Heart rate adjustment of ST depression in patients with coronary disease and negative standard exercise tests

Heart rate (HR) adjustment of ST depression (STD) has been shown to correct ly classify exercise test findings in up to 85% of normal subjects and pati ents with "equivocal" electrocardiographic (ECG) responses (greater than or equal to 100 mu V upsloping STD), but the performance of these methods in patients with truly negative ECG responses (<100 mu V STD) has not been exa mined in detail. We reviewed negative standard exercise ECGs in 54 men and women (mean age 61 years) with coronary disease, comprising 16% of consecut ive treadmill tests that were performed in 337 patients with angiographic c oronary artery disease or stable angina. Mean STD was only 63 +/- 21 mu V ( 0.63 mm) in these negative tests. Despite these subthreshold values for STD , the ST/HR index was abnormal (greater than or equal to 1.6 mu V/bpm) in 2 7 of 54 patients (50%) when STD was adjusted for the change in KR during ex ercise. Compared with patients with normal values for KR-adjusted STD, pati ents with an abnormal ST/HR index were slightly older (64 vs. 58 years, P < 0.05) and demonstrated a trend toward lower exercise duration (10.0 vs. 11 .8 min). An abnormal ST/HR index was associated with greater subthreshold S TD (73 vs. 53 mu V, P < 0.0005) and smaller HR change (35 vs. 56 bpm, P < 0 .0001) with exercise. Among the 27 patients with a normal ST/HR index by si mple HR adjustment, 11 (44%) had abnormal ST/HR slopes (greater than or equ al to 2.4 mu V/bpm) by the more complex linear regression method. Therefore , KR adjustment of STD contributes to the improved sensitivity of the exerc ise ECG by correct classification of some patients with truly negative stan dard tests. The magnitude of subthreshold STD and the extent of KR change w ith exercise both contribute to improved test performance. The increased se nsitivity afforded by HR adjustment of STD highlights the importance of the precise measurement of subthreshold STD that is afforded by computerized E CG during exercise testing.