Effect of ST segment measurement point on performance of standard and heart rate-adjusted ST segment criteria for the identification of coronary artery disease

ST segment/heart rate hysteresis improves the diagnostic accuracy of ECG stress test for coronary artery disease in patients with left ventricular hypertrophy

BACKGROUND

The exercise electrocardiographic stress test (ExET) is the most widely used non-invasive diagnostic method to detect coronary artery disease. However, the sole ST depression criteria (ST-max) have poor specificity for coronary artery disease in patients with left ventricular hypertrophy. We hypothesised that ST-segment depression/heart rate hysteresis, depicting the relative behaviour of ST segment depression during the exercise and recovery phase of the test might increase the diagnostic accuracy of ExET for coronary artery disease detection in such patients.

METHODS

In three cardiology centres, we studied 113 consecutive patients (mean age 66 ± 2 years; 88% men) with hypertension-related left ventricular hypertrophy at echocardiography, referred to coronary angiography after an ExET. The following ExET criteria were analysed: ST-max, chronotropic index, heart rate recovery, Duke treadmill score, ST-segment depression/heart rate hysteresis.

RESULTS

We detected significant coronary artery disease at coronary angiography in 61 patients (53%). At receiver-operating characteristic analysis, ST-segment depression/heart rate hysteresis had the highest area under the curve value (0.75, P < 0.001 when compared with the 'neutral' receiver-operating characteristic curve value of 0.5). Area under the curve values were 0.68 (P < 0.01) for the chronotropic index, 0.58 (P = NS) for heart rate recovery, 0.57 (P = NS) for ST-max and 0.52 (P = NS) for the Duke treadmill score.

CONCLUSIONS

Among currently available ExET diagnostic variables, ST-segment depression/heart rate hysteresis offers a substantially better diagnostic accuracy for coronary artery disease than conventional criteria in patients with hypertension-related left ventricular hypertrophy.

ST changes and temporal relation to the J point during heart rate increase and myocardial ischemia

There is no concensus concerning where in the ST segment to measure. We studied the relation between different J point intervals to ST results during tachycardia and ischemia. Symptomatic (anesthetized) patients with coronary artery disease were paced at ascending incremental levels until they became ischemic. ST vector magnitude and ST vector change from baseline (STC-VM) as well as the sum of ST changes from all 12 electrocardiogram (ECG) leads (ECG ST sum) were measured at J point 0 millisecond, J + 20, J + 60, and J + 80 milliseconds for 34 patients. ST segments increased in similar fashion during pacing and ischemia. There was no difference in ST results when measurement was performed at different time intervals for both STC-VM and ECG ST sum. We conclude that ST assessment by ST change from baseline is not affected by different J point intervals during increased heart rate and ischemia in this clinical model of pacing-induced ischemia and vectorcardiographic ST analysis.

Receiver operating characteristic (ROC) curves and the definition of threshold levels to diagnose coronary artery disease on electrocardiographic stress testing. Part II: the use of ROC curves in the choice of electrocardiographic stress test markers of ischaemia

A common problem in diagnostic medicine, when performing a diagnostic test, is to obtain an accurate discrimination between 'normal' cases and cases with disease, owing to the overlapping distributions of these populations. In clinical practice, it is exceedingly rare that a chosen cut point will achieve perfect discrimination between normal cases and those with disease, and one has to select the best compromise between sensitivity and specificity by comparing the diagnostic performance of different tests or diagnostic criteria available. Receiver operating characteristic (or receiver operator characteristic, ROC) curves allow systematic and intuitively appealing descriptions of the diagnostic performance of a test and a comparison of the performance of different tests or diagnostic criteria. This review will analyse the basic principles underlying ROC curves and their specific application to the choice of optimal parameters on exercise electrocardiographic stress testing. Part II will be devoted to the comparative analysis of various parameters derived from exercise stress testing for the diagnosis of underlying coronary artery disease.

The effects of enhanced external counterpulsation on myocardial perfusion in patients with stable angina: a multicenter radionuclide study

BACKGROUND

Enhanced external counterpulsation (EECP) reduces angina and extends time to exercise-induced ischemia in patients with symptomatic coronary disease. One- and two-center studies and a retrospective case series reported that EECP improves myocardial perfusion in stable angina pectoris. We sought to critically evaluate and quantify the effect of EECP on myocardial perfusion.

METHODS

In 6 US university hospitals, EECP was performed for 35 hours in patients with class II to IV angina who had exercise-induced myocardial ischemia. Symptom-limited quantitative gated technetium Tc 99m sestamibi single photon emission computed tomography exercise perfusion imaging was performed at baseline and 1 month post-EECP. Sestamibi was injected at the same heart rate in both stress tests. Single photon emission computed tomography images were read at a blinded core laboratory.

RESULTS

Thirty-seven patients were enrolled, 34 of whom completed pre- and post-EECP stress testing. The mean age was 61 +/- 10 years, 81% were male, 78% had prior revascularization, and 68% had 3-vessel disease. The mean angina class decreased from 2.7 +/- 0.7 at baseline to 1.7 +/- 0.7 after EECP (P < .001). Exercise duration increased from 9.1 +/- 3.7 minutes at baseline to 10.2 +/- 3.6 minutes post-EECP (P = .03). The average percentage of tracer uptake, magnitude of reversibility, average thickening fraction, and the left ventricular ejection fraction remained unchanged after EECP.

CONCLUSIONS

We confirm previous report that EECP reduces angina and improves exercise capacity. There were no significant changes in mean defect magnitude, amount of reversibility, thickening fraction, and ejection fraction measured using myocardial quantitative single photon emission computed tomography imaging when compared at identical pre- and post-EECP heart rates.

ST-segment deviations during pacing-induced increased heart rate in patients without coronary artery disease

INTRODUCTION

In order to interpret ST-segment changes as an indicator of ischemia in patients with higher heart rates (HRs), the relation between ST-segment levels and HR needs to be well defined in subjects without coronary artery disease.

