Prediction of the frequency and duration of ambulatory myocardial ischemia in patients with stable coronary artery disease by determination of the ischemic threshold from exercise testing: importance of the exercise protocol

The relation between ambulatory myocardial ischemia and the results of exercise testing in patients with ischemic heart disease remains undefined, because of the dissimilar results of previous reports. To further investigate this issue and, in particular, to ascertain the importance of the exercise protocol in determining that relation, 70 patients with stable coronary artery disease underwent 48 h ambulatory electrocardiographic (ECG) monitoring and treadmill exercise tests after withdrawal of medications. Patients exercised using two different protocols with slow (National Institutes of Health [NIH] combined protocol) and brisk (Bruce protocol) work load increments. Exercise duration was longer with the NIH combined protocol (14.1 +/- 5 versus 6.8 +/- 2 min; p less than 0.0001), but the maximal work load and peak heart rate achieved were greater with the Bruce protocol (9.8 +/- 2 versus 6.5 +/- 2 METs, and 142 +/- 19 versus 133 +/- 22 beats/min, respectively; p less than 0.0001). A close inverse correlation between exercise testing and the results of ambulatory ECG monitoring was observed using the NIH combined protocol; the strongest correlation was observed between time of exercise at 1 mm of ST segment depression and number of ischemic episodes (r = -0.86; p less than 0.0001). With the Bruce protocol a significantly weaker inverse correlation was found (r = -0.35). The mean heart rate at the onset of ST segment depression was similar during monitoring and during exercise testing with the NIH combined protocol (97.2 +/- 13 versus 101.0 +/- 17 beats/min, respectively) but it was significantly higher (110.4 +/- 13) when using the Bruce protocol (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Evaluation of coronary artery disease by an improved method of exercise electrocardiography: the ST segment/heart rate slope

Analysis of the rate-related change in exercise-induced ST segment depression, the ST/HR slope, has been shown to significantly improve the accuracy of the exercise ECG for the identification of patients with coronary artery disease and for the recognition of patients with stable angina pectoris who have anatomically or functionally severe coronary artery obstruction. This method, in effect, normalizes the extent of ST segment depression for heart rate, which serves as an index of exercise-induced augmentation of myocardial oxygen demand. While preserving the specificity of the exercise ECG at greater than 90%, an ST/HR slope value of 1.1 microV/bpm as an upper limit of normal improved exercise test sensitivity from 57% to 91% in patients with stable angina who were examined using standard Bruce protocols and three monitoring leads. In addition, an ST/HR slope value of 6.0 microV/bpm was found to partition patients with and without three-vessel coronary artery disease with a sensitivity of 78%, specificity of 97%, positive predictive value of 93%, and overall test accuracy of 90%. No other criteria based on standard ECG interpretation performed as well as the ST/HR slope for the recognition of three-vessel disease in these patients. Further, patients with high ST/HR slopes who did not have three-vessel coronary disease could be shown to have functionally severe two-vessel disease by radionuclide cineangiography. These data suggest that the ST/HR slope can improve the evaluation and management of patients with possible coronary disease. Additional improvement in ST/HR slope accuracy and applicability is likely to result from modification of exercise protocols to reduce heart rate increments between stages, an increase in monitoring leads to include CM5, and computer analysis of the ST segment depression.     

Comparison of the ST/heart rate slope with the modified Bruce exercise test in the detection of coronary artery disease

The rate of depression of the ST segment with increasing heart rate (HR) during exercise has been claimed to predict the extent of coronary artery disease (CAD). To determine whether the maximal ST/HR slope is better than the Bruce treadmill exercise test for predicting the presence of CAD, the maximal ST segment/HR slope was calculated in 81 patients and compared with the results of a standard 12-lead exercise test. In 21 patients (26%), the ST/HR slope could not be calculated. In 60 patients with ST/HR slope values, the extent of CAD was predicted in 24 patients (40%). The sensitivity and specificity of the ST/HR slope in predicting the presence of CAD in the 60 patients with slope values were 91% and 27%, respectively. The sensitivity and specificity of the modified Bruce treadmill exercise test in the 81 patients were 81% and 64%, respectively. Thus, the use of the ST/HR slope does not provide additional information that cannot be obtained using the standard Bruce exercise test.     

