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Consideration of QRS complex in addition to ST-segment abnormalities in the estimation of the “risk region” during acute anterior or inferior myocardial infarction
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ScienceDirect Journal of Electrocardiology xx (2014) xxx – xxx www.jecgonline.com
Consideration of QRS complex in addition to ST-segment abnormalities in the estimation of the “risk region” during acute anterior or inferior myocardial infarction F.E. Vervaat, Bsc, a,⁎ S. Bouwmeester, MD, b I.E.G. van Hellemond, MD, c G.S. Wagner, MD, d A.P.M. Gorgels, MD, PhD a a
Department of Cardiology, University Hospital Maastricht, Maastricht, the Netherlands b Department of Cardiology, Catharina Hospital, Eindhoven, the Netherlands c Department of Internal Medicine, Catharina Hospital, Eindhoven, the Netherlands d Department of Cardiology, Duke Clinical Research Institute, Durham, NC, USA
Abstract
The myocardial area at risk (MaR) is an important aspect in acute ST-elevation myocardial infarction (STEMI). It represents the myocardium at the onset of the STEMI that is ischemic and could become infarcted if no reperfusion occurs. The MaR, therefore, has clinical value because it gives an indication of the amount of myocardium that could potentially be salvaged by rapid reperfusion therapy. The most validated method for measuring the MaR is 99mTc-sestamibi SPECT, but this technique is not easily applied in the clinical setting. Another method that can be used for measuring the MaR is the standard ECG-based scoring system, Aldrich ST score, which is more easily applied. This ECG-based scoring system can be used to estimate the extent of acute ischemia for anterior or inferior left ventricular locations, by considering quantitative changes in the ST-segment. Deviations in the ST-segment baseline that occur following an acute coronary occlusion represent the ischemic changes in the transmurally ischemic myocardium. In most instances however, the ECG is not available at the very first moments of STEMI and as times passes the ischemic myocardium becomes necrotic with regression of the ST-segment deviation along with progressive changes of the QRS complex. Thus over the time course of the acute event, the Aldrich ST score would be expected to progressively underestimate the MaR, as was seen in studies with SPECT as gold standard; anterior STEMI (r = 0.21, p = 0.32) and inferior STEMI (r = 0.17, p = 0.36). Another standard ECG-based scoring system is the Selvester QRS score, which can be used to estimate the final infarct size by considering the quantitative changes in the QRS complex. Therefore, additional consideration of the Selvester QRS score in the acute phase could potentially provide the “component” of infarcted myocardium that is missing when the Aldrich ST score alone is used to determine the MaR in the acute phase, as was seen in studies with SPECT as gold standard: anterior STEMI (r = 0.47, p = 0.02) and inferior STEMI (r = 0.58, p b 0.001). The aim of this review will be to discuss the findings regarding the combining of the Aldrich ST score and initial Selvester QRS score in determining the MaR at the onset of the event in acute anterior or inferior ST-elevation myocardial infarction. © 2014 Elsevier Inc. All rights reserved.
Keywords:
QRS complex; ST-segment abnormalities; Acute anterior or inferior myocardial infarction
Introduction The myocardial area at risk (MaR) is an important aspect in acute ST-elevation myocardial infarction (STEMI) [1]. It represents the myocardium at the onset of the STEMI that is
⁎ Corresponding author. E-mail address: [email protected] http://dx.doi.org/10.1016/j.jelectrocard.2014.04.009 0022-0736/© 2014 Elsevier Inc. All rights reserved.