METHODS

Eighteen patients with normal ECGs in the catheterization laboratory, after radiofrequency ablation of AV nodal re-entry tachycardia or an accessory pathway were included. Computerized online vectorcardiography (VCG) was performed during step-wise atrial pacing-induced increases in HR up to 150 beats min(-1) (bpm). The ST-vector magnitude (ST-VM) and the relative ST change vector magnitude (STC-VM) were analysed at the J point, J + 20 and J + 60 ms.

RESULTS

There was no divergence in the course of ST-VM or STC-VM based on J point + 0, 20, or 60 ms during increasing HR. The STC-VM mean values increased progressively during increases in HR above 100 bpm, with an average increase in STC-VM of 15-20 microV per 10 bpm increases in HR. The ST-VM response during HR increases showed a heterogeneous and unpredictable pattern.

CONCLUSION

The STC-VM increases linearly with rising HRs above 100 bpm. The STC-VM can exceed widely recognized ischemic thresholds during higher HRs in the absence of ischemia. The choice of J point time to ST-VM measurements as tested here is not important for the STC-VM relation to HR at these HR levels. Further clinical testing is needed to improve the diagnostic specificity of STC-VM measurements during increased HRs.

Coronary artery disease diagnosis based on exercise electrocardiogram indexes from repolarisation, depolarisation and heart rate variability

Several indexes have been reported to improve the accuracy of exercise test electrocardiogram (ECG) analysis in the diagnosis of coronary artery disease (CAD), compared with the classical ST depression criterion. Some of them combine repolarisation measurements with heart rate (HR) information (such as the so-called ST/HR hysteresis); others are obtained from the depolarisation period (such as the Athens QRS score); finally, there are heart rate variability (HRV) indexes that account for the nervous system activity. The aim of this study was to identify the best exercise ECG indexes for CAD diagnosis. First, a method to automatically estimate repolarisation and depolarisation indexes in the presence of noise during a stress test was developed. The method is divided into three stages: first, a preprocessing step, where QRS detection, filtering and baseline beat rejection are applied to the raw ECG, prior to a weighted averaging; secondly, a post-processing step in which potentially noisy averaged beats are identified and discarded based on their noise variance; finally, the measurement step, in which ECG indexes are computed from the averaged beats. Then, a multivariate discriminant analysis was applied to classify patients referred for the exercise test into two groups: ischaemic (positive coronary angiography) and low-risk (Framingham risk index < 5%). HR-corrected repolarisation indexes improved the sensitivity (SE) and specificity (SP) of the classical exercise test (SE = 90%, SP = 79% against SE = 65%, SP = 66%). Depolarisation indexes also achieved an improvement over ST depression measurements (SE = 78%, SP = 81%). HRV indexes obtained the best classification results in our study population (SE = 94%, SP = 92%) by means of the very high-frequency power (VHF) (0.4-1 Hz) at stress peak.

Differences between local investigator and core laboratory interpretation of the admission electrocardiogram in patients with unstable angina pectoris or non-Q-wave myocardial infarction (a Thrombin Inhibition in Myocardial Ischemia [TRIM] substudy)

The present study compares the on-site interpretation of an admission electrocardiogram (ECG) with core laboratory results in a large, multicenter trial of 516 patients diagnosed with unstable angina pectoris or non-Q-wave myocardial infarction. The local investigators evaluated the admission ECG regarding ST-T changes before the ECGs were sent to the core laboratory for blinded interpretation. The strength of agreement between the observations was described by kappa statistics. There was a poor agreement regarding identification of ST-segment elevation, with 17 patients identified by the local investigator versus 92 by the core laboratory (kappa = 0.05). There was a fair agreement on ST-segment depression with 158 patients diagnosed on-site versus 64 by the core laboratory (kappa = 0.38). Identification of T-wave inversion demonstrated good agreement with 306 patients diagnosed on-site versus 280 by the core laboratory (kappa = 0.63). A moderate agreement regarding identification of a normal ECG was found with 101 patients on-site versus 135 in the core laboratory (kappa = 0.42). Independent variables, including peak creatine kinase-MB and 30-day outcome, were more closely related to core laboratory results than the local investigator's interpretation of the admission ECG. Thus, in the present study, considerable differences were demonstrated between the on-site interpretation of the admission ECG and the blinded evaluation performed in the core laboratory regarding relatively simple electrocardiographic variables. The results suggest that more widespread use of independent evaluation of clinical data should be incorporated in future clinical trials.

Correct utilization of exercise electrocardiographic leads in differentiation of men with coronary artery disease from patients with a low likelihood of coronary artery disease using peak exercise ST-segment depression

In this study we compared the diagnostic characteristics of the individual exercise electrocardiographic leads, 3 different lead sets comprising standard leads and the effect of the partition value in the detection of coronary artery disease (CAD). The diagnostic variable used was ST-segment depression at peak exercise, and the study population consisted of 101 patients with CAD and 100 patients with a low likelihood of the disease. The lead system used was the Mason-Likar modification of the standard 12-lead system and exercise tests were performed on a bicycle ergometer. The comparisons were performed by means of receiver-operating characteristic analysis and by determining sensitivities at a fixed 95% specificity. These properties, defined here as diagnostic capacity, were the most efficacious in leads I, -aVR, V4, V5, and V6. Diagnostic capacities in leads aVL, aVF, III, V1, and V2 were quite poor; statistical comparisons indicated significant differences between these leads and lead V5 (p < or = 0.0001 in each case). Use of the maximum value of ST-segment depression at peak exercise derived from all 12 leads produced a considerable decrease in the diagnostic capacity of the exercise electrocardiogram compared with lead V5. The exclusion of leads aVL, V1, and III improved the diagnostic capacity compared with the 12-lead set, but it was still smaller than that of lead V5. With use of a lead set with the 5 best leads increased the diagnostic capacity over other lead sets and over any individual lead. Further improvement was noted when a 50% smaller partition value was applied to leads I and -aVR than for the other leads (p = 0.041). In conclusion, this study suggests that use of leads I, -aVR, V4, V5, and V6 is the most influential when differentiating between patients with CAD and patients with a low likelihood of disease using peak exercise ST-segment depression. The effective use of leads I and -aVR requires the partition value applied for these leads to be 50% smaller than that used for the lateral precordial leads.