Exercise performance-based outcomes of medically treated patients with coronary artery disease and profound ST segment depression

OBJECTIVES

We sought to determine the relationship between exercise duration and cardiovascular outcomes in patients with profound (≥2 mm) ST segment depression during exercise treadmill testing (ETT).

BACKGROUND

Patients with stable symptoms but profound ST segment depression during ETT are often referred for a coronary intervention on the basis that presumed severe coronary artery disease (CAD) will lead to unfavorable cardiovascular outcomes, irrespective of symptomatic and functional status. We hypothesized that good exercise tolerance in such patients treated medically is associated with favorable long-term outcomes.

METHODS

We prospectively followed 203 consecutive patients (181 men; mean age 73 years) with known stable CAD and ≥2 mm ST segment depression who are performing ETT according to the Bruce protocol for an average of 41 months. The primary end point was occurrence of myocardial infarction (MI) or death.

RESULTS

Eight (20%) of 40 patients with an initial ETT exercise duration ≤6 min developed MI or died, as compared with five (6%) of 84 patients who exercised between 6 and 9 min and three (3.8%) of 79 patients who exercised ≥9 min (p = 0.01). Compared with patients who exercised ≤6 min, increased ETT duration was significantly associated with a reduced risk of MI/death (6 to 9 min: relative risk [RR] = 0.25, 95% confidence interval [CI] 0.08 to 0.76; >9 min: RR = 0.14, 95% CI 0.04 to 0.53). This protective effect persisted after adjustment for potentially confounding variables. We observed a 23% reduction in MI/death for each additional minute of exercise the patient was able to complete during the index ETT.

CONCLUSIONS

Optimal medical management in stable patients with CAD with profound exercise-induced ST segment depression but good ETT duration is an appropriate alternative to coronary revascularization and is associated with low rates of MI and death.     

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.     

Comparison of ischemic and physiologic responses during exercise tests in men using the standard and modified Bruce protocols.

The importance of low-level (warm-up) exercise for reducing exercise-induced myocardial ischemic symptoms in patients with coronary artery disease is well-recognized by clinicians. Whether altering the abruptness of exercise, such as that which occurs during different frequently used testing protocols, affects myocardial ischemic variables and maximal exercise capacity has not been resolved. This study seeks to determine the effects of altering the increment of work-rate change per exercise stage on both the ischemic threshold and maximal exercise capacity using 2 frequently used exercise testing protocols. Thirty-two patients with documented coronary artery disease and previously positive exercise tests (ischemic ST depression greater than or equal to 1.0 mm) performed symptom-limited exercise tests using both the standard and modified Bruce protocols in random order, 1 hour apart. Exercise electrocardiograms were analyzed to determine the ischemic threshold, defined as heart rate at onset of greater than or equal to 1.0 mm ischemic ST depression. Patients achieved a higher peak heart rate (124 +/- 19 vs 117 +/- 21 beats/min; p less than 0.0001), rate-pressure product (21.4 +/- 3.9 vs 19.8 +/- 4.1 beats/min x mm Hg x 10(3); p less than or equal to 0.0001) and oxygen consumption (VO2) (18.5 +/- 3.7 vs 16.5 +/- 4.4 ml/kg/min; p less than or equal to 0.001) with the standard than with the modified Bruce protocol. At matched submaximal exercise stages there were no differences in VO2, heart rate or oxygen pulse between protocols. Time to ischemic threshold was significantly reduced with the standard compared with the modified Bruce protocol (312 +/- 107 vs 607 +/- 221 seconds; p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of exercise protocol and lead selection on the accuracy of heart rate-adjusted indices of ST-segment depression for detection of three-vessel coronary artery disease

