Propranolol in Tetralogy of Fallot

W HILE TOTAL surgical correction is the goal for all patients with tetralogy of Fallot, drug therapy is required for emergency treatment of severe dyspneic spells and could be of value in preventing dyspneic spells and exercise hypoxia in children awaiting operation. /3-adrenergic inhibition has been of value in the management of patients with functional obstruction to left ventricular outflow. Since there appears to be a functional element to the outflow obstruction in many patients with Fallot's tetralogy, pronethaloll 2 and later propranolol3 have received therapeutic trial. Some experiences with propranolol in the management of patients with Fallot's tetralogy in three situations follow: (1) management of the acute dyspneic attack, (2) prevention of dyspneic spells, and (3) improvement in children 2 to 6 years old while awaiting corrective surgery. 1. Dyspneic attacks in patients with Fallot's tetralogy are a unique phenomenon that may occur in patients who have little or no cyanosis under usual conditions. The attacks, characterized by dyspnea, cyanosis, and limpness, usually occur in such patients between 6 and 30 months of age; they may disappear spontaneously, but if severe, may be fatal. During the attack the right-to-left shunt increases markedly and arterial oxygen saturation drops precipitously.3 With prolonged attacks, hypoxia leads to lactic acid accumulation and severe acidosis. The time-honored treatment introduced by Taussig4 is often all that is necessary; namely, knee-chest position, oxygen, maternal comfort, and for severe attacks intramuscular injection of morphine, 0.2 mg/kg. Intravenous administration of sodium bicarbonate is invaluable in severely acidotic infants.5 In the laboratory, angiotensin will promptly abort the attack by increasing the systemic vascular resistance,6 and attacks are precipitated by reductions in systemic resistance. There is ample evidence that f3-adrenergic blocking drugs can be used to terminate dyspneic spells.2'3 Propranolol in a dose of 0.2 mg/kg of body weight has been used in this hospital in the catheterization laboratory and on the wards to abort severe attacks, some of which were resistant to the other therapeutic measures, including morphine. The mechanism of action is not completely worked out, but we have demonstrated a decrease in the right-to-left shunt following propranolol, presumedly due to a change in right ventricular contractility.7 2. While the spells in an individual patient may follow a set pattern, they often recur with unpredictable frequency and severity. Preventive measures include avoidance of precipitating factors, anticipation of the time of an attack, and sedation with phenobarbital. Continued attacks are a strong indication for surgery. The surgical creation of an adequate pulmonary blood flow usually eliminates the spells. In suitable patients, we7 and others" have been able to prevent the majority of these spells with propranolol in divided oral doses of 20 to 60 mg daily. Most suitable for treatment are infants with mild cyanosis at rest (arterial oxygen saturation of 70 to 85%) whose selective angiograms show marked cyclic changes in the caliber of the right ventricular outflow tract. Infants with severe cyanosis (oxygen saturation, below 60%) and severe hypoplasia of the right ventricular outflow tract and pulmonary arteries are not significantly improved with propranolol and are better managed surgically. We7 have treated a few patients with propranolol for 2 to 6 months; their dyspneic spells were eliminated and did not recur after discontinuing the drug. One such patient, however, later