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European Journal of Heart Failure 2001 3(6):709-716; doi:10.1016/S1388-9842(01)00186-6
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© 2001 European Society of Cardiology

Exercise-induced ST-elevation is related to left ventricular dysfunction but not to myocardial viability in patients with healed myocardial infarction

Alain Manriquea,b,*, René Koningb, Anne Hitzela, Alain Cribierb and Pierre Véraa

a GIE de Médecine Nucléaire, Centre Henri Becquerel et CHU de Rouen 1 rue d'Amiens, 76038 Rouen Cedex, France
b Service de Cardiologie, Hopital Charles Nicolle CHU de Rouen, Rouen, France

* Corresponding author. Tel.: +33-232-08-2258; fax: +33-232-08-2550. E-mail address: alain.manrique{at}rouen.fnclcc.fr (A. Manrique).


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
Background: Exercise-induced ST-segment elevation was proposed as a marker of myocardial viability after a recent myocardial infarction.

Aims: The aim of this study was to evaluate whether exercise-induced ST segment elevation is related to viability or to left ventricular dysfunction in patients with history of old Q wave myocardial infarction.

Methods: Fifty patients (43 men, age 57±11 years) were studied 31±49 months after a Q wave myocardial infarction. They all underwent stress, reinjection-redistribution, and late redistribution Tl-201 SPECT, completed by equilibrium radionuclide angiography. Viability was defined by defect reversibility or significant (>60%) persistent Tl-201 uptake in dyssinergic segments on late redistribution SPECT. Relative post-exercise and reinjection-redistribution LV volumes were calculated using validated software (QGS).

Results: Twenty-one out of 50 patients (42%, G1) had significant stress-induced ST-elevation (>1 mm 80 ms after J point in at least 2 ECG leads with Q wave), and 29/50 (58%, G2) did not. Seventeen out of 50 patients (34%) demonstrated myocardial viability on late redistribution scan. The diagnostic accuracy of exercise-induced ST-elevation was only 52% for viability assessment. Significant LVEF reduction and increased relative LV volumes were observed in G1 compared to G2 (LVEF: 39±10% vs. 49±11%, P=0.003; post-stress LV volume: 134±98 ml vs. 81±41 ml, P<0.02; reinjection-redistribution LV volume: 123±86 ml vs. 79±40 ml; P<0.02). Perfusion defects were similar in G1 and G2 (post-exercise: 38±12% vs. 37±14%, ns; reinjection-redistribution: 31±11% vs. 30±11%, ns; late redistribution: 30±10% vs. 28±11%, ns).

Conclusion: These results suggest that, in patients with history of myocardial infarction, exercise-induced ST-segment elevation is not related to persistent myocardial viability but is associated to left ventricular dysfunction.

Key Words: ST segment • Single photon emission tomography • Left ventricular function • Viability

Received November 10, 2000; Accepted May 28, 2001


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
The evaluation of myocardial ischemia, viability and left ventricular ejection fraction is clinically relevant in patients with myocardial infarction for assessing prognosis and deciding coronary artery revascularization [1,2]. In the past, several methods were proposed to assess myocardial viability: post-extrasystolic potentialization [3]; improvement of myocardial wall motion after nitroglycerin administration [4] or inotropic stimulation [3,5,6]. Dobutamine stress echocardiography [5] as well as thallium-201 scintigraphy [6–8] are now widely used to differentiate myocardial scar from dysfunctional but viable myocardium. Although rest-redistribution thallium-201 single photon emission tomography is considered preferable, stress-reinjection with late redistribution offers the advantage of being able to evaluate both ischemia and viability [8]. Moreover, the evaluation of transient dilation and thallium-201 lung uptake is feasible in the setting of exercise thallium-201 SPECT and provides useful additional prognostic information [9–12].

