TOF

Question 1

What are conotruncal defects

Answer 1

malformations of ventricular outflow region
o VSD
o Tetralogy of Fallot
o Persistent truncus arteriosus

Question 2

Etiology

Answer 2

lesion specific genetic factors
o ↑ frequency in certain breeds

Question 3

What did keeshond family studies showed

Answer 3

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

Question 4

Patterson et al. grade 1 lesions

Answer 4

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

Question 5

Patterson et al. grade 2 lesions

Answer 5

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

Question 6

Patterson et al. grade 3 lesions mild form

Answer 6

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

Question 7

Patterson et al. grade 3 lesions moderate form

Answer 7

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

Question 8

Patterson et al. grade 3 lesions severe form

Answer 8

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

Question 9

How might pulmonary atresia or truncus arteriosus communis fit into this scheme?

Answer 9

PA atresia: extreme form of TOF

Truncus arteriosus: in the spectrum of conotruncal abn = complete absence of PA

Question 10

Features of VSD and type

Answer 10

• 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

Question 11

Features of overriding Ao

Answer 11

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

Question 12

Overriding Ao vs DORV

Answer 12

absence of AoV-MV continuity + bilateral conus = DIFFERENT DZ
 >50% Ao override

Question 13

What additional abnormalities are found in the RVOT of dogs with tetralogy of Fallot?

Answer 13

 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

Question 14

Possible causes of RVOTO

Answer 14

pulmonic stenosis, pulmonary atresia, absent pulmonary valve

Question 15

What determines severity of RVOTO

Answer 15

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

Question 16

Contrast the RV outflow tract in tetralogy of Fallot from that of the Eisenmenger VSD.

Answer 16

• 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

Question 17

Conotruncal anomalies: conotruncus

Answer 17

= 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

Question 18

Conotruncal anomalies def

Answer 18

• Abnormality in development of neural crest-derived tissue

= malformation of
o Infundibulum = conus arteriosus
o Great arteries = truncus arteriosus
o Abnormal ventriculo arterial alignment

Question 19

Spectrum of conotruncal abn

Answer 19

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