ischemic and could become necrotic if no reperfusion occurs. Assessment of the MaR, therefore, has clinical value because it gives an indication of the amount of myocardium that could potentially be salvaged by rapid reperfusion therapy. Several methods have been developed to assess the MaR. The most validated method is the 99mTc-sestamibi singlephoton emission cardiac tomography (SPECT) [2]. The primary limitation of this method is that it is not easily applied in the clinical setting. Therefore other methods are
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being or have been developed such as cardiac magnetic resonance imaging (CMR) or ECG-based scoring systems. In 1972, before the reperfusion era, Selvester et al. [3] developed the first quantitative ECG-based scoring system for estimating final myocardial infarct size. It consisted of a 54 criteria/32-point QRS scoring system in which each point represents approximately 3% of the left ventricle. In 1988, Aldrich et al. [4] developed an ECG-based scoring system to estimate the extent of acute ischemia by considering quantitative changes in the ST-segments for either anterior or inferior left ventricular locations. The aim was to determine the MaR at onset, based on the assumption that this would serve as an estimate of the final infarct size in patients not receiving reperfusion therapy. Quantitative aspects of the ST-segment were evaluated on the presenting ECG and compared to the final infarct size, which was determined by applying the Selvester QRS score to the predischarge ECG. Different formulas for acute inferior and acute anterior myocardial infarction were developed: 3[0.6 (ΣST-elevation II, III, aVF) + 2.0] and 3[1.5 (number leads ST-elevation) − 0.4] respectively. Subsequent studies have been performed to determine how accurate the Aldrich ST formulas were in predicting the MaR in the acute phase. It was seen that the Aldrich ST score underestimated the MaR compared to the final infarct size determined by the Selvester QRS score [5,6] and also compared to the 99mTc-sestamibi SPECT [7,8]. The ST-segment changes that occur following an acute coronary occlusion represent the ischemic changes that take place in the transmurally jeopardized myocardium. As times passes the ischemic myocardium will become necrotic, if no rapid resolution of the occlusion occurs, with regression of the ST-segment deviation along with progressive changes of the QRS complex [9]. The Aldrich score based on the STsegment deviation only considers the ischemic myocardium. Thus over the time course of the acute event the Aldrich ST score alone would be expected to progressively underestimate the MaR. Therefore, additional consideration of the Selvester QRS score in the acute phase could potentially provide the “component” of infarcted myocardium that is missing when the Aldrich ST score alone is used to determine the MaR in the acute phase. This concept led to the studies of van Hellemond et al. [10,11] to determine if the correlation with 99mTc-sestamibi SPECT improved when the Aldrich ST score was combined with the initial Selvester QRS score, so that both the ischemic and infarcted myocardium are considered when determining the MaR in the acute phase. The aim of this review will be to discuss the findings regarding the combining of the Aldrich ST score and initial Selvester QRS score in determining the MaR at the onset of the event in acute anterior or inferior STelevation myocardial infarction. Combining Aldrich ST score and Selvester QRS score Van Hellemond et al. [10,11] combined the Aldrich ST score and the initial Selvester QRS score to see whether this would improve the estimated MaR in the acute phase as compared to the Aldrich ST score, using the 99mTc-sestamibi
SPECT as gold standard. In the first study, the population consisted of 25 patients with an acute anterior STEMI [10]. All patients underwent coronary angiography (CAG) and prior to this the tracer (bolus of 700 ± 70 MBq technetium Tc 99 m-sestamibi) was injected. Tomographic imaging was performed within 2 hours after CAG. Since the tracer has minimal redistribution once bound to viable myocardium, the perfusion defects reflect the MaR prior to intervention [12]. The target ECG was recorded immediately prior to the CAG. The Aldrich ST score formula for anterior STEMI was applied. The result represented the ischemic component of the MaR in % of the left ventricle (%LV). In the same ECG, the initial Selvester QRS score was determined, representing the infarcted component of the MaR in %LV. The combined score was the sum of the Aldrich ST score and the initial Selvester QRS score (%LV). The correlation was assessed between the individual/combined ECG scores and the myocardial perfusion SPECT. The best correlation with myocardial perfusion SPECT was achieved by the combined ECG score (r = 0.47, p = 0.02) and the Selvester QRS score (r = 0.49, p = 0.01). All ECG scores separately (Aldrich ST score: r = 0.21, p = 0.32) or combined underestimated the total MaR (p b 0.01) (Fig. 1). However the difference between the MaR calculated by myocardial perfusion SPECT was smaller for the combined ECG method than either ECG method alone (p b 0.01). The second study by van Hellemond et al. [11] was done in a study population consisting of 32 patients with an acute inferior STEMI. In this study the Aldrich ST score for inferior STEMI was applied. Again it was found that the best correlation with myocardial perfusion SPECT was achieved by the combined ECG score (r = 0.58, p ≤ 0.001. Aldrich ST score: r = 0.17, p = 0.36. Selvester QRS score: r = 0.55, p = 0.001). Due to the fact that an acute inferior STEMI can be caused by either an RCA (71.9%) or LCX (28.1%) occlusion, the study population was divided into two subgroups for analysis. The results showed that the correlation between the combined ECG score and
Fig. 1. The mean (± 1SD) estimated total MaR by four different methods [10]. The three ECG methods significantly underestimated the total MaR by SPECT (p b 0.01), although the difference with the total MaR by SPECT for the sum of Aldrich and Selvester scores was significantly lower than for either score alone (p b 0.01; number bars represent the mean MaR in %LV for each method).
