ST/HR variables in firefighter exercise ECG – relation to ischemic heart disease

Exercise electrocardiography (ExECG) is regularly performed by Swedish firefighters by law. Heart rate‐corrected analysis of ST segment variables (ST/HR) has shown improved prediction of ischemic heart disease (IHD) compared to ST depression alone. This has not previously been extensively studied in asymptomatic persons with a low probability of IHD. We therefore evaluated the predictive performance of ST/HR analysis in firefighter ExECG. ExECG was studied in 521 male firefighters. During 8.4 ± 2.1 years, 2.3% (n = 12) were verified with IHD by catheterization or myocardial scintigraphy (age 51.5 ± 5.5 years) and were compared with firefighters without imaging proof of IHD (44.2 ± 10.1 years). The predictive value of ST depression, ST/HR index, ST/HR slope, and area and rotation of the ST/HR loop was calculated as age‐adjusted odds ratios (OR), in 10 ECG leads. Predictive accuracy was analyzed with receiver operating characteristics (ROC) analysis. ST/HR index ≤−1.6 μV/bpm and ST/HR slope ≤−2.4 μV/bpm were associated with increased IHD risk in three individual leads (all OR > 1.0, P < 0.05). ST/HR loop area lower than the fifth percentile of non‐IHD subjects indicated IHD risk in V4, V5, aVF, II, and –aVR (P < 0.05). ST depression ≤−0.1 mV was associated with IHD only in V4 (OR, 9.6, CI, 2.3‐40.0). ROC analysis of each of these variables yielded areas under the curve of 0.72 or lower for all variables and leads. Clockwise‐rotated ST/HR loops was associated with increased risk in most leads compared to counterclockwise rotation. The limited clinical value of ExECG in low‐risk populations was emphasized, but if performed, ST/HR analysis should probably be given more importance.