Haemodilution tolerance in patients with mitral regurgitation

Haemodynamic parameters and oxygen consumption were determined in 20 patients with mitral regurgitation before and after a 12 ml.kg-1 isovolaemic exchange of blood for 6% hydroxyethyl starch. During haemodilution, mean (SEM) haemoglobin concentration decreased from 13.0 (0.4) to 10.3 (0.4) g.dl-1 (p = 0.001). With cardiac filling pressures maintained at predilution levels, cardiac index increased from 1.84 (0.08) to 1.94 (0.08) l.min-1.m-2 (p = 0.025) while systemic vascular resistance decreased from 1556 (86) to 1425 (83) dyne.s.cm-5 (p = 0.002) and oxygen extraction increased from 31.7 (1.1) to 37.3 (1.4)% (p = 0.001) resulting in an unchanged oxygen consumption. The haemodynamic response to haemodilution was not affected by the patients' cardiac rhythm, i.e. whether it was sinus rhythm or atrial fibrillation. In conclusion, isovolaemic haemodilution to a haemoglobin of 10.3 g.dl-1 is well tolerated in patients with mitral regurgitation. Compensatory mechanisms include both an increase in cardiac index and an increase in oxygen extraction.

Effect of ST segment measurement point on performance of exercise ECG analysis

To evaluate the effect of ST-segment measurement point on diagnostic performance of the ST-segment/heart rate (ST/HR) hysteresis, the ST/HR index, and the end-exercise ST-segment depression in the detection of coronary artery disease, we analysed the exercise electrocardiograms of 347 patients using ST-segment depression measured at 0, 20, 40, 60 and 80 ms after the J-point. Of these patients, 127 had and 13 had no significant coronary artery disease according to angiography, 18 had no myocardial perfusion defect according to technetium-99m sestamibi single-photon emission computed tomography, and 189 were clinically 'normal' having low likelihood of coronary artery disease. Comparison of areas under the receiver operating characteristic curves showed that the discriminative capacity of the above diagnostic variables improved systematically up to the ST-segment measurement point of 60 ms after the J-point. As compared to analysis at the J-point (0 ms), the areas based on the 60-ms point were 89 vs. 84% (p=0.0001) for the ST/HR hysteresis, 83 vs. 76% (p<0.0001) for the ST/HR index, and 76 vs. 61% (p<0.0001) for the end-exercise ST depression. These findings suggest that the ST-segment measurement at 60 ms after the J-point is the most reasonable point of choice in terms of discriminative capacity of both the simple and the heart rate-adjusted indices of ST depression. Moreover, the ST/HR hysteresis had the best discriminative capacity independently of the ST-segment measurement point, the observation thus giving further support to clinical utility of this new method in the detection of coronary artery disease.

Accuracy of heart rate-adjusted ST segments in populations with and without posttest referral bias

We compared the accuracy of the ST segment/heart rate (STHR) index and slope to standard criteria (> or =1 mm horizontal/downsloping ST-segment depression at J + 60 msec) in 1358 patients (152 underwent angiography). All exercise tests used the Cornell protocol and computer measurements of maximum ST-segment depression at J + 60 msec. Test accuracy was determined for the entire group with a probability-based method. Thresholds with equal specificity to standard criteria were determined. By using only patients who underwent angiography, neither STHR index nor slope was more accurate than standard criteria (maximum sensitivity: standard criteria, 42%; STHR index, 51%; STHR slope, 40%). However, by using the entire group, both STHR index and slope were more accurate than standard criteria, but only STHR index achieved statistical significance (maximum sensitivity: standard criteria, 31%; STHR index, 60%; STHR slope, 47%). We conclude that heart rate-adjusted ST-segment criteria are more accurate than standard ST-segment criteria. A lack of demonstration of improved accuracy of STHR index and slope only occurs in patients affected by posttest referral bias.

Usefulness of a quantitative analysis of the recovery phase patterns of the ST-segment depression in the diagnosis of coronary artery disease

PURPOSE

To assess the diagnostic value of the recovery phase patterns of the ST-segment depression in patients referred for chest pain.

PATIENTS AND METHODS

Continuous plots of ST-segment depression against heart rate during exercise and recovery were constructed within a population of 160 consecutive symptomatic patients who all had undergone catheterization (80 with > or = 1 stenosis > or = 50%). We used a new quantitative method of measurement allowing all kinds of rate recovery loops (even the so-called "intermediate" loops) to be considered for analysis. The measurements of the heart rate (HR)-adjusted ST-segment depression were performed at 20 and 60 ms from the J point, providing two different values of a quantified recovery loop index (RLI): RLI 20 and RLI 60.

RESULTS

Both RLI showed a higher specificity (0.81 +/- 0.04 and 0.74 +/- 0.05, respectively) than did the standard criterion (0.65 +/- 0.10), but the difference was significant regarding RLI 20 only (P = 0.011). As to the sensitivity, no significant differences were found among all of the criteria (0.74 +/- 0.05, 0.80 +/- 0.04, 0.76 +/- 0.05, respectively). The timing of measurements of the RLI within the repolarization phase did not affect their overall accuracy (0.77 +/- 0.03 for both RLI). The values of the receiver-operating characteristic (ROC) curve areas were significantly greater for both RLI (0.83 +/- 0.06 and 0.84 +/- 0.06 respectively) than for the standard criterion (0.75 +/- 0.07; P < 0.02). Finally, both RLI allowed to differentiate accurately the study subjects according to the number of diseased vessels, whereas the standard criterion could only distinguish between CAD patients and subjects with normal angiograms.

CONCLUSION

The quantitative analysis of the rate recovery phase patterns appears to be useful for the diagnosis of coronary heart disease and the assessment of its severity in symptomatic patients.

Intraoperative automated ST segment analysis: a reliable 'black box'?

PURPOSE

To review the application of intraoperative computerized ST analysis and its potential impact on postoperative outcomes.

SOURCE

Existing anaesthesia and cardiology literature.

