Echocardiographic Findings in Tetralogy of Fallot
Echocardiography in TOF must demonstrate the four cardinal anatomic features: a malalignment ventricular septal defect (VSD), right ventricular outflow tract obstruction (RVOTO), an overriding aorta (biventricular origin), and right ventricular hypertrophy. 1, 2
Pre-Repair Echocardiographic Assessment
Essential Anatomic Features
The echocardiographic evaluation must systematically identify:
Ventricular Septal Defect: A large, nonrestrictive malalignment-type VSD in the subaortic position 1, 3. The VSD should be characterized by type, size (qualitative and quantitative), and number 2
Aortic Override: The most sensitive finding is the abrupt ending of interventricular septal echoes with the aorta overriding the VSD 4. The aorta overrides by less than 50% of its diameter 1. Aortic widening is present in most cases 4
RVOT Obstruction: This occurs at multiple levels and requires detailed assessment 5, 1:
- Subinfundibular/infundibular stenosis (muscle resection site)
- Pulmonary valve: Assess cusp mobility, doming, excursion, dysplasia, thickening, and annular dimension (absolute value and z-score) 6
- Supravalvular stenosis: Main pulmonary artery and branch pulmonary arteries (often hypoplastic) 1
- Severity grading by peak Doppler gradients: mild <36 mmHg, moderate 36-64 mmHg, severe >64 mmHg 5
Right Ventricular Hypertrophy: Secondary to RV hypertension 1, 3
Critical Additional Anatomic Details
Coronary artery anatomy must be defined before any RVOT incision 6, 7. The most common anomaly is an aberrant left anterior descending coronary artery 1. If echocardiographic visualization is inadequate, CT angiography should be obtained 6.
Additional structures requiring assessment include 1, 6, 7:
- Pulmonary artery anatomy (left PA narrowing from ductus insertion, bifurcation stenosis, absent pulmonary artery)
- Atrial septum (secundum ASD may be present)
- Additional VSDs (may be masked by the large malalignment VSD)
- Aortic arch sidedness (right-sided in 25% of cases)
- Vascular rings and systemic venous anomalies
- Mitral valve and left ventricular outflow tract (rarely abnormal)
Post-Repair Echocardiographic Assessment
Comprehensive echocardiographic imaging should be performed in a regional adult congenital heart disease center to evaluate anatomy and hemodynamics in patients with repaired TOF 8.
Key Post-Repair Findings to Assess
The most common post-repair problem is pulmonary regurgitation 8. Systematic evaluation must include:
Pulmonary Regurgitation Severity 9:
- Multiple parameters required: jet size and duration, pressure half-time (PHT), reversal flow in pulmonary arteries
- Severe PR indicators: flow reversal in main/branch pulmonary arteries, PHT <100 ms, PR duration <100 ms
- Vena contracta measurement
- Ratio of diastolic to systolic velocity time integral in main PA
Right Ventricular Assessment 8:
- RV size and function (qualitative assessment; MRI is gold standard for quantification)
- RV systolic pressure estimation via tricuspid regurgitation velocity
- RV myocardial performance index for serial functional assessment
- Significant when RV pressure >2/3 systemic pressure 5
Residual RVOT Obstruction 8:
- Doppler gradients across narrowed segments
- Note: measurements may be unreliable with long-segment narrowing or multilevel obstruction 5
Other Lesions 8:
- Residual or patch-leak VSD
- Tricuspid regurgitation severity
- Aortic root dilation and aortic regurgitation (assess at regular intervals)
- Atrial size
- Left ventricular function
Post-Repair Clinical Correlates
Physical examination findings correlate with echo abnormalities 1:
- Soft ejection systolic murmur: residual RVOT obstruction
- Low-pitched delayed diastolic murmur with absent P2: pulmonary regurgitation
- Pansystolic murmur: VSD patch leak
- Diastolic murmur: aortic regurgitation
ECG findings 1: Complete right bundle branch block is nearly universal after transventricular repair. QRS duration ≥180 ms is a risk factor for sustained ventricular tachycardia and sudden cardiac death.
Common Pitfalls
- Proximal obstruction masks distal obstruction severity 6 - systematically evaluate all levels of RVOT
- Underfilled pulmonary arteries make assessment challenging 6
- Multiple VSDs may be difficult to visualize adjacent to the large malalignment defect 6
- Standard 2D techniques unreliably quantify RV volumes - MRI is the reference standard 8
- 3D color frame rates are often too slow for proper regurgitation quantification in children 9