Influence of the prevalence of coronary artery disease in patients with normal myocardial perfusion SPECT imaging. Cooperative study in South America

An important feature of myocardial perfusion imaging is the ability to predict prognosis and identify high- and low-risk patients for coronary events. According to Bayes' theorem, the significance of test's results, relates not only the sensitivity and specificity of a test but also the prevalence of disease in the population under study. Aim: evaluate the relationship between pretest likelihood (PTL) and coronary events (CE) in patients with normal myocardial perfusion SPECT imaging during a long period of time. Material and Methods: The population included 709 patients (411 men and 298 women, mean age 58 years old) who underwent stress/rest myocardial perfusion SPECT imaging at nuclear cardiology laboratories in Argentina and Brazil, with scintigraphic images interpreted as normal. Analyzed variables: clinical, EKG and stress test. Perfusion agents: Tc-99m-tetrofosmin: 36.5%, Tc99m-sestamibi 5.8% and Tl-201 57.7%. Mean follow up: 919 days. CE: soft (unstable angina and need for revascularization) and hard (AMI and cardiac death). Results: Stress test: exercise stress test 72.2%, dipyridamole 25%, adenosine 1.7%, dobutamine 1.1%. PTL [<= 15%]: 41%, PTL [16-78%]: 28%, PTL [79-99%]: 8% and known CAD: 23%. Gender: male/female (M/F): 58/42%, age (M/F): 56.1/60.7 years old, smoker (M/F): 39/22% (p<0.0001), high blood pressure (M/F): 48/56% (p=0.043), PTL [16-78%] (M/F): 24/33% (p=0.022), PTL [79-99%] (M/F): 56/12% (p<0.0001), known CAD (M/F): 29/14% (p<0.0001), stress time >9' (M/F): 59/11% (p<0.0001). Cumulative CE rate and mean PTL in patients with CE during follow up are presented. Relationship between PTL and CE in total population vs. patients with CE: mean PTL 46 vs. 68.5% (p=0.041) and PTL [>78%] 31 vs. 50%. Conclusions: 1) There was a relationship between PTL, events rate and time to event. 2) We found a low hard events rate (0.85%). 3) The results in this group of patients with normal myocardial perfusion SPECT imaging may suggest a guarantee period of low risk of coronary events between 2-3 years. 4) In spite of there is a low event rate in total population with normal myocardial perfusion imaging, patients with highest prevalence of coronary artery disease have more statistical probabilities of coronary events and therefore they have to be watched closely