Single photon emission computed tomography v. planar imaging in recent myocardial infarction using technetium-99m pyrophosphate
Radionuclide imaging of the myocardium with technetium-99m-labelled pyrophosphate (PYP) is a sensitive method for the diagnosis of a recent (2-7 days old) myocardial infarct. Although the sensitivity of planar imaging with PYP is more than 95% for recent transmural infarcts, it varies between 30% and 95% in nontransmural infarcts. It has, however, been shown that single photon emission computed tomography (SPECT) considerably enhances the sensitivity of this technique in patients with proven non-transmural infarcts. In the present study SPECT is evaluated in patients with a doubtful diagnosis of a recent myocardial infarct. Ninety-nine consecutive patients, who were referred from a cardiology unit with an uncertain diagnosis of a recent myocardial infarction, were studied with routine planar and SPECT imaging with PYP. Images were obtained 3 hours after an intravenous injection of 600 MBq PYP. The images were viewed independently by 3 experienced nuclear medicine physicians in a retrospective analysis of the results. These were reported as positive, equivocal or negative for myocardial infarction. There were 30 patients with positive and 44 with negative images using both methods of imaging. Twenty-three patients with normal or equivocal images on the planar views were regarded as positive on the SPECT studies. The difference was highly significant (P < 0,001). SPECT considerably improved the sensitivity of PYP imaging in this series. It increased image quality, gave a much clearer delineation of the infarct and enhanced observer confidence during reporting. Furthermore, the method is non-invasive and inexpensive and should considerably shorten the hospital stay of many patients in whom a firm diagnosis of a recent myocardial infarction could not be made by conventional means.