Tetralogy of Fallot Workup

Updated: Dec 21, 2017
  • Author: Shabir Bhimji, MD, PhD; Chief Editor: Yasmine Subhi Ali, MD, FACC, FACP, MSCI  more...
  • Print

Hematologic Studies

Hemoglobin and hematocrit values are usually elevated in proportion to the degree of cyanosis. Prolonged cyanosis causes reactive polycythemia that increases the oxygen-carrying capacity. The oxygen saturation in systemic arterial blood typically varies from 65-70%. All patients with tetralogy of Fallot who experience significant cyanosis have a tendency to bleed because of decreased clotting factors and low platelet count. Hyperviscosity and coagulopathy often ensue and are particularly deleterious in patients with a right-to-left intracardiac shunt. The usual findings are diminished coagulation factors, and diminished total fibrinogen, which are associated with prolonged prothrombin and coagulation times.

Stroke and brain abscess are natural corollaries caused by paradoxical blood flow.


ABG and Oximetry

Arterial blood gas (ABG) results show varying oxygen saturation, but pH and partial pressure of carbon dioxide (pCO2) are normal, unless the patient is in extremis, such as during a tet spell.

Oximetry is particularly useful in a dark-skinned patient or an anemic patient whose level of cyanosis is not apparent. Generally, cyanosis is not evident until 3-5 g/dL of reduced hemoglobin is present.

A decrease in systemic vascular resistance (SVR) during exercise, bathing, or fever potentiates a right-to-left shunt and precipitates hypoxemia.


Radiologic Studies

Imaging studies used in the evaluation of tetralogy of Fallot (TOF) include echocardiography, chest radiographs, and magnetic resonance imaging (MRI).


Ductus arteriosus, muscular ventricular septal defect (VSD), or atrial septal defect (ASD) is accurately diagnosed with color-flow Doppler echocardiography. The coronary anatomy can be revealed with some degree of accuracy, and valvar alterations can be detected with ease. In many institutions, echocardiography is the only diagnostic study used before surgery.

Echocardiograms will usually reveal a large VSD with an overriding aorta and variable degrees of right ventricular (RV) outflow tract obstruction (RVOTO).


Initially, chest radiographs may not reveal any abnormality; however, diminished vascularity in the lungs and diminished prominence of the pulmonary arteries gradually become apparent.

The hallmark of tetralogy of Fallot is the classic boot-shaped heart (coeur en sabot) (see the following image).

An uplifted apex and absence of pulmonary artery s An uplifted apex and absence of pulmonary artery segment typifies the "coeur en sabot" (ie, boot-shaped heart) of tetralogy of Fallot.

Magnetic resonance imaging

MRI provides good delineation of the aorta, RVOT, VSDs, RV hypertrophy, and the pulmonary artery and its branches. [1] MRI can also be used to measure intracardiac pressures, gradients, and blood flows.

Drawbacks to MRI include the need for prolonged imaging times and the requirement for sedation in small children to prevent motion artifacts. Additionally, sick infants cannot be observed when enclosed in an MRI tunnel.



The use of electrocardiography (ECG) may be limited if multiple ventricular septal defects (VSDs) or coronary artery anomalies are present or if the distal pulmonary artery cannot be visualized adequately.

Right axis deviation (+120° to +150°) with right ventricular (RV) enlargement may be seen. [12] Combined ventricular hypertrophy and right atrial hypertrophy may be present.

If RV hypertrophy is absent on ECG, the diagnosis of tetralogy of Fallot should be in doubt.

A typical preoperative ECG is shown below.

This is a typical preoperative electrocardiogram ( This is a typical preoperative electrocardiogram (ECG) for tetralogy of Fallot.

Partial or complete right bundle branch block may be present; this is especially true of patients after surgical repair (see the following image).

Typical findings on postoperative electrocardiogra Typical findings on postoperative electrocardiogram (ECG) for tetralogy of Fallot are shown.

Cardiac Catheterization and Angiography

Cardiac catheterization provides angiographic visualization of ventricular and pulmonary artery size. Catheterization also helps obtain pressure and oxygen saturation measurements in different chambers and identifies any possible shunts. In the presence of preexisting shunts, angiograms should be obtained before complete surgical repair.

Cardiac catheterization findings include the following:

  • Assessment of the pulmonary annulus size and pulmonary arteries
  • Assessment of the severity of right ventricular (RV) outflow tract obstruction (RVOTO)
  • Location of the position and size of the ventricular septal defect (VSD)
  • Eliminating/ruling out possible coronary artery anomalies

Automatic internal cardiac defibrillator (AICD) placement is recommended in patients with sustained ventricular tachycardia and those resuscitated after a sudden death event. [13, 14]

Angiograms help identify coronary artery anomalies (see the image below); however, catheterization is not mandatory in all patients. Cardiac catheterization is extremely useful if the anatomy cannot be completely defined by echocardiography, if disease in the pulmonary arteries is a concern, or if pulmonary vascular hypertension is possible.

This angiogram shows a catheter in the right ventr This angiogram shows a catheter in the right ventricle—severe infundibular stenosis.