Primarily attributed to left ventricular dysfunction or dyskinesia [13,14] and more extensive coronary artery disease [15,16], exercise-induced ST-elevation in patients with prior myocardial infarction has been recently suggested as a marker of myocardial viability [17,18]. However, these data are still controversial. Candell-Riera and colleagues [19] recently reported an association between exercise-induced ST-elevation and both ischemia and left ventricular aneurysm. The aim of this study was to assess the respective roles of myocardial ischemia, residual viability and left ventricular function in the genesis of exercise-induced ST-elevation in patients with healed myocardial infarction.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 5. Conclusion
 References
 
2.1. Patients
We studied 50 patients with history of Q wave myocardial infarction (43 men, 7 women, mean age=57±11 years) consecutively referred to our Nuclear Medicine Department for a combined evaluation of residual ischemia, myocardial viability and left ventricular function. The diagnosis of a previous myocardial infarction was based on hospital records, serial ECG recordings and serum enzyme determination. The clinical characteristics of the patients are presented in Table 1. The mean interval between myocardial infarction and thallium SPECT was 31±49 months. Patients with unstable angina, left or right bundle branch block, valvular heart disease, left ventricular hypertrophy or patients unable to exercise were excluded from the study.


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  		Table 1
 
2.2. Exercise testing
All patients performed a symptom-limited exercise stress test on a treadmill according to the Bruce or modified Bruce protocol (depending on their exercise capability). A 12-lead ECG, systolic and diastolic blood pressure (cuff sphygmomanometer) were recorded at rest, during the third minute of each stage, at peak exercise and 1 min after the termination of exercise. Leads II, V1 and V5 were continuously monitored and ST segment was continuously calculated in the 12 leads using signal averaging by a computer-assisted exercise system (Max Personal, Marquette Electronics Inc, Milwaukee, WI, USA). Termination exercise criteria were: achievement of the maximal predicted heart rate (calculated as 220–age), angina, severe dyspnea, fatigue, decrease in blood pressure more than 20 mmHg, ST segment depression >3 mm. The occurrence of ST segment elevation in infarct-related leads was not a criterion for exercise termination. At the time of exercise testing, 33 patients (66%) were receiving beta-blockers, 12 (24%) calcium antagonists, 24 (48%) ACE inhibitors and 16 (32%) nitrates.

According to previous studies [19–21], exercise-induced ST-segment elevation was defined as new or additional elevation >1 mm above the baseline segment level (80 m after the J point) on at least two electrocardiographic leads showing abnormal Q wave. The PQ segment was regarded as the isoelectric line.

2.3. Thallium-201 SPECT acquisition
At the end point of exercise, 111 MBq (3 mCi) of thallium-201 were injected intravenously, followed by a 10-ml saline flush, and the patient continued exercise for an additional 30–45 s. The acquisition of post-stress SPECT imaging was started within 10 min after injection. Redistribution images were obtained after a 4-h resting period, 30 min after the reinjection of 44 MBq (1.2 mCi) of thallium-201. Finally, late redistribution SPECT were acquired 24 h after the first injection, after an overnight fast, without further thallium-201 administration.

All images were acquired with a 90° dual-detector gamma camera (DST-XL, SMVi, Buc, France) equipped with low energy high resolution parallel-hole collimators. Acquisition parameters were as follows: 32 projections over an 180° orbit, 60 s/projection, acquisition zoom 1.33 and 64x64 matrix (pixel size: 6.8x6.8 mm). Energy discrimination was provided by two 20% windows centered on 70 and 167 keV photopeaks. Thallium-201 SPECT images were reconstructed after low pass prefiltering (Hamming 0.5 cycle/pixel) and ramp-filtered back-projection. No attenuation correction was performed.

The exercise, reinjection-redistribution, and late redistribution data were reconstructed as tomographic images oriented along the three standard orthogonal planes of the left ventricle.

2.4. Thallium-201 SPECT analysis
2.4.1. Qualitative analysis
Myocardial perfusion was qualitatively assessed by two experienced observers on reconstructed tomographic slices. Regional myocardial uptake was assessed on a 13-segment division of the left ventricle. A hypo or akinetic myocardial segment was considered viable if it showed persistent thallium-201 uptake >60% on late redistribution SPECT [6,22], or showed defect reversibility [23]. Persistent defects with a post-exercise thallium-201 uptake <60% were considered to be non-viable. The presence of remote ischemia was based on the presence of reversible myocardial thallium defect in at least one normokinetic myocardial segment. Discrepancies were resolved by consensus. Intraobserver and interobserver agreements were high (Kappa respectively, 0.87 and 0.82).

