The effects of amyl nitrite and phenylephrine on the intracardiac murmurs of small ventricular septal defects

Abstract

1. 1. Synchronous external and internal phonocardiographic tracings were recorded in 8 patients who had small ventricular septal defect (less than 45 per cent left-to-right shunt) and normal pulmonary arterial pressure, and were without pulmonary stenosis. The external phonocardiograms showed a widely radiating pansystolic murmur, either plateau shaped or with a late crescendo. The internal phonocardiogram showed a similar murmur in the right ventricle. In 3 patients the murmur due to the ventricular septal defect radiated widely into both pulmonary arteries but was not equally loud at all sites in the right ventricle, suggesting jet flow of shunted blood down the pulmonary arteries. In 3 patients the septal-defect murmur was confined to the ventricle, and a separate pulmonary ejection murmur was recorded beyond the pulmonary valve. 2. 2. Amyl nitrite softened the pansystolic regurgitant murmur recorded in the right ventricle. In the pulmonary artery, however, the short ejection murmur was intensified, but this had no influence on the externally recorded murmur, which also softened. 3. 3. Phenylephrine produced marked intensification and prolongation of the murmur in the right ventricle and of the externally recorded murmur, and in one subject the intrapulmonary ejection murmur intensified. 4. 4. Since changes in the chest-wall murmur closely parallel changes in the right ventricular murmur, variation in intensity of the chest-wall murmur alone provides information of the change in volume rate of shunt flow. 5. 5. In the case of minute ventricular septal defect the tracings recorded at the fourth left intercostal space and in the right ventricle both showed the characteristic crescendo-decrescendo murmur which softened after amyl nitrite and intensified and lengthened after phenylephrine. The intrapulmonary ejection murmur increased with amyl nitrite. Since the septal-defect murmur is softer and more localized in the case of minute septal defect, a separate pulmonary ejection murmur may be heard in the pulmonary area. Unless auscultation is made at the correct site, the diagnostic effect of amyl nitrite may not be detected. 6. 6. This study has thrown some light on the different behavior of the regurgitant systolic murmur of ventricular septal defect and the pulmonary ejection murmur under the influence of vasoactive drugs. It has clarified the interpretation of these murmurs when they are heard at the chest wall.