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myocardial perfusion SPECT was significant for the RCA subgroup (r = 0.46, p = 0.03) but not for the LCX subgroup (r =0.58, p = 0.104). The not significant correlation found for the LCX subgroup could be due to the fact that the Aldrich ST score is based on ST-segment elevation, while in a STEMI due to an LCX occlusion ST-segment depression in the precordial leads predominates [13]. The comparison of the measured MaR between the individual/combined ECG scores and myocardial perfusion SPECT in the whole study population (p = 0.636), as well as both subgroups (RCA: p = 0.483, LCX: p = 0.636) showed that there was no significant difference (Fig. 2). The results of both studies confirm previous findings that the Aldrich ST score underestimates the MaR compared to myocardial perfusion SPECT [7,8]. Myocardial perfusion SPECT does not differentiate between ischemic and infarcted myocardium, whereas in the ECG the ST-segment is related to ischemia and the QRS complex is related to infarction. The correlation between the Aldrich ST score and SPECT would be expected to be higher if the coronary occlusion had only just occurred, because there has not been time for necrosis to form. Persson et al. [14] performed a study that looked at this hypothesis. ST-segment changes in patients undergoing 5-minute single balloon inflation by elective prolonged percutaneous transluminal coronary angioplasty were compared to 99mTc-sestamibi SPECT, looking specifically at the measured MaR. Significant but moderate correlations were found (RCA: r = 0.57, p = 0.01, LAD: r = 0.63, p = 0.07, LCx: r = 0.75, p = 0.02). However these were not as high as would have been expected. Correlation between cardiac magnetic resonance imaging endocardial surface area calculations and both the Aldrich ST score and combined Aldrich ST score & Selvester QRS score Körver et al. [15] performed a study to see whether the findings by van Hellemond et al. could be reproduced using
Fig. 2. The mean (± 1SD) estimated total MaR by four different methods [11]. Both the Aldrich and Selvester score alone underestimated the MaR measured by SPECT (p = 0.007 and p b 0.0001, respectively). There was no statistically significant difference between the MaR estimated by the sum of Aldrich and Selvester and the MaR measured by SPECT (p = 0.636; number bars represent the mean MaR in %LV for each method).
