Background: Thallium-201 myocardial perfusion scintigraphy is commonly used for prognostication of patients with known or suspected coronary artery disease. The accuracy of scintigraphy for this purpose is far from optimal however. This study was conducted to determine the prognostic value of quantitative washout parameters in stress TI-201 myocardial perfusion scintigraphy.
Methods and Results: Qualitative (visual interpretation for myocardial perfusion defects) as well as quantitative (TI-201 washout analysis) studies were done in a group of 100 consec tive patients who underwent stress TI-201 myocardial perfusion scintigraphy . Thirty-six scans were qualitatively interpreted as abnormal. Three of the 100 patients had abnormal washout studies defined as washout rate less than 28%. The patients were followed-up for a mean of 26.3 ± 14.4 months for the occurence of cardiac events (unstable angina, non-fatal MI infarction, death revascularization). A total of 13 cardiac events were recorded. Twelve of these events were seen in the group with qualitatively abnormal scans (33% event rate), while all three patients with abnormal washout had cardiac events (100% event rate, p<0.05). Qualitative interpretation had a higher sensitivity for predicting cardiac events than quantitative washout analysis (92.3 versus 23.1%, p<0.05), but a lower specificity (72.4% versus 100%, p<0.05) and accuracy (75% and 90%, p<0.05). When washout data was added to qualitative interpretation, specificity significantly increased from 72.4% to 100% (p<0.05), and accuracy increased from 75% to 90% (p<0.05). There was no significant difference between the sensitivity, specificity and accuracy of washout and qualitative plus washout parameters. The three-year event-free rate was 98% for those in the normal qualitative group and 67% in the abnormal group (p<0.05). The event-free rate in the group with a normal washout rate was 89.6%, dropping to 0% in the group with ahnormal washout.
Conclusion: TI-201 quantitative washout analysis is a highly specific and accurate method for predicting future cardiac events and has incremental prognostic value over qualitative interpretation alone. The presence of abnormal washout discriminates between the low- and high-risk groups of patients, and addition of washout parameter to visual interpretation increases the accuracy of myocardial perfusion scintigraphy for prognostication.