CLINICAL STUDIES
Reciprocal ST-segment depression associated with exercise-induced ST-segment elevation indicates residual viability after myocardial infarction
Akira Nakano, MD*,
Jong-Dae Lee, MD*,
Hiromasa Shimizu, MD*,
Tatsuro Tsuchida, MD ,
Yoshiharu Yonekura, MD ,
Yasushi Ishii, MD and
Takanori Ueda, MD*
* First Department of Internal Medicine, Fukui Medical University, 23 Shimoaizuki, Matsuoka-cho, Fukui, 910-1193, Japan
Department of Radiology, Fukui Medical University, 23 Shimoaizuki, Matsuoka-cho, Fukui, 910-1193, Japan
Biomedical Imaging Research Center, Fukui Medical University, 23 Shimoaizuki, Matsuoka-cho, Fukui, 910-1193, Japan
Manuscript received January 13, 1998;
revised manuscript received September 18, 1998,
accepted October 30, 1998.
Reprint requests and correspondence: Dr. Jong-Dae Lee, The First Department of Internal Medicine, Fukui Medical University, 23, Shimoaizuki, Matsuoka-cho, Fukui, 910-1193, Japan
jdlee{at}fmsrsa.fukui-med.ac.jp
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Abstract
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OBJECTIVES
We evaluated the clinical significance of reciprocal ST-segment depression associated with exercise-induced ST-segment elevation for detecting residual viability within the infarcted area.
BACKGROUND
Although the relation between residual viability and exercise-induced ST-segment elevation has been described, there are no reports focusing on the relation between myocardial viability and reciprocal ST-segment depression associated with exercise-induced ST-segment elevation.
METHODS
We evaluated regional blood flow and glucose utilization using N-13 ammonia (NH3) and F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in 30 patients with a previous Q-wave myocardial infarction (anterior in 15, inferior in 15). All subjects had single-vessel disease and had exercise-induced ST-segment elevations ( 1 mm) in electrocardiographic leads.
RESULTS
Reciprocal ST-segment depression (1 mm) was present in 16 patients (Group A; anterior in 6, inferior in 10) but not in the remaining 14 patients (Group B). The degree of exercise-induced ST-segment elevation (1.8 ± 0.2 vs. 2.0 ± 0.2 mm) and the time from the onset of infarction to the study (75 ± 49 vs. 74 ± 52 days) did not differ between groups. There were no significant differences between groups in the severity of left ventricular dysfunction and the residual luminal narrowing in the infarct-related artery (45 ± 21 vs. 48 ± 25%). The presence and site of infarction were confirmed by NH3-PET in all patients. FDG-PET demonstrated residual tissue viability within infarct-related area in all patients in Group A and in 3 (21%) of 14 patients in Group B (p < 0.01). The sensitivity, specificity and accuracy of reciprocal ST-segment depression associated with exercise-induced ST-segment elevation for detecting residual viability were 84%, 100% and 90%, respectively.
CONCLUSIONS
The occurrence of reciprocal ST-segment depression associated with exercise-induced ST segment elevation in patients with a previous Q-wave infarction who had single-vessel disease indicates residual tissue viability within the infarct-related area.
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Abbreviations and Acronyms
| | FDG | = F-18 fluorodeoxyglucose | | NH3 | = N-13 ammonia | | PET | = positron emission tomography | | WMAS | = wall motion abnormality score |
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Exercise-induced ST-segment elevation in patients with old myocardial infarction has been attributed to myocardial ischemia (1,2), to abnormalities in left ventricular wall motion, typically due to ventricular aneurysm (3–7) and to both myocardial ischemia and abnormal left ventricular wall motion (8). Moreover, Katori et al. suggested that this phenomenon is closely related to sympathetic-nerve activity (9). Thus, the clinical significance of ST-segment elevation during exercise testing has not been fully elucidated. Margonato et al. demonstrated that exercise-induced ST-segment elevation was associated with residual tissue viability in the infarct-related area using thallium-201 myocardial scintigraphy (10) and F-18 fluorodeoxyglucose-positron emission tomography (FDG-PET) (11), and others reported that ST-segment elevation during dobutamine administration was associated with residual viability in the infarct-related area (12,13). Since evaluation of residual viability within the infarct-related area is important for determining whether or not coronary revascularization is indicated, these reports are very attractive.
