Adenosine stress test

Use of adenosine, a direct coronary arterial vasodilator that causes a 3.5 to 4 fold increase in myocardial blood flow.

Areas of the heart muscle supplied by diseased coronary arteries have attenuated hyperemic response.

Induces relative flow heterogeneity dependent upon degree of coronary artery narrowing and coronary flow reserve.

In the presence of severe coronary artery disease a coronary steal phenomenon may occur.

The myocardium takes up the tracer proportionally to the local myocardial blood flow, and in the presence of abnormal blood vessels an unequal distribution of radiotracer occurs.

Can result in a modest increase in hart rate and systolic and diastolic blood pressures.

Indications for the study include: inability to perform adequate exercise because of peripheral vascular disease, musculoskeletal problems or impaired pulmonary function, presence of left bundle block and concomitant treatment with agents that blunt the heart’s response (beta-blockers, calcium channel blockers).

Contraindications include: asthmatic patients with wheeze, presence of bronchoconstrictive disease, drug hypersensitivity, greater than first degree heart block in the absence of pacemaker, systolic blood pressure les than 90 mm Hg, recent myocardial infarction, presence of congestive heart failure, use of dypyridamole in the prior four hours, or use of xanthenes 12 hours prior to the test, and severe bradycardia of less than 40 beats per minute.

Administered under physician guidance.

Adenosine given as a continuous infusion at a rate of 140 ug/kg/min over 4 minutes and the radiotracer infusion between 2.5- 3 minutes after the start of the adenosine infusion.

EKG monitoring occurs throughout the study.

Adverse reactions include: flushing, chest discomfort, headache, nausea, dyspnea, throat and neck pain, and heart block.

Should be discontinued with the presence of severe hypotension, ST depression of greater than 3 mm beyond baseline without angina or greater than 2 mm with angina, persistent 2nd or 3rd degree heart block, severe chest pain, dizziness, dyspnea, nausea, syncope, dysrrhythmia headache and wheezing.

Half life of adenosine is less than 10 seconds, so adverse effects are short lived.

By stopping the infusion most adverse effects resolve within 30-60 seconds.

Persistence of symptoms after stopping the infusion, the addition of aminophylline 125 mg, IV over 1 minute is advised.

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