The use of phenylephrine in the differentiation of Fallot's tetralogy from pulmonary stenosis with intact ventricular septum

Abstract

1. 1. The effect of phenylephrine on the systemic, right ventricular, and pulmonary arterial pressures and on the systolic murmur and heart sounds has been studied in patients with Fallot's tetralogy and pulmonary stenosis with intact ventricular septum. 2. 2. In both conditions, phenylephrine caused a pronounced elevation in systemic blood pressure and bradycardia, depending on the dose given and the individual response. The change in the contour of the pulse wave suggested a marked increase in peripheral systemic resistance. 3. 3. In cases of Fallot's tetralogy, whether severe or acyanotic, the systemic and right ventricular systolic pressures behaved in identical fashion, both rising and falling together. The elevated right ventricular pressure and pressure gradient across the stenosis caused increased pulmonary blood flow and pressure, as reflected by marked intensification and lengthening of the murmur, and intensification of the pulmonary second sound, respectively. The arterial oxygen saturation greatly improved in the cyanosed patients. Amyl nitrite reversed the beneficial effects by abruptly reducing the high systemic resistance. 4. 4. In cases of pulmonary stenosis with intact ventricular septum, whether mild or severe, the systemic and right ventricular pressures behaved quite independently of one another. The change in right ventricular pressure was insignificant, as reflected by insignificant change in the intensity and length of the murmur, allowing for the increased stroke volume from bradycardia. When the hypertensive response was marked, left ventricular systole appeared to be selectively delayed, as judged by marked delay in aortic valve closure, closing a previously widely split second sound. 5. 5. The different behavior of the right ventricular pressure and systolic murmur was attributed to the presence of a large ventricular septal defect. This was proved in a case of tetralogy studied before and after complete repair of the septal defect. 6. 6. The observations support the thesis that pulmonary blood flow, and hence the length and intensity of the murmur, in cases of tetralogy is determined both by the systemic resistance and the severity of the stenosis. 7. 7. Phenylephrine was shown to be a useful tool in studying the pulmonary second sound in cases of tetralogy. By increasing pulmonary blood flow and pressure, this drug greatly intensified the very soft, fleeting, pulmonary component in cases of mild tetralogy, thereby assisting in its recognition. It was also capable of eliciting a pulmonary component in severe cases of tetralogy. 8. 8. The diagnostic value of phenylephrine is described and its possible aid in selecting the operative procedure for severe tetralogy is discussed.