Tissue Doppler parameters of the tricuspid annulus and the RV free wall show reasonable correlation with CMR data in TOF [ 17 ], while myocardial deformation indices such as strain and strain rate are abnormal in repaired TOF for both the RV and the LV as a result of ventricular-ventricular interaction [ 18 ]. Diastolic RV dysfunction can be assessed using a combination of transtricuspid Doppler tracing, late diastolic antegrade flow in the pulmonary artery, right atrial dilatation, hepatic venous flow reversal, and inferior vena cava respiratory changes, but values for TOF have not been ascertained [ 2 ].
Echocardiography evaluation in TOF has shown abnormalities in right atrial size and emptying [ 19 ], as well as LV size and function [ 20 ]. It can also assess the presence of residual shunts and aortic dilation, a common long term complication of repaired TOF. Further information on most previously described echocardiographic parameters is needed in TOF before they can be used in clinical practice for patient follow up and prognosis.
Transesophageal echocardiography TEE in the hands of a skilled operator in CHD plays an important role in preoperative evaluation of the tricuspid valve and septal defects, in intraoperative assessment of the repair and postoperative imaging of vegetations, RV to pulmonary artery conduits, implanted pulmonary valves, and functional assessment of ventricles and valves, especially in the case of poor acoustic windows in transthoracic studies. Stress echocardiography, either with exercise or dobutamine, may provide useful information on biventricular function in TOF, especially in a population with increasing age that may develop coronary artery disease [ 21 ].
Newer techniques have shortened acquisition times so that bright-blood imaging can be performed during a short breath hold.
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High-resolution cardiac-gated MR angiography of the heart and great vessels can now be obtained using free-breathing techniques, such as blood-pool contrast enhancement with or without gadolinium contrast, using a high native-contrast steady-state free precession sequences and allowing for multiplanar reformats and 3-D imaging of the heart and coronaries.
Late gadolinium enhancement LGE technique in repaired TOF assesses myocardial perfusion, ischemia and scar tissue that may be associated with impaired mechanics and adverse outcome [ 24 ]. Unlike echocardiography that is mostly used qualitatively, CMR provides objective, accurate and reproducible quantitative measurements of RV size and function, valve regurgitation, pulmonary and systemic flows, differential pulmonary artery flow and myocardial scar tissue detection [ 2 ], all parameters being extremely important in long-term sequential follow up of TOF. Absolute or relative contraindications include allergy to gadolinium, presence on non-CMR compatible pacemakers and defibrillators, renal insufficiency, claustrophobia, and need for sedation in younger patients.
CMR may not be ideal in depiction of small septal defects, calcifications or metallic artifacts common in postoperative TOF, especially in conduits and intravascular stents. It also has elevated cost and requires significant medical and technological personnel expertise both for image acquisition and postprocessing. CMR is less frequently used in preoperative TOF in young patients, where echocardiography offers good imaging and is usually sufficient for surgical planning.
Preoperatively, CMR is reserved for complex anatomy, such as pulmonary atresia for better delineation of the frequently hypoplastic pulmonary branches and the aortopulmonary collaterals. Postoperatively, CMR is rarely needed in preadolescent patients unless ventricular dysfunction or right heart failure necessitates further workup and possible intervention. The role of CMR becomes crucial in older postoperative TOF patients, where serial evaluations guide management and planning of surgical or interventional pulmonary valve replacement according to well validated, heavily relying on CMR criteria.
Measurement of ventricular volumes and of mass is then performed with special attention to complete chamber coverage, especially in the basal sections as well as correct determination of end-diastole and end-systole for each ventricle given the usual RV conduction delay [ 25 ].
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Imaging for volume measurements should be performed in multiple views, including RV and LV two-chamber and four-chamber views and RV and LV outflow tract long-axis and short-axis views. Using the measured end-diastolic and end-systolic ventricular volumes, stroke volumes and ejection fractions are derived for each ventricle, while ventricular mass is calculated by subtracting endocardial from epicardial volume for the RV and the LV respectively, knowing that systolic measurements show more reproducibility [ 26 ].
CMR parameters of RV size, function and hypertrophy have been identified as predictors of death and ventricular tachycardia in repaired TOF [ 27 ].
Magnetic resonance MR angiography with gadolinium contrast is then used for depiction of pulmonary arteries, branches and collaterals Fig. Subsequently, flow measurements are performed in planes perpendicular to the blood flow to quantify pulmonary or other valve regurgitation, differential pulmonary artery flow and pulmonary and systemic flow Fig. Fractional pulmonary regurgitation calculated as the ratio of retrograde to antegrade flow as well as the absolute retrograde volume through the pulmonary valve area is calculated [ 29 ]. In the absence of other significant valve lesions or left to right shunt the degree of PR is also reflected by the difference in RV and LV stroke volumes Fig.