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cardiac magnetic resonance imaging (CMR) endocardial surface area (ESA) calculations as the reference method. The reason for choosing ESA was based on a recent study [16], suggesting this to be the best CMR variable for determining the MaR. It was hypothesized that the correlation between the Aldrich ST score and ESA estimation of the MaR would be improved by using the combined ECG score. The study population consisted of 84 patients with either an acute inferior or anterior STEMI and the admission ECG was used for the analysis. To determine the Aldrich ST score and the initial Selvester QRS score, the same methods were used as described by van Hellemond et al. [10,11]. CMR was performed approximately 6 ± 2 days after admission. Even though CMR was performed several days after the event, the measured MaR is still representative of the MaR at the onset of STEMI: studies [17,18] have shown that the extent of subendocardial infarction will remain stable from approximately 40 minutes up to 8 weeks after the initial occlusion. The correlation between the methods was assessed and it was found that the correlation between ESA and the Aldrich ST score (r = 0.55, p b 0.0001) was slightly better than between ESA and the combined ECG score (r = 0.45, p b 0.0001). Furthermore the Aldrich ST score showed an underestimation of the ESA estimated MaR, whereas the combined ECG score showed an overestimation. This is in contrast to findings by van Hellemond et al. One possible explanation for the different findings is the ECG analyzed. Körver et al. used the admission ECG, whereas van Hellemond et al. used the ECG that was recorded later, i.e. at the time of CAG. The QRS changes that were present on the admission ECG could signify conduction delay [19], whereas the QRS changes on the ECG immediately prior to CAG are more likely to represent necrosis. Another possible explanation could be attributed to the different imaging techniques used. Körver et al. used the CMR ESA calculations, whereas van Hellemond et al. used 99mTc-sestamibi SPECT. No studies could be found in which these two methods were compared. One study [20] did compare T2-weighted CMR with SPECT in determining the MaR and no statistical significant difference was found. T2-weighted CMR is an imaging technique that gives increased signal intensity of fluid collections. During a myocardial infarction tissue edema will occur and this is highlighted using the T2-weighted CMR [20]. Previous studies [21] have suggested that this tissue edema is representative of the MaR, although there are clinicians who do not believe this to be the case [22]. Another study by Ubachs et al. [23] compared T2-weighted CMR to CMR ESA calculations in measuring the MaR and found that the CMR ESA calculations underestimated the MaR compared to T2-weighted CMR. Based on these findings it could be concluded that it is possible that the CMR ESA calculations underestimate the MaR as compared to 99mTc-sestamibi SPECT. Predictive value of an ECG-based Acute Ischemia Index for 3-month prognosis of myocardial salvage and infarct healing Hassell et al. [24] performed a study in which the combined ECG score was used to create the Acute Ischemia Index—[Aldrich ST score ECG1/(Aldrich ST score
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ECG1 + Selvester QRS score ECG1)] × 100%. This index represents the ischemic component of the MaR that could potentially be salvaged with reperfusion therapy. To determine how successful reperfusion therapy was the portion of the MaR that has remained viable 3 months after the intervention was determined using the Chronic Salvage Index—[(Aldrich ST score ECG1 + Selvester QRS score ECG1 − Selvester QRS score ECG2)/(Aldrich ST score ECG1 + Selvester QRS score ECG1)] × 100%. It was hypothesized that 1) there would be a significant positive relationship between the Acute Ischemia Index and the Chronic Salvage Index and 2) delay in performing reperfusion therapy would cause the Chronic Salvage Index to be lower than predicted by the Acute Ischemia Index. The study population consisted of 59 patients with an acute inferior STEMI. To determine the scores, the same methods were used as described by van Hellemond et al. [10,11]. Two ECGs were analyzed; the first ECG was recorded on admission (ECG1) and the second ECG was recorded approximately 3 months after discharge (ECG2). The found measurements were input in the formulas for the Acute Ischemia Index and Chronic Salvage Index. Subgroups were created based on the relationship between the Acute Ischemia Index and the Chronic Salvage Index: 1) The concordance group, represented those patients whose Chronic Salvage Index was consistent with the prediction made using the Acute Ischemia Index (− 30%–+30%). 2) The Salvage and Healing (S&H) underestimated group
represented those patients whose Chronic Salvage Index was larger than was predicted by the Acute Ischemia Index (N+30%). 3) The S&H overestimated group represented those patients whose Chronic Salvage Index was smaller than predicted by the Acute Ischemia Index (b−30%) (Fig. 3). The mean measured amount of salvaged MaR was less after 3 months (Chronic Salvage Index: 53.8%) than initially expected (Acute Ischemia Index: 74.6%) and the correlation between the two scoring systems was not significant (r = 0.253, p = 0.053). It was also shown that the time between admission and PCI did not have a significant (p = 0.130) effect on the relationship between the two indexes. In the analysis of the subgroups, it was found that in the S&H overestimated group 6 patients had a Chronic Salvage Index b 0, showing that the ECG-estimated infarct size was larger 3 months after discharge than the total MaR that was estimated at admission. These results show that the Acute Ischemia Index can provide a modest contribution to the prediction of the amount of viable MaR 3 months postreperfusion. Furthermore it was shown that patients with a high acute ischemia index had the potential to retain more viable MaR than patients with lower index scores, giving the clinician an indication of how much myocardium can be saved by reperfusion therapy. This score is however not accurate enough to influence the decision making as regards the reperfusion therapies in the acute setting.
