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

Exercise-Induced QRS Amplitude Changes in Patients with Isolated Myocardial Bridging: A Marker of Myocardial Ischemia

Myocardial bridging (MB) of coronary arteries has been considered as an incidental angiographic finding; however, several reports suggest its association with angina pectoris, myocardial ischemia, and even infarction. In this study the authors aimed to assess exercise-induced QRS changes in patients with isolated MB and to compare those with coronary artery disease (CAD) and healthy subjects. The study population consisted of 17 patients with angiographically proven MB (group 1), 16 patients with left anterior descending (LAD) artery stenosis (group 2), and 14 healthy subjects (group 3). Each subject underwent treadmill exercise testing according to Bruce protocol. In each subject amplitude of the Q, R, and S waves in leads aVF and V5 was measured manually before and immediately after exercise. The Athens QRS score was calculated by subtracting the Q-, R-, and S-wave differences in leads aVF and V5. Baseline characteristics of each group were similar. There was no difference among the groups with respect to exercise testing parameters (peak heart rate, blood pressure, test duration, etc). In group 1, ST-segment depression ratio was found to be higher than that of group 3 but lower than that of group 2. In group 1, exercise QRS score was found to be lower than that of group 3 while it was higher than that of group 2 (2.9 ±2.3 vs 6.5 ±3.2 p=0.001 and 2.9 ±2.3 vs 2.6 ±2.4 p=0.001, respectively). In patients with MB exercise, QRS score was significantly lower than in those with normal coronary flow while it was higher in those with CAD. This may result from exercise-induced ischemia at the area perfused by the bridged artery.

Diagnostic value of the recovery time-course of st slope on exercise ECG in discriminating false-from true-positive ST-segment depressions

BACKGROUND

Using the exercise ECG for diagnosing coronary artery disease (CAD) is hampered by the occurrence of false-positive (FP) ST-segment depression. Because it is known that the recovery ST-T time-course in CAD differs from that in FP subjects, the ST slope may help discriminate FP from true-positive (TP) results.

METHODS AND RESULTS

Treadmill digitized ECG from patients with significant ST-segment depressions and normal resting ECG were analyzed in 134 patients with CAD on angiography (>50% narrowing) and reversible perfusion defects (TP group), and 64 subjects with normal perfusion (FP group) on exercise single photon emission computed tomography. The ST slope between the J-point and J(80) was measured every minute up to 6-min postexercise. The ST slope was significantly higher in FP than in TP at peak exercise, and at postexercise 1-, 2- and 3-min (p<0.01, all). Thereafter, it gradually increased in TP, while monotonically decreasing in FP. Its decrease from 3- to 6-min could correctly diagnose 88% of FP subjects, whereas it was found in only 19% of TP patients (total accuracy 83%).

CONCLUSIONS

The ST slope change from early to late recovery is a simple yet reliable marker for discriminating FP from TP ST-segment responses in subjects with a normal resting ECG.

ST-segment level and slope in exercise-induced myocardial ischemia evaluated with body surface potential mapping

Body surface potential mapping (BSPM) is superior to 12-lead electrocardiography for detection of acute and old myocardial infarctions (MIs). We used BSPM to examine electrocardiographic criteria for acute reversible myocardial ischemia. BSPM with 123 channels was performed in 45 patients with coronary artery disease (CAD) and 25 healthy controls during supine bicycle exercise testing. Of the 45 patients, 18 patients had anterior, 14 had posterior, and 13 had inferior ischemia documented by coronary angiography and thallium scintigraphy. The ST amplitude was measured 60 ms after the J-point and the ST slope calculated by fitting a regression line from the J-point to 60 ms after it. The optimal locations for detecting ST depression and ST-slope decrease were identified. In the pooled CAD patient group, the optimal location for ST depression was 5 cm below standard lead V(5) (CAD group: -70 +/- 70 microV; controls: 70 +/- 80 microV, p <0.001). Using a cut-off value of -10 microV, the ST depression separated the patients with CAD from controls with a sensitivity of 84% and a specificity of 96%. The ST slope became more horizontal in the patient group than in the control group. The optimal location for ST-slope decrease was over the left side (CAD group: 20 +/- 20 microV/s; controls: 720 +/- 320 microV/s, p <0.001). Using a cut-off value of 320 microV/s, the ST slope separated patients with CAD from controls with a sensitivity of 93% at a specificity level of 88%. The area under the receiver operating characteristic curve of ST slope tended to be higher than the one of ST depression (97% vs 93%; p = 0.097). In conclusion, regions sensitive for ST depression and for ST-slope decrease could be identified in BSPM, despite variation in the location of ischemia and the presence or absence of a history of MI. ST slope is a sensitive and specific marker of transient myocardial ischemia, and might perform even better than ST depression.

