Pharmacological agents




Pharmacologic stress testing relies on coronary steal. Vasodilators are used to dilate coronary vessels, which causes increased blood velocity and flow rate in normal vessels and less of a response in stenotic vessels. This difference in response leads to a steal of flow and perfusion defects appear in cardiac nuclear scans or as ST-segment changes.

The choice of pharmacologic stress agents used in the test depends on factors such as potential drug interactions with other treatments and concomitant diseases.

Pharmacologic agents such as Adenosine, Lexiscan (Regadenoson), or dipyridamole is generally used when a patient cannot achieve adequate work level with treadmill exercise, or has poorly controlled hypertension or left bundle branch block. However, an exercise stress test may provide more information about exercise tolerance than a pharmacologic stress test.

Commonly used agents include:

  • Vasodilators acting as adenosine receptor agonists, such as adenosine itself, and dipyridamole (brand name "Persantine"), which acts indirectly at the receptor.
  • Regadenoson (brand name "Lexiscan"), which acts specifically at the adenosine A2A receptor, thus affecting the heart more than the lung.
  • Dobutamine. The effects of beta-agonists such as dobutamine can be reversed by administering beta-blockers such as propranolol.

Lexiscan (Regadenoson) or Dobutamine is often used in patients with severe reactive airway disease (asthma or COPD) as adenosine and dipyridamole can cause acute exacerbation of these conditions. If the patient's Asthma is treated with an inhaler then it should be used as a pre-treatment prior to the injection of the pharmacologic stress agent. In addition, if the patient is actively wheezing then the physician should determine the benefits versus the risk to the patient of performing a stress test especially outside of a hospital setting. Caffeine is usually held 24 hours prior to an adenosine stress test, as it is a competitive antagonist of the A2A adenosine receptor and can attenuate the vasodilatory effects of adenosine.

Aminophylline may be used to attenuate severe and/or persistent adverse reactions to Adenosine and Lexiscan.

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