Effects of recent and remote infarction on the predictive accuracy of the ST segment/heart rate slope

A new method to quantify postexercise ST-deviation--the ST-deficit. A study in men at high and low-risk for coronary heart disease

BACKGROUND

Quantitative heart rate adjusted exercise ST criteria like microV/beats per minute (bpm) improve the diagnostic accuracy of the exercise ECG. However, there are few quantitative HR adjusted postexercise variables available. The aim of the present exercise study was to evaluate a new such variable from computerized averaging of the postexercise ECG.

METHODS

The presence of possible myocardial ischaemia in a population based sample of 74 elderly male hypertensives at high-risk of coronary heart disease, and in 42 age-matched clinically healthy males (reference group) at low-risk was assessed by exercise ECG. All men had a normal resting ECG without signs of ischaemia.

VARIABLES STUDIED

standard ST-criteria, ST/HR slope < or =-2.4 microV. bpm-1, shape of the rate-recovery loop, the latter also with a new quantitative variable, the ST-deficit.

RESULTS

In spite of a normal resting ECG many subjects showed an abnormal ST/HR slope during exercise, 43% in the hypertension group and 26% in the reference group. An abnormal rate-recovery loop (ST-deficit) also contributed substantially to identify patients with possible myocardial ischaemia, 30 vs. 10%, respectively (P<0.02); cumulatively for the two HR adjusted criteria 53% vs. 29%, respectively (P<0.02). Mean ST-deficit was significantly lower in the high-risk group.

CONCLUSIONS

Effort-related myocardial ischaemia is frequently silent in elderly high-risk hypertensives and necessitates testing, preferably with computerized exercise ECG and heart rate adjusted ST criteria. A new quantitative variable to assess the postexercise rate-recovery loop in the time domain, the ST-deficit is described. This variable seems to effectively discriminate between subjects with low and high-risk for coronary heart disease and thus provides new information. Further studies are warranted to validate this variable against myocardial perfusion scintigraphy and coronary angiography.

Diagnosis of silent myocardial ischemia using ambulatory electrocardiographic monitoring with pedometer, analysis of heart rate, and ST loop in ambulatory electrocardiogram

BACKGROUND

It has been suggested that episodes of silent myocardial ischemia (SMI) might influence the prognosis of patients with ischemic heart disease, as its consequences are similar to those of myocardial ischemia accompanied by pain. Ambulatory electrocardiogram (ECG) is generally employed in diagnosis as well as in evaluation of clinical efficacy in patients with SMI, but problems related to its application remain because of the difficulty in differentiating between nonischemic and ischemic ST-segment depressions and because of the absence of data concerning body movement.

METHODS AND RESULTS

We developed a method for simultaneously recording onto magnetic tape both the ECG chart and pedometer count, as well as a program which enables semi-automatic analysis of the heart rate (HR)-ST relationship. This new method was employed to record ambulatory ECG along with pedometer count for a total of 70 patients, consisting of 53 with coronary heart disease who were shown to have ischemic heart disease, and 17 with various heart diseases in whom coronary angiography revealed no coronary stenosis. The HR-ST relationship was assessed for periods during which steps were recorded by the pedometer, that is, when patients were confirmed to have been under exertion effort. Patients demonstrating the following findings were diagnosed as true positive for SMI: the ST segment level did not decline until HR increased to a certain threshold, and the rate of change in the ST-segment level noted thereafter was -0.025 mm/beats/min or lower; or the ST-segment depression induced by effort continued even after discontinuation of exercise, after which time HR began to decrease, and the HR-ST loop consequently described a counterclockwise rotation. Evaluation of the HR-ST relationship based on these criteria revealed excellent results, as demonstrated by values of 79.2% for sensitivity and 94% for specificity.

CONCLUSION

Our newly developed method of assessment of the HR-ST relationship via analysis of simultaneous data from an ambulatory ECG and a pedometer appears to be time saving, highly objective, and useful with regard to the diagnosis of SMI and evaluation of the therapeutic effect of drugs in patients with ischemic heart disease.

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.