On the other hand, a few studies have suggested that ST-segment depression associated with this ST-segment elevation predicts multivessel coronary artery disease (3,14–16). However, patients with myocardial infarction due to single-vessel coronary artery disease often show ST-segment depression in the ECG lead opposite to the lead showing ST-segment elevation during exercise stress testing. These ST-segment depressions, considered to be passive electrical phenomena (reciprocal ST-segment depression) associated with exercise-induced ST-segment elevations, are usually accompanied by ST-segment elevation (17,18) as at the onset of acute myocardial infarction and during attacks of variant angina pectoris (19). In this study, we evaluated regional blood flow and exogenous glucose utilization in patients with previous single-vessel Q-wave myocardial infarctions using N-13 ammonia (NH3) and FDG-PET, which is considered to be the most accurate method for differentiating dysfunctional but viable myocardium from the scar tissue (20), to determine whether reciprocal ST-segment depression associated with exercise-induced ST-segment elevation in patients with previous single-vessel myocardial infarction indicates the presence of residual viability in the infarct-related area.
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Methods
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Recruitment of patients.
Patients were recruited between 1 October 1994 and 31 December 1996 from subjects admitted to the Fukui Medical University Hospital for acute myocardial infarction. Myocardial infarctions were confirmed by: chest pain at least 30 min, ST-segment elevation of more than 0.2 mV in at least two contiguous leads and elevation of the serum creatine kinase level to more than three times the upper level of normal. In these subjects, we evaluated if they met the following criteria: 1) Q-wave myocardial infarction, 2) underwent treadmill exercise testing at 4 or more weeks after onset, 3) showed exercise-induced ST-segment elevations (1 mm at 80 msec after the J point) in the infarct-related ECG leads. Patients with right or left bundle-branch block, valvular heart disease, left ventricular hypertrophy, overt diabetes and patients taking drugs known to affect the ST-segment were excluded. Then, coronary angiography was performed and patients with multivessel coronary artery disease, which may cause myocardial ischemia in a remote region, were excluded.
During the recruitment period, 39 patients out of 86 were evaluated for inclusion. Of these, nine were not enrolled for exclusion criteria. Finally, 30 patients (25 men, 5 women; 46 to 79 years old, mean [±SD] age 67±9) were evaluated in this study. Mean time interval from onset to exercise testing was 75 ± 50 days (range 29–177) in these 30 patients. Written informed consent was obtained from all patients.
Exercise testing.
All patients underwent symptom-limited exercise testing on a treadmill according to the modified Bruce protocol using a computer-assisted system (ML-4500, Fukuda-Denshi Co., Tokyo, Japan). Antianginal drugs were not discontinued during exercise testing. A 12-lead ECG and blood pressure were recorded at rest, at peak exercise and every minute during exercise into recovery. Leads II, a VF and V5 were continuously recorded. The test was terminated when severe chest pain, dyspnea, fatigue or complex ventricular arrhythmias occurred. ST-segment elevation in infarct-related leads was not in itself considered a reason for exercise termination. Reciprocal ST-segment depression was defined as an ST-segment depression (1 mm at 80 msec after the J point) in noninfarct-related leads that corresponded to the ST-segment depression at the onset of myocardial infarction.
Coronary angiography and left ventriculography.
Coronary angiography and biplane left ventriculography were performed within two weeks of the exercise testing. Coronary stenosis was measured by experienced cardiologists using a quantitative cardiovascular angiographic software program (Automated Coronary Analysis D.C.I., Phillips, Best, Netherlands). Significant stenosis was defined as a luminal narrowing of 50%. Retrograde collateral vessels were graded on a four-point scale according to the system of Cohen and Rentrop (21). The left ventricular silhouette was divided into seven segments according to the recommendations of the American Heart Association (22) and regional wall motion was visually scored using a five-point scale (0: normal; 1: mild hypokinesis; 2: severe hypokinesis; 3: akinesis; 4: dyskinesis). In each patient, the wall motion abnormality score (WMAS) represents the sum of the scores in all segments.
