Fatal myocardial toxicity during continuous infusion intravenous isoproterenol therapy of asthma

We recently utilized continuous infusion intravenous isoproterenol in the treatment of respiratory failure in an 18-yr-old steroid-dependent asthmatic female. Aminophylline, hydrocortisone, aerosolized isoetharine, and oxygen were also administrered. The patient responded to this therapy, with PaCO2 falling from 70 torr to 33 torr in 18 hr. The maximum isoproterenol dosage administered was 0.32 microgram/kg/min. Thirty-six hours following the institution of therapy, while the isoproterenol was being tapered, the patient experienced an increase in respiratory distress followed by cardiac arrest. Postmortem examination revealed multiple small areas of myocardial necrosis. These findings, unusual in asthma, probably were related to the effects of isoproterenol or the combination of isoproterenol and aminophylline on the stressed myocardium. The vulnerability of the hypoxic myocardium to the effects of isoproterenol suggests that careful cardiac monitoring is essential in the management of patients receiving this medication for treatment of respiratory failure secondary to severe asthma.