Conclusions It has been shown that combining the Aldrich ST score and the initial Selvester QRS score increases the accuracy of estimating the MaR in the acute phase, especially in the acute inferior STEMI, as compared to the Aldrich ST score. One study [15] did find that the combined ECG score actually overestimated the MaR at onset, whereas other studies did not [10,11]. Explanations for this different finding are the ECGs analyzed and the method the ECG score was compared to. Finally it was reported that there was a moderate relation between the Acute Ischemia Index and the Chronic Salvage Index, representing the MaR expected to be viable after 3 months and the MaR that was actually still viable 3 months post-discharge. These results show that the combined ECG score does improve the accuracy of measuring the MaR in the acute phase. However the correlations found and associated variances are still not high enough to influence decision making with regard to reperfusion therapy in the acute setting and further validation of the combined ECG score. Better alternatives for measuring the MaR are required.
Future studies
Fig. 3. Scatterplot depicting the relationship between the Acute Ischemia Index and the Chronic Salvage Index (Pearson's r = 0.253, p = 0.05) [24]. The regression line is depicted as the continuous line and the middle dashed line represents the identity line. The subjects located between the two outer dashed lines are defined as the concordance group.
It would be interesting to see whether the combined ECG score will remain stable over time. Bouwmeester et al. [25] have already shown that the Aldrich ST score alone is not sufficiently stable over time. A study is currently being performed to see whether the combined ECG score will remain stable over time. If the scores are correct the MaR
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should remain stable—the Aldrich ST score declining and the Selvester QRS score increasing over time. Another important aspect that needs further validation is the use of the Selvester QRS score in the acute phase of myocardial infarction. The Selvester QRS score has only been validated for use after the acute phase, although studies have used it during the acute phase [9]. A method for testing the Selvester QRS score in the acute phase would be to determine the score before and after successful reperfusion. If the Selvester QRS score represents infarcted myocardium, then the scores should not differ. Finally, an important limitation of the combined ECG score is the Aldrich ST score. The Aldrich ST score was created based on the assumption that the MaR would be equal to final infarct size if no reperfusion occurs. However it is known that in some patients, even if no reperfusion occurs, the final infarct size will be reduced due to protection of the myocardium through collaterals and metabolic conditioning [26]. These statements make it clear that additional research regarding the combined ECG score can still be performed.
