The Use of Isoproterenol (Isuprel) in the Evaluation of Congenital Cardiac Defects

Isoproterenol was infused intravenously at a rate of 0.03 to 0.07 µg. per Kg. per minute in 38 patients undergoing cardiac catheterization to evaluate the routine postoperative condition of 19 patients and to support or confirm the clinical diagnosis in 19 others. A steady response was obtained in 2 to 4 minutes, and no toxic effects were observed. During the infusion the heart rate increased an average of 55 per cent; the respiratory rate, 23 per cent. The right atrial pressure fell. In general the pulmonary and systemic arterial pressures also decreased. Limited observations on the cardiac output confirmed the previously reported increase. Ten patients developed a significant systolic gradient between the right ventricle and pulmonary artery (greater than 20 mm. Hg) during the infusion. Four of these were postoperative patients, three of whom were considered completely corrected prior to infusion of the isoproterenol. Four patients with aortic stenosis were studied, and the systolic gradient increased in three (80, 93, and 145 per cent). The results indicate that infusion of isoproterenol is a safe, practical, and effective means of simulating exercise in infants and children. Used in addition to the customary cardiac catheterization studies, it is of distinct value in appraising congenital cardiac defects.