Tetralogy of Fallot
Introduction
A congenital heart defect
By definition, tetralogy of Fallot - four heart malformations which present together:
Understood to involve four anatomical abnormalities (although only three of them are always present).
The most common cyanotic heart defect
The most common cause of blue baby syndrome.
The defects
Pulmonary stenosis - narrowing of the right ventricular outflow tract - can occur at the pulmonary valve (valvular stenosis) or just below the pulmonary valve (infundibular stenosis).
Over riding aorta - an aortic valve with biventricular connection - situated above the ventricular septal defect and connected to both the right and the left ventricle.
Ventricular Septal Defect - A hole between the ventricles. The defect is centered around the most superior aspect of the ventricular septum (the outlet septum), and in the majority of cases is single and large.
Right ventricular hypertrophy - The right ventricle is more muscular than normal, causing a characteristic boot-shaped (coeur-en-sabot) appearance as seen by chest X-ray.
Clinical Features
Tet spells (cyanotic spells) are characterized by a sudden, marked increase in cyanosis followed by syncope, and may result in hypoxic brain injury and death. Older children will often squat during a cyanotic spell, which cuts off circulation to the legs and therefore improves blood flow to the brain and vital organs.
Investigations
X-ray Chest - coeur-en-sabot shaped (Boot Shaped) heart
Echocardiography
Total surgical repair
Surgery in infants 1 year of age or younger with a <5% perioperative mortality.
Incisions into the heart muscle
Relieving the right ventricular outflow tract stenosis by careful resection of muscle
Repairing the VSD using a Gore-Tex patch or a homograft.
Additional reparative or reconstructive work as required by their particular anatomy.
Emergency management of cyanotic spells
Treated with beta-blockers such as propranolol,
But acute episodes may require rapid intervention with morphine to reduce ventilatory drive and a vasopressor such as epinephrine, phenylephrine, or norepinephrine to increase blood pressure. Oxygen is ineffective in treating hypoxic spells because the underlying problem is lack of blood flow through the lungs and not oxygenation within the lungs.
There are also simple procedures such as squatting in the knee-chest position which increases aortic wave reflection, increasing pressure on the left side of the heart, decreasing the right to left shunt thus decreasing the amount of deoxygenated blood entering the systemic circulation.
Prognosis
Ninety percent of patients with total repair as infants develop a progressively leaky pulmonary valve because the heart grows to its adult size but the valve does not grow.
Patients also often have damage to the electrical system of the heart from surgical incisions, causing abnormalities as detected by ECG and/or arrhythmias.
Treated patients are at risk for sudden cardiac death and for heart failure.
Therefore, lifetime follow-up care by an adult congenital cardiologist is recommended Interventional procedures or re-operation may become necessary.
Antibiotic prophylaxis is indicated during dental treatment in order to prevent infective endocarditis.
