ST/HR Index as a Parameter for Predicting Thallium Results in Patients with an Abnormal Exercise Electrocardiogram

Neil L. Coplan, Alejandro Junger, Victor Atallah, Gilbert W Gleim.

Lenox Hill Hospital, New York, N.Y.

This study evaluated use of the ST/HR index in patients with an abnormal exercise-related EKG for predicting the presence of a reversible thallium defect (ThPOS) of a normal scan (ThNEG). The SPECT Thallium-201 scans of 144 women and 148 men with >= 1 mm horizontal/downsloping ST depression during symptom-limited exercise (treadmill) thallium testing were reviewed. Patients with baseline ST abnormalities or a prior exercise test as a reason for referral were not included. ThPOS was present in 41/144 (28%) of women and in 84/148 (57%) of men. ThPOS had a significantly higher age than ThNEG (women: 65 +/- 1.6 vs 60 +/- l, P<.02, men: 62 +/- 1 vs 57.6 +/- 1.4, P<.01); there were no other significant differences in risk factors for CAD. There was no difference in magnitude of ST depression between ThPOS and ThNEG in men or women. ThPOS women had a significantly higher ST/HR index than ThNEG women (3 +/- .2 vs 2.2 +/- .l, P<.0l); ThPOS men had a significantly higher ST/HR index than ThNEG men (3.4 +/- .3 vs 2.4 +/- .2, P<.0l). Using ST/HR index of 1.6 identified 40% of ThNEG women and 27% of THNEG men correctly, but failed to identify 22% of ThPOS women and 19% of ThPOS men. Using the ST/HR index of 2.6 improved identification of ThNEG, but showed worse results for ThPOS. The receiver operating curve characteristics suggest that the ST/HR index has limited applicability for predicting thallium results in patients with an abnormal exercise EKG.

             WOMEN            WOMEN              MEN              MEN

        ---------------  ---------------   ---------------  ---------------

ST/HR    < 1.6   > 1.6    < 2.6   > 2.6     < 1.6   > 1.6    < 2.6   > 2.6

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ThPOS      9       32       17      24        16      68       36      48
ThNEG     41       62       76      27        17      47       43      21
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*p<0.05

Circulation, Vol. 94, No. 8, Supplement 1, October 1994.