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EQUIVOCAL STRESS THALLIUM SCINTIGRAMS DO NOT HAVE AN EQUIVOCAL PROGNOSIS

Although the interpretation of “equivocal” exercise thallium-201 scintigrams for the diagnosis of coronary artery disease is recognized as intermediate between normal and abnormal, the prognostic implication of this pattern has not been defined. Therefore, we followed for 1 year all 1484 pts referred to our laboratory for exercise thallium scintigrams between 1/1/79 and 1/1/81. The 233 pts with prior coronary bypass grafting (CABG), 110 with early CABG after testing, and 79 lost to followup were excluded. In the 819 diagnostic pts without previous myocardial infarction (MI) or CABG and the 243 MI pts with previous MI but not CABG, there were 58 events (11 deaths from a cardiac cause, 19 nonfatal MI's, and 28 worsening of chest pain requiring late CABG). The 1 year event rate (for 100 pts/year) and percentage of each thallium pattern were: Tl Pattern Diagnostic Post MI RATE PER CENT RATE PER CENT NORMAL 1.1 46.2 8.6 14.4 EQUIVOCAL 0.5 23.0 4.9 16.9 FIXED 7.8 7.8 10.7 34.6 REVERSIBLE 11.6 23.1 14.5 34.2 Pts with equivocal scintigrams had similar symptom classifications, exercise ECG and exercise duration as the entire population. CONCLUSION Equivocal exercise thallium scintigrams occur frequently in clinical practice. Since the event rate for pts with equivocal scintigrams is comparable to that of pts with normal scintigrams, equivocal lesions should be considered as normal for prognostic purposes.