II: Perioperative Holter monitoring: clinical relevance and practice

Perioperative, mostly silent ischaemia in patients with coronary heart disease is difficult to detect by clinical examinations. Methods. During the clinical evaluation (part I of this study) we monitored patients with prior myocardial infarction (MI) by continuous electrocardiographic (ECG) recording from the evening before until the first 24?h after operation. Excluded from Holter ECG studies were patients with a bundle branch block, pacemaker, valvular heart disease, cardiomyopathy, severe hypokalaemia, and digitalis treatment. Data were recorded with a Holter 8500 recorder (Marquette Electronics) using modified V2, V4, and V5 leads (Fig. 1). Holter tapes were analysed twice with a Holter computing system (Software 5.8, Marquette Electronics), first by a blinded technician and then by the authors themselves. We defined the following criteria as pathological ST segment changes and as ischaemic episodes [7]: horizontal or downsloping ST depression of at least 1?mm or elevation of 2?mm of at least 1?min duration measured at the J-point plus 60?ms. To quantify individual levels of ischaemia we used the definition “ischaemic load” [3]: ischaemic min/h monitored per patient. The statistic evaluation did not differ from that used in part I. Results. Out of 160 patients, 100 could be examined by Holter monitoring. Because of technical problems we could not record a Holter ECG in 2 of 6 patients with reinfarction. We found one or more perioperative episodes of ST-segment depression in 25 patients (25%). Ischaemic episodes were detected in 15 patients preoperatively, in 12 intraoperatively, and in 10 postoperatively. Three patients had ischaemic episodes during all periods. Patients with pathological ST segments suffered significantly more reinfarctions (3 of 25 vs. 1 of 75 patients) and were older (mean age difference 7 years, P<0.05). Patients with ischaemic episodes and a clinical diagnosis of reinfarction (n=3) demonstrated a dramatic postoperative increase in ischaemic load. Preoperative use of beta-blocking agents did not influence the incidence of ischaemic events. The sensitivity of postoperative Holter ECG monitoring in the diagnosis of reinfarction was 50%, the specificity 92%. Conclusions. Perioperative Holter ECG monitoring is time-consuming, expensive, not very sensitive, and therefore not generally applicable for all patients with prior MI.     

Hemodynamic effect of the clamping of the carotid in the surgically treated coronary patient

To determine both the incidence of myocardial ischaemia and haemodynamic response to carotid cross-clamping in coronary artery disease, 30 patients undergoing carotid endarterectomy were studied with a clear history of effort related disabling angina pectoris. Myocardial ischaemia was detected by a recording of lead CM5 of the electrocardiogram. A radial arterial and a thermodilution pulmonary catheter were inserted to obtain haemodynamic measurements before and after carotid cross-clamping and unclamping. Anaesthesia was induced with increments of thiopental, fentanyl 6 micrograms X kg-1 and pancuronium. Additional fentanyl (2 micrograms X kg-1) was injected before skin incision and before carotid cross-clamping. Carotid cross-clamping results in a significant increase in both mean arterial blood pressure and capillary wedge pressure. Two patients experienced myocardial ischaemia with ST segment depression during carotid cross-clamping. Nitroglycerin infusion led to the improvement of ST segment depression. When halothane was additionally administered to patients who developed hypertension in response to carotid cross-clamping, arterial blood pressure returned to normal value. These results indicate that carotid cross-clamping increases determinants of myocardial oxygen demand and may cause myocardial ischaemia in patients suffering from angina pectoris.     

Intraoperative myocardial ischemia: localization by continuous 12-lead electrocardiography