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ScienceDirect Journal of Electrocardiology xx (2014) xxx – xxx www.jecgonline.com
Consideration of QRS complex in addition to ST-segment abnormalities in the estimation of the “risk region” during acute anterior or inferior myocardial infarction F.E. Vervaat, Bsc, a,⁎ S. Bouwmeester, MD, b I.E.G. van Hellemond, MD, c G.S. Wagner, MD, d A.P.M. Gorgels, MD, PhD a a
Department of Cardiology, University Hospital Maastricht, Maastricht, the Netherlands b Department of Cardiology, Catharina Hospital, Eindhoven, the Netherlands c Department of Internal Medicine, Catharina Hospital, Eindhoven, the Netherlands d Department of Cardiology, Duke Clinical Research Institute, Durham, NC, USA
Abstract
The myocardial area at risk (MaR) is an important aspect in acute ST-elevation myocardial infarction (STEMI). It represents the myocardium at the onset of the STEMI that is ischemic and could become infarcted if no reperfusion occurs. The MaR, therefore, has clinical value because it gives an indication of the amount of myocardium that could potentially be salvaged by rapid reperfusion therapy. The most validated method for measuring the MaR is 99mTc-sestamibi SPECT, but this technique is not easily applied in the clinical setting. Another method that can be used for measuring the MaR is the standard ECG-based scoring system, Aldrich ST score, which is more easily applied. This ECG-based scoring system can be used to estimate the extent of acute ischemia for anterior or inferior left ventricular locations, by considering quantitative changes in the ST-segment. Deviations in the ST-segment baseline that occur following an acute coronary occlusion represent the ischemic changes in the transmurally ischemic myocardium. In most instances however, the ECG is not available at the very first moments of STEMI and as times passes the ischemic myocardium becomes necrotic with regression of the ST-segment deviation along with progressive changes of the QRS complex. Thus over the time course of the acute event, the Aldrich ST score would be expected to progressively underestimate the MaR, as was seen in studies with SPECT as gold standard; anterior STEMI (r = 0.21, p = 0.32) and inferior STEMI (r = 0.17, p = 0.36). Another standard ECG-based scoring system is the Selvester QRS score, which can be used to estimate the final infarct size by considering the quantitative changes in the QRS complex. Therefore, additional consideration of the Selvester QRS score in the acute phase could potentially provide the “component” of infarcted myocardium that is missing when the Aldrich ST score alone is used to determine the MaR in the acute phase, as was seen in studies with SPECT as gold standard: anterior STEMI (r = 0.47, p = 0.02) and inferior STEMI (r = 0.58, p b 0.001). The aim of this review will be to discuss the findings regarding the combining of the Aldrich ST score and initial Selvester QRS score in determining the MaR at the onset of the event in acute anterior or inferior ST-elevation myocardial infarction. © 2014 Elsevier Inc. All rights reserved.
Keywords:
QRS complex; ST-segment abnormalities; Acute anterior or inferior myocardial infarction
Introduction The myocardial area at risk (MaR) is an important aspect in acute ST-elevation myocardial infarction (STEMI) [1]. It represents the myocardium at the onset of the STEMI that is
⁎ Corresponding author. E-mail address: [email protected] http://dx.doi.org/10.1016/j.jelectrocard.2014.04.009 0022-0736/© 2014 Elsevier Inc. All rights reserved.
ischemic and could become necrotic if no reperfusion occurs. Assessment of the MaR, therefore, has clinical value because it gives an indication of the amount of myocardium that could potentially be salvaged by rapid reperfusion therapy. Several methods have been developed to assess the MaR. The most validated method is the 99mTc-sestamibi singlephoton emission cardiac tomography (SPECT) [2]. The primary limitation of this method is that it is not easily applied in the clinical setting. Therefore other methods are
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being or have been developed such as cardiac magnetic resonance imaging (CMR) or ECG-based scoring systems. In 1972, before the reperfusion era, Selvester et al. [3] developed the first quantitative ECG-based scoring system for estimating final myocardial infarct size. It consisted of a 54 criteria/32-point QRS scoring system in which each point represents approximately 3% of the left ventricle. In 1988, Aldrich et al. [4] developed an ECG-based scoring system to estimate the extent of acute ischemia by considering quantitative changes in the ST-segments for either anterior or inferior left ventricular locations. The aim was to determine the MaR at onset, based on the assumption that this would serve as an estimate of the final infarct size in patients not receiving