PRINCIPAL FINDINGS

Computerized ST analysis was introduced into the operating room using exercise electrocardiographic (ECG) systems. In spite of sophisticated algorithms, errors do occur. Downsloping or horizontal ST depression are the classical criteria for ischaemia. Although algorithms have been developed and evaluated in exercise stress testing, only limited evaluation has been carried out in the operating room. This may be a concern since circumstances in the operating room may frequently lead to false positives. Similarly, studies suggest that all myocardial ischaemia may not exhibit ST changes. The diagnostic accuracy of ST depression in exercise stress testing also cannot be assumed in the operating room. Finally, if ST analysis is applied widely, without considering the population or disease prevalence, misdiagnosis may occur.

CONCLUSION

Given the number of anaesthetic tasks at-hand, on-line computerized ST analysis in the operating room can be a useful asset. The technology has its problems and should be applied with an understanding of its limitations and potential for errors. It should be applied in the operating room within the context of the population and disease prevalence.

Hemodilution tolerance in elderly patients without known cardiac disease

Hemodilution tolerance is not well defined in elderly patients. In 20 patients older than 65 yr and free from known cardiovascular disease, hemodynamic variables, ST segment deviation, and O2 consumption were determined prior to and after 6 and after 12 mL/kg isovolemic exchange of blood for 6% hydroxyethyl starch. The mean age of the patients was 76 +/- 2 yr (mean +/- SEM, range 66-88 yr). During hemodilution, hemoglobin decreased from 11.6 +/- 0.4 to 8.8 +/- 0.3 g/dL (P < 0.05). With stable filling pressures, cardiac index increased from 2.02 +/- 0.11 to 2.19 +/- 0.10 L.min-1.m-2 (P < 0.05) while systemic vascular resistance decreased from 1796 +/- 136 to 1568 +/- 126 dynes.s.cm-5 (P < 0.05) and O2 extraction increased from 28.0% +/- 0.9% to 33.0% +/- 0.8% (P < 0.05) resulting in a stable O2 consumption during hemodilution. No alterations in ST segments were observed in lead II during hemodilution. In lead V5, ST segment deviation became slightly less negative during hemodilution from -0.03 +/- 0.01 to -0.02 +/- 0.01 mV (P < 0.05). The moderate decrease in hemoglobin was fully compensated by both an increase in cardiac index and in O2 extraction. Electrocardiographic signs of myocardial ischemia were not observed in this population. In conclusion, isovolemic hemodilution to a hemoglobin value of 8.8 +/- 0.3 g/dL is well tolerated in elderly patients free from known cardiac disease at the ages of 65-88 yr.

Hemodilution tolerance in patients with coronary artery disease who are receiving chronic beta-adrenergic blocker therapy

Hemodilution tolerance is not well defined in patients with coronary artery disease receiving beta-adrenergic blockers chronically. Ninety patients scheduled for coronary artery bypass graft (CABG) surgery were randomized to a hemodilution (n = 60) and a control group (n = 30). During midazolam-fentanyl anesthesia, hemodynamic variables, ST segment deviation, and O2 consumption were determined prior to and after 6 and 12 mL/kg isovolemic exchange of blood for 6% hydroxyethyl starch. Hemoglobin decreased from 12.6 +/- 0.2 to 9.9 +/- 0.2 g/dL (mean +/- SEM, P < 0.05). With stable filling pressures, cardiac index increased from 2.05 +/- 0.05 to 2.27 +/- 0.05 L.min-1.m-2(P < 0.05) and O2 extraction from 27.4% +/- 0.6% to 31.2% +/- 0.7% (P < 0.05), resulting in stable O2 consumption. No alterations in ST segments were observed in leads II and V5 during hemodilution. Individual increases in cardiac index and O2 extraction were not linearly related to age and left ventricular (LV) ejection fraction (P = 0.841, P = 0.799). We conclude that isovolemic hemodilution to a hemoglobin value of 9.9 +/- 0.2 g/dL is well tolerated and fully compensated in patients with coronary artery disease receiving beta-adrenergic blockers chronically. Within the investigated ranges, the compensatory mechanisms during hemodilution are largely independent of age (35-81 yr) and LV ejection fraction (26%-83%).

Asymptomatic coronary artery disease detection: update 1996. A screening protocol using 16-lead high-resolution ECG, ultrafast CT, exercise testing, and radionuclear imaging

The authors have proposed a new four-step screening algorithm to detect asymptomatic coronary artery disease (CAD) in flight school candidates, cadets, and rated flyers of the Unites States Air Force (USAF). In step 1, the USAF Armstrong Laboratory (USAF/AL) risk profile and improved 16-lead high-resolution electrocardiogram/vectorcardiogram will be recorded at baseline. On routine follow-up evaluations, quantitative serial comparisons will be performed by the method of Kornreich. In step 2, beginning with flight school candidates and cadets, all three groups will be studied by the ultrafast computed tomograph (CT) protocol. Those candidates positive for coronary calcium will be studied by coronary angiography and ventriculography, and their eligibility for continued rated flight status will be determined by present criteria. In step 3, those candidates negative for coronary calcium by ultrafast CT will then be screened by the newly defined and improved high-sensitivity treadmill exercise test criteria. In step 4, candidates with a positive treadmill exercise test result, or who are also found in the upper quintile of the USAF/AL risk profile, wild also have exercise nuclear wall motion studies and perfusion scans. If these are abnormal and suggestive of myocardial ischemia, this subset will also be studied by heart catheterization and coronary angiography, and their eligibility for continued rated flight status will be determined by present criteria. The incidence of coronary calcium/no calcium for each degree of stenosis in the 6,000 flyers in each quintile was used to develop the following projections: (1) that more than 3 of 4 rated flyers with unsuspected CAD, and (2) more than 9 of 10 with severe flow-limiting CAD can be identified by these upgraded screening procedures. Evidence is herein presented that these enhancements will result in a major (5-8-fold) increase in case finding of this disease. Based on the estimate of four lost high-performance aircrafts per year from sudden incapacitation of the pilot due to CAD, when this four-step screen is fully operational, it can be expected to reduce the $80 million annual losses to the United States government from CAD by 85%, a savings of $68 million per year.