Based primarily on results obtained during exercise treadmill testing, electrocardiographic (ECG) leads II and V5 are the suggested optimal leads for detecting intraoperative myocardial ischemia. However, these recommendations have not been validated in this setting using all 12 ECG leads. Accordingly, the authors studied 105 patients with known or suspected coronary artery disease (CAD) undergoing noncardiac surgery with general anesthesia by continuously recording the 12-lead ECG intraoperatively in all patients. The average duration of monitoring was 8.2 +/- 2.7 h (mean +/- SD). Ischemic episodes (i.e., greater than or equal to 1-mm horizontal or downsloping ST depression, greater than or equal to 1.5-mm slowly upsloping ST depression or greater than or equal to 1.5-mm ST elevation in a non-Q wave lead) occurred in 25 patients (24%). Out of 51 ischemic episodes, 45 involved ST depression alone, and the remaining six involved both ST depression and elevation. ST segment changes occurred in a single lead only in 14 episodes, while multiple leads were involved in 37 episodes. Lead sensitivity was estimated assuming that all ST segment changes were true positive responses. Sensitivity using a single lead was greatest in V5 (75%) and V4 (61%), and intermediate in II, V3, and V6 (33%, 24%, and 37%, respectively). The remaining seven leads demonstrated very low sensitivity (2-14%) or exhibited no ischemic changes (I and a VL). Combining leads V4 and V5 increased sensitivity to 90%, while the standard clinical combination, II and V5, was only 80% sensitive. Sensitivity increased to 96% by combining II, V4, and V5. The further addition of V2 and V3 (five leads) increased sensitivity to 100%. This study confirms previous recommendations for the routine use of a V5 lead (either uni- or bipolar) in all patients at risk for ischemia. V4 is more sensitive than lead II, and should be considered as a second choice. However, lead II, superior for detection of atrial dysrhythmias, is more easily obtained with conventional monitors. The use of all three would appear to be the optimal arrangement for most clinical needs, and is recommended if the clinician has the capability.     

CONTINUOUS AMBULATORY ECG MONITORING IN THE PERIOPERATIVE PERIOD: RELATIONSHIP OF PREOPERATIVE STATUS AND OUTCOME

We have used continuous ambulatory electrocardiographs in theperioperative period to monitor 108 patients with known cardiovasculardisease undergoing non-cardiac surgery. There was a high incidenceof ischaemic ST segment changes and ventricular arrhythmias.For the group as a whole, anaesthesia and surgery were followedby increased ventricular ectopic activity, but did not worsenmyocardial ischaemia. However, the mean duration of ischaemicST segment changes was increased significantly in those patientswith treated hypertension. Of the risk factors considered, preoperativeischaemia and peroperative systolic arterial pressure were significantcorrelates with postoperative myocardial ischaemia.     

Detection of intraoperatiye myocardial ischaemia — a comparison among electrocardiographic,myocardial metabolic,and haemodynamic measurements in patients with reduced ventricular function

This study determined the sensitivity and specificity of haemodynamic and ECG monitors to detect the development of intraoperative myocardial ischaemia utilizing myocardial lactate production as the standard. In 29 patients with reduced ejection fraction (0.27–0.50) undergoing coronary artery revascularization, measurements were made at the awake, post-induction, post-intubation, first skin incision, post-sternotomy, preprotamine, immediately post-cardiopulmonary bypass, and skin suture intervals. At each interval, measurement of a haemo-dynamic profile (including pulmonary artery occlusion (PAOP) and central venous (CVF) pressures, heart rate, and pressure rate quotient); myocardial lactate extraction and flux; changes in ST segments in ECG leads, V₅ and II utilizing a Siemens 1280® intraoperative monitor, and a Marquette 8500® Hotter monitor utilizing leads V₅, V₂, and AVF were made. “Ischaemia” was considered to be present when myocardial lactate production (MLP) occurred, PAOP or CVP increased by 5 mmHg above the baseline value, the pressure rate quotient was <1, or ST segment deviation (>1 mm) occurred in any lead for >1 min. Variables positive when MLP was positive were the pressure rate quotient (sensitivity 32.8%, specificity 71.9%), CVP (sensitivity 10.9%, specificity 92.6%), and PAOP (sensitivity 1.6%, specificity 99.2%). Holter monitoring had a 100% positive predictive value but poor sensitivity (1.6%). The ECG (Lead V₅ + II) measures of ischaemia were insensitive (17.5%) and relatively non-specific (87.7%). We conclude that, in this patient group and using myocardial lactate production as the standard, the pressure rate quotient, elevations in CVP or PAOP, or ST segment changes are insensitive measures of intraoperative myocardial ischaemia.     

