembranous VSD
* Obstruction exacerbated by hypertrophy of muscular outlet septum, RVH, hypertrophy of components of septomarginal trabeculations
o Septomarginal trabeculations/moderate band obstruction = double chambered RV
Additional areas of obstruction within RVOT and PA common
* Few have small, hypoplastic PA
* Normal PAP
PV: small, stenotic
* Supravalvular ridge at level of attachments of pulmonary leaflets common
Possible causes of RVOTO
pulmonic stenosis, pulmonary atresia, absent pulmonary valve
What determines severity of RVOTO
o Anterior and cranial deviation of outlet septum + degree/nature of this deviation
Different types of obstruction changes physiology significantly
Different levels of PS changes clinical symptoms significantly
Contrast the RV outflow tract in tetralogy of Fallot from that of the Eisenmenger VSD.
- R to L shunting VSD secondary to pulmonary vascular disease
o Reversal of L to R shunting when PVR > SVR
o Large defects → pulmonary overcirculation + transmission of systemic pressures into pulmonary circulation → pulmonary vascular disease → PH - Mild anterior malalignment type VSD (same direction of TOF)
o Ao override
o No significant RVOTO (which is a hallmark of TOF)
Atretic, hypoplastic, or stenotic right ventricular outflow tract → incompatible with the dx of Eisenmenger’s physiology. - RVH will be present 2nd to the PH
- Dilated MPA and lobar arteries
Conotruncal anomalies: conotruncus
= 2 myocardial subsegments
o Conus: myocardial segment btw ventricles and semilunar valves
Gives rise to subarterial coni
Inferior to AoV and PV
o Truncus: fibrous segment btw semilunar valves and Ao sac
Gives rise to great arteries
Conotruncal anomalies def
- Abnormality in development of neural crest-derived tissue
= malformation of
o Infundibulum = conus arteriosus
o Great arteries = truncus arteriosus
o Abnormal ventriculo arterial alignment
Spectrum of conotruncal abn
o Mild: transposition of GA
Lack of subpulmonary conus
Pulmonary mitral fibrous continuity
o Moderate: double outlet RV, subaortic VSD
Both GA arise from RV
No fibrous continuity with AV valves
o Severe: Tetralogy of Fallot
PS + RVH
Overriding Ao
VSD
Mitral-aortic fibrous continuity
Conotruncal system malformation
o Precursor of ventricular OT: distal bulbus cordis + truncus arteriosus → form conotruncus
o Endocardial truncal and bulbar cushions fusion will form spiral septum
Malrotation of truncal-bulbar ridge → misalignment of outlet/trabecular septum
Subpulmonic obstruction → from anterior septation of conotruncus
o Responsible for partition of fetal truncus arteriosus into PA and Ao
Posterior alignment of LVOT with establishment of MV-AoV continuity
RVOT retain muscular properties → subpulmonic infundibulum = conus
Malformation w/ TOF
- Underdevelopment of subpulmonary infundibulum
o PS → RVH
o Overriding Ao - Malalignment of lower conotruncal septum
o Overriding Ao
o VSD
o Spectrum: patent RVOT → PA atresia
VSD features
- Malalignment VSD (ventral and dorsal components)
o Subaortic VSD: roofed by AoV, in Y of septal band
Fibrous continuity btw AoV and TV
= perimembranous defect
o Usually large defect, non-restrictive
If restrictive: secondary to accessory or redundant TV tissue attaching to septal crest or prolapsing into defect
Ao features
- Dextroposition/overriding Ao
o R Ao sinus override normal position of IVS in normal heart → VSD = impression of straddling Ao
Accentuated by malalignment + rotation of R Ao sinus toward L and anterior
If >50%: considered DORV
o Ao dilation from conotruncus malseptation
RVOTO features
PS, PV atresia, PA atresia
o Subpulmonic stenosis from anterior and cranial deviation of outlet/conal septum
Muscular/subvalvular narrowing
Obstruction can be exacerbated by RVH and hypertrophied IVS
o Degree/nature of deviation determines severity of obstruction
Type of obstruction affect physiology
Severity of obstruction affect c/s
o Pulmonary valvular anatomy
Small, stenotic
Supravalvular ridge at level of attachment of leaflets is common
Diffuse of focal PA hypoplasia can be present
* RVH
CA anomalies
- Coronary artery anomalies reported in Hu
o LAD origin from RCA w anterior course across RVOT
o Single coronary
o Small CA to PA fistula
Ao arch anomaly
o R sided in 25% of TOF
o Aberrant origin of subclavian artery from descending Ao or PA
Other anomaly reported
- Aortopulmonary collateral arteries: bronchial artery collaterals reported in TOF
Grades of conotruncal defects
o Grade 1: subclinical malformations
Persistence of conus septum fusion line
Aneurysm of IVS
Absence of papillary muscle of the conus
o Grade 2: grade 1 lesions +
PS
Infundibular VSD
o Grade 3: grade 2 lesions + dextropositioned Ao
Pentalogy of Fallot
PDA
Pathophys
- ↑ RVP from RVOTO (PS) → R to L shunting through VSD → mix to blood in LV
o ↓ pulmonary blood flow → small L side
o - ↓LV venous return → ↓SV → hypoxia
o ↓O2 saturation → 2nd polycythemia
What happens w/ exercise
↓SVR → ↑shunting
Signalment
Keeshond, English Bulldog
PE
o Cyanosis: symmetric
Hypercyanotic episodes: severe/prolonged ↓ in arterial saturation
* Dynamic change in RVOTO
o Pulmonary crackles
o Systolic murmur: from PS (ejection, basilar) or VSD
o Diastolic murmur can be present if AI
BW
polycythemia
o >70% → ↑ blood viscosity → ↑ resistance to flow → ↓CO
ECG
- R axis deviation from RVH
- RBBB
CTX
- ↓ reduced pulmonary circulation
Echo
- Large VSD with associated overriding great vessels
o If Overriding Ao >50%: suggest DORV
Investigate from presence of both conus - PS changes + RVH
Cardiac KT oximetry
step down in LV
Cardiac KT pressure study
o RVP = LVP, usually normal end diastolic P
o PG across RVOT
o Normal PAP
Cardiac KT angio
o Selective RV: infundibular and PA imaging
Degree of subpulmonic obstruction
Deviation of outlet septum
o Selective LV:
VSD
Degree of Ao override
Natural history
- Sudden death is common: hypoxia, hyperviscosity, arrhythmia
- CHF uncommon
Treatments
o BV of PS: should not be done if VSD cannot be closed
Can reverse to L to R shunting and provoke L sided myocardial failure
o Surgical palliation: creating systemic to pulmonary shunt
↑ pulmonary venous return to L heart → ↓ hypoO2
Waterson: ascending Ao → RPA
Potts: descending Ao → LPA
Blalock Taussig: L subclavian artery → PA
Modified Blalock Taussig: subclavian artery/Ao → PA
o Adjunctive therapy, control PCV
Options palliative
Phlebotomy if PCV >65%
Hydroxyurea: myelosuppressive agent
* Reversible bone marrow suppression
B blocker: ↓ hypoxemic episodes
* ↓ RVOT contractility → ↓ shunting and dynamic component
* ↑SVR
Phenylephrine: α2 agonist
* Vasoconstriction → ↑SVR → ↓shunt
Avoid exercise
O2 does not help since blood shunting
Sx options
↑ pulmonary venous return to L heart → ↓ hypoO2
Waterson: ascending Ao → RPA
Potts: descending Ao → LPA
Blalock Taussig: L subclavian artery → PA
Modified Blalock Taussig: subclavian artery/Ao → PA