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.

Exercise stress testing. An overview of current guidelines

Exercise stress testing (ET) is an inexpensive noninvasive tool that provides valuable cardiopulmonary information in healthy and diseased populations. It is most commonly used for diagnosing coronary artery disease (CAD) and developing appropriate exercise prescriptions (EP). With its widespread use and application, it is imperative that safe and appropriate guidelines and procedures are used, as there are a number of risks associated with testing in a population with or suspected of having CAD. The focus should be on the patient's safety: personnel must be properly trained and aware of all emergency procedures, contra-indications for ET and indications for test termination must be strictly adhered to. Three main types of testing are prevalent: submaximal, maximal and maximal utilising gas exchange. The maximal test is most commonly used, and the submaximal is appropriate for hospitalised patients. Gas exchange data is essential when assessing congestive heart failure and timing for heart transplantation. ET is commonly performed using a treadmill or a bicycle ergometer. The treadmill provides a more familiar exercise modality and has been shown to have greater diagnostic sensitivity than the bicycle ergometer; it is, however, more expensive and requires more space in the testing room. The bicycle ergometer is more appropriate for those individuals who are severely obese or have problems with extended periods of walking. Regardless of the modality used, an appropriate exercise protocol should be used. In North America, the Bruce protocol is the most common. However, the Bruce protocol, and others that estimate exercise capacity based on equations, tend to overestimate exercise capacity. They may be too demanding for those with limited exercise capacity, and too long for those with high exercise capacity. For these people, an exercise protocol that reaches maximal capacity in 8 to 12 minutes using smaller increments in workload should be considered. Once completed, the results of ET needs to be correctly interpreted. This includes reviewing the test results while considering the patient's history, medications and indication for the test. ET can also be used to develop an EP for the participant. An EP should take into account the intensity, modality of exercise, frequency and duration, as well as being realistic for the individual and the goals to be achieved. All the information from the test results and the pre-test examination should be presented in a report that also includes the advised EP.

Predicting severe angiographic coronary artery disease using computerization of clinical and exercise test data

Currently the standard exercise test is shifting from being a tool for the cardiologist to utilization by the nonspecialist. This change could be facilitated by computerization similar to the interpretation programs available for the resting ECG. Therefore, we sought to determine if computerization of both exercise ECG measurements and prediction equations can substitute for visual analysis performed by cardiologists to predict which patients have severe angiographic coronary artery disease. We performed a retrospective analysis of consecutive patients referred for evaluation of possible or known coronary artery disease who underwent both exercise testing with digital recording of their exercise ECGs and coronary angiography at two university-affiliated Veteran's Affairs medical centers and a Hungarian hospital. There were 2,385 consecutive male patients with complete data who had exercise tests between 1987 and 1997. Measurements included clinical and exercise test data, and visual interpretation of the ECG paper tracings and > 100 computed measurements from the digitized ECG recordings and compilation of angiographic data from clinical reports. The computer measurements had similar diagnostic power compared with visual interpretation. Computerized ECG measurements from maximal exercise or recovery were equivalent or superior to all other measurements. Prediction equations applied by computer were only able to correctly classify two or three more patients out of 100 tested than ECG measurements alone. beta-Blockers had no effect on test characteristics while ST depression on the resting ECG decreased specificity. By setting probability limits using the scores from the equations, the population was divided into high-, intermediate-, and low-probability groups. A strategy using further testing in the intermediate group resulted in 86% sensitivity and 85% specificity for identifying patients with severe coronary disease. We conclude that computerized exercise ST measurements are comparable to visual ST measurements by a cardiologist and computerized scores only minimally improved the discriminatory power of the test. However, using these scores in a stratification algorithm allows the nonspecialist physician to improve the discriminatory characteristics of the standard exercise test even when resting ST depression is present. Computerization permitted accurate identification of patients with severe coronary disease who require referral.

Can computerization of the exercise test replace the cardiologist?

BACKGROUND

The type of practitioners who use the standard exercise test is changing. Once a tool of the cardiologist, the standard exercise test is now being performed by internists and other noncardiologists. Because this change could be facilitated by computerization similar to the computerized interpretation programs available for the resting electrocardiograph (ECG), we performed this analysis. A secondary aim was to demonstrate the effects of medication status and resting ECG abnormalities on test diagnostic characteristics because these factors affect utility of the exercise test by the generalist.