The detection of intra-operative myocardial ischaemia Preliminary experience with the right-sided precordial lead

The value of monitoring the right precordial lead, V4R, to detect peri-operative ischaemic events during coronary artery surgery was studied in 60 patients. Thirty-four patients had only left-sided coronary disease (Group 1). The other 26 patients had both left-sided occlusive coronary artery disease and significant right-sided occlusive lesions on coronary angiography (Group 2). Lead sensitivity was estimated, assuming that all ST segment changes were true positive responses. Sensitivity using a single lead was greatest for lead V5 in the two groups (73% for Group 1 and 69% for Group 2). Sensitivity in Group 1 for lead II was intermediate (55%), whereas sensitivity for lead V4R was only 9%. In Group 2, on the other hand, lead V4R was 54% sensitive and lead II only 31%. The combination of leads V4R and V5 increased the sensitivity to 92% in Group 2, whereas lead II or V5 combined with V4R failed to improve sensitivity in Group 1. The monitoring of lead V4R allowed detection of 23% of the ischaemic episodes in Group 2 that would have passed undetected if only lead II and V5 were monitored. These results demonstrate the value of an additional right precordial lead during coronary artery bypass grafting in patients with right-sided occlusive disease.     

Myocardial ischaemia after coronary artery bypass grafting: early vs late extubation

The technique of early extubation after coronary artery bypass grafting is increasing in popularity, but its safety and effect on myocardial ischaemia remain to be established. In a randomized, prospective study, patients undergoing routine elective coronary artery bypass grafting were managed with either early or late tracheal extubation. The incidence and severity of electrocardiographic myocardial ischaemia were compared. Data were analysed from 85 patients (43 early extubation; 42 late extubation). Median time to extubation was 110 min in the early extubation patients and 757 min in the late extubation patients. After correction for randomization bias, there were no significant differences between groups in ischaemic burden, maximal ST- segment deviation, incidence of ischaemia and area under the ST deviation-time curve (integral of ST deviation and time). Similarly, there were no differences between groups in postoperative creatine kinase MB-isoenzyme concentrations and duration of stay in the ICU or hospital. Therefore, this study provides evidence for the safety of early extubation after routine coronary artery bypass grafting.      

Perioperative ST-segment depression and troponin T release. Identification of patients with highest risk for myocardial damage

BACKGROUND: Patients undergoing major vascular surgery are at constant risk of developing perioperative myocardial complications, especially myocardial infarction. The following study was performed to answer the question whether ST segment changes, analysed by Holter monitoring and ST segment analysis, are accompanied by release of cardiac troponin T, a highly specific marker of myocardial damage. METHODS: Twenty patients undergoing elective aortic resection were studied by performing Holter ECG, including ST segment analysis, beginning on the evening before surgery until the third postoperative day. Within this period serum levels of cardiac troponin T were determined at 8 timepoints. RESULTS: A total of 8/20 of the patients (40%) showed significant ST depressions (range -0.17/-0.68 mV), without any clinical symptom, with a median of 9 episodes (range 2-24). In 3 of the 8 patients, each with repetitive periods of ST depression, elevated troponin T levels were found (0.45/0.52/1.69 micrograms/l). No troponin T release nor cardiac events were noticed in the remaining patients. No dependency could be found between troponin T release and the magnitude of ST depression or the number of ST depression episodes. CONCLUSION: Haemodynamic changes, oxygen imbalance and stress during major vascular surgery frequently lead to an ischaemic burden, which is indicated by ST segment changes during ECG ST analysis. Longlasting ST depression reaching an individual critical cut-off limit followed by structural myocardial damage may be verified by elevated levels of cardiac troponin T. Prolonged periods of ST depression should be followed by determination of cardiac troponin T.     

Automated, continuous ST segment analysis in the ECG as a monitor of myocardial ischemia during aortocoronary bypass surgery