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)

Performance characteristics of various exercise ECG classifiers in different clinical populations

To improve the diagnostic power of the exercise electrocardiographic test in detecting myocardial ischemia, the authors have recently developed a diagnostic method called multivariate ST-segment/heart rate (ST/HR) analysis (MUSTA). The goal of this study was to evaluate the validity of MUSTA in different clinical populations and to compare its performance characteristics with ST-segment depression, the ST/HR slope, and the delta ST/HR index in these populations. The computerized exercise electrocardiographic measurements were performed on 1,507 cases, and 382 patients were selected as the study population: 161 with significant coronary artery disease according to coronary angiography and 221 with a low likelihood of coronary artery disease. The diagnostic accuracy of MUSTA in the pooled population was 77.7% (297 out of 382 patients), which was clearly better than the accuracy of 69.6% (266 out of 382 patients) using the conventional ST-segment depression criterion of 0.10 mV in detecting coronary artery disease and exercise-induced myocardial ischemia. According to receiver operating characteristics analysis, MUSTA had significantly better diagnostic power than the other classifiers. These findings suggest that multivariate and compartmental analysis methods like MUSTA can further improve the clinical importance of the exercise electrocardiogram.

Exercise-induced ST depression and ST/heart rate index to predict triple-vessel or left main coronary disease: a multicenter analysis

The aim of this investigation was to determine the difference in accuracy between two frequently published noninvasive indicators of severity of coronary artery disease (exercise-induced ST segment depression and heart rate-adjusted ST depression [ST/HR index]). The study was designed as a survey of consecutive patients undergoing exercise electrocardiography and coronary angiography. There were a total of 2,270 patients without prior myocardial infarction or cardiac valvular disease referred for angiography from eight institutions in three countries; 401 of these patients had triple-vessel or left main coronary artery disease. The sensitivities of ST depression and ST/HR index in detecting triple-vessel or left main coronary artery disease were, respectively, 75% and 78% (p = 0.08) at cut point values where their specificities were equal (64%). This small increase in the accuracy of the ST/HR index was evident only at peak exercise heart rates below the median value of 132 beats/min, where the sensitivities of ST depression and ST/HR index were 73% and 76% (p = 0.03), respectively, at cut point values corresponding to a specificity of 60%. These results were consistent at all eight participating institutions. The increase in accuracy achieved by dividing exercise-induced ST depression by heart rate is small and confined exclusively to a low exercise heart rate. This lack of superiority cannot be generalized to all methods of heart rate adjustment.

ST/HR slope and improved exercise ECG detection of myocardial ischemia in patients with suspected coronary artery disease

Predictive values of ST/HR slope and ST-segment displacement during symptom-limited exercise were determined in 85 patients who underwent coronary angiography for suspected coronary artery disease, using perfusional and functional radionuclide images with 99mTc-2-methoxy-isobutil-isonitrile as an index of stress-induced myocardial ischemia. ST/HR slope showed a better sensitivity than conventional stress-induced changes of ST-segment displacement (96% vs. 73%, respectively). In patients with clinical suspicion of coronary artery disease, the main result was the negative predictive value of ST/HR slope when compared with conventional ST-segment displacement (98% vs. 41%). ST/HR slope was unable to perfectly separate patients with different degrees of ischemia, however, subjects without scintigraphic signs of stress-induced ischemia and patients with ischemic impairment in three myocardial regions were correctly identified as distinct populations. In patients with a previous myocardial infarction, no difference was found between the two criteria and a wide overlap of ST/HR slope values was present. The authors conclude that ST/HR slope is useful to detect the rate of change in electric parameters during exercise and might therefore more adequately be used to separate normal from definitely abnormal responses to exercise.

A lesson from the controversy about heart rate adjustment of ST segment depression

To summarize the literature review, the heart rate adjustment appears to be able to perfectly discriminate patients with different numbers of diseased coronary vessels in one center, to increase the diagnostic accuracy of three-vessel or left main disease in eight centers, and unable to improve accuracy in seven centers. To explain those differences, several methodological and statistical biases have been considered. However, a recent report regarding the application of the method in eight centers and a meticulous literature review could not explain the superior performance in some laboratories.

Improved diagnostic performance of the exercise ECG test by computerized multivariate ST-segment/heart rate analysis

The exercise ECG test is the most widely used noninvasive method of evaluating myocardial ischemia. To determine whether it is possible to enhance its diagnostic power, the authors carried out computerized ECG measurements on 118 nonischemic patients and 38 ischemic patients with or without myocardial infarctions (MIs). Forty-seven (all ischemic and nine normal cases) underwent T1-201 SPECT. The diagnostic variables include ST-segment deviation, modified ST/HR-slope, ST-segment shape, and maximum heart rate. These variables are interrelated by means of compartmental and specific decision rules by computer. The diagnostic method discussed in this article is called the multivariate ST/HR analysis (MUSTA). When compared with MUSTA, the T1-201 SPECT images detected myocardial ischemia with a sensitivity of 100% and a specificity of 89%. Its diagnostic performance was influenced by neither previous MIs nor cardiac medication of the 47 patients tested. MUSTA was also compared to the nonmodified ST/HR analyses (ST60/HR and ST80/HR) and the standard exercise ECG test. It performed significantly better than these methods. The authors conclude that the multivariate ST/HR analysis is comparable to T1-201 SPECT in diagnosing myocardial ischemia among the study subjects. Furthermore, MUSTA is executed during the noninvasive exercise ECG test and is easily applied using an IBM/AT-compatible microcomputer. However, further evaluation of MUSTA with a separate and unselected patient population is needed.