2.4.2. Quantitative analysis
Bull's eye polar maps were obtained from all three datasets. According to previous studies [24,25], the defect size was delineated on each polar map by a 60% level isocontour and quantified as a percentage of the whole left ventricle surface planimetered on bull's eye polar map.

2.4.3. Left ventricular volumes
To assess transient left ventricular dilation, relative left ventricular volumes were calculated for post-stress and reinjection-redistribution SPECT acquisition using a previously validated software (QGS, Cedars Sinai, CA, USA), capable of estimating endocardial volumes from ungated SPECT data [9,26]. Relative volumes were calculated without additional reconstruction zoom, and expressed as milliliters. The transient ischemic dilation (TID) ratio was then calculated as follows:

TID ratio=Vol. post-stress/Vol. reinjection-redistribution

Normal values were obtained in 24 patients with low likelihood (<5%) of coronary artery disease. The normal value for TID ratio was 0.97±0.18.

2.4.4. Quantification of thallium lung uptake
The sum of five projections centered on the anterior projection was used for quantification of thallium lung uptake. A 4x4 pixels region of interest (ROI) was placed over the hottest point of left ventricle, and a 8x8 pixels ROI was placed over the upper right lung. Thallium-201 lung uptake was quantified as the lung-to-myocardium uptake ratio (LMR). In a group of 24 patients with low likelihood of coronary artery disease, the normal value of LMR in our laboratory was 44±7%.

2.5. Radionuclide angiography
All patients underwent planar first pass and equilibrium radionuclide angiography immediately after late redistribution thallium-201 SPECT. Acquisitions were performed on a single head gamma camera (DS7, SMVi, Buc, France) equipped with a low-energy, all purpose, parallel hole collimator. 925 MBq (25 mCi) of 99m-Tc labelled serum albumin was intravenously administered. First pass angiography was performed in the 30 RAO projection, and gated equilibrium angiography in a 30–45 left oblique projection with a 5–10 caudal tilt (best septal view). Images were gated at 16 frames per cardiac cycle. A total of 350 000 counts were obtained for each frame with a zoom factor of 2 in a 64x64 acquisition matrix. Left ventricular ejection fraction was calculated on equilibrium angiography using a validated [27] software (NXT, SMVi, Buc, France). Segmental wall motion analysis was performed on a cineloop display of first past (inferior and apical walls) and equilibrium angiography (anterior, septal and lateral walls).

2.6. Statistical analysis
Continuous data are expressed as mean±S.D. Univariate analysis for categorical variables were performed using the Chi-square test. Comparisons of continuous data between groups were performed using the Student unpaired t-test. The effects and interactions of categorical variables on quantitative parameters were tested by multiple ANOVA. A P-value <0.05 was considered statistically significant.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 5. Conclusion
 References
 
3.1. Clinical and exercise test characteristics
Results of exercise stress test are summarized in Table 1. Fifty patients (males: 43; females: 7, mean age: 57±11 years) were enroled in the study. Twenty-one patients (42%, Group 1) had new or additional exercise-induced ST segment elevation on >2 leads with abnormal Q wave (mean±S.D.: 2.9±1.6 mV, 16 male, 5 female; mean age 58±12 years) and 29 patients did not (58%, group 2). The occurrence of symptoms (angina or dyspnea) during exercise was similar in the two groups (Table 1).

The association between the occurrence of a stress-induced ST segment elevation and the anterior location of myocardial infarction was statistically significant (Chi2=12.46, P=0.0004). Among the 21 patients in group 1, 19 (90%) had an anterior and 2 (10%) had an inferior myocardial infarction. In group 2, 12 patients (41%) had an anterior and 17 (59%) had an inferior myocardial infarction.

There was no difference between the two groups for exercise work load and rate-pressure product at peak exercise. The percentage of predicted maximal heart rate was significantly higher in group 1 (Table 1). This difference for the percentage of predicted maximal heart rate was independent of beta-blocker therapy using analysis of variance (F-value=2.13; P=ns).