Patients with coronary artery disease (CAD) who are subjected to cardiac and major noncardiac surgical procedures have a high incidence of perioperative myocardial ischemia. Earlier studies in patients undergoing coronary artery bypass graft surgery (CABG) indicated the frequency of postoperative myocardial infarction to be directly proportional to the incidence and severity of pre-bypass myocardial ischemia. METHODS. We investigated the incidence of pre-bypass ischemia in 50 patients undergoing elective CABG using an automated ST segment monitoring system (Marquette 7010). Analyzing leads I, II, and V5, this device measures ST segment deviations 60 ms after the J-point. Occurrence of myocardial ischemia was defined as follows: new ST segment deviations larger than 1 mm = 0.1 mV that lasted for more than at least 10 consecutive heartbeats. RESULTS. In 19 out of 50 patients (38%) we found 96 episodes of myocardial ischemia in the pre-bypass period; 47% of all ischemic episodes were associated with significant hemodynamic changes, e.g., tachycardia, hypertension, or hypotension. The incidence of ischemia was different between population sub-groups: patients with a previous infarction had a lower incidence of ischemia (35%) than patients without infarction (44%). Patients with preoperative left ventricular end diastolic pressure (LVEDP) less than 15 mm Hg had a lower incidence of ischemia (29%) than patients with LVEDP greater than 15 mm Hg (50%). Patients treated preoperatively with beta-blockers showed a significantly lower incidence of ischemia (9%) when compared to untreated patients (46%, p less than 0.05). No difference was found between patients with or without unstable angina pectoris or between patients of NYHA classes II, III, or IV. Postoperative myocardial infarction occurred in 2 patients, both with evidence of pre-bypass myocardial ischemia. CONCLUSION. Our study confirms that automated ST segment analysis is able to detect myocardial ischemia similarly to that documented in previous studies using conventional ECG lead analysis.     

Stability of myocardial perfusion during revascularization under propofol anesthesia

During coronary artery bypass grafting surgery (CABGS) there are many factors which may disturb myocardial oxygen balance with consequent irreversible myocardial damage. Anesthesiologists are expected to use drugs with tendency to optimize hemodynamics and myocardial oxygen balance, making in that way conditions for preserving myocardial perfusion. In this study, performed on 19 patients undergoing CABGS under dominant propofol anesthesia, there were no signs of intraoperative ischemia manifested by statistically significant dislocation of ST segment in EKG leads D11, V5 and aVL.     

Myocardial ischaemia during tracheal extubation in patients after cardiac surgery: an observational study

This study examines whether there is a temporal relationship between tracheal extubation and myocardial ischaemia in haemodynamically stable patients extubated within 6 h of cardiac surgery. Fifty-two patients were studied during three time periods: 1, from 2 h until 30 min before extubation (90 min); 2, from 30 min before until 30 min after extubation (60 min); 3, from 30 min until 2 h after extubation (90 min). Significant ST segment changes were defined as a reversible ST segment depression of 2 mm or greater or an elevation of 3 mm or greater from baseline, lasting for 1 min or more. Fourteen patients (26.9%) had ST segment changes. The ischaemic burden in periods 2 and 3 was increased compared with that in period 1; the mean (SD) was: period 1, 19.2 (18.8) min; period 2, 35.4 (24.9) min; period 3, 39.6 (24.5) min; however, the mean ST deviation (mm) did not change. ST segment changes were associated with an increased heart rate; they were not related to arterial pressure. We conclude that there is a temporal relationship between ST segment changes and tracheal extubation after cardiac surgery.      

Evaluation of the post-exercise time-course behaviour of ST-segment and T-wave changes in the elimination of the false-positive stress ECG

Routine stress ECG has been criticised for yielding too many so-called false-positive results because ST-segment and T-wave (ST/T) changes that develop during and after exercise are prevalent. Recent studies in our institutions indicate that the time-course behaviour patterns of ST/T configurational abnormalities after exercise reflecting myocardial ischaemia are different from those that do not. The epicardial coronary arteries of 111 patients, who had positive stress tests for ischaemia based on ST/T configurational changes alone but were considered non-ischaemic when the ST/T time-course behaviour was analysed, were assessed. Of these patients, 102 had normal coronary arteries, 7 had insignificant stenoses and only 2 had significant coronary artery diseases. ST/T abnormalities on stress testing with a non-ischaemic time-course pattern should be regarded in the same category as ST segments that remain normal as far as the detection of myocardial ischaemia due to epicardial coronary artery disease is concerned. This policy has resulted in an improved predictive value of exercise testing and has considerably decreased the number of patients subjected to coronary arteriography in our institutions. The assessment of the post-exercise stress ECG remains the most practical and cost-effective method for detecting ischaemic heart disease.     