PET studies.
All subjects underwent NH3 and FDG dual PET after overnight fast within 2 weeks of the exercise testing. Antianginal medications were not discontinued. Regional myocardial blood flow was assessed with NH3, and glucose utilization was assessed with FDG using a whole-body tomograph (ADVANCE, GE, Milwaukee, Wisconsin). The characteristics of this camera have been previously described (23). The spatial resolution of the reconstructed clinical PET images is 8 mm in full-width half-maximum (FWHM) at the center of the field of view, and the axial resolution is 4 mm. Before the emission scan was performed, a 10-min transmission scan was performed using two rotating Ge-68 pin sources for attenuation correction. Static PET images were acquired over 10 minutes beginning 10 min after an intravenous bolus injection of NH3 ( 20 mCi). FDG ( 10 mCi) was then injected intravenously, and static images were acquired over 10 minutes beginning 60 minutes after the injection (24).
Image analysis.
The reconstructed images of the left ventricular slice (2 short axial slices and 1 vertical long axial slice) were divided into 9 segments (Fig. 1) and the myocardial tissue activity per pixel (CT; cpm/ml) was measured in the region of interest of the NH3 and FDG images. Hypoperfused segments were defined as those showing less than 70% of the maximal (100%) NH3 uptake (20). The FDG uptake in each segment was quantified as the FDG Uptake Index (% injected dose of FDG/100 mL of 60 kg of body weight) according to the method of Tamaki et al. (25):
CF is the calibration factor between mCi on the curie meter and cpm/ml on the PET images and BW (kg) is the patient’s body weight.
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Figure 1 Schematic representation of tomographic segments. BASE: basal level slice of left ventricle; MID: middle level slice of left ventricle.
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The normal range of FDG uptake was defined as the mean ± 2SD of the FDG uptake in remote regions (supplied by vessels without significant stenosis) in all 30 subjects. Hypoperfused segments in infarct-related areas with an increase in FDG uptake above the normal range were classified as ischemic but viable tissue, whereas segments with no increase in FDG uptake were classified as scar tissue. We determined that the patients showing ischemic but viable myocardial segments have residual tissue viability.
Reciprocal ST-segment depression for detection of residual tissue viability.
We determined the sensitivity, specificity and predictive accuracy of reciprocal ST-segment depression for detection of residual tissue viability based on the relation between the presence of reciprocal ST-segment depression and increased FDG uptake as follows: Sensitivity = True positive/(True positive + False negative); Specificity = True negative/(True negative + False positive); and Predictive accuracy = (True positive + True negative)/(True positive + True negative + False positive + False negative). True positive was defined as the presence of both increased FDG uptake and reciprocal ST-segment depression. False negative was defined as the presence of increased FDG uptake and the absence of reciprocal ST-segment depression. True negative was defined as the absence of increased FDG uptake and reciprocal ST-segment depression. False positive was defined as the absence of increased FDG uptake and the presence of reciprocal ST-segment depression.
Statistical analysis.
Statistical assessment of the data used an individual patient as the unit of analysis. All data are presented as the mean value ± SD. The unpaired Student t tests were used to assess differences in mean values between groups. The Fisher exact test was used to compare the frequencies of residual viability for PET studies in the two groups of patients. A p value <0.05 was considered significant.
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Results
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Clinical and exercise testing data.
Reciprocal ST-segment depression associated with exercise-induced ST-segment elevation in infarct-related ECG leads was present in 16 patients (53%; Group A, 65 ± 9 yr) but not in 14 patients (47%; Group B, 69 ± 9 yr) (Table 1). There was no significant difference in the degree of exercise-induced ST-segment elevation, the total exercise or the rate-pressure product at peak exercise between groups (Table 2). Anterior myocardial infarctions had been diagnosed in 6 Group A patients (38%) and 9 Group B patients (64%). The remaining 15 patients had inferior myocardial infarctions. No patients had either lateral or strictly posterior myocardial infarction. There was no significant difference in the interval from the onset of infarction between groups (Table 2). Figure 2 and Figure 3 illustrate findings in 2 representative patients.