Comparison of the diagnostic accuracy of different methods of measurement of heart rate-adjusted ST-segment depression during exercise testing for identification of coronary artery disease

Within a population of 160 consecutive symptomatic patients who all had undergone catheterization (80 with > or = 1 stenosis > or = 50%), we compared the accuracy of different computerized measurements of the exercise-induced changes in ST-segment: (1) the standard criterion (> or = 0.1 mV flat/downsloping ST depression or > or = 0.15 mV upsloping depression, both 60 ms after the J point); (2) heart rate (HR)-adjusted ST-segment depression (ST/HR index measured at 0, 20, 40, 60, and 80 ms from the J point); (3) the HR-adjusted ST integral (ST/HR integral measured from 0 to 40 ms and from 40 to 80 ms after the J point). None of the ST/HR indexes or integrals were found to have a significantly greater sensitivity than the standard criterion. On the contrary, all ST/HR indexes and integrals showed a higher specificity (0.78 to 0.89) than did the standard criterion (0.65); moreover, the earlier the measurement within the repolarization phase, the better the overall accuracy: 0.71 for the standard criterion, 0.83 (p < 0.001), 0.80 (p < 0.01), 0.78 (p < 0.02), 0.78 (p < 0.02), 0.74 (p = NS) for the ST/HR indexes at 0, 20, 40, 60, and 80 ms, respectively; 0.81 (p < 0.001) and 0.78 (p < 0.02) for the ST/HR integrals calculated from 0 to 40 and from 40 to 80 ms, respectively. Consistently, the receiver-operating characteristic curve areas of ST/HR at 0, 20, and 40 ms were greater than those of ST/HR at both 60 and 80 ms. These findings are divergent from some other results given in published reports. We conclude that the accuracy of all exercise criteria is influenced by the population analyzed: our patients were representative of those currently seen by clinicians.

Comparison of ST-segment/heart rate slope analysis with standard ST-segment measurement criteria to outcome of exercise thallium-201 imaging

We compared standard ST-segment analysis and ST/HR slope analysis of exercise ECG studies with reference to outcome of exercise thallium-201 studies in 341 patients. Sensitivity was significantly better using ST/HR slope compared with standard ST analysis. Specificity was not significantly different.

Heart rate adjustment of ST segment depression and performance of the exercise electrocardiogram: a critical evaluation

Analysis of the rate-related change in exercise-induced ST segment depression using the exercise ST segment/heart rate slope and ST segment/heart rate index can improve the accuracy of the exercise electrocardiogram (ECG) for the identification of patients with coronary artery disease, recognition of patients with anatomically or functionally severe coronary obstruction and detection of patients at increased risk for future coronary events. These methods provide a more physiologic approach to analysis of the ST segment response to exercise by adjusting the apparent severity of ischemia for the corresponding increase in myocardial oxygen demand, which in turn can be linearly related to increasing heart rate. Solid-angle theory provides a model for the linear relation of ST segment depression to heart rate during exercise and a framework for understanding the relation of the ST segment/heart rate slope to the presence and extent of coronary artery disease. False positive and false negative test results of the heart rate-adjusted methods are well known in selected populations and require further clarification. Application of these methods is also highly dependent on the type of exercise protocol, number of ECG leads examined, timing of ST segment measurement relative to the J point and accuracy and precision of ST segment measurement. These methodologic details have been an important limitation to test application when traditional protocols and measurement procedures are required. When applied with attention to required details, the heart rate-adjusted methods can improve the usefulness of the exercise ECG in a range of clinically relevant populations.

Prevalence, characteristics, and risk stratification of electrocardiographic and symptomatic silence of myocardial ischemia despite scintigraphically evidenced ischemia in symptomatic patients presenting with severe coronary artery stenosis

Symptoms of angina pectoris and transient ST-segment depression are most commonly used to evidence acute myocardial ischemia during exercise testing. However, the diagnostic accuracy of either or both criteria in relation to clinical characteristics and the patient's exercise response has been a subject of controversy. The prevalence and severity of symptoms of angina pectoris and/or ST-segment depression were studied prospectively in 147 consecutive patients with a history of daily angina pectoris, scintigraphic evidence of exercise-induced myocardial ischemia, and coronary artery stenosis > 75%. Logistic regression analysis was applied to determine absence of any or both criteria by the clinical characteristics or exercise response of the patient. During exercise testing, ST-segment response failed to prove scintigraphically evidenced myocardial ischemia in 14/147 patients (10%) and 35/147 patients (24%) when ST-segment depression > or = 0.1 in either > or = 1 or > or = 2 ECG leads was chosen. Symptoms of angina pectoris were found to be absent in 69/147 patients (47%). Only 58 patients (40%) suffered from angina and met the ECG criterion at the time of scintigraphic myocardial ischemia. Absence of ST-segment depression was best predicted by clinical variables such as large myocardial infarction (increase: 2.6 times, p = 0.007), number of stenoses < or = 2 (2.0 times, p = 0.023), and presence of diabetes mellitus (4.3 times, p = 0.035). Painless myocardial ischemia was determined by blood response to exercising. Thus, a double product > 23 increased the risk of painless myocardial ischemia by 1.5 times (p = 0.017).(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic accuracy of heart rate-adjusted ST segments compared with standard ST-segment criteria

We compared the accuracy of ST segment/heart rate (ST/HR) index with that of standard criteria (> or = 0.1 mV horizontal/downsloping ST depression 80 ms after the J point) in 121 patients who had undergone angiography (49 with > or = 1 lesion with > or = 50% stenosis) and 50 clinically normal subjects. All exercise tests used the Cornell protocol and computer measurements of maximal ST depression 80 ms after the J point. Thresholds with equal specificity to standard criteria were determined for ST/HR index using each of the 2 normal groups (those who were normal by angiography and those who were clinically normal). In using only patients who underwent angiography, we found that the ST/HR index had a sensitivity that was not significantly greater than that of standard criteria (standard criteria 51%, ST/HR index 59%; p = 0.21). However, the receiver-operating characteristic curve area increased from 64 +/- 4 to 68 +/- 4 (p < 0.02). When clinically normal subjects were used instead of patients without angiographic disease, there was a clearly discernible improvement in sensitivity of ST/HR index over standard criteria (standard criteria 51%, ST/HR index 69%; p < 0.05). The associated curve areas were 69 +/- 4 and 79 +/- 3 (p < 0.001). Therefore, accuracy of the ST/HR index was marginally better than standard criteria only in patients who underwent angiography. When clinically normal subjects were used, the accuracy of the ST/HR index was definitely better than standard criteria. We conclude that the demonstration of improved accuracy of the ST/HR index depends on the population being tested.

