Dipyridamole is a synthetic indirect vasodilator. Dipyridamole was the first pharmacological stress test agent introduced in the early 80-ties, it was initially administered as capsules (with many GI side effects) and later as IV infusion.

Dipyridamole inhibits the normal faciliated re-absorption of natural vasodilator Adenosine, which is synthesized and released from endothelial cells as part of local vaso-regulatory systems. Dipyridamole thus leads to increased amount of extra-cellular Adenosine available to react with Adenosine receptors, stimulation of which leads to vascular smooth muscle cell relaxation and therefore coronary vasodilation (increased flow).

Dipyridamole and Adenosine protocols are probably equally effective.

The side effects with Dipyridamole are however often more severe and more difficult to control. Protracted broncospam which respond poorly to the standart antidote: Theophylline, is a well known problem.

The Adenosine receptors are blocked by CAFFEINE and THEOPHYLLINE. Dipyridamole stress testing is unreliable if there caffeine (coffe, thee, coke) on nboard (i.e. consumed within the last 12 h).

The Dipyridamole protocol is particularly well suited for patient with LBBB. The false positive rate with this protocol is 2-5% compared30-40% for treadmill testing.

Ongoing treatment with beta-blockers does not effect the efficiency of Dipyridamole. Pharmacological vasodilation is the protocol of choice for patients on beta-blockers.