ANTIARRHYTHMIC DRUGS Brief History. M.R. is a 48-year-old man with a history of coronary artery disease and cardiac rhythm disturbances. Specifi cally, he has experienced episodes of paroxysmal supraventricular tachycardia, with his heart rate often exceeding 180 beats per minute. He has been treated for several years with the beta blocker propranolol (Inderal). Taking this drug orally at a dose of 60 mg/d has successfully diminished his episodes of tachycardia. M.R. had also been a cigarette smoker but quit recently to improve his health and reduce the risk of cigarette-related diseases. In an effort to improve his myocardial function and overall cardiovascular fi tness, M.R. underwent a graded exercise test and was subsequently enrolled as an outpatient in a cardiac rehabilitation program. Under the supervision of a physical therapist, he attended cardiac training sessions three times each week. A typical session consisted of warm-up calisthenics, bicycle ergometry, and cool-down stretching activities. Each session lasted approximately 45 minutes.

Problem/Influence of Medication. During the initial rehabilitation sessions, the therapist noticed that M.R. seemed to be having some trouble breathing during the bicycle exercises. The therapist placed a stethoscope over M.R.’s chest and heard distinct wheezing sounds indicative of bronchoconstrictive disease. M.R. apparently had some residual effects of cigarette smoking, most likely in the form of mild to moderate emphysema.

1. Could M.R.’s current drug regimen be contributing to the bronchoconstrictive symptoms?

2. What potential change in drug therapy may reduce the risk of bronchoconstriction?