case continues:

The patient was started on isoetharine (Bronkosol) for his wheezing at a dose of 0.5 in 1.5 cc of normal saline on a q 4 hour basis. He was also given methylprednisolone sodium succinate (Solumedrol) 125 mg q 6 hours. The specialist thought about the use of theophylline, but decided it was not the best drug. He also adjusted the antibiotic regimen. The patient was transferred to the Med. I.C.U. for closer observation and treatment and frequent use of isoetharine.

One day later the pulmonary specialist was called to the ICU. The patient's pulse had gone to 150 bpm and his blood pressure was now 90/50. He was light-headed, although he did note that his breathing was improved. EKG strip seemed to indicate some form of an atrial tachycardia with multiple premature atrial contractions.

What is the most likely etiology of this patient;s new heart rhythm disturbance?