To assess the effect of exercise protocol and number of monitoring leads on the ability of the ST/HR slope and delta ST/HR index to identify three-vessel coronary artery disease, the exercise ECGs of 50 patients who had coronary arteriography were reviewed. Test performance of the ST/HR slope using the Cornell exercise protocol with 13 leads was compared with performance obtained from the standard 12 leads and from sets of only 3 leads, as well as with test outcome using Bruce protocol equivalent stages with multiple-lead sets. ST/HR slopes could be calculated in 100% of patients using data from the Cornell protocol, but in only 80% of patients using the Bruce protocol with 13 leads (chi 2 = 8.1, p less than 0.005) and 54% of patients using the Bruce protocol with 3 leads (chi 2 = 21.0, p less than 0.001). With the Cornell protocol and 13 leads, an ST/HR slope partition of 6.0 microV/bpm identified three-vessel disease with a sensitivity of 96%, specificity of 58%, and overall test accuracy of 76%. At matched specificity, the Bruce protocol 13-lead ST/HR slope partition of 5.0 microV/bpm had a sensitivity of only 48% and overall test accuracy of 53% for three-vessel disease in those patients with calculable test outcomes (each p less than 0.01). Receiver operating characteristic curve analysis confirmed the superior performance of data acquired with the Cornell protocol and demonstrated no significant loss of Cornell ST/HR slope performance calculated from fewer monitored leads. Performance of the delta ST/HR index was similar with 3 leads and with 13 leads.(ABSTRACT TRUNCATED AT 250 WORDS)     

Usefulness of severity of myocardial ischemia on exercise testing in predicting the severity of myocardial ischemia during daily activities

To determine the relation between myocardial ischemic indexes on exercise testing and on ambulatory Holter recording, 60 patients with stable coronary artery disease who exhibited an ischemic response to both testing procedures were studied. All patients performed a Bruce protocol exercise test and underwent 24-hour Holter recording within 2 weeks without antianginal medications. Mean exercise duration was 7.4 +/- 2.8 minutes, mean heart rate at 1-mm ST depression was 118 +/- 20 beats/min and mean maximal ST depression during exercise was 2.2 +/- 1 mm. During Holter recording the average number of ischemic episodes was 4.7 +/- 2.6 per patient, mean duration of daily ischemia was 62 +/- 54 minutes, mean maximal ST depression was 3.2 +/- 1.3 mm and average heart rate at 1-mm ST depression was 93 +/- 17 beats/min. Overall, the correlations between ischemic indexes on both testing procedures were very weak (mean r2 = 0.054). The only exercise variable that had a significant correlation (p less than 0.05) with all Holter variables was heart rate at 1-mm ST depression, yet it correlated very weakly (0.064 less than or equal to r2 less than or equal to 0.125) with most Holter covariates and had a better correlation (r2 = 0.256) only with average heart rate at 1-mm ST depression during Holter. Thus, ischemic indexes on exercise testing cannot accurately predict ischemic indexes on ambulatory Holter recording in patients with stable coronary artery disease who exhibit ischemic changes on both tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise testing for assessment of the significance of ST segment depression observed during episodes of paroxysmal supraventricular tachycardia

Sixteen patients who had manifested ST segment depression duringepisodes of paroxysmal supraventricular tachycardia (PSVT) werestudied with exercise testing in order to detect coronary arterydisease and myocardial ischaemia. No ST segment depression wasobserved during exercise testing in 15 out of the 16 patientstested. Paroxysms of supraventricular tachycardia associatedwith ST segment depression occurred during exercise testingin three cases. The ST segment depression was immediately apparent,remained constant throughout the supraventricular tachycardiaand was almost instantly abolished following conversion to sinusrhythm. Patients with heart rates > 250 beats min^–1during PSVT had marked ST segment depression associated withthe tachycardia. These results suggest that coronary artery disease and myocardialischaemia are not involved in the genesis of ST segment depressionduring PSVT. Tachycardia per se may be the cause of ST segmentdepression by altering the slope of phase 2 of the ventricularaction potential. Retrograde atrial activation may also induceST segment shifts in some of the cases.     

