How to Assess Non-Responsiveness to Vasodilator Stress

Myocardial perfusion imaging (MPI) is a powerful tool for the functional assessment of ischemia in patients with suspected or known coronary artery disease (CAD). Given that the diagnostic accuracy and prognostic value of MPI and post-test management are highly dependent on achieving an adequate stress vasodilatory response, it is critical to identify those who may not have adequately responded to vasodilator pharmacological stress agents such as adenosine, dipyridamole, and regadenoson. Caffeine, a potent inhibitor of the adenosine receptor, is a compound that can affect vasodilatory hemodynamics, result in false negative studies, and potentially alter management in cases of inaccurate test results. Vasodilator non-responsiveness can be suspected by examining hemodynamics, quantitative positron emission tomography (PET) metrics such as myocardial flow reserve (MFR) and splenic response to stress. Quantitative MFR values of 1-1.2 should raise the suspicion for non-responsiveness in the setting of normal perfusion, along with the absence of splenic switch off. Newer metrics such as splenic response ratio can be used to aid identification of potential non-responders to pharmacologic vasodilators.