Tomographic thallium-201 myocardial perfusion scintigrams after maximal coronary artery vasodilation with intravenous dipyridamole. Comparison of qualitative and quantitative approaches.

Abstract

SUMMARY Eighty-six patients had thallium-201 (20'Tl) myocardial perfusion scintigrams after intense coronary artery dilation with i.v. dipyridamole. The dipyridamole was infused at 0.15 mg/kg/min for 4 minutes. Significant side effects were infrequent. Coronary angiography showed that 24 of our 86 patients had normal coronary vessels or -30% luminal obstruction in one coronary artery; 11 patients had a moderate coronary obstruction (30-55% diameter narrowing or systolic compression) in one major vessel; and 51 patients had significant coronary artery disease (CAD) (G 70% luminal obstruction in one or more major vessels). Tomographic and planar 201T1 scintigrams were obtained in each patient. Tomographic scintigrams were interpreted using quantitative or visual criteria; planar scintigrams were assessed using visual criteria only. From the tomographic images, "lower limit of normal" curves were derived from the normal group by computing a "mean minus N standard deviations" curve and by computing a range curve. Using the mean minus standard deviations curve, we could not obtain a test with high (> 80%) sensitivity and specificity. The range approach produced better results. Inclusion of patients with moderate obstructions in the normal group significantly distorted the resulting lower limit of normal curve. When visual criteria were used, interobserver variability was 40% for tomographic scintigrams and 44% for planar scintigrams. In the 24 patients with normal or nonsignificant CAD, quantitative analysis of the tomograms (range approach) indicated that one of 24 (4%) had a positive image (specificity 96%); in contrast, when visual criteria were used to interpret the tomographic or planar 201TI scintigrams, eight of 24 (33%) had positive scintigrams (specificity 67%). In the 51 abnormal patients, the sensitivity of detecting CAD was 46 of 51 (90%) for tomographic scintigrams interpreted quantitatively, 39 of 51 (76%) for tomographic scintigrams interpreted visually and 41 of 51 (80%) for planar scintigrams assessed visually. The tomographic imaging procedure (quantitative interpretation) also demonstrated a high sensitivity (89%) and specificity (100%) in 28 patients (10 normal and 18 CAD), with a clinical diagnosis of unstable angina pectoris. Overall, the predictive accuracy of an abnormal scintigram with quantitative tomographic imaging (98%) was significantly better (p < 0.05) than either qualitative planar or pinhole imaging.THALLIUM-201 (201T1) perfusion scintigraphy is widely used in the diagnosis of coronary artery disease (CAD).'-8 Although it enhances our ability to detect CAD, three major problems are associated with conventional 201Tl perfusion images: interpretation of the scintigrams has usually involved qualitative visual criteria; exercise is required to induce coronary vasodilation;'-' and sensitivity (usually 65-90%) is not optimal.' 8 When 201T1 myocardial perfusion scintigrams are interpreted using qualitative criteria, many problems arise, including considerable interobserver variability,9 obs...

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