Myocardial cell membrane stress ionic dyskinesia reversal by diltiazem

Based on previous observations of cardioplegic ionic myocardial distress, myocardial stress dyskinesia was investigated as another possible cause of exercise stress testing-induced silent myocardial ischemia by analyzing the efficacy of the myocytic calcium channel blocker diltiazem in normalizing the results of patients who previously tested positive.From October 2004 to February 2006, 25 patients (13 women [52%]; aged between 28 and 71 years; mean age 56.9 years) complaining of precordial pain, with no coronary artery obstruction detected by scintigraphy and coronary cineangiography studies, presenting with positive ergometric testing, defined by ST segment depression, with no precordial pain or arrhythmia during testing, were treated with diltiazem in three daily doses of 90 mg, and were restudied five or seven days after the first examination. Treadmill electrocardiography exercise testing was performed using the standard Bruce protocol, analyzing the following parameters: the J point and Y point of the ST segment depression, maximum oxygen uptake reached, heart rate, double product and exercise performance measured in metabolic equivalents.The administration of diltiazem abolished patients' complaints of atypical precordial pain in all cases and blocked ST segment depression, both J point (control: mean 2.3+/-0.5 mm; with treatment: 0.4+/-0.5 mm; P<0.001) and Y point (control: mean 1.9+/-0.7 mm; with treatment: 0.1+/-0.3 mm; P<0.001). The heart rate variations were not significant (P>0.05), with mean values of 156.2+/-12.0 beats/min for the control and 149.0+/-19.2 beats/min with treatment. There was significant (P<0.01) improvement in the functional classification of the heart with treatment (mean 2.7+/-0.9 for the control and 2.0+/-0.7 with treatment), without significant variations (P>0.05) in maximum oxygen uptake and double product results.The administration of the myocytic calcium channel blocker diltiazem impeded the occurrence of the silent ST segment depression, previously induced by exercise stress testing in patients without confirmed obstructive coronary artery disease, supporting the involvement of calcium-dependent myocardial contraction ionic dyskinesia in the genesis of silent ST segment depression.     

Exercise test parameters after acute myocardial infarction. Relationship with coronary angiography]

OBJECTIVE: To analyze the relation between characteristics of symptom-limited treadmill exercise stress test, after acute myocardial infarction (MI) and coronariographic results (number of diseased vessels). Both tests were performed before hospital discharge. DESIGN: Retrospective study with comparative analysis between variable defined groups. POPULATION AND SETTING: From 232 patients interned in the department of Cardiology of Hospital de Santa Marta with a first acute MI, a population of 112 patients submitted to exercise stress test and coronary angiography before discharge were selected (aged 29 to 69 years). METHODS: Symptom-limited treadmill exercise stress tests were performed according to Bruce protocol, with no heart-rate limitation. The following parameters were analyzed: Stress test duration (DUR); Double product variation (varDP); Metabolic equivalent units (METS); Maximal heart rate (FCmax); Percentage of the maximal reached heart rate (% FCmax); Incidence of ST segment depression (InfST); Maximal ST segment depression (Max-InfST); Onset minute of ST segment depression (MinInfST); Heart rate at the onset of ST segment depression (FCInfST); Double product at the onset of ST segment depression (DPInfST); Recovery minute of ST segment depression (MinRInfST); Onset minute of angina (MinAng); Heart rate at the onset of angina (FCAng); Double product at the onset of angina (DPAng). RESULTS: Statistical significant differences were obtained between coronariographic groups concerning the following parameters: DUR: 1-vessel/3-vessel P = 0.02; VarDP: 1-vessel/3-vessel p = 0.008, 2-vessel/3-vessel p = 0.004; METS: 1-vessel/3-vessel p = 0.01. No differences were seen between anterior and inferior myocardial infarctions regarding all the stress test parameters. However in patients with anterior MI significant differences were obtained concerning the following variables: VarDP: 1-vessel/2-vessel p = 0.02; InfraST: 1-vessel/2-vessel p = 0.006, 1-vessel/3-vessel p = 0.03; MaxInfST: 1-vessel/2-vessel p = 0.01, 1-vessel/3-vessel p = 0.0006; Angina: 1-vessel/2-vessel p = 0.0005, 1-vessel/3-vessel p = .001. In inferior myocardial infarctions only the stress duration differed between 1-vessel and 3-vessel groups (p = 0.003). CONCLUSIONS: Symptom-limited treadmill exercise stress tests, safely performed in our institution, were an important method for post MI evaluation and allowed the diagnosis of a great number of patients with residual ischemia. Statistical significant differences were found in ergometric parameters, between coronariographic groups (defined by the number of diseased vessels), emphasising the importance of stress tolerance analysis.     