Compartmental multivariate analysis of exercise ECGs for accurate detection of myocardial ischaemia

An accurate computer-assisted diagnostic method for detection of myocardial ischaemia, called MUSTA, is developed. MUSTA is based on compartmental multivariate analysis of variables available in the exercise ECGs, and is definitively implemented in Prolog. It is heuristically developed by determining diagnostic criteria, which interrelate a modified ST/HR-slope, ST-segment value and shape, and maximum heart rate, so that concordance with the TI-201 SPECT is maximised. In the learning group consisting of 47 patients, MUSTA provides a diagnostic accuracy of 98%, the detection of ischaemia being in absolute concordance with TI-201 SPECT. MUSTA is evaluated in a similar but independent group of 60 patients. Then, accuracy is 90%, and sensitivity is 94%. The performance characteristics are significantly better than those of the standard exercise ECG, whose diagnostic accuracy in these groups is 77% and 70%, respectively. This study suggests that MUSTA is a significant improvement for computerised assessment of myocardial ischaemia.

Solid-angle theory and heart rate adjustment of ST-segment depression for the identification and quantification of coronary artery disease

Determinants of the ST-segment response to exercise can be mathematically modeled by solid-angle theory, and heart rate adjustment of the magnitude of exercise-induced ST-segment depression can remodel the solid-angle relationship to provide a theoretic and practical basis for application of heart rate-adjusted indexes of ST depression in exercise electrocardiography. Solid-angle theory indicates that the magnitude of ST depression recorded at a surface electrode (epsilon) can be described as the product of spatial and nonspatial determinants: epsilon = (omega/4 pi).(delta Vm).K (equation 1), where omega is the solid angle subtending the boundary of the ischemic territory, delta Vm is the difference in transmembrane voltage between the ischemic and adjacent nonischemic regions, and K is a term correcting for differences in intracellular and extracellular conductivity and changes in end-plate conductance. As a consequence, the magnitude of ST depression recorded by a surface electrode will be proportional both to the area of ischemic territory subtended by the recording electrode, which reflects the solid angle, and to the local transmembrane potential difference, which in turn reflects the electric consequences of the metabolic severity of ischemia at the level of the myocardial cell. It follows from equation 1 that the amplitude of ST depression can accurately reflect the area of ischemic boundary only when the severity of ischemia is constant or otherwise controlled, and differences in ST depression will only reflect varying areas of underlying ischemia when similar severity of ischemia is present. During exercise the severity of ischemia is directly proportional to changes in myocardial oxygen demand and coronary blood flow, which in turn are directly related to increasing heart rate (delta HR). Because the change in transmembrane voltage across the ischemic boundary is linearly proportional to delta HR, delta Vm/delta HR remains constant as ischemia develops. Dividing the solid-angle relationship in equation 1 by delta HR and making the appropriate substitution for a constant delta Vm/delta HR then indicates that epsilon/delta HR = (omega/4 pi).(c . K) [equation 2], where c is the new constant. Under conditions where changes in conductance are proportional or small, this simplified relationship reduces to delta ST/delta HR = c'.omega [equation 3], where delta ST reflects the magnitude of ST depression recorded by the surface electrode, delta HR the change in heart rate during developing ischemia, and c' the resulting empiric constant.

Population selection and performance of the exercise ECG for the identification of coronary artery disease

To quantify the effect of population selection on the performance of exercise ECG criteria for the detection of coronary artery disease, the exercise ECGs of 212 clinically normal nonvolunteer subjects, 31 patients with no significant coronary disease at angiography, 153 patients with clinically stable angina, and 184 patients with catheterization-proved coronary disease were examined. Test specificity was examined separately in clinically normal subjects and in patients with angiographically normal coronary arteries, and test sensitivity was determined separately in patients with stable angina and those with catheterization-proved disease. Definition and selection of normal and abnormal study populations had marked effects on test performance. Standard ECG criteria, a simple ST depression magnitude partition of 150 microV, an ST segment/heart rate (ST/HR) index partition of 1.60 microV/beat/min, and an ST/HR slope partition of 2.40 microV/beat/min, identified coronary disease with comparably high specificities (94% to 97%) in clinically normal subjects, but with significantly lower specificities (68% to 77%, p = 0.002 to 0.0001) in patients with angiographically normal coronary arteries. Although sensitivity was significantly lower in patients with stable angina than in patients with catheterization-proved coronary disease for standard criteria (54% vs 70%, p = 0.004) and for the ST/HR index (88% vs 95%, p = 0.04), there was no significant difference in the poor sensitivity of the simple ST depression magnitude criteria (51% vs 58%) or in the high sensitivity of the ST/HR slope (93% vs 96%) in these abnormal patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement variables for optimal performance of the ST integral

OBJECTIVES

This study examined the effect of varied onset and offset of ST measurement on performance of the ST integral for the detection of coronary artery disease.

BACKGROUND

The J point and other early ST segment measurements may significantly reduce the accuracy of ST segment depression criteria.

METHODS

The exercise electrocardiograms (ECGs) from 112 normal subjects and 163 patients with known or likely coronary disease were analyzed, using the J point or 20 ms after the J point onset and 60 or 80 ms after the J point offset of ST integral calculation.

