The use of amyl nitrite in the differentiation of Fallot's tetralogy and pulmonary stenosis with intact ventricular septum

Abstract

The effect of the inhalation of amyl nitrite on the systemic and right ventricular pressures and on the systolic murmur and heart sounds has been studied in pulmonary stenosis with intact ventricular septum and Fallot's tetralogy. In pulmonary or infundibular stenosis with intact ventricular septum the inhalation of amyl nitrite results in a pronounced fall in systemic pressure and a marked rise in right ventricular pressure. The increased right ventricular pressure results in a striking increase in the loudness of the systolic murmur. After cessation of the inhalation, pressures and murmur gradually return to their original state in about 4 minutes. In Fallot's tetralogy the inhalation of amyl nitrite results in a moderate fall in both the systemic and right ventricular systolic pressures, with an increase in right-to-left shunt. The reduced right ventricular pressure results in a diminution in pulmonary flow, which is reflected by a decrease in the intensity and duration of the systolic murmur. As the effect of the vapor wears off, the pressures, murmur, and cyanosis return to the basal level, usually within 3 to 4 minutes. The reasons for these striking differences are discussed fully. The effect was similar whether the case of pulmonary stenosis or Fallot's tetralogy was mild, moderate, or severe. The amyl nitrite test is of value in settling the difficult and important diagnosis of mild (acyanotic) Fallot's tetralogy and moderately severe pulmonary or infundibular stenosis with intact ventricular septum, in cases in which the clinical, electrocardiographic, radiologic, and catheter findings may be identical. The different behavior of the systolic murmur at the bedside and of the pressures during cardiac catheterization readily distinguishes the two conditions.