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.     

Prognostic value of heart rate adjustment of exercise-induced ST segment depression in the multiple risk factor intervention trial

Objectives.We sought to assess the effect of heart rate adjustment of ST segment depression on risk stratification for the prediction of death from coronary artery disease.Background.Standard analysis of the ST segment response to exercise based on a fixed magnitude of horizontal or downsloping ST segment depression has demonstrated only limited diagnostic sensitivity for the detection of coronary artery disease and has variable test performance in predicting coronary artery disease mortality. Heart rate adjustment of the magnitude of ST segment depression has been proposed as an alternative approach to increase the diagnostic and prognostic accuracy of the exercise electrocardiogram (ECG).Methods.Exercise ECGs were performed in 5,940 men from the Usual Care Group of the Multiple Risk Factor Intervention Trial at entry into the study. An abnormal ST segment response to exercise was defined according to standard criteria as ≥ 100 μV of additional horizontal or downsloping ST segment depression at peak exercise. The ST segment/heart rate index was calculated by dividing the change in ST segment depression from rest to peak exercise by the exercise-induced change in heart rate. An abnormal ST segment/heart rate index was defined as >1.60 μV/beats per min.Results.After a mean follow-up of 7 years there were 109 coronary artery disease deaths. Using a Cox proportional hazards model, a positive exercise ECG by standard criteria was not predictive of coronary mortality (age-adjusted relative risk [RR] 1.5,95% condence interval [CI] 0.6 to 3.6, p = 0.39). In contrast, an abnormal ST segment/heart rate index significantly increased the risk of death from coronary artery disease (age-adjusted RR 4.1, 95% CI 2.7 to 6.0, p < 0.0001). Excess risk of death was confined to the highest quintile of ST segment/heart rate index values, and within this quintile, risk was directly related to the magnitude of test abnormality. After multivariate adjustment for age, diastolic blood pressure, serum cholesterol and cigarettes smoked per day, the ST segment/heart rate index remained a significant independent predictor of coronary death (RR 3.6, 95% CI 2.4 to 5.4, p < 0.001).Conclusions.Simple heart rate adjustment of the magnitude of ST segment depression improves the prediction of death from coronary artery disease in relatively high risk, asymptomatic men. These findings strongly support the use of heart rate-adjusted indexes of ST segment depression to improve the predictive value of the exercise ECG.     

平板运动试验心率校正的ST段压低参数对冠心病诊断价值的探讨

探讨心率校正的ST段压低参数诊断冠状动脉 (简称冠脉 )病变的准确性 ,12 8例患者接受次极量平板运动试验和冠脉造影。观察各例患者运动中心率相关的ST段压低最大速度即最大ST段 /心率斜率 ,最大心率时ST段与静息时ST段压低值之差除以最大心率与静息心率之差即ΔST/HR指数 ,以及ST段压低 ,观察值与阳性判断标准比较。结果显示 ,最大ST/HR斜率诊断冠心病的敏感性、特异性及诊断符合率最高 ,分别为 94.1%、92 .3%、94.5 % ,ST段压低诊断冠心病的敏感性、特异性及诊断符合率最低 ,分别为 74.5 %、6 9.2 %、73.4%。最大ST/HR斜率在冠脉不同程度病变间无重叠 ,其它参数虽与冠脉病变程度有平行关系 ,但有较大程度的重叠。结论 :心率校正的ST段压低参数显著提高了对冠心病的诊断价值 ,其中最大ST/HR斜率对冠脉病变支数有定量诊断价值     

Does the exercise protocol matter when assessing the anti-anginal effects of drug therapy?

