Haemodynamic Management and Graphical Representation in Tetralogy of Fallot
The haemodynamics of Tetralogy of Fallot (TOF) are best managed through comprehensive assessment of right ventricular outflow tract obstruction (RVOTO), pulmonary regurgitation, right ventricular function, and residual ventricular septal defects (VSD), with graphical representation focusing on pressure-volume relationships, regurgitant fractions, and ventricular dimensions. 1
Key Haemodynamic Parameters in TOF
Right Ventricular Outflow Tract Obstruction
- RV/LV pressure ratio >0.7 indicates significant RVOTO
- Peak instantaneous echocardiography gradient >50 mm Hg warrants intervention
- Graphical representation includes:
- Pressure gradients across RVOT
- RV/LV pressure ratios
- Dynamic pressure changes during cardiac cycle
Pulmonary Regurgitation
- Quantified by regurgitant fraction (RF)
- Severe PR: RF >40-50%
- Graphical representation includes:
- Pulmonary regurgitant fraction
- Flow-time curves showing regurgitant flow
- Pressure-volume loops demonstrating regurgitant effects
Right Ventricular Function
- RV end-diastolic volumes >150 ml/m² (normal: 75 ml/m²) indicate significant dilation
- RV ejection fraction <0.40 indicates dysfunction
- Graphical representation includes:
- RV volume curves
- Pressure-volume loops
- RV ejection fraction trends over time
Imaging Modalities for Haemodynamic Assessment
Echocardiography
- First-line assessment tool for RVOT obstruction, PR, RV function, and residual VSD
- Provides real-time visualization of:
- RVOT gradient
- Tricuspid annular plane systolic excursion (TAPSE)
- RV fractional area change (FAC)
Cardiac MRI
- Gold standard for RV volume quantification and PR measurement
- Provides:
- Precise RV end-diastolic and end-systolic volumes
- Accurate pulmonary regurgitant fraction
- 3D visualization of RV morphology
Cardiac Catheterization
- Direct pressure measurements of RVOT gradients
- Dynamic assessment of regurgitant flow
- Pressure-volume loops showing:
- RV-pulmonary artery coupling
- Ventricular interdependence
- Effects of interventions
Haemodynamic Force Analysis
Recent research has demonstrated the value of analyzing haemodynamic forces in TOF patients 2:
- Patients with repaired TOF and PR show:
- Higher systolic and diastolic LV forces in lateral-septal/LV outflow tract directions
- Higher RV diastolic forces along the regurgitant flow direction
- Forces less aligned with intraventricular blood flow compared to normal hearts
Stress Echocardiography for Dynamic Assessment
Exercise echocardiography provides valuable insights into RV response to stress 3:
- Parameters measured at rest and peak exercise:
- TAPSE
- RV pressure
- RV fractional area change (FAC)
- Graphical representation includes:
- RV FAC variation during exercise
- RV pressure changes with exercise
- TAPSE changes during stress
Risk Stratification and Monitoring
Electrical Risk Assessment
- QRS duration >180 ms correlates with RV size and predicts malignant ventricular arrhythmias 4
- Graphical representation includes:
- QRS duration trends
- Correlation between QRS duration and RV volumes
- Risk stratification charts
Ventricular Interdependence
- LV dysfunction may influence RV performance
- Graphical representation includes:
- Ventricular septal position throughout cardiac cycle
- Biventricular pressure-volume relationships
- Interventricular dependence during respiration
Common Pitfalls in TOF Haemodynamic Assessment
Underestimation of pulmonary regurgitation by echocardiography
- Solution: Use multiple imaging modalities including MRI
Failure to recognize branch pulmonary artery stenosis
- Solution: Comprehensive assessment with cardiac MRI and catheterization
Overlooking RV diastolic dysfunction
- Solution: Include diastolic parameters in assessment
Misinterpreting RV dilation as purely volume overload
- Solution: Assess for residual RVOTO contribution
Long-term Haemodynamic Monitoring
Annual cardiac evaluation at specialized ACHD centers
Regular assessment of:
- RV function and size
- Pulmonary valve function
- RVOT gradient
- QRS duration
- Exercise capacity
Imaging schedule:
- Echocardiography at each visit
- CMR every 2-3 years or when clinical status changes
- Cardiac catheterization when non-invasive tests are inconclusive
By systematically evaluating these parameters and representing them graphically, clinicians can better understand the complex haemodynamics of TOF, guide interventions, and improve long-term outcomes for patients with this condition.