RESULTS

At a matched specificity of 97%, incorporation of J point measurements into the ST integral significantly reduced test performance. The ST integrals measured from the J point to 80 and to 60 ms after the J point were significantly less sensitive (31% and 25%, respectively) than those measured from 20 to 80 ms and 20 to 60 ms after the J point (39% and 31%, p < 0.001 and p < 0.01, respectively). For either J point or 20 ms after the J point onset of the ST integral measurement, the sensitivity was higher using 80 ms than 60 ms after the J point offset (31% vs. 25%, p < 0.01 and 39% vs. 31%, respectively, p < 0.001). Comparison of areas under receiver operating characteristic curves confirmed the superior performance of the ST integral measured from 20 to 80 ms after the J point relative to the other measurement intervals.

CONCLUSIONS

These findings demonstrate that J point and early repolarization phase time-voltage measurements reduce performance of the ST integral for the identification of coronary artery disease and provide further evidence that optimal signal to noise content of repolarization for the identification of ischemia can be localized to later phases of the ST segment.

Value and limitations of heart rate-adjusted ST segment depression criteria for the identification of anatomically severe coronary obstruction: test performance in relation to method of rate correction, definition of extent of disease, and beta-blockade

Performance of the linear regression-based ST/HR (heart rate) slope, the simple ST/HR index, and ST segment depression alone for the identification of anatomically severe coronary obstruction was examined in relation to the definition of the extent of disease and the presence or absence of beta-blockade during treadmill exercise using the Cornell protocol in 172 catheterized patients. Whether severe disease was defined by three-vessel obstruction, by Gensini scores partitioned at 35 or at 48, or by Duke jeopardy scores exceeding 6, the 83% to 100% sensitivities of an ST/HR slope criterion of 6.0 microV/beat/min were each significantly higher than the corresponding 65% to 80% sensitivities of 150 microV of ST segment depression closely matched specificities. The ST/HR slope was significantly more sensitive than a simple ST/HR index criterion of 3.4 microV/beat/min for detection of high Gensini scores, but despite consistently intermediate performance trends, in no case did sensitivity of the simple ST/HR index criterion significantly exceed that of ST depression alone. Each method performed better and with comparable sensitivity in patients not receiving beta-blockers. In contrast, the 82% to 100% sensitivities of the ST/HR slope for identification of severe disease were significantly higher than the 63% to 77% sensitivities of ST depression in patients taking beta-blocking drugs; however, simple heart rate adjustment using the ST/HR index had intermediate performance that in no case was significantly more sensitive than ST segment depression alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of computer ST criteria for diagnosis of severe coronary artery disease

To determine which computer ST criteria are superior for predicting patterns and severity of coronary artery disease during exercise testing, 230 male veterans were studied who had both coronary angiography and a treadmill exercise test. Significant (p < or = 0.05) differences in computer-scored ST criteria were observed among patients with progressively increasing disease severity. Three-vessel/left main disease produced responses significantly different from 1- and 2-vessel disease or those with < 70% occlusion. Discriminant function analysis revealed that horizontal or downsloping ST depression measured at the J junction during exercise or recovery, or both, was the most powerful predictor of severe disease. With use of a cut point of 0.075 mV ST depression, horizontal or downsloping ST depression alone yielded a sensitivity of 50% (95% confidence interval = 35 to 65%) and specificity of 71% for prediction of severe disease; the only additional variable that added significantly to the prediction was exercise capacity, which improved sensitivity to 57% (95% confidence interval = 41 to 72%) with no change in specificity. Measurements of ST amplitude at the J junction and at 60 ms after the J point without slope considered and other scores, including the Treadmill Exercise Score, ST Integral, and ST/heart rate index, had a lower but comparable predictive accuracy when compared with horizontal or downsloping ST depression. Prediction of coronary artery disease severity can be achieved using computerized electrocardiographic measurements obtained during exercise testing. The most powerful marker for severe coronary artery disease is the amount of horizontal or downsloping ST-segment depression during exercise or recovery, or both, a measurement that stimulates the traditional visual approach.

Identifying coronary artery disease in women by heart rate adjustment of ST-segment depression and improved performance of linear regression over simple averaging method with comparison to standard criteria

Performance of exercise electrocardiography for the detection of coronary artery disease (CAD) in women has been limited by relatively poor sensitivity and specificity of standard test criteria. Recent studies suggest that diagnostic methods incorporating heart rate (HR) adjustment of ST-segment depression during exercise may improve the accuracy of exercise testing in women, but the relative performance of different rate-adjusted methods for this purpose is unknown. To assess the effect of gender on relative test performance of the ST-segment/HR (ST/HR) slope, the simple ST/HR index, the HR-recovery loop, and standard ST-depression criteria for the identification of CAD, the exercise electrocardiograms of 254 patients with known or suspected CAD (67 women and 187 men) and of 150 clinically normal subjects (29 women and 121 men) were analyzed. Specificity of each method was comparable in men and women: ST/HR slope 98% (118 of 121) vs 97% (28 of 29), ST/HR index 97% (117 of 121) vs 97% (28 of 29), and HR-recovery loop 96% (116 of 121) vs 93% (27 of 29). In contrast, although there was no difference in sensitivity of the ST/HR slope (95% [177 of 187] vs 93% [62 of 67]; p = not significant [NS]) or HR-recovery loop (90% [168 of 187] vs 87% [58 of 67]; p = NS) between men and women, the ST/HR index was less sensitive for CAD in women than in men (82% [55 of 67] vs 93% [173 of 187]; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of severe coronary artery disease using computerized ECG measurements and discriminant function analysis

