Evaluation of radioactive potassium and its analogues for imaging myocardial infarcts

An extensive clinical evaluation was undertaken to assess the value of myocardial infarct imaging with radioactive potassium and analogues. Of 130 patients so examined, 80 were diagnosed as having suffered infarcts in the recent or distant past on the basis of all information other than the scan. The radionuclide imaging results were abnormal in 87.5% overall, 97% in acute transmural infarcts, and 83% in lesions over 3 weeks old. In 50 patients not considered to have had myocardial infarcts or contusions, apparently false abnormal results were obtained in 15%. These were all patients in whom additional diagnostic help was desired after the ordinary laboratory tests and electrocardiograms. Excellent agreement of infarct location was discovered on comparing radionuclide scans with radiographic contrast ventriculography. On comparing electrocardiograms with scans for infarct location, 85% complete or partial correlation was revealed. Agreement between scan abnormalities and significant-appearing coronary arteriographic lesions was rather poor, causing one to realize that 43K scan abnormalities indicate regions of poor blood extraction by old or recent infarcts, rather than just poor regional arterial perfusion. While costly, radionuclide scans often provide worthwhile information about presence or absence of infarcts as well as about their location and size. Electrocardiograms and blood enzyme levels each cost less, but are almost always performed in serial fashion. This makes them actually more expensive than a single scan. Furthermore, a normal scan in a patient being considered for acute coronary care may be used as potent argument against the presence of an infarct, thereby saving costly intensive care and monitoring.