Heart rate adjustment of exercise-induced ST segment depression. Improved risk stratification in the Framingham Offspring Study

BACKGROUND

Simple heart rate adjustment of ST segment depression during exercise (delta ST/HR index) and the pattern of ST depression as a function of heart rate during exercise and recovery (the rate-recovery loop) have been shown to improve the ability of the exercise electrocardiogram to detect the presence of coronary heart disease (CHD), but the performance of these methods for the prediction of future coronary events remains to be examined.

METHODS AND RESULTS

We compared the delta ST/HR index and the rate-recovery loop with standard electrocardiographic criteria for prediction of CHD events in 3,168 asymptomatic men and women in the Framingham Offspring Study who underwent treadmill exercise electrocardiography and who, at entry, were free of clinical and electrocardiographic evidence of CHD. After a mean follow-up of 4.3 years, there were 65 new CHD events: four sudden deaths, 24 new myocardial infarctions, and 37 incident cases of angina pectoris. When a Cox proportional hazards model with adjustment for age and sex was used, a positive exercise electrocardiogram by standard criteria (greater than or equal to 0.1 mV horizontal or downsloping ST segment depression) was not predictive of new CHD events (chi 2 = 0.40, p = 0.52). In contrast, stratification according to the presence or absence of a positive delta ST/HR index (greater than or equal to 1.6 microV/beat/min) and a positive (counterclockwise) rate-recovery loop was associated with CHD event risk (chi 2 = 9.45, p less than 0.01) and separated subjects into three groups with varying risks of coronary events: high risk, when both tests were positive (relative risk 3.6; 95% confidence interval, 2.4-5.4); intermediate risk, when either the delta ST/HR index or the rate-recovery loop was positive (relative risk, 1.9; 95% confidence interval, 1.3-2.8); and low risk, when both tests were negative. After multivariate adjustment for age, sex, smoking, total cholesterol level, fasting glucose level, diastolic blood pressure, and electrocardiographic evidence of left ventricular hypertrophy, the combined delta ST/HR index and rate-recovery loop criteria remained predictive of coronary events (chi 2 = 5.45, p = 0.02).

CONCLUSIONS

Heart rate adjustment of ST segment depression by the delta ST/HR index and the rate-recovery loop during exercise electrocardiography can improve prediction of future coronary events in asymptomatic men and women.

Comparison of ST segment/heart rate index to standard ST criteria for analysis of exercise electrocardiogram

The objective of our study was to compare the discriminating power of a proposed ST segment/heart rate index with that of a standard method of assessing exercise-induced ST segment depression for diagnosing coronary artery disease. We used a cross-sectional retrospective analysis of exercise test and coronary angiographic data. The study took place in a 1,200-bed Veterans Affairs Medical Center; participants were 328 male patients who had undergone both a sign and symptom-limited treadmill test and coronary angiography. The sensitivity of the ST segment/heart rate index was 54% at a cut point of 0.021 mm/(beats/min), corresponding to a specificity of 73%. The standard visual ST segment analysis had a sensitivity of 58% at this same specificity, which corresponded to an ST segment cut point of 1-mm depression relative to rest (p = NS). Similarly, for diagnosing three-vessel or left main coronary disease, no significant difference was found between the sensitivities or the two measurements at cut points of equivalent specificity. In this consecutive series of patients presenting for routine clinical testing, the ST segment/heart rate index did not improve the diagnostic accuracy of the exercise test for identifying the presence or severity of coronary artery disease relative to standard visual criteria.

