Tetralogy of Fallot (TOF) is a congenital heart defect that affects the normal blood flow through the heart. TOF is made up of four defects of the heart and blood vessels.
The hemodynamics of Tetralogy of Fallot (TOF) depends on the degree of right ventricular outflow tract obstruction (RVOTO) or pulmonary stenosis (PS). The ventricular septal defect (VSD) is commonly non-restrictive, which results in both right and left lower chambers (ventricles) having similar or equal pressures. If the RVOTO or PS is severe, the blood cannot leave the right ventricle easily. This obstruction of pulmonary blood flow causes a right-to-left intracardiac shunt which means not enough blood is flowing to the lungs. Some of the more severe cases of RVOTO or PS require continuous intravenous medication to keep a blood vessel known as the ductus arteriosus open, which allows blood to have an alternate path to the lungs where it can be oxygenated.
Symptoms of TOF are often first noticed by a murmur or cyanosis. The murmur may be discovered by a medical professional when listening to the baby’s heart at the time of a routine exam. Cyanosis, or a bluish appearance, may be seen on certain areas of the skin.
It is not uncommon for the ductus arteriosus to remain open (known as patent ductus arteriosus or PDA) in the first few days immediately after a baby is born. This PDA provides additional blood flow to the lungs, and the baby may not appear cyanotic until the PDA begins to close. Cyanosis may develop or become more severe during this time frame.
The amount of cyanosis is directly related to the amount of pulmonary blood flow to the lungs, where less flow results in less oxygen which makes the baby more cyanotic (blue). This blood flow may become lessened if any combination of either the degree of pulmonary obstruction or the closing of the PDA occurs.
Babies with too little pulmonary blood flow appear bluer more often and have lower oxygen levels (saturation) in their blood. They typically develop rapid breathing during times of rest and activities such as feeding or physical exertion. They may also not take feedings and other babies, not grow well for their age, tire or sleep more often than expected.
Specifically, babies with the Tetralogy of Fallot can appear “normal” and then have sudden episodes of looking blue. Initially, the baby may become highly irritable, followed by severe cyanosis. Sometimes comforting measures or placing the baby in a knee-to-chest position will temporarily help. However, this sudden drop in their oxygen levels may result in sleepiness or even unresponsiveness if they persist. Any degree of an episode like this is referred to as a “tet spell” and often requires immediate medical attention.
Considerable controversy persists regarding the optimal timing for the repair of babies with TOF. Advantages of early repair include protecting the developing pulmonary vasculature and promoting lung development. Also, re-leaving the RVOTO helps prevents the formation of abnormal right ventricular hypertrophy and fibrosis.
In a prostaglandin-dependent (PDA-dependent) newborn, the degree of fixed RVOTO is so severe that another source of pulmonary blood flow must be established. Often the surgical team will choose either a systemic to pulmonary shunt (a BT shunt) or will perform a transannular patch augmentation to provide unobstructed flow to the baby’s lungs.
In babies who can undergo “elective” repair (those with mild cyanosis), typically undergo complete repair between 3-6 months of age.
A midline incision is made over the sternum, and the child is placed on cardiopulmonary bypass. Typically, cardiac defects are repaired through a small incision in the right ventricle of the heart. Our surgical team can close the ventricular septal defect (VSD) using a synthetic patch material using this exposure. The right-sided outflow obstruction is also resected (removed) to allow blood to easily flow into the lungs for oxygenation. In many instances, the valve is completely removed, and a large synthetic patch is placed over the outflow tract to augment or enlarge the size. In children who have anomalous (not in the normal location) coronary arteries, our surgical team may need to use a conduit (a synthetic tube) to create a new RVOT.
It is also not uncommon for the baby to need repair of the branch pulmonary arteries (blood vessels going from the heart to the lungs).
Recovery for the post-operative period after a Tetralogy of Fallot repair is variable based on the surgical approach. Monitoring will include invasive lines, such as an arterial line and central venous line, to monitor blood pressure and deliver medications.
Medications may be needed to control hemodynamics (epinephrine, milrinone), support adjusting heart function, provide sedation and maintain hydration during recovery. Perfusion is monitored by non-invasive pulse oximetry and NIRS (near-infrared spectroscopy) probes. Depending on a variety of factors specific to each individual, the breathing tube (endotracheal tube) may or may not still be present after surgery. Pacing wires, which give the ability to assist with any rhythm issues that may arise in the post-operative period, will be placed in the operating room. Pacing wires are typically removed a few days after surgery if not needed. Chest tubes will be present to remove air, blood or fluid from around the heart or lungs. These tubes will be removed in the ICU as soon as medically able.
Length of hospital stay is variable depending on many factors, but the average is approximately two weeks.