Vasodilator Stress Agents

	Mechanism of action	T 1/2	Administration	Side effects	Contraindications
Adenosine	A2A receptor à direct coronary vasodilation à 3.5- 4 x increased blood flow à stenotic epicardial coronaries will have attenuated hyperemic response. True ischemia may be induced by coronary steal phenomenon.	Secs	140 mcg/kg/min over a 6 min period Minimum time to tracer injection: 2 mins Continue infusion for 2 mins after tracer injection	Nonspecific chest pain: not an indicator of CAD ST depression >1mm: indicative of significant CAD A1 receptor: AV block à does not require termination of infusion A2b receptor: Hypotension A2b and A3 receptors: Bronchospasm Resolve in few seconds (due to extremely short half-life of adenosine)	Asthma with ongoing wheezing 2/3 AV block without a pacemaker SBP <90 mmHg Use of dipyridamole in last 48 hours; aminophylline in 24 hours or caffeine in last 12 hours (pentoxifylline OK) ACS
Regadenoson	A2A receptor à direct coronary vasodilation (lower affinity than adenosine)	2-4 mins	0.4mg/10 ml given as rapid injection followed by saline flush Tracer injection 10-20 secs after	SOB, flushing, headache Most resolve within 15 mins, headaches resolve in 30 mins (Use aminophylline 50-250 mcg infused slowly) Hypotensionѱ	Asthma with ongoing wheezing 2/3 AV block without a pacemaker SBP <90 mmHg Use of dipyridamole in last 48 hours; aminophylline in 24 hours or caffeine in last 12 hours (pentoxifylline OK) ACS
Dipyridamole	Prevents reuptake and deamination of adenosine à indirect coronary vasodilator Dipyridamole induced hyperemia lasts more than 15mins	30-45 mins (liver)	0.56mg/kg IV over 4 mins (142mcg/kg/min) Tracer injection after 3-5 mins	Flushing, chest pain, headaches, dizziness. Resolve in 15-25 mins (Use aminophylline 125-250 mcg infused slowly- should also be used in the presence of ischemic changes after dipyridamole)	Same as adenosine. CAN be used in patients taking oral dipyridamole.
Dobutamine	Direct B1 and B2 stimulation Increase in heart rate, blood pressure and myocardial contractility. Increases regional myocardial blood flow (similar to exercise, less than adenosine). Does not increase venous return (no increase in wall stress)	2 mins	5mcg/kg/min increased at 3 minute intervals to 40mcg/kg/min. Tracer injection at peak dose and continue infusion for 2 mins after	Palpitations, chest pain, headache, flushing, dyspnea (Use esmolol 0.5mg/kg over 1 min)	ACS Hemodynamically significant LVOT obstruction Severe AS Prior h/o VT Aortic dissection/large aortic aneurysm Uncontrolled hypertension B blockers

Ѱ Risk of hypotension higher in patients with autonomic dysfunction, hypovolemia, left main coronary artery stenosis, stenotic valvular heart disease, pericarditis, pericardial effusions, stenotic carotid artery disease with cerebrovascular insufficiency