Four exercise test protocols (Bruce, Balke, Ellestad and Steep)were compared in 16 patients with proven coronary artery diseasein demonstrating the anti-anginal effects of sublingual glyceryltrinitrate in a randomization double-blind trial. Glyceryl trinitrate significantly improved the time, heart rateand rate pressure product to peak exercise, onset of anginaand 1 mm ST segment depression in all four protocols (P<0.05)(except rate pressure product to angina in the Balke protocol).The increase in exercise time was greatest for the Balke protocolat peak exercise (188.1±187.1) (mean±SD in s),at onset of angina (251.9±247.1) and at 1 mm ST depression(233.6±243.8), followed by the Steep and Bruce protocols,and was lowest for the Ellestad protocol 41.9±42.4, 96.5±65.8,82.6±74.0, respectively. Increase in time to peak exercisewith glyceryl trinitrate was significantly greater for the Balkeprotocol in comparison with the other three protocols and forthe Bruce and Steep protocols when compared to the Ellestadprotocol. Time to 1 mm ST depression with treatment was significantlygreater on the Balke and Bruce protocols than the Ellestad protocol,and to onset of angina for the Balke compared to other threeprotocols. There were no significant differences between theBruce and Steep protocols for any of the endpoints. The magnitudeof treatment effect in the different protocols was accompaniedby correspondingly greater inter-patient variability such thatno protocol was more, or less, sensitive than another in detectingtreatment effect. Changes in heart rate and rate pressure productwith treatment were generally similar between the differentprotocols. In conclusion, a protocol with small and frequent increments(Balke), although able to show greater increase in exerciseduration with glyceryl trinitrate than more aggressive protocols,is no more sensitive at detecting treatment effect.     

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.     

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.     

Ambulatory electrocardiographic ST segment changes in healthy volunteers.

Twenty four hour ambulatory monitoring was performed on 120 healthy volunteers using a frequency modulated recorder: 50 men and 50 women below 40 years and 20 men between 40 and 60 years were studied. Twenty eight subjects had episodes of ST segment elevation (range 1-3 mm), which occurred almost invariably at night with a slow heart rate 62.4 +/- 10.4 beats/min). ST segment elevation occurred most often in men, and was not found in subjects over the age of 37. Also in 10 subjects horizontal or downsloping ST segment depression (range 1-2 mm) was recorded, usually in association with tachycardia (135 +/- 10.5 beats/min). Nine of these exercised on a bicycle ergometer, and widespread ST segment depression was observed in eight. Thus ST segment changes, which are often interpreted as myocardial ischaemia in patients with ischaemic heart disease, are commonly seen in 24 hour electrocardiographic monitoring of healthy volunteers.     

Exercise testing in women with chest pain. Are there additional exercise characteristics that predict true positive test results?

Women have a notoriously high rate of false positive exercise test results. Since the exercise ST segment response has low specificity in predicting CAD in women, we examined additional exercise parameters in 200 women with a history of chest pain compatible with angina and having ST segment depression greater than or equal to 1 mm recorded during a Bruce treadmill test. All subsequently had coronary arteriography. Two groups were compared: group A (n = 80) with CAD (greater than or equal to 70 percent stenosis of one or more coronary artery) and group B (n = 120) with angiographically confirmed normal coronary arteries (normal or minimal placquing). The exercise criteria analyzed included: (1) chest pain during exercise, (2) percent target heart rate, (3) extent of ST shift, (4) morphology of the ST segment slope, (5) time to normalization of the ST segment, and (6) total exercise duration. Multivariate analysis (using a stepwise logistic regression model) identified four independent exercise variables associated with the likelihood of CAD: (absence of MVP, p = .003; exercise duration less than 5 min, p = .02; ability to reach target heart rate, p = .027; time to ST normalization greater than or equal to 6 min, p less than .001). False positive exercise test results were more likely to occur when the following exercise test variables were present: ability to exercise to stage 3 of the Bruce protocol and a rapid (less than or equal to 4 minutes) normalization of ST shift after cessation of exercise. Attention to these additional exercise variables allows more careful selection of women requiring more definitive (and expensive) testing.