reperfusion therapy. Quantitative aspects of the ST-segment were evaluated on the presenting ECG and compared to the final infarct size, which was determined by applying the Selvester QRS score to the predischarge ECG. Different formulas for acute inferior and acute anterior myocardial infarction were developed: 3[0.6 (ΣST-elevation II, III, aVF) + 2.0] and 3[1.5 (number leads ST-elevation) − 0.4] respectively. Subsequent studies have been performed to determine how accurate the Aldrich ST formulas were in predicting the MaR in the acute phase. It was seen that the Aldrich ST score underestimated the MaR compared to the final infarct size determined by the Selvester QRS score [5,6] and also compared to the 99mTc-sestamibi SPECT [7,8]. The ST-segment changes that occur following an acute coronary occlusion represent the ischemic changes that take place in the transmurally jeopardized myocardium. As times passes the ischemic myocardium will become necrotic, if no rapid resolution of the occlusion occurs, with regression of the ST-segment deviation along with progressive changes of the QRS complex [9]. The Aldrich score based on the STsegment deviation only considers the ischemic myocardium. Thus over the time course of the acute event the Aldrich ST score alone would be expected to progressively underestimate the MaR. Therefore, additional consideration of the Selvester QRS score in the acute phase could potentially provide the “component” of infarcted myocardium that is missing when the Aldrich ST score alone is used to determine the MaR in the acute phase. This concept led to the studies of van Hellemond et al. [10,11] to determine if the correlation with 99mTc-sestamibi SPECT improved when the Aldrich ST score was combined with the initial Selvester QRS score, so that both the ischemic and infarcted myocardium are considered when determining the MaR in the acute phase. The aim of this review will be to discuss the findings regarding the combining of the Aldrich ST score and initial Selvester QRS score in determining the MaR at the onset of the event in acute anterior or inferior STelevation myocardial infarction. Combining Aldrich ST score and Selvester QRS score Van Hellemond et al. [10,11] combined the Aldrich ST score and the initial Selvester QRS score to see whether this would improve the estimated MaR in the acute phase as compared to the Aldrich ST score, using the 99mTc-sestamibi
SPECT as gold standard. In the first study, the population consisted of 25 patients with an acute anterior STEMI [10]. All patients underwent coronary angiography (CAG) and prior to this the tracer (bolus of 700 ± 70 MBq technetium Tc 99 m-sestamibi) was injected. Tomographic imaging was performed within 2 hours after CAG. Since the tracer has minimal redistribution once bound to viable myocardium, the perfusion defects reflect the MaR prior to intervention [12]. The target ECG was recorded immediately prior to the CAG. The Aldrich ST score formula for anterior STEMI was applied. The result represented the ischemic component of the MaR in % of the left ventricle (%LV). In the same ECG, the initial Selvester QRS score was determined, representing the infarcted component of the MaR in %LV. The combined score was the sum of the Aldrich ST score and the initial Selvester QRS score (%LV). The correlation was assessed between the individual/combined ECG scores and the myocardial perfusion SPECT. The best correlation with myocardial perfusion SPECT was achieved by the combined ECG score (r = 0.47, p = 0.02) and the Selvester QRS score (r = 0.49, p = 0.01). All ECG scores separately (Aldrich ST score: r = 0.21, p = 0.32) or combined underestimated the total MaR (p b 0.01) (Fig. 1). However the difference between the MaR calculated by myocardial perfusion SPECT was smaller for the combined ECG method than either ECG method alone (p b 0.01). The second study by van Hellemond et al. [11] was done in a study population consisting of 32 patients with an acute inferior STEMI. In this study the Aldrich ST score for inferior STEMI was applied. Again it was found that the best correlation with myocardial perfusion SPECT was achieved by the combined ECG score (r = 0.58, p ≤ 0.001. Aldrich ST score: r = 0.17, p = 0.36. Selvester QRS score: r = 0.55, p = 0.001). Due to the fact that an acute inferior STEMI can be caused by either an RCA (71.9%) or LCX (28.1%) occlusion, the study population was divided into two subgroups for analysis. The results showed that the correlation between the combined ECG score and
Fig. 1. The mean (± 1SD) estimated total MaR by four different methods [10]. The three ECG methods significantly underestimated the total MaR by SPECT (p b 0.01), although the difference with the total MaR by SPECT for the sum of Aldrich and Selvester scores was significantly lower than for either score alone (p b 0.01; number bars represent the mean MaR in %LV for each method).
