Ever since the initial description of the Master step test in 1942 1 exercise electrocardiography (ECG) is the most widely used non-invasive method for the diagnosis of angina pectoris and the risk stratification of patients with known coronary artery disease (CAD). Its diagnostic accuracy in detecting significantly obstructive CAD based on the development of 'ischaemic' horizontal or down-sloping ST-segment depressions during exercise is, however, rather mediocre, with a sensitivity of 68% and a specificity of 77%.2 When tested in populations without referral bias from coronary angiography the sensitivity dropped to 50% whereas the specificity increased to 90%.3 However, the diagnostic and prognostic value of exercise ECG testing can be enhanced by incorporating in the assessment additional clinical data that exercise testing provides beyond the detection of ST-segment depression: exercise capacity, chronotropic and blood pressure response, heart rate recovery, calculation of the Duke treadmill score, T-wave alternans. [4][5][6][7] The diagnostic accuracy of exercise ECG can further be improved by analysis of the relation between ST-segment depression and heart rate changes during exercise and recovery.8 Heart rate adjustment of ST-segment depression during exercise performed by calculating the ST-segment/heart rate (ST/HR) slope or the ST/HR index can improve the sensitivity with preservation of specificity, mainly from improved classification of patients with equivocal test responses related to up-sloping ST-segments.9 Analysis of the ST/HR loop during exercise and early recovery for the presence of hysteresis provides an alternative method for determining exercise ECG test positivity and negativity. ST-segment depression caused by myocardial ischaemia resolves in patients more slowly during the early recovery phase than in normal individuals. This leads to the presence of a positive ST/HR hysteresis in ischaemic patients as the ST-depression during the first few minutes is greater than it was at the same heart rate during exercise, whereas normal individuals show a negative ST/HR hysteresis ( Figure 1). Analysis of post-exercise ST/HR hysteresis has been shown to provide higher diagnostic and prognostic test accuracy than that found for the standard ST-segment depression criteria and other ST/HR indices.
10,11Exercise ECG has a much lower specificity in patients with left ventricular hypertrophy in whom false positive tests are frequently observed.13-15 The present study by Zimarino et al. shows an enhanced diagnostic accuracy of ST/HR hysteresis in patients with hypertension-related left ventricular hypertrophy and confirms the very low specificity of the classic maximal ST-segment depression criterion that is clinically largely unreliable in detecting significant CAD in those patients. 16 The authors call for the adoption of the ST/HR hysteresis analysis in the interpretation of exercise testing in patients with left ventricular hypertrophy in order to limit the need for additional functional imaging tests...