Possible Diphenylhydantoin-Induced Arrhythmia in Hypothyroidism

WE HAVE RECENTLY seen a patient with hypothyroidism and heart disease who developed supraventricular tachycardia following the administration of diphenylhydantoin. The use of this drug for treatment of cardiac arrhythmias has received favorable attention¹,²and so the circumstances in this case are of interest. Report of a Case A 53-year-old white woman with rheumatic heart disease had a mitral commissurotomy in 1954. Although euthyroid, she was given an ablative dose of sodium iodide 1131 in 1955 in an effort to slow her heart rate. With the development of symptomatic hypothyroidism, she was given thyroid replacement therapy. She took sodium levothyroxine (Synthroid) (0.15 mg) daily and quinidine sulfate (0.3 gm) three times a day during the year before the present hospitalization, and digoxin (0.25 mg) daily during the preceding month. She was hospitalized in May 1965 because of the renewed appearance of atrial flutter with 2:1 to 4:1 atrioventricular (AV)