A New Criterion Combining ST/HR Slope and ΔST/ΔHR Index for Detection of Coronary Artery Disease in Patients on Digoxin Therapy

We evaluated the clinical value of a new index combining ΔST/Δheart rate (HR) index and ST/HR slope for diagnosing coronary artery disease (CAD) in patients on digoxin therapy. Exercise treadmill tests were performed by 72 patients on digoxin therapy. Simple HR–adjusted indexes of ST-segment depression during exercise (ΔST/ΔHR index) and the decline calculated from the final 12 data points relating ST-segment depression to HR (ST/HR slope) were determined. A new index was obtained by subtracting the ΔST/ΔHR index from the ST/HR slope. On thallium scintigraphy, 37 of the 72 patients showed reversible perfusion defects related to the diseased coronary artery. The new index derived from this ST-HR relation was 4.1 ± 3.6 μV/beats/min in the ischemic group and 1.3 ± 1.0 μV/beats/min in the group of patients without ischemia (p <0.0001). An ST-HR relation ≥1.5 was found in 33 of the 37 patients in the ischemic group, and in 7 of the 35 patients without ischemia (p <0.0001). The sensitivity of this criterion for prediction of myocardial ischemia was 89%, the specificity was 80%, and the predictive accuracy was 85%. Thus, this new ST-HR index is useful for detecting CAD in patients on digoxin therapy.