Imaging considerations in tetralogy of Fallot: A comprehensive review

Table 1 Parameters assessed on pre-operative transthoracic echocardiography

Parameter
Assessment of normal atrio-ventricular and ventriculo-arterial relations
Spatial relations of the great arteries
Adequacy of the size of the VSD and the routability of the left ventricle to the aorta. Additional VSDs can also be evaluated
Function of the aortic valve
Level of obstruction in RVOT
Size of the pulmonary annulus, main pulmonary artery, and branch PAs
Coronary origin and presence of any anomalous branch crossing the RVOT
In the presence of pulmonary atresia, the adequacy of native PA size and blood supply to them (via patent ductus arteriosus / aortopulmonary collaterals)
Systolic and diastolic function of the ventricles
Aortic arch abnormalities

VSD: Ventricular septal defect; RVOT: Right ventricular outflow tract; PA: Pulmonary artery.

Table 2 Key reporting elements in magnetic resonance imaging of post-operative tetralogy of Fallot

Parameter
RVOT	Residual obstruction or dyskinesia/aneurysm
	Location, extent, and size
Functional assessment of RV and RVOT	Quantification of pulmonary regurgitation fraction
	Right ventricle volume and function assessment
	Screening for tricuspid regurgitation
Pulmonary artery stenosis	Site
	Extent
	Degree
	Post-stenotic dilatation: Present/absent
Residual VSD	Location and size
	Quantification of shunt (Qp/Qs)
Aortic root assessment	Aortic root dilatation
	Quantification of aortic regurgitation
	Left ventricle volume and functional assessment

RVOT: Right ventricular outflow tract; RV: Right ventricle; VSD: Ventricular septal defect.

Table 3 Key computed tomography angiography reporting elements in pre-operative tetralogy of Fallot

Parameter
Situs	Solitus/ambiguous
Cardiac position	Levocardia/mesocardiac/dextrocardia
VSD	Size
	Site	Perimembranous/muscular
	Aortic override	50% or > 50%
ASD	Present/absent
Status of the main pulmonary artery	Atresia/stenosis
	Site of stenosis	Infundibular/valvular/supravalvular
	Pulmonary valve	Present/absent
Status of branch pulmonary arteries	Confluent/isolated
	Size	Good-sized/small-sized (Mcgoon ratio and Nakata index1)
Collateral vessels	PDA	Size and opacification
		Presence of proximal/distal end stenosis
	Aortopulmonary collaterals	Origin (DTA/aortic arch branches, etc.)
		Calibre (major/small); o’clock position, course and supply
Aortic arch	Side	Right/Left
	Branching pattern	Left: Normal; bovine; aberrant right subclavian artery; truncus bicaroticus; direct origin of the vertebral artery
		Right: Mirror image; independent origin of the vertebral artery; aberrant left subclavian artery
Coronary artery	Origin	Separate sinuses/common sinus/LAD originating from RCA
	Course	Course anterior to RVOT; inter-arterial course; hypertrophied conus branch of RCA coursing anterior to the infundibulum

¹McGoon ratio is calculated by dividing the sum of diameters of right and left pulmonary arteries by the diameter of the descending aorta at the level of the diaphragm. The Nakata index is obtained from the sum of areas of right and left pulmonary arteries, divided by the body surface area.

VSD: Ventricular septal defect; ASD: Atrial septal defect; PDA: Patent ductus arteriosus; DTA: Descending thoracic aorta; RCA: Right coronary artery; LAD: Left anterior descending artery; RVOT: Right ventricular outflow tract.

Table 4 Imaging modalities and their use in different stages of care in patients with tetralogy of Fallot

Stage of care	Imaging modality	Information provided	Advantages
At initial diagnosis	TTE	Defines the position of the VSD, degree of aortic override, and location and severity of the RVOT obstruction	Widely available, safe (no radiation), and assesses the basic defects
	CMR	Assessment of pulmonary arteries- size/confluence; MAPCAs	High-resolution, objective data on ventricular volumes, function, and pulmonary artery anatomy without using ionizing radiation
	CT angiography - as an alternative to CMR, however choice depends upon centre to centre; should preferably be an ECG-gated acquisition	Detailed assessment of pulmonary artery anatomy and branches; MAPCAs; coronary arteries anatomy; additional defects: ASD; PAPVC, muscular VSD	High spatial and temporal resolution, compared with CMR, less time is required for data acquisition
Post-surgical shunts	CT angiography	Shunt patency, stenosis	High accuracy
Post-intra-cardiac repair	CMR	Quantification of PR; RV volume and function; complications: RVOT aneurysms and myocardial fibrosis	Highly accurate and gold standard for volumetry
	Catheter angiography	Assessment of residual stenosis in pulmonary arteries and management (balloon dilation or stenting); management of residual VSDs; percutaneous PVR procedures	Diagnosis and therapeutic interventions

TTE: Transthoracic echocardiography; VSD: Ventricular septal defect; RVOT: Right ventricular outflow tract; CMR: Cardiac magnetic resonance; MAPCAs: Major aortopulmonary collateral arteries; CT: Computed tomography; ECG: Electrocardiogram; ASD: Atrial septal defect; PAPVC: Partial anomalous pulmonary venous connection; PR: Pulmonary regurgitation; RV: Right ventricular; PVR: Pulmonary valve replacement.