Effect of baseline ST segment elevation on test performance of standard and heart rate-adjusted ST segment depression criteria

Whether the ST segment shift used to evaluate the presence and severity of myocardial ischemia should include the additional deviation due to decreasing amounts of baseline ST segment elevation was examined in 100 clinically normal subjects and in 124 patients with coronary disease. Exercise ST segment depression was calculated in two ways: as the difference between exercise and resting ST segment depression, but excluding any resting ST elevation (STdep), and as the total ST segment difference or excursion, including any baseline resting ST elevation (STdiff). These values were also used for separate calculation of the maximal ST/heart rate slope and delta ST/heart rate index in each case. Given partition values with matched specificity of 95% in clinically normal subjects, 150 microV of STdep was significantly more sensitive for coronary disease than 220 microV of STdiff (61% [76 of 124] versus 50% [62 of 124], p less than 0.005). Comparison of receiver operating characteristic curves confirmed the superior test performance of STdep for the identification of coronary disease in this population (area under the curve 0.920 versus 0.869, p = 0.0019). In contrast, detection of three-vessel coronary obstruction by standard ST segment criteria was not affected by definition of ST segment excursion. Substitution of STdiff for STdep did not change the performance of the ST/heart rate slope of the delta ST/heart rate index for either the detection of coronary disease or for the identification of three-vessel coronary obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise-induced ST segment depression in the diagnosis of multivessel coronary disease: a meta analysis

To evaluate the variability in the reported accuracy of the exercise electrocardiogram (ECG) for predicting severe coronary disease, meta analysis was applied to 60 consecutively published reports comparing exercise-induced ST depression with coronary angiographic findings. The 60 reports included 62 distinct study groups comprising 12,030 patients who underwent both tests. Both technical and methodologic factors were analyzed. Wide variability in sensitivity and specificity was found (mean sensitivity 81% [range 40% to 100%, SD 12%]; mean specificity 66% [range 17% to 100%, SD 16%]). All three variables found to be significantly and independently related to sensitivity were methodologic (the exclusion of patients with right bundle branch block, the comparison with another exercise test thought to be superior in accuracy and the exclusion of patients taking digitalis). Exclusion of patients with right bundle branch block and comparison with a "better" exercise test were both significantly associated with sensitivity for the prediction of triple vessel or left main coronary artery disease. Adjustment of exercise-induced ECG changes for changes in heart rate was strongly associated with the specificity for critical disease (partial R2 = 0.436, p = 0.0001).

Computer-based implementation of the ST-segment/heart rate slope

The ST-segment/heart rate (ST/HR) slope has markedly improved the accuracy of the exercise electrocardiogram for the identification and quantification of coronary artery disease. However, clinical use of this technique has been limited by time-consuming manual ST-segment measurements and calculator-based linear regression analyses after testing. To assess the accuracy of on-line computerized measurement of ST-segment depression and recently implemented ST/HR slope algorithms, 50 patients exercised with a Marquette Electronics CASE 12 system and 50 patients exercised with a Quinton Q5000 system were evaluated. Computerized ST-segment measurements, to the nearest 10 microV, were compared with averaged manual measurements from the raw signal, to the nearest 25 microV, at peak exercise in leads II and CM5. The CASE 12 and Q5000 algorithms for selection of data and calculation of the maximal ST/HR slope were compared with the ST/HR slope calculated from end-stage data points according to a standard off-line procedure. Manual ST-segment measurements correlated highly with CASE 12 and Q5000 determinations (r = 0.996 to 0.998). The slopes of their regression lines approached unity (range 0.98 to 1.02), and the standard errors of the estimate ranged from 12 to 15 microV. Each on-line program selected data points and determined ST/HR slopes in complete accordance with standard calculations. It is concluded that computer-based measurement of the ST/HR slope can be performed with a high degree of accuracy.

Recovery-phase patterns of ST segment depression in the heart rate domain. Identification of coronary artery disease by the rate-recovery loop

Although the time course of ST segment depression after exercise has been related to the presence and severity of coronary artery disease, recovery-phase patterns of ST segment depression with reference to changing heart rate have not been quantified. We have found distinct recovery loop patterns of ST segment depression that distinguish subjects without coronary disease from patients with coronary artery disease when ST segment depression is examined in the heart rate domain. Continuous plots of ST segment depression and heart rate were constructed throughout treadmill exercise and recovery in 100 clinically normal subjects, in 124 patients with coronary artery disease proven by catheterization, and in 17 patients with no significant coronary disease at catheterization. Among clinically normal subjects, 95% (95 of 100) had normal (clockwise) rate-recovery loops, and 5% (five of 100) had abnormal (counterclockwise) rate-recovery loops. In these normal subjects, the resulting 95% specificity of a normal rate-recovery loop was similar to the 93% (93 of 100) specificity of standard end-exercise ST segment depression criteria. Among patients with coronary disease proven by angiography, 93% (115 of 124) had abnormal (counterclockwise) rate-recovery loops, and 7% (nine of 124) had normal rate-recovery loops. In contrast was the significantly lower 74% (92 of 124) sensitivity of standard ST segment criteria (p less than 0.001 vs. the rate-recovery loop). Specificity of a normal rate-recovery loop (71%, 12 of 17) and standard ST segment depression criteria (71%, 12 of 17) were similar in the patients with normal coronary arteries at angiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise-induced ST depression in the diagnosis of coronary artery disease. A meta-analysis

