Are you stressed?

Excerpt

Myocardial perfusion imaging is still a mainstay for the diagnosis and management of coronary artery disease. As a consequence, millions of US patients are examined with this technique every year.1 There are crucial points regarding the conduction of the procedure in order to guarantee optimal patient preparation, image quality, and analysis. Among those critical points are the choice and dose of the radiotracer, ECG-gated testing (for the assessment of left ventricular volumes and ejection fraction) and the compulsory quantification of the extent of affected myocardium (scar vs. ischemia, percentage of the left ventricular myocardium). (More details on state-of-the-art myocardial perfusion imaging can be found in the respective guidelines as released, e.g., by ASNC, SNMMI, or EANM).2 Another utterly important point regarding the conduction of myocardial perfusion imaging tests is that patients are recommended to be stressed adequately.3 Whenever possible, physical exercise using either a treadmill or a bicycle ergometer should be the preferred method. If the patient is unable to exercise adequately, pharmacological agents to increase myocardial blood flow sufficiently to detect hemodynamically relevant coronary stenoses can be applied with comparable sensitivity and specificity.4,5 Currently, the most frequently used pharmacological stressors are regadenoson and adenosine. These substances bind to the adenosine receptor A2A in coronary arteries and initiate a dilatation of these vessels, which, in turn, increases myocardial blood flow up to fourfold. Dipyridamole acts via the same axis by an increase of intrinsic adenosine (through the inhibition of the cellular reuptake of adenosine into platelets, red blood cells, and endothelial cells). Unfortunately, all of these pharmacological stressors may have considerable side effects: Adenosine also binds to other adenosine receptor subtypes, which may result in significant arrhythmias (e.g., AV block and other arrhythmias), dilatation of peripheral vessels, hypotension, reflex tachycardia, and bronchoconstriction. Regadenoson is thought to have less side effects as it binds to the other adenosine receptor subtypes with lower affinity. The only infrequently used pharmacological stressor in myocardial perfusion imaging is dobutamine. Dobutamine is a sympathomimetic drug and is used in patients with severe COPD or asthma as it does not cause bronchoconstriction. …