Both flow and planimetry derived RV forward volumes during systole coincide due to absence of significant tricuspid regurgitation. Myocardial enhancement at the hinge points of the ventricular wall to the septum is very common in repaired TOF but if present in other regions may be related to decreased exercise tolerance and ventricular dysfunction [ 30 ]. Of note, late gadolinium enhancement at the hinge points of the ventricular wall to the septum red arrows is common and nonspecific in TOF.
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CMR objectively evaluates right atrial size, function and emptying influenced by TR and RV function, depicts arch sidedness and anomalies and offers excellent visualization and serial measurements of the aortic root and ascending aorta that are frequently dilated in TOF. CMR also assesses size, global and regional dysfunction of the LV, present in the late stages of repaired TOF due to ventricular-ventricular interaction, which has been associated with adverse outcome, death and ventricular tachycardia [ 31 ]. Multidetector CCT in the current era offers excellent spatial and reasonable temporal resolution producing static and cine imaging as well as 3D reconstructions and can be very helpful in TOF evaluation.
Compared to CMR, CCT provides superior delineation of small vessels, aortopulmonary collaterals and pulmonary arteries, is less affected by stainless steel artifacts and has shorter acquisition times reducing the need for sedation, all qualities that may prove important in selected TOF patients [ 5 ]. Coronary computed tomography angiography CCTA has been shown to provide high resolution and quality depiction of the origin and course of coronary arteries [ 32 ], an important issue for surgical planning in preoperative TOF, as well as in older TOF patients with possible coronary abnormalities or proximity of the RV outflow tract to coronary vessels that may get obstructed during percutaneous pulmonary valve implantation [ 33 ].
CCT imaging does not interfere with pacemakers and defibrillators, even the older, non-compatible with CMR models. Disadvantages of CCT include its inability to provide reliable flow rate or velocity data and the use of ionizing radiation with its possible risks.
Newer techniques reducing radiation dose such as prospective triggering, adaptive statistical iterative reconstruction, and high-pitch spiral acquisition are not widely usable yet as they depend on heart rate, rhythm, body habitus and type of scanner but may further decrease the dosage in cardiac and coronary CT angiography [ 5 ].
Use of contrast media during CCT may aggravate preexisting renal dysfunction but is associated with overall few adverse events with the low osmolality agents [ 35 ]. The protocol for CCT assessment in TOF includes visualization of pulmonary artery anatomy, size and arborization, especially in cases with prior aortopulmonary shunts [ 36 ], as well as measurement of the lumen and wall thickness of the ascending aorta in older patients and comparison with normal values [ 37 ], since progressive root dilation is common in TOF as in other conotruncal diseases.
Biventricular end-diastolic and end-systolic volumes can be measured by retrospective reconstruction of the electrocardiogram ECG gated acquired data set, from which LV and RV ejection fractions, stroke volumes and cardiac output can be calculated with reasonable accuracy compared to the CMR gold standard if the RV cavity is adequately opacified [ 38 ]. CCT demonstrates intracardiac anatomy such as ventricular septal defects, taking into account its relative deficiency in atrial septum and membranous ventricular septum visualization Fig. Finally, it is extremely helpful in depicting the origin and course of coronaries [ 32 ], as well as RV to pulmonary artery conduits and their relation to surrounding structures, thus enabling correct planning of surgical or transcatheter interventions.
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CCT in postoperative TOF showing dilated RV with bowing of the ventricular septum towards the LV, the surgical ventricular patch black arrow and a significant residual ventricular septal defect white arrow. LV, left ventricle; RV, right ventricle. Despite the good imaging quality of CCT in TOF, it should be reserved only for patients with absolute contraindications to CMR, given its ionizing radiation, the young age of the patients and the need for serial imaging throughout their lifespan.
Although this technique is costly, time consuming and requires significant operator experience, it is anticipated that such reconstructions will be increasingly used in the future as technology progresses, especially in complicated cases. Traditionally, nuclear scintigraphy has been used in TOF for assessment of RV and LV size, function and myocardial viability at rest and during exercise, quantification of intracardiac shunts, and differential pulmonary perfusion between right and left lung [ 5 ].
Most of these indications are better served with CMR in the current era without the ionizing radiation risks, but with probably increased sedation requirements in small children compared to nuclear imaging. Nuclear imaging retains its role in the assessment of differential lung perfusion, especially in the presence of left pulmonary artery stenosis and PR [ 41 ].
It also permits evaluation of pulmonary ventilation as well as ventilation perfusion mismatch [ 42 ], frequently present in repaired TOF due to thoracic cage and postoperative abnormalities. For the remainder of indications, nuclear imaging is used very sparingly and is reserved for patients with clear contraindications to CMR and cardiac CT [ 2 ]. CCA provides invasive pressure and oximetry data in the pulmonary and systemic circulations, evaluates stenoses, direction and volume of shunts between the two circulations, pulmonary and systemic cardiac outputs by thermodilution or the Fick method, as well as pulmonary and systemic vascular resistances.
