Stress Myocardial Perfusion Imaging for Assessing Prognosis: An Update

A strength of nuclear myocardial perfusion imaging (MPI) is the wealth of prognostic data accumulated over 30 years of experience with this technique. Nuclear MPI can predict outcomes and guide revascularization decisions in symptomatic patients and is well validated in special populations such as patients with diabetes and chronic renal disease. Known limitations, such as underestimation of ischemia and radiation burden, are being progressively reduced through advances such as positron emission tomography absolute flow quantification and fusion with computed tomography, new camera hardware and software, and stress-only protocols. Advanced statistical techniques and increasing focus on comparative effectiveness and appropriateness will continue to optimize nuclear cardiology going forward

Prevalence of and variables associated with silent myocardial ischemia on exercise thallium-201 stress testing

AbstractThe prevalence of silent myocardial ischemia was prospectively assessed in a group of 103 consecutive patients (mean age 59 ± 10 years, 79% male) undergoing symptom-limited exercise thallium-201 scintigraphy. Variables that best correlated with the occurance of patients ischemia by quantitative scintigraphic criteria were examined. Fifty-nine patients (57%) had no angina on exercise testing. A significantly greater persent of patients with silent ischemia than of patients with angina had a recent myocardial infarction (31% versus 7%, P < 0.01), had no prior angina (91% versus 64%, p < 0.01), had dyspnea as an exercise test end point (56% versus 35%, p < 0.05) and exhibited redistribution defects in the supply regions of the right and circumflex coronary arteries (50% versus 35%, p < 0.05). The group with exercise angina had more ST depression (64% versus 41%, p < 0.05) and more patients with four or more redistribution defects.However, there was no difference between the two groups with respect to mean total thallium-201 perfusion score, number of redistribution defects per patient, multivessel thallium redistribution pattern or extent of angiographic coronary artery disease. There was also no difference between the silent ischemia and angina groups with respect to antianginal drug, usage, prevalence of diabetes mellitus, exercise duration, peak exercise heart rate, peak work load, peak double (rate-pressure) product and percent of patients achieving ≥85% of maximal predicted heart rate for age.Thus, in this study group, there was a rather high prevalence rate of silent ischemia (57%) by exercise thallium-201 criteria. Patients with silent ischemia and those with exercise angina had comparable 1) exercise tolerance and hemodynamics, 2) extent of angiographic coronary artery disease, and 3) extent of exercise-induced hypoperfusion. Finally, more patients with recent infarction had silent ischemia than had exercise angina

Do false positive thallium-201 scans lead to unnecessary catheterization? outcome of patients with perfusion defects on quantitative planar thallium-201 scintigraphy

AbstractObjectives. We postulated that artifactually abnormal thallium-201 scans are well identified at the time of initial clinical interpretation by experienced readers and do not lead to unnecessary coronary angiography.Background. Exercise thallium-201 scintigraphy employing quantitative imaging techniques has yielded sensitivity and specificity values of 80% to 90%. There are image artifacts, such as breast shadows, and variants of normal that, if not correctly identified, can lead to a high false positive rate for detection of coronary artery disease.Methods. Data from 338 consecutive patients with one or more focal thallium-201 defects on quantitative planar Images were reviewed. All patients had undergone symptom-limited exercise scintigraphy and were classified as having either artifactual or nonartifactual thallium-201 defects after review of clinical reports.Results. Of the 265 patients with defects judged to be nonartifactual on clinical readings, 167 underwent coronary angiography, which demonstrated significant coronary artery disease (≥50% stenosis) in 161 (96%) and normal findings in 6. Four of the latter six had documented prior myocardial infarction. The remaining 73 patients (85% female) had thallium-201 defects deemed to be artifactual on clinical readings, chiefly as a result of breast (66%) and diaphragmatic (8%) attenuation or variants of normal (26%). Only 4 (5%) of the 73 patients underwent subsequent coronary angiography; none had coronary artery disease. One had aortic stenosis and two had variant angina. Follow-up (mean 20 ± 2 months) of the 69 patients in this group who did not undergo coronary angiography revealed no deaths and one nonfatal non-Q wave myocardial infarction.Conclusions. Artifactual defects on quantitative planar thallium-201 scintigraphy are well recognized by experienced interpreters and do not result in a high false positive rate leading to unnecessary cardiac catheferization. The incidence of coronary artery disease is high in patients with thallium-201 defects judged to be nonartifactual, and many patients with perfusion defects and angiographically normal coronary arteries have organic heart disease

Influence of propranolol, enalaprilat, verapamil, and caffeine on adenosine A2A-receptor–mediated coronary vasodilation

AbstractObjectivesThe study was done to determine the effects of propranolol, enalaprilat, verapamil, and caffeine on the vasodilatory properties of the adenosine A2A-receptor agonist ATL-146e (ATL).BackgroundATL is a new adenosine A2A-receptor agonist proposed as a vasodilator for myocardial stress perfusion imaging. Beta-blockers, angiotensin-converting enzyme (ACE) inhibitors, and calcium blockers are commonly used for the treatment of coronary artery disease (CAD), and their effect on ATL-mediated vasodilation is unknown. Dietary intake of caffeine is also common.MethodsIn 19 anesthetized, open-chest dogs, hemodynamic responses to bolus injections of ATL (1.0 μg/kg) and adenosine (60 μg/kg) were recorded before and after administration of propranolol (1.0 mg/kg, ATL only), enalaprilat (0.3 mg/kg, ATL only), caffeine (5.0 mg/kg, ATL only), and verapamil (0.2 mg/kg bolus, ATL and adenosine).ResultsNeither propranolol nor enalaprilat attenuated the ATL-mediated vasodilation (225 ± 86% and 237 ± 67% increase, respectively, p = NS vs. control). Caffeine had an inhibitory effect (97 ± 28% increase, p < 0.05 vs. control). Verapamil blunted both ATL- and adenosine-induced vasodilation (63 ± 20% and 35 ± 7%, respectively, p < 0.05 vs. baseline), and also inhibited the vasodilation induced by the adenosine triphosphate-sensitive potassium (KATP) channel activator pinacidil.ConclusionsBeta-blockers and ACE inhibitors do not reduce the maximal coronary flow response to adenosine A2A-agonists, whereas verapamil attenuated this vasodilation through inhibition of KATPchannels. The inhibitory effect of verapamil and KATPchannel inhibitors like glybenclamide on pharmacologic stress using adenosine or adenosine A2A-receptor agonists should be evaluated in the clinical setting to determine their potential for reducing the sensitivity of CAD detection with perfusion imaging