99Tcm-Sn pyrophosphate scanning in suspected acute myocardial infarction using a mobile rectilinear scanner

99Tcm stannous pyrophosphate injected intravenously gives a positive image of freshly damaged myocardium but not of normal or scarred myocardium. It is safe, cheap and generally available. One hundred and forty patients admitted to hospital with possible myocardial infarction were scanned with a mobile rectilinear scanner of the type available in most district general hospitals. When the diagnosis of infarction was definite on clinical, electrocardiographic and enzyme criteria the anterior scan was positive in 31 out of 36 patients (86%); and when it was probable, the scan was positive in 28 out of 41 (68%) and when it was doubtful the scan was positive in 23 out of 63 (37%). The optimum time for scanning was between the second and seventh days. Pyrophosphate scanning is a very valuable investigation even though it is not an absolute discriminator of myocardial infarction. It is useful in assessing patients with atypical or doubtful symptoms of infarction where the ECG is already abnormal or where there are other causes of raised enzyme concentrations. False negative scans are not common, but a negative scan does not outweigh strong alternative evidence of infarction. Positive scans occur in some patients with unstable angina without confirmatory evidence of infarction. Positive scans due to extracardiac lesions are distinguished readily.