The predictability of the Tc-99m pyrophosphate scan and statistical evaluation of the trade-off point

ABSTRACT

The technetium (Tc)-99m pyrophosphate scans have been used to diagnose acute myocardial infarctions and to confirm the equivocal cases. Many articles have been reported about its diagnostic performance and pitfalls. But there has been no evaluation of its predictability according to the grades of the radioactivity land statistical evaluation of the trade-off point, i.e., grade 2 and the area under the receiver operating characteristic curve. To achieve the goals, we reviewed 252 cases of Tc-99m pyrophosphate scans (acute transmural infarction [n=99], acute subendocardial infarction [n=7], unstable angina[n=16], old myocardial infarction [n=19] others [n=111]). The predictabilities of the scan are 98% in grade 4, 84% in grade 3, 83% in grade 2, 53% in grade 1 and 18% in non-uptake. The usual trade-off point, grade 2 is not statistically significant(Z=1.945, P=0.0259>0.01). The area under the receiver operating characteristic curve(Az) is 0.885. Our study shows that the probable main cause of the false negative cases is the time interval between the onset of symptoms and the test.