To evaluate the variability in the reported diagnostic accuracy of the exercise electrocardiogram, we applied meta-analysis to 147 consecutively published reports comparing exercise-induced ST depression with coronary angiography. These reports involved 24,074 patients who underwent both tests. Population characteristics and technical and methodologic factors, including publication year, number of electrocardiographic leads, exercise protocol, use of hyperventilation, definition of an abnormal ST response, exclusion of certain subgroups, and blinding of test interpretation were analyzed. Wide variability in sensitivity and specificity was found (mean sensitivity, 68%; range, 23-100%; SD, 16%; and mean specificity, 77%; range, 17-100%; SD, 17%). The four study characteristics found to be significantly and independently related to sensitivity were the treatment of equivocal test results, comparison with a "better" test such as thallium scintigraphy, exclusion of patients on digitalis, and publication year. The four variables found to be significantly and independently related to specificity were the treatment of upsloping ST depressions, the exclusion of subjects with prior infarction or left bundle branch block, and the use of preexercise hyperventilation. Stepwise linear regression explained less than 35% of the variance in sensitivities and specificities reported in the 147 publications. There is wide variability in the reported accuracy of the exercise electrocardiogram. This variability is not explained by information reported in the medical literature.

Heart rate adjustment of ST segment depression for improved detection of coronary artery disease

Normal values for heart rate-adjusted indexes of ST segment depression during treadmill exercise electrocardiography (the ST segment/heart rate slope and the delta ST segment/heart rate index) were derived from evaluation of 150 subjects with a low likelihood of coronary artery disease, including 100 normal subjects and 50 subjects with nonanginal chest pain. Partitions chosen by the method of percentile estimation to include 95% of normal subjects remained highly specific in subjects with nonanginal pain syndromes. Sensitivities of the derived partitions for detection of myocardial ischemia were tested in an additional 150 patients with a high likelihood of coronary disease, including 100 patients with angiographically demonstrated coronary obstruction and 50 patients with stable angina. In contrast to the 68% (102 of 150 subjects) sensitivity of standard exercise electrocardiographic criteria for the detection of disease in this population, the sensitivity of an ST segment/heart rate slope partition of 2.4 muV/beats/min was 95% (142 of 150 subjects, p less than 0.001), and the sensitivity of a delta ST segment/heart rate index partition of 1.6 muV/beats/min was 91% (137 of 150 subjects, p less than 0.001). Analysis of receiver-operating curves confirmed the superior performance of the heart rate-adjusted indexes throughout a wide range of test specificities. These findings suggest that heart rate adjustment of ST segment depression can markedly improve the clinical usefulness of the treadmill exercise electrocardiogram.

Identification of anatomically extensive coronary artery disease by the exercise ECG ST segment/heart rate slope

To assess the ability of the ST segment/heart rate (ST/HR) slope to identify three-vessel coronary disease and the relationship between the ST/HR slope and the anatomic extent of disease as determined by the Gensini and Duke jeopardy scores, the exercise ECGs of 128 patients with stable angina were compared with findings at coronary cineangiography. A ST/HR slope greater than or equal to 6 microV/beat/min identified three-vessel coronary disease with a sensitivity of 93% compared with sensitivities of only 50% for early positive standard test responses (p less than 0.001) and 66% for markedly positive standard test responses (p less than 0.01). The negative predictive value of this ST/HR slope partition for three-vessel disease was 94%. Patients with ST/HR slopes greater than or equal to 6 who did not have three-vessel disease had anatomically more extensive obstruction than did patients with lower test values (mean Gensini score 43 +/- 5 vs 22 +/- 3, p less than 0.002 and mean jeopardy score 4.8 +/- 0.4 vs 3.0 +/- 0.3, p less than 0.01). Test performance of the calculated ST/HR slope exceeded that of a simplified index derived by dividing the total change in ST segment depression by the total change in heart rate. These findings demonstrate that a ST/HR slope greater than or equal to 6 is highly sensitive for the identification of three-vessel coronary disease and also identifies patients with anatomically severe obstruction. A ST/HR slope less than 6 makes three-vessel coronary disease or otherwise anatomically extensive coronary obstruction unlikely.