This study tested the hypothesis that discriminant function analysis of clinical and exercise-test variables including computerized ST measurements could improve the prediction of severe coronary artery disease. Secondary objectives were to demonstrate the effect of digoxin and/or resting electrocardiographic (ECG) abnormalities, and to evaluate the relative importance of ST measurements made during the recovery phase and in the three lead group areas. The design was a retrospective analysis of data collected during exercise testing and coronary angiography. The ECG data were gathered and stored in digital format on optical discs and all ST measurements were made off-line using the authors' own software. Univariate and multivariate analytic methods were used to analyze all pretest characteristics as well as hemodynamic and computerized ECG responses to exercise. A 1,000-bed Veterans Affairs Medical Center served as the setting. The study included 446 male veterans who underwent a sign or symptom limited treadmill exercise test and coronary angiography. Analysis was also performed on a subset of this population formed by excluding patients receiving digoxin or with resting ECGs exhibiting left ventricular hypertrophy or ST depression (n = 328). In the total study population, the authors derived a treadmill score using discriminant function analysis. This score included: (1) the time-slope area in lead V5 during recovery; (2) delta heart rate; (3) angina pectoris during the exercise test; and (4) presence of diagnostic Q waves on the resting ECG. This score was effective in predicting triple vessel/left main disease and outperformed exercise-induced ST depression for predicting severe coronary artery disease. After exclusion of patients with ECGs exhibiting left ventricular hypertrophy or resting ST depression and patients receiving digoxin, discriminant function analysis chose: (1) the time-slope area in lead V5 during recovery and (2) delta heart rate. Exclusion of these patients resulted in a nonsignificant decrease in specificity of all ST criteria. ST-segment amplitude or slope in lead V5 at 3.5 minutes in recovery clearly outperformed the maximal exercise measurements in both groups. Summing the depressions or selecting the most depression in the three areas (ie, lateral-V5, inferior-II, anterior-V2) did not improve test performance. Leads other than V5 did not contain significant diagnostic information. A quantitative approach to exercise testing using discriminant function analysis enhanced the tests' performance for predicting severe coronary disease. The inclusion of patients taking digoxin or with resting ECG abnormalities nonsignificantly decreases the specificity of all ST criteria.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of measurement interval on performance of the ST integral for the identification of three-vessel coronary disease

Measurement of the ST integral has usually incorporated ST-segment depression integrated between the J point and 80 ms after the J point (J + 80). To assess the effect of varied onset and offset of ST measurement on performance of the ST integral for the identification of three-vessel coronary disease, the exercise electrocardiograms (ECGs) of 60 patients with angiographically proven coronary disease were analyzed using J point or J + 20 onsets and J + 60 or J + 80 offsets of ST integral calculation. Simple ST-segment depression of greater than 200 microV, measured at 60 ms after the J point, identified three-vessel disease with a specificity of 68% (17 out of 25 patients) and sensitivity of 69% (22 out of 35 patients). At a matched specificity of 68% (17 out of 25 patients), there was identical sensitivity (54%, 19 out of 35 patients) of ST integrals measured either from the J point to J + 80, from the J point to J + 60, or from J + 20 to J + 60. A trend toward increased sensitivity (60%, 21 out of 35 patients) when the ST integral was measured from J + 20 to J + 80 did not reach statistical significance, and comparison of receive operating characteristics (ROC) curves demonstrated that varying the onset and offset of ST-segment measurement had no significant effect on the overall performance of ST integral criteria for the detection of three-vessel disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Heart rate adjustment of the time-voltage ST segment integral: identification of coronary disease and relation to standard and heart rate-adjusted ST segment depression criteria

To assess the effect of heart rate adjustment of the magnitude of the ST integral (ST-HR integral) on exercise test performance, the exercise electrocardiogram (ECG) of 50 clinically normal subjects and 100 patients with known or suspected coronary artery disease was analyzed. At matched specificity of 96% with standard ECG criteria (greater than or equal to 0.1 mV of additional horizontal or downsloping ST segment depression), an unadjusted ST integral partition of 16 microV-s identified coronary disease in the 100 patients with known or suspected disease with a sensitivity of only 41%, a value significantly lower than the 59% sensitivity of standard ECG criteria (p less than 0.01) and the 65% sensitivity of an ST depression partition of 130 microV (p less than 0.001). However, test performance of the ST integral was greatly improved by simple heart rate adjustment: at a matched specificity of 96%, an ST-HR integral partition of 0.154 microV-s/beat per min identified coronary disease in the 100 patients with a sensitivity of 90%, a value significantly greater than the 59% sensitivity of standard criteria and 65% sensitivity of ST depression criteria (each p less than 0.001) and similar to the 91% sensitivity of the ST-HR index and 93% sensitivity of the ST-HR slope (each p = NS). Comparison of receiver-operating characteristic curves confirmed the superior overall test performance of the ST-HR integral relative to the ST integral and ST segment depression, and demonstrated improved performance that was comparable with that of the ST-HR index and the ST-HR slope.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of precision of ST-segment measurement on identification and quantification of coronary artery disease by the ST/HR index

To assess the effect of varying precision of ST-segment depression measurement on test performance of the ST-segment/heart rate (ST/HR) index for the identification and quantification of coronary artery disease, the exercise electrocardiograms (ECGs) of 100 clinically normal subjects and 154 patients with angiographically proved coronary disease were reviewed. The ST/HR index was calculated by dividing the maximal additional ST-segment depression at end exercise by the exercise-induced change in heart rate. ST-segment depression was measured to the nearest 10 microV (ST10) at a point 60 ms after the J point on a computerized exercise ECG system, and was subsequently rounded down to the nearest 50 microV (ST50) and the nearest 100 microV (ST100) to simulate measurements to these precisions. An ST10/HR index partition of 1.60 microV/bpm with a specificity of 95% (95/100) in normal subjects identified the presence of coronary disease with a sensitivity of 94% (144/154). Precision of ST-segment measurement significantly affected sensitivity for coronary disease. At matched specificity of 95%, an ST50/HR index partition of 1.55 microV/bpm had a sensitivity of 88% (135/154, p less than 0.01) and an ST100/HR index partition of 1.22 microV/bpm had a sensitivity of 84% (130/154, p less than 0.001) for the detection of coronary obstructions. Comparison of receiver-operating characteristic curves (ROC) confirmed the superior overall performance of the ST/HR index using ST10 measurements for the identification of coronary disease. By contrast, test performance for the identification of three-vessel coronary disease was not affected by the precision of ST-segment measurement with no significant difference in test sensitivity or areas under respective ROCs.(ABSTRACT TRUNCATED AT 250 WORDS)