METHODS AND RESULTS

A retrospective analysis was performed of consecutive patients referred at 2 university-affiliated Veteran's Affairs Medical Centers and a Hungarian Hospital for evaluation of chest pain and possible ischemic heart disease. There were 1384 consecutive male patients without a prior myocardial infarction with complete data who had exercise tests and coronary angiography between 1987 and 1997. Measurements included clinical, exercise test data, and visual interpretation of the ECG recordings as well as more than 100 computed measurements from the digitized ECG recordings and compilation of angiographic data from clinical reports. The computer measurements had similar diagnostic power compared with visual interpretation. Computerized measurements from maximal exercise or recovery were equivalent or superior to all other measurements. Prediction equations applied by computer were superior to single ECG measurements. Beta-blockers had no effect on test characteristics, whereas resting ST depression was associated with decreased specificity and increased sensitivity.

CONCLUSIONS

Computerized exercise ST measurements are comparable to visual ST measurements by a cardiologist; computerized scores that included clinical and exercise test results exhibited the greatest diagnostic power. Applying scores with a computer allows the practicing physician to improve the diagnostic characteristics of the standard exercise test. This approach is successful even when there is resting ST depression, thus lessening the need for more expensive nuclear or imaging studies.

Determinants of exercise-induced ST segment depression in patients with coronary artery disease: a multivariate approach

The purpose of this study was to delineate among the usually gathered parameters in an electrocardiographic exercise test the determinants of its positive outcome (delta ST decreases > or = 1 mm measured at 80 msec from the J point). The authors studied 832 patients investigated with Bruce's exercise testing and with diagnostic coronary arteriography, all of whom were shown to have significant coronary artery disease (diameter stenosis > or = 50%). Twenty-five demographic, clinical, electrocardiographic, exercise, and anatomic/hemodynamic parameters were analyzed. The stepwise forward logistic regression analysis retained seven among them as significant independent predictors: four as positive contributors: (1) three-vessel and/or left main disease (P = 0.0000), (2) Gensini's angio-graphic score for disease extent (P = 0.0025), (3) anginal pain during the test (P = 0.0000), and (4) age (P = 0.0031) and three as negative contributors: (1) resting heart rate (P = 0.0004), (2) history of old myocardial infarction (P = 0.0019), and (3) pathological Q waves at the resting ECG (P = 0.0018). These findings establish standards that permit the prediction of the positive electrocardiographic exercise outcome in patients with significant coronary disease.

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.

Clinical evaluation of algorithms for ST measurement during exercise test

HYPOTHESIS

Computer processing of the exercise electrocardiogram (ECG) has many advantages, but the reliability of the analysis algorithms is not easily evaluable. No standard annotated database, nor recommended practice for testing and reporting performance results is available: thus, performance evaluation of such devices can be accomplished only by using a set of unannotated recordings, obtained in clinical practice. We evaluated the accuracy of an original microcomputer-based exercise test analyzer comparing the ST computer output with the measurements obtained by two experienced cardiologists.

METHODS

Six hundred ECG strips were randomly selected from the exercise test recordings of 60 patients. The ST shift (at J + 80 ms) was blindly assessed by two observers (with the aid of a calibrated lens) and compared with computer measurements. Correlation coefficients, linear regression equations, percent of discrepant measurements, and 95% confidence limits of the mean error were calculated for all leads, peripheral leads, precordial leads, and "stress-test" leads (II, III, aVF, V4, V5, V6).

RESULTS

The computer did not analyze five samples on a total of 600 (0.83%) ECG strips because of excessive noise or signal loss, while 51 (8.5%) were considered unreadable by both observers and 67 (11.2%) were rejected by at least one observer. Correlation between the measurements taken by computer and observer(s) measurements was statistically significant (p < 0.001 for all lead groups), no systematic measurement bias was found, and the mean difference was lower than human eye resolution.

CONCLUSIONS

Our algorithms provide results as good as those provided by trained cardiologists in measuring ST changes occurring during exercise test. However, this study did not evaluate whether computer improvement of the signal-to-noise ratio would allow accurate measurements even on cardiologists' uninterpretable ECG. This potential advantage of computer-assisted analysis could be assessed only by using a dedicated exercise test database, in which different patterns of noise are superimposed on noise-free recordings previously annotated for ST level.

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.