Sensitivity and Specificity of Tc-99m-Pyrophosphate Myocardial Scintigraphy for the Detection of Acute Myocardial Infarction

Tc-99m-pyrophosphate myocardial scintigraphy was performed on 1,077 patients admitted to the Coronary Care Unit. Results of scintigraphy were compared to the diagnosis as established by ECG, enzymes, and clinical findings to determine the sensitivity and specificity of scintigraphy for the diagnosis of acute myocardial infarction (AMI). Scintigrams were graded according to the intensity of myocardial radioactivity and the distribution pattern of activity as either diffuse or localized. In a coronary care unit, a scintigram of positive intensity grade is 92% sensitive and 68% specific for the diagnosis for AMI. A localized pattern of myocardial radioactivity is 66% sensitive and 93% specific for AMI. With a localized pattern of the highest intensity, the sensitivity is 28% with a specificity of 99.8% for AMI. Therefore, a myocardial scintigram of normal intensity grade excludes the diagnosis of AMI with a 92% probability. A localized pattern is a strong indicator of an AMI and a localized pattern of the greatest intensity is very specific for AMI.