Myocardial ischemia score as a preoperative screening method for intraoperative myocardial ischemia

Three hundred patients for abdominal surgery with risk factors of ischemic heart disease (IHD), such as hypertension, diabetes mellitus, hyperlipidemia, smoking, old age, obesity, familial history, electrocardiographic abnormality, other perivascular diseases and male, were included in this study. Patients older than forty years were included in the study. ST segment in lead II and V5 was recorded by ST trend monitor from the time of entering the operating room to the time of exit and intraoperative myocardial ischemia occurred in 58 patients (19.3%). Correlation coefficients between each risk factor of IHD and intraoperative myocardial ischemia were calculated by multiple regression analysis and myocardial ischemia score (MIS) was determined. Intraoperative myocardial ischemia increased in patients with more than 10 points of MIS by discriminant analysis and hitting ratio of MIS was 86.3%.     

Medical problems of surgical patients. Hypertension and ischaemic heart disease.

Pre-existing disease in the form of hypertension or ischaemic heart disease may increase morbidity and mortality in patients presenting for anaesthesia and surgery. The interaction of these two cardiovascular conditions in relation to anaesthesia has been studied in a series of 115 patients. The results did not support the view that antihypertensive drugs and beta-receptor blocking agents should be withdrawn before anaesthesia and surgery. The main cause for concern in providing anaesthesia for these patients is that sympathetic nervous activation induced either by anaesthetic manoeuvres or by surgical stimulation may lead to reflex cardiovascular responses which, by increasing myocardial oxygen demand, lead to episodes of myocardial ischaemia. In this respect beta-receptor blocking drugs appear to have a protective effect on the ischaemic myocardium.     

Resistant hypertension and preoperative silent myocardial ischaemia in surgical patients

We studied 325 patients undergoing elective noncardiac surgerywho had preoperative ambulatory ECG monitoring performed fora duration of 5130 h (range 8–24 h; mean 15.8h). Sixty-foursubjects (20%) had one or more episodes of ST segment depressionconsistent with myocardial ischaemia. Of all preoperative cardiovascularvariables measured, the presence of elevated arterial pressure,despite patients being maintained on long term antihypertensivetherapy, was the only factor associated significantly with thepresence of preoperative silent myocardial ischaemia (P<0.002).This correlation was confirmed when arterial hypertension wasdefined in four separate ways. The incidence of silent ischaemiain these patients was 33–55%. We suggest that admissionarterial pressure may therefore be a useful screening test toidentify patients at risk of preoperative myocardial ischaemia.      

Correlation of ST changes in leads V4–V6 to area of ischemia by CMR in inferior STEMI

Objective. We aim to determine the correlation between ST-segment changes in leads V4–V6 and the extent of myocardial injury by cardiac magnetic resonance (CMR) in patients with inferior ST elevation (STE) myocardial infarction (iSTEMI). Design. Admission electrocardiogram and CMR data from the MITOCARE trial were used. Differences in mean myocardium at risk, infarct size, ejection fraction and myocardial segment involvement by CMR were compared in patients with first iSTEMI with STE, ST depression (STD) or no ST changes (NST) in V4–V6. Myocardial segment involvement was further evaluated by comparing proportion of patients in each group with ≥25% and?≥50% segment involvement. Results. Fifty-four patients were included. Patients with STE (n?=?22) and STD (n?=?16) in V4–V6 had significantly lower ejection fraction compared to NST (n?=?16) (48% vs 48% vs 54%, p?=?.02). STE showed more apical, apical lateral and mid-inferolateral involvement but less basal inferior involvement than NST. STD exhibited greater basal inferoseptal involvement compared to STE. There were more patients with STE that had ≥25% and ≥50% apical lateral involvement compared with STD and NST groups. Patients with STD were more likely to have ≥25% and ≥50% basal inferoseptal involvement compared with STE and NST groups.Conclusion. Our study suggests that in iSTEMI, ST changes in the precordial leads V4–V6 correlates with greater myocardial injury and distribution of myocardium at risk.     

Electrocardiographic studies during hypotensive anaesthesia using sodium nitroprusside

Multiple lead electrocardiographic recordings from 20 patients were studied before, during and after a period of induced hypotension with sodium nitroprusside. Although small changes in ST segment and T wave were observed in 9 patients, none of these persisted into the postoperative period. Other significant changes were confined to a temporary disturbances of cardiac rhythm in 2 patients, both of whom spontaneously reverted to sinus rhythm during the anaesthetic. Our findings indicate that there are no permanent ischaemic myocardial changes associated with induced hypotension using sodium nitroprusside.     

