Value of positive myocardial infarction imaging in coronary care units

Technetium-99m-pyrophosphate scintigraphy in patients with suspected acute myocardial infarction: impact of interobserver variability

Technetium-99m-pyrophosphate (TcPYP) scintigraphy may have great value in patients with suspected acute myocardial infarction (AMI), but interobserver variability undoubtedly has adverse impact on predictive value. TcPYP scintigrams for 133 (80%) of 166 consecutive patients admitted for suspected AMI were interpreted independently by three experienced readers. Although there was complete agreement for 87 interpretations (65%), major discrepancies (i.e., at least one positive and one negative reading on the same scan) occurred for 28 scans (21%). To assess predictive accuracy, patients were categorized as follows: 36 had definite AMI manifest by new ECG Q waves and/or CK-MB evidence of AMI (group I), 56 were classified as possible AMI (group II), and 41 had AMI excluded (group III). Using only the definitive diagnostic categories (groups I and III), accuracy for each reader approximated 0.68, with no single reader being correct more often than any other.

Accuracy of hospital diagnosis of myocardial infarction

The accuracy of diagnosis of myocardial infarction (MI) was investigated in 380 consecutive patients admitted to hospital with suspected MI. Patients were classified according to World Health Organization criteria as having either definite MI, possible MI, no MI or unclassified through insufficient information. Of 214 patients with definite MI, 202 were diagnosed as MI in the case records (false negative rate 6%). Of 32 patients with possible MI, one was diagnosed as MI in the case records (false negative rate 97%). All 129 patients with MI were correctly diagnosed in the case records. Five patients were unclassified. MI was therefore diagnosed with high specificity. A correct diagnosis in the group with possible MI may not be essential for optimal hospital management, since no deaths occurred in these patients and most were not monitored in hospital.

How long should patients with suspected myocardial infarction be under observation in hospital?

Out of 368 patients admitted to hospital for chest pain and suspected acute myocardial infarction, 267 were discharged within 24 hours on the basis of the clinical picture, electrocardiogram, and serum activities of aspartate transaminase, alpha-hydroxybutyrate dehydrogenase, and creatine phosphokinase. The patients were followed up for 28 days, during which 17 were readmitted, two of them twice and one three times. Two of the patients were readmitted with non-fatal acute myocardial infarction, and two died. The patients had been primarily divided into two groups: those admitted with presumably non-coronary chest pain (77 patients) formed group 1 and those with obvious coronary chest pain (190 patients) group 2. Both deaths occurred in patients in group 2 but the incidences of events during the follow-up period were otherwise similar in the two groups, and some patients in both groups may have had small acute myocardial infarctions when first admitted. The decision to keep in hospital or discharge a patient with chest pain of recent onset can be made within 24 hours of admission. To discharge the patient acute myocardial infarction need not necessarily be excluded and conventional tests are enough to enable a decision to be made.