3.2. Radionuclide angiography
Mean left ventricular ejection fraction (LVEF) was 45±12% in the overall population. In group 1, LVEF was significantly reduced compared to group 2 (39±10% vs. 49±11%, P=0.003, Table 1). ERNA demonstrated the presence of a left ventricle dyskinesia in 12 patients (57%) in group 1 and in 4 patients (14%) in group 2. In all cases, the location of dyskinesia was the apex. The association of apical dyskinesia and stress-induced ST segment elevation was statistically significant (Chi2=10.52, P=0.001).

3.3. Volume measurements and thallium lung uptake
As shown in Table 2, post-exercise and reinjection-redistribution relative volumes were significantly increased in patients compared to control. Moreover, this volume increase was significantly higher in patients with stress-induced ST-elevation. Furthermore, TID ratio was significantly increased in patients compared to control, and particularly in group 1. At last, thallium-201 lung uptake was increased only in patients with stress-induced ST-elevation compared to control.


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  		Table 2 Scintigraphic data

 
3.4. Myocardial perfusion study
Qualitative analysis of reconstructed tomographic slices showed fixed perfusion defects in all patients, consistent with the location of previous myocardial infarction. A reversible perfusion defect was seen in 24 patients (48%). Residual myocardial viability was noted in 17/50 patients (34%). Extent of myocardial scar, evaluated by defect size on bull's eye polar maps of late redistribution scans, was not different between group 1 and groups 2 (Table 1).

In the whole population, neither myocardial viability nor myocardial ischemia was associated with the presence of stress-induced ST-elevation (viability: Chi2=0.07, ns; ischemia: Chi2=0.384, ns). The sensitivity, specificity and accuracy of a stress-induced ST-elevation were respectively, 41, 58 and 52% for detection of myocardial viability and 37, 54 and 46% for detection of myocardial of ischemia (Table 3).


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  		Table 3 Sensitivity, specificity and diagnostic accuracy of exercise-induced ST-elevation in detecting myocardial viability, ischemia and LV dyskinesia

 
3.5. Multivariate analysis
Multiple ANOVA was performed to analyse the factors that may influence ST-segment elevation during exercise. The following variables were entered in the model: stress thallium-201 defect size, late redistribution thallium-201 defect size, exertional symptoms (typical angina and/or dyspnea), beta-blocker therapy (that may limit the increase of heart rate during exercise), infarct location, remote ischemia and residual viability. The significant factors were: symptoms (P<0.03), infarct location (P<0.005), and remote ischemia (P<0.02).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
5. Conclusion
 References
 
Exercise-induced ST-segment elevation has been recently suggested to be associated with myocardial viability [17,18] or ischemia in patients with recent myocardial infarction [19,28]. However, underlying mechanisms of stress-induced ST-elevation are not equivocal and early studies attributed this common phenomenon to left ventricular dysfunction or aneurysm [13,29–31]. Moreover, the presence and amount of viability depends on many factors, including ischemia and left ventricular function [6]. In fact, only limited data are available on global evaluation including myocardial viability, ischemia and left ventricular function in patients with ischemic cardiomyopathy and stress-induced ST-elevation [19,32]. In our study, exercise-induced ST-elevation had poor sensitivity, specificity and diagnostic accuracy for the prediction of viability in patients with ischemic cardiomyopathy. Nevertheless, this electrocardiographic pattern was associated with impaired LV function.

4.1. Viability and ischemia
Stress-induced ST-elevation was frequently observed (42% of the population) and its occurrence was independent of peak exercise workload. ST-elevation during exercise was associated with the anterior location of infarct. The size of myocardial scar assessed on bull's eye polar maps was similar in the two groups, and no association was found between stress-induced ST-elevation and myocardial ischemia or viability on the basis of thallium-201 SPECT findings. The diagnostic accuracy of exercise-induced ST-elevation for the detection myocardial viability was very poor in our population (52%). Margonato et al. [18] found a high sensitivity and specificity of ST-segment elevation for detecting residual viability in patients with anterior infarction (respectively, 82 and 100%). However, they studied a selected subset of patients with recent myocardial infarction and moderate left ventricular involvement as demonstrated by patient's ability to perform a maximal exercise test and by the absence of left ventricular dyskinesia. In our study, patients had large myocardial scar involving 30% of the myocardium, with impaired left ventricular function and a high incidence of LV dyskinesia (26%). These characteristics may explain the differences with Margonato et al. Actually, our results are more similar to that obtained in the pre-thrombolytic era.