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Figure 2 Patient No. 1 (Group A). Left panel: Electrocardiograms recorded at rest (R) and at peak exercise (Ex). Exercise-induced ST-segment elevations (V2-3) with reciprocal ST-segment depressions (II, III, aVF) were observed. Right panel: NH3-PET images showed perfusion defects in the anterior and apical walls. Increased FDG uptake was observed within the hypoperfused area.
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Figure 3 Patient No. 8 (Group A). Left panel: Electrocardiograms recorded at rest (R) and at peak exercise (Ex). Exercise-induced ST-segment elevations (II, III, aVF) with ST-segment depressions (aVL, V4-6) were observed. Right panel: NH3-PET images showed perfusion defects in the inferior wall. Increased FDG uptake was observed within the hypoperfused area.
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Left ventriculography and coronary angiography.
Left ventriculography showed abnormal wall motion in the infarct-related area in all 30 patients. The WMAS did not differ significantly between groups (Table 2). No patient had significant stenosis in arteries other than the infarct-related artery. In eight patients in group A and 5 patients in group B, the infarct-related arteries were totally occluded and filled by collateral circulation (grade 3 in seven patients, grade 2 in two patients, grade 1 in 4 patients). In the remaining 17 patients, the infarct-related artery was patent with residual luminal narrowing (45 ± 21% in group A vs. 48 ± 25% in group B; p = 0.68).
Myocardial perfusion and glucose utilization.
The presence and the site of infarction were confirmed by NH3 perfusion studies in all 30 subjects. No patients had hypoperfused areas supplied by noninfarct-related arteries. Hypoperfusion was present in 50 (35%) of 144 segments in group A and in 42 (33%) of 126 segments in Group B. Based on the mean FDG Uptake Index in normoperfused segments (0.339 ± 0.118), we defined the upper limit of the normal FDG Uptake Index as 0.575 (0.339 + 2 x 0.118; Fig. 4). Increase FDG uptakes in hypoperfused areas were observed in all subjects (41 [82%] of 50 hypoperfused segments) in group A, and three of 14 patients (7 [17%] of 42 hypoperfused segments) in group B. When we calculated the mean FDG Uptake Index in hypoperfused area confirmed by NH3 perfusion studies in each patient, FDG Uptake Index was significantly greater in Group A than in Group B (0.839 ± 0.325 vs. 0.396 ± 0.149; p < 0.0001; Fig. 4).
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Figure 4 The FDG Uptake Index in hypoperfused segments in both groups. N: Upper limit of the normal range of the FDG Uptake Index (0.575); *p < 0.0001.
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Clinical significance of reciprocal ST-segment depression.
PET studies indicated that residual tissue viability within the infarct-related area was present in all Group A patients, but only in three (21%) of 14 in group B patients (p < 0.01). The sensitivity, specificity and accuracy of reciprocal ST-segment depression associated with exercise-induced ST-segment elevation for the detection of residual viability were 84%, 100% and 90%, respectively. In 15 patients with anterior myocardial infarction, all group A patients considered to have viable myocardium but only in two (22%) of nine in group B patients. The sensitivity, specificity and accuracy of reciprocal ST-segment depression in 15 patients with anterior myocardial infarction were 75%, 100% and 87%, respectively.
In 13 patients whose infarct-related arteries were totally occluded at the time of this study (eight patients in group A and 5 in group B), PET studies revealed residual viability in the infarcted area in nine patients. Coronary arteriography showed good collateral circulation ( grade 2) in eight (89%) of these nine patients. The sensitivity, specificity and accuracy of reciprocal ST-segment depression in these 13 patients were 90%, 100% and 92%, respectively.