On line ST-segment analysis for detection of myocardial ischaemia during and after coronary revascularization

Purpose

A paucity of information exists to validate the accuracy and reliability of ECG monitoring in the operating room or ICU. The purpose of this study was to determine the accuracy, sensitivity, specificity, and predictive values of the Marquette ECG monitor for detection of perioperative myocardial ischaemia (PMI) as measured by ST segment changes in a high risk population.

Methods

Monitoring for PMI in 28 patients scheduled for aortocoronary bypass surgery was done with the Cardiodata PR® ambulatory continuous electrocardiography (ACECG) monitor lead V₅, and compared with lead V₅ of the Marquette® Series 7000 ECG/ Surgical operating room monitor, and ECG/Resp ICU monitor. The Marquette lead V₅ was evaluated using current criteria for the assessment of diagnostic tests including concordance, sensitivity, specificity, positive and negative predictive values, false positive and false negative rates and compared with the ACECG monitor which served as the reference or “gold standard.” Agreement beyond chance between the two methods was assessed using the Kappa statistic.

Results

Of the 53 observation data points, 27 were defined as ischaemic episodes by ACECG. Concordance between lead V₅ in each system was 83% (44/53 episodes). Discordance was 17% (9/53 episodes), predominantly in the postbypass interval (77%, 7/9; P = 0.0184). The incidences of false negatives and false positives for Marquette lead V₅ was 26% (7/27) and 7.7% ( 2/26), respectively. The sensitivity and specificity of the Marquette was 0.74 and 0.92. Positive predictive value was 0.91, negative predictive value was 0.77, and Kappa statistic was 66%.

Conclusion

Automated ST segment analysis with the Marquette® Series 7000 monitoring system demonstrates good diagnostic accuracy, moderate sensitivity, and high specificity. However, clinically significant false negative and false positive rates of ischaemia detection are associated with its use, especially in the postoperative period.     

Perioperative Myocardial Ischemia and Infarction: Identification by Continuous 12-lead Electrocardiogram with Online ST-segment Monitoring

Background: Perioperative myocardial ischemia is conventionally monitored using five electrocardiographic leads, with only one precordial lead placed at V5. This is based on studies from more than a decade ago. The authors reassessed this convention by analyzing data obtained from continuous on-line 12-lead electrocardiographic monitoring.

Methods: One hundred eighty-five consecutive patients undergoing vascular surgery were monitored by continuous 12-lead ST-trend analysis during and for 48-72 h after surgery. Cardiac troponin I was measured in the first 3 postoperative days, and cardiac outcome was prospectively recorded. Ischemia was defined as ST deviation, relative to the reference preanesthesia electrocardiogram, of 0.2 mV or more in one lead or 0.1 mV or more in two contiguous leads, lasting more than 10 min.

Results: During 11,132 patient-hours of monitoring, 38 patients (20.5%) had 66 transient ischemic events, with all but one denoted by ST-segment depression. Twelve patients (6.5%) sustained postoperative infarction (cardiac troponin I > 3.1 ng/ml). Among the 38 patients with ischemia, lead V3 most frequently (86.8%) demonstrated ischemia, followed by V4 (78.9%) and V5 (65.8%). Among the 12 patients with infarction, V4 was most sensitive to ischemia (83.3%), followed by V3 and V5 (75% each). Combining two precordial leads increased the sensitivity for detecting ischemia (97.4% for V3 + V5 and 92.1% for either V4 + V5 or V3 + V4) and infarction (100% for V4 + V5 or V3 + V5 and 83.3% for V3 + V4). On average, baseline preanesthesia ST was above isoelectric in V1 through V3 and below isoelectric in V5 through V6. Lead V4 was closest to the isoelectric level on the baseline electrocardiogram, rendering it most suitable for ischemia monitoring.     

Pre-bypass myocardial ischaemia in patients undergoing coronary artery surgery

One hundred patients undergoing elective coronary artery surgery were studied to determine the incidence of pre-bypass myocardial ischaemia. Leads II, aVF and V5 of the electrocardiogram (ECG) were recorded at five-minute intervals from arrival in the anaesthetic room until onset of cardiopulmonary bypass. Thirteen patients developed sixteen episodes of significant ST depression on the ECG during the study period. Three patients were diagnosed as having postoperative myocardial infarction by ECG criteria and creatine phosphokinase-MB rise above 80 units. None of these patients had pre-bypass ST depression. Comparisons of these results with similar studies are presented.