Elhendy et al. [21] reported that dobutamine stress-induced ST-elevation was related to long-term functional improvement in patients with recent myocardial infarction (<2 weeks), thus suggesting myocardial viability as a possible mechanism. However, although a biphasic response could identify patients with hibernating myocardium, no difference was made between segmental wall motion improvement at low dose and worsening at high dose dobutamine infusion. In a larger trial, Ricci et al. [32] recently found that dobutamine-induced ST-elevation was not associated with viable myocardium but related to a greater extent of wall motion abnormalities at rest. In addition, the diagnostic accuracy for identification of homozonal ischemia was respectively, 54 and 58% in patients with anterior and inferior myocardial infarction.

4.2. Left ventricular function
In our study, left ventricular ejection fraction was significantly impaired and dyskinesia was more frequently observed in patients with stress-induced ST-elevation. Moreover, relative left ventricular volumes and thallium-201 lung uptake were increased in those patients. These findings are consistent with early reports demonstrating an association between stress-induced ST-elevation and left ventricular function [13,15,29,31,33]. Exercise in patients with coronary artery disease results in an increase in left ventricular volumes, indicating that those patients use the Franck–Starling mechanism during exercise. As thallium-201 SPECT acquisitions were not gated to the ECG, measurements of end-diastolic and end-systolic volumes were not available. However, relative stress and rest volume may be calculated on the basis of non-gated SPECT as previously described [9]. Litchfield et al. [34] evaluated the mechanisms that maintain a normal exercise capacity in patients with severe left ventricular dysfunction. They also indicated that chronotropic competence, left ventricular dilation during exercise and plasma levels of catecholamines might be possible mechanisms for maintaining normal exercise capacity. In our study, patients with stress-induced ST-elevation achieved higher percentage of maximal predicted heart rate and showed left ventricular dilation on post stress and rest thallium-201 SPECT, although the exercise work load was similar in both groups. Resting left ventricular ejection fraction was significantly decreased in these patients and ST-elevation during exercise was associated with left ventricular dyskinesia.

Finally, patients with exercise-induced ST-elevation had significant increased thallium-201 lung uptake compared to the normal population. This phenomenon correlates with exercise-induced LV dysfunction, more extensive coronary artery disease and patient prognosis [10–12].

Our results indicate that in this population, exercise-induced ST-elevation was associated with left ventricular dysfunction. Coma-Canella et al. [35] found similar results using high dose dobutamine infusion as a pharmacological stress for both thallium-201 SPECT and radionuclide angiography in 88 patients. In this latter study, dobutamine-induced ST-elevation was correlated to stress-induced ventricular asynergy but not to thallium redistribution.

4.3. Limitation of the study
The mean interval between myocardial infarction and thallium-201 SPECT was high (31±49 months). Our results defer from those of Margonato et al. [17,18] who studied patients with recent myocardial infarctions. It is likely that the delay from myocardial infarction has to be considered for interpreting the presence of a tress-induced ST-elevation. However, as we studied patients with old infarction, this point could not be demonstrated here.


   5. Conclusion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
References
 
In the present study, exercise-induced ST-elevation had a poor sensitivity, specificity and diagnostic accuracy for predicting either myocardial viability or ischemia in patients with history of myocardial infarction. However, this electrocardiographic pattern is associated with impaired left ventricular function, as demonstrated by decreased ejection fraction, left ventricular dilation, increased thallium-201 lung uptake, and the common occurrence of LV dyskinesia in those patients. In patients with large myocardial infarction and left ventricular dysfunction, exercise-induced ST-elevation may not be recommended as a useful tool for the selection of patients that could benefit from myocardial revascularization.


   Acknowledgements
 
The authors thank Mr Richard Medeiros for his advice in editing the manuscript.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 

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