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Morphologic imaging is achieved usually by biplane cine angiograms in angulated views, using iodinated contrast material and ionizing radiation. Although invasive, CCA is relatively safe with few risks such as hematomas, arterial and venous injuries, renal function deterioration, contrast reactions, radiation exposure, and very low but definite mortality [ 5 ].
With the advent and optimization of noninvasive tools, CCA is reserved for delineation of complex CHD anatomy, such as TOF with pulmonary arterial tree abnormalities or prior aortopulmonary shunts, or during evaluation for possible transcatheter interventions, which are increasingly common in this population [ 43 ].
Still, CCA remains the gold standard for evaluation of intracardiac pressures, peripheral pulmonary arteries and coronaries and may well be used increasingly in this population with advancing age and possible coronary artery disease [ 2 ]. Aortic root, arch and descending aorta injections assess aorta size, aortic valve insufficiency, and aortopulmonary collaterals, possibly amenable to transcatheter occlusion if indicated. Depiction of coronary origin and, if need be, selective coronary angiography during balloon interrogation of the RV outflow tract Fig.
Patient history and physical exam
Note the atrial septal defect occluder black arrow. PA, pulmonary artery; RV, right ventricle. Rotational angiography with 3D reconstruction is a relatively new technique that can be very helpful in diagnostic and interventional CCA in TOF, especially in complex RV outflow tract anatomy and proximal pulmonary artery stenosis [ 44 ].
Data are acquired with rapid pacing and breath holding, minimizing radiation exposure, and the reconstructed 3D image can be overlaid on the active fluoroscopy, thus facilitating catheter manipulations and the choice of optimal camera angles [ 45 ]. Patients are mostly followed with yearly echocardiography in conjunction with physical examination, as well as periodic arrhythmia monitoring and cardiopulmonary exercise testing.
All imaging modalities previously described, with the critical help from CMR, are used for establishing indications for surgical or transcatheter pulmonary valve replacement to alleviate the detrimental effect of PR on RV dilation and function. Indications for pulmonary valve replacement include severe diastolic and systolic RV dilation, decreased RV and LV ejection fraction, large RV outflow tract aneurysms, prolonged QRS or tachyarrhythmias, severe RV outflow tract or pulmonary branch stenosis, severe tricuspid or aortic insufficiency and significant residual septal defects [ 46 ].
Echocardiography represents the main imaging tool used at least on a yearly basis because it provides good functional assessment of the RV, pulmonary and tricuspid valves with low cost, wide availability and absence of contraindications or ionizing radiation. CMR is performed yearly in case of progressive RV dilation and dysfunction or significant right heart failure symptoms. Lung perfusion scan is performed in case of considerable pulmonary branch stenosis, where significant decrease in ipsilateral lung perfusion is suspected and may warrant intervention.
These issues become increasingly important as we lack concrete data on the rate and predictors of disease progression in TOF, while economic factors greatly affect allocation of funds and resources in our current environment. Further research is needed on the factors influencing disease progression in TOF concerning PR, RV dilation and dysfunction and aortic dilation in order to optimize management and follow up as well as timing of interventions in these patients.
Unnatural history of tetralogy of Fallot: prospective follow-up of 40 years after surgical correction. Multimodality imaging guidelines for patients with repaired tetralogy of fallot: a report from the AmericanSsociety of echocardiography: developed in collaboration with the Society for Cardiovascular Magnetic Resonance and the Society for Pediatric Radiology.
The absence of well-formed papillary muscles is a clue to the diagnosis. Figure 3 demonstrates the imaging features of LVNC. ARVC is a genetic desmosomal disease characterised pathologically by progressive RV myocyte loss and fibrofatty replacement. Aborted SCD from arrhythmia is often the initial presentation.
ARVC task force criteria TFC forms the cornerstone of the diagnosis, and the revision has improved sensitivity for gene carriers with limited disease and patients with left-sided disease. RV regional wall motion abnormality akinesia, dyssynchrony or aneurysm and one of the following:.
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Major and minor criteria have been defined for histology, ECG and family history, and are applied in the diagnosis. CMR transaxial cine stack is included as part of the work-up and detects regional and global RV dysfunction, wall motion abnormalities, aneurysms and wall thinning. Fat can appear in the RV in healthy individuals and can be difficult to image in the thin RV wall or discriminate with confidence from epicardial fat.
LGE is part of the ARVC protocol and its absence does not preclude the diagnosis but, when present, it has a high diagnostic sensitivity and specificity. However, RV LGE presents imaging problems: 20 Firstly, it is difficult to discriminate from RV fat; and secondly it requires significantly different inversion times compared with the LV.