Asystole and bradycardia during dipyridamole stress testing in patients receiving beta blockers

Only rarely have serious side effects been reported with the use of intravenous dipyridamole. We describe two cases of severe bradycardia, of which one led to asystole, in patients undergoing dipyridamole-thallium studies. The association between beta blocker therapy and the seven reported cases of asystole with dipyridamole is discussed and mechanisms postulated. Some caution is advised when patients on beta blockers or similar medications have dipyridamole-thallium studies.