Dual isotope thallium and indium antimyosin SPECT imaging to identify acute infarct patients at further ischemic risk

Forty-two patients (28 men and 14 women) with acute myocardial infarction (35 Q, seven non-Q wave) were injected with 2.0 mCi indium 111-labeled antimyosin (AM) monoclonal antibody (¹¹¹In AM) within 48 hours of the onset of chest pain. Forty-eight hours later (72-96 hours after onset of chest pain), patients were injected with 2.2 mCi thallium 201, and two sets of single-photon emission computed tomography (SPECT) images were obtained simultaneously using dual energy windows set for the 247 keV indium photopeak and the 70 keV thallium peak. Seventeen patients had repeat scans at 4 hours. ¹¹¹In AM uptake and ²⁰¹Tl defects were localized to one or more of 24 coronal and sagittal segments. Scans with only ²⁰¹Tl defects and corresponding ¹¹¹In AM uptake were classified as matches; scans with unmatched ²⁰¹Tl defects in addition to matching regions corresponding to electrocardiographic infarct location were classified as mismatches; and scans with ²⁰¹Tl and ¹¹¹In AM uptake in the same segments were classified as overlap. Scan patterns were correlated with clinical evidence for residual ischemia occurring within 6 weeks of infarct and including infarct extension, recurrent angina, and positive predischarge low-level or 6-week symptom-limited stress tests and with coronary anatomy. Fourteen patients had only matching patterns (group 1), 23 had mismatches (group 2), and five had ²⁰¹Tl-¹¹¹In overlap as the predominant pattern. None of the patients in group 1 had previous myocardial infarction; in each, the matched area corresponded to the Q wave location on electrocardiogram, and none had further in-hospital ischemic events or positive stress tests. In contrast, nine patients in group 2 had previous myocardial infarction, and 16 of the 23 went on to have further evidence of ischemia. There was a significant correlation between further ischemic events and mismatching ²⁰¹Tl-¹¹¹In AM activity (p<0.01). In conclusion, these results suggest that simultaneous SPECT imaging with ²⁰¹Tl and ¹¹¹In AM, performed 72-96 hours postinfarct, might be useful for identifying patients with benign in-hospital courses and those with myocardium at further ischemic risk.