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Discussion
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Patients with single-vessel Q-wave myocardial infarction often exhibit reciprocal ST-segment depression in the noninfarcted area associated with exercise-induced ST-segment elevation in the infarcted area. However, to our knowledge, there are no reports focusing on the relation between myocardial viability and reciprocal ST-segment depression associated with exercise-induced ST-segment elevation although the relation between residual viability and exercise-induced ST-segment elevation has been described (10,11). Previous studies have suggested that ST-segment depression associated with ST-segment elevation indicates the presence of multivessel coronary artery disease (3,14–16). In the present study, reciprocal ST-segment depression associated with exercise-induced ST-segment elevation indicated residual tissue viability in the infarcted region in patients with single-vessel Q-wave infarction. We used FDG-PET to confirm the presence of myocardial viability. This method is useful for evaluating exogenous glucose utilization and allows excellent assessment of myocardial viability by visualizing enhancement of the glucose utilization in areas of marked ischemia (26,27). Tamaki et al. recommended the use of the FDG Uptake Index for quantitative assessment of FDG accumulation (20,25). The upper limit of the normal FDG Uptake Index in the present study was similar to the data of Tamaki et al. (0.575 vs. 0.576  0.677) (20,25).
Relation between residual viability and reciprocal ST-segment depression.
Reciprocal ST-segment depression was a sensitive, specific and an accurate indicator of residual viability in patients with previous single-vessel Q-wave myocardial infarction in the present study. In Group A patients, who had reciprocal ST-segment depression, 82% of hypoperfused segments showed residual viability in the infarct-related area whereas only 17% of segments exhibited viability in Group B patients, who did not have reciprocal ST-segment depression. Viable myocardium in the infarct-related area was present in all Group A patients but in only 3 (21%) of 14 Group B patients. The sensitivity, specificity and accuracy of reciprocal ST-segment depression associated with exercise-induced ST-segment elevation for the detection of residual viability were 84%, 100% and 90%, respectively. When analyses were performed in 15 patients with anterior myocardial infarction, the sensitivity, specificity and accuracy of reciprocal ST-segment depression were 75%, 100% and 87%, respectively. Its predictive value did not decrease even when an analysis was limited to patients with totally occluded infarct-related arteries (90% sensitivity, 100% specificity and 92% accuracy). There were no significant differences in the severity of left ventricular dysfunction and the degree of residual narrowing of the infarct-related coronary arteries between groups. The degree of development of collateral circulation was associated with the presence of reciprocal ST-segment depression in patients with totally occluded infarct-related arteries. Thus, the presence of reciprocal ST-segment depression in the noninfarcted area was useful for assessing the indication of coronary revascularization in patients with chronic coronary obstruction.
Possible mechanism underlying the phenomenon.
Paradoxically, myocardial viability may be indicated by transient ischemia. In the present study, reciprocal ST-segment depression during exercise testing was related to the presence of myocardial viability in the infarct-related area, indicating that the reciprocal ST-segment depression occurred as the passive electrical phenomenon of ST-segment elevation due to myocardial ischemia in the infarct-related area during exercise testing (17,18), as at the onset of acute myocardial infarction and during attacks of variant angina pectoris (19).
ST-segment elevation unaccompanied by reciprocal ST-segment depression is believed to be caused by abnormal left ventricular wall motion, typically by ventricular aneurysm, and mechanical extension of the myocardium during exercise (3,14–16), being differed from the mechanism of ST-segment elevation during ischemia. It is unlikely that ST-segment elevations in the infarct-related area without viable myocardium would be accompanied by reciprocal ST-depression. FDG-PET showed residual tissue viability within the infarcted area in three (21%) of 14 Group B patients in the absence of reciprocal ST-segment depression during the exercise stress test. However, the FDG Uptake Index was smaller in these patients (0.723, 0.699, 0.639) than in group A patients (0.843 ± 0.383), suggesting that the mass of transiently ischemic myocardium was small, corresponding to a small amount of viable myocardium.
Clinical implication.
The present findings demonstrated that the presence of reciprocal ST-segment depression in the noninfarcted area associated with ST-segment elevation in infarct-related ECG leads during exercise stress testing in patients with a previous Q-wave myocardial infarction indicated residual viability within the infarct-related area. The use of exercise stress ECG to assess the presence of residual viability in patients with single-vessel coronary artery disease is a clinically useful marker and may be helpful for determining the need for coronary revascularization.
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Acknowledgments
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We are grateful to Dr. Akihiko Seo (Department of Environmental Health, Fukui Medical University) for his statistical advice. We also thank Atsuo Waki, PhD, Katsuya Sugimoto, and the other cyclotron staffs for their technical assistance.
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Abstract
Methods