Validation of ST/HR Hysteresis in Detection of
Coronary Artery Disease among Exercise Tested Patients Referred for Coronary Angiography

Rami Lehtinen^af, Jari Viik^b, Janne Kallio^ba, Willi Kaiser^c, Martin Findeis^c, Tiit Kööbi^a,
Kari Niemelä^d, Terho Lehtimäki^e, Väinö Turjanmaa^ag

^aDepartment of Clinical Physiology, Tampere University Hospital; ^bRagnar Granit Institute, Tampere University of Technology; ^dDivision of Cardiology, Dept. of Internal Medicine, Tampere University Hospital; ^eDepartment of Clinical Chemistry, Tampere University Hospital; ^fTampere Polytechnic; ^gMedical School, University of Tampere, Tampere, Finland, ^cGE Medical Systems Information Technologies GmbH, Freiburg i.B, Germany

Correspondence: Dr. Rami Lehtinen, Tampere Polytechnic, P.O. Box 21, FIN-33521 Tampere, Finland.
E-mail: rami.lehtinen@tpu.fi, phone +358 3 2647 499, fax +358 3 2647 490

1.    Introduction

Exercise ECG test remains the most widely used method for assessing myocardial ischemia and coronary artery disease (CAD) [Viik et al., 1997]. ST-segment/heart rate (ST/HR) hysteresis is a novel method integrating the diagnostic information of exercise and recovery phase of the test in heart rate adjusted manner [Lehtinen et al., 1996ab]. The objective of this study was to evaluate the validity of ST/HR hysteresis in detection the presence of significant (³50 % stenosis at least in one major coronary artery) CAD among exercise tested patients referred for coronary angiography.

2.    Methods

2.1.   Study Population

The computerized exercise ECG measurements of 1147 consecutive patients were digitally stored for later analysis in Tampere University Hospital, Finland, between October 2, 2001 and January 14, 2003. Each of these patients was referred by a physician for a routine clinical exercise ECG test and gave their informed consent. Of these patients, 158 were also examined by coronary angiography within 180 days of the exercise test, were not treated by coronary bypass surgery or coronary angioplasty between the exercise test and coronary angiography, and had exercise ECG successfully digitally stored. Of these 158 patient, 116 had a significant (³50 %) stenosis at least in one of the major coronary arteries (Patients with CAD) and 42 had either no stenosis or not significant (<50 %) stenosis in major coronary arteries (patients with no CAD). Population is described in Table 1.

Table 1.     Study population.

2.2.   Exercise Electrocardiography

Exercise tests were done with bicycle ergometer with commercial ECG recording system (CardioSoft®, GE Medical Systems). The full disclosure data were stored for later processing. The data were analyzed off-line by a modified CASE® (GE Medical Systems), in which the ST/HR hysteresis algorithm was implemented. Implemented algorithm was tested against the original one developed by Lehtinen et al. [1996b] and found to be identical.

In this study, the ST/HR hysteresis, ST/HR index, ST segment depression at peak exercise (STpeak) and ST segment depression at 3 minutes of postexercise recovery (STrec) were determined based on ST-segment depression at 60 ms after QRS-offset. Each classifier was determined as its maximum values obtained from Mason-Likar modification of standard 12 lead system (aVR, aVL and V1 excluded).

3.    Results

The classifiers were compared by selected cut points and comparing diagnostic accuracy. The cut points were selected equalizing the specificities of the classifiers with our previous study in different population having clinical reference group of 220 cases [Lehtinen et al., 1996a]. Based on that, the thresholds used for positive test values were 0.01 mV, 1.60 mV/bpm, 0.10 mV and 0.04 mV for ST/HR hysteresis, ST/HR index, STpeak and STrec, respectively. Results are presented in Table 2.

Table 2.    Sensitivities, specificities and diagnostic accuracies of diagnostic classifiers.

4.    Discussion

ST/HR hysteresis provided the highest diagnostic accuracy of 72.2 % in this population. STrec resulted to almost equal accuracy (70.3 %). The diagnostic accuracies of ST/HR index (58.9 %) and STpeak (53.8 %) were clearly poorer. The result was in line with our earlier studies and strengthens further the clinical importance of ST/HR hysteresis and recovery phase of exercise ECG test.

Acknowledgements

The financial support of the Academy of Finland, Medical Research Fund of Tampere University Hospital, and Research and Development Fund of Tampere Polytechnic are gratefully acknowledged.

References

Lehtinen R, Sievänen H, Viik J, Turjanmaa V, Niemelä K, Malmivuo J. Accurate detection of coronary artery disease by integrated analysis of the ST-segment depression/heart rate patterns during the exercise and recovery phases of the exercise electrocardiography test. American Journal of Cardiology, 78: 1002-1006, 1996a.

Lehtinen R, Vänttinen H, Sievänen H, Malmivuo J. A computer program for comprehensive ST-segment depression/heart rate analysis of the exercise ECG test. Computer Methods and Programs in Biomedicine, 50: 63-71, 1996b.

Viik J, Lehtinen R, Turjanmaa V, Niemelä K, Malmivuo J. The effect of lead selection on traditional and heart rate-adjusted ST segment analysis in the detection of coronary artery disease during exercise testing. American Heart Journal 134: 488-494, 1997.