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myocardial perfusion SPECT was significant for the RCA subgroup (r = 0.46, p = 0.03) but not for the LCX subgroup (r =0.58, p = 0.104). The not significant correlation found for the LCX subgroup could be due to the fact that the Aldrich ST score is based on ST-segment elevation, while in a STEMI due to an LCX occlusion ST-segment depression in the precordial leads predominates [13]. The comparison of the measured MaR between the individual/combined ECG scores and myocardial perfusion SPECT in the whole study population (p = 0.636), as well as both subgroups (RCA: p = 0.483, LCX: p = 0.636) showed that there was no significant difference (Fig. 2). The results of both studies confirm previous findings that the Aldrich ST score underestimates the MaR compared to myocardial perfusion SPECT [7,8]. Myocardial perfusion SPECT does not differentiate between ischemic and infarcted myocardium, whereas in the ECG the ST-segment is related to ischemia and the QRS complex is related to infarction. The correlation between the Aldrich ST score and SPECT would be expected to be higher if the coronary occlusion had only just occurred, because there has not been time for necrosis to form. Persson et al. [14] performed a study that looked at this hypothesis. ST-segment changes in patients undergoing 5-minute single balloon inflation by elective prolonged percutaneous transluminal coronary angioplasty were compared to 99mTc-sestamibi SPECT, looking specifically at the measured MaR. Significant but moderate correlations were found (RCA: r = 0.57, p = 0.01, LAD: r = 0.63, p = 0.07, LCx: r = 0.75, p = 0.02). However these were not as high as would have been expected. Correlation between cardiac magnetic resonance imaging endocardial surface area calculations and both the Aldrich ST score and combined Aldrich ST score & Selvester QRS score Körver et al. [15] performed a study to see whether the findings by van Hellemond et al. could be reproduced using
Fig. 2. The mean (± 1SD) estimated total MaR by four different methods [11]. Both the Aldrich and Selvester score alone underestimated the MaR measured by SPECT (p = 0.007 and p b 0.0001, respectively). There was no statistically significant difference between the MaR estimated by the sum of Aldrich and Selvester and the MaR measured by SPECT (p = 0.636; number bars represent the mean MaR in %LV for each method).
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cardiac magnetic resonance imaging (CMR) endocardial surface area (ESA) calculations as the reference method. The reason for choosing ESA was based on a recent study [16], suggesting this to be the best CMR variable for determining the MaR. It was hypothesized that the correlation between the Aldrich ST score and ESA estimation of the MaR would be improved by using the combined ECG score. The study population consisted of 84 patients with either an acute inferior or anterior STEMI and the admission ECG was used for the analysis. To determine the Aldrich ST score and the initial Selvester QRS score, the same methods were used as described by van Hellemond et al. [10,11]. CMR was performed approximately 6 ± 2 days after admission. Even though CMR was performed several days after the event, the measured MaR is still representative of the MaR at the onset of STEMI: studies [17,18] have shown that the extent of subendocardial infarction will remain stable from approximately 40 minutes up to 8 weeks after the initial occlusion. The correlation between the methods was assessed and it was found that the correlation between ESA and the Aldrich ST score (r = 0.55, p b 0.0001) was slightly better than between ESA and the combined ECG score (r = 0.45, p b 0.0001). Furthermore the Aldrich ST score showed an underestimation of the ESA estimated MaR, whereas the combined ECG score showed an overestimation. This is in contrast to findings by van Hellemond et al. One possible explanation for the different findings is the ECG analyzed. Körver et al. used the admission ECG, whereas van Hellemond et al. used the ECG that was recorded later, i.e. at the time of CAG. The QRS changes that were present on the admission ECG could signify conduction delay [19], whereas the QRS changes on the ECG immediately prior to CAG are more likely to represent necrosis. Another possible explanation could be attributed to the different imaging techniques used. Körver et al. used the CMR ESA calculations, whereas van Hellemond et al. used 99mTc-sestamibi SPECT. No studies could be found in which these two methods were compared. One study [20] did compare T2-weighted CMR with SPECT in determining the MaR and no statistical significant difference was found. T2-weighted CMR is an imaging technique that gives increased signal intensity of fluid collections. During a myocardial infarction tissue edema will occur and this is highlighted using the T2-weighted CMR [20]. Previous studies [21] have suggested that this tissue edema is representative of the MaR, although there are clinicians who do not believe this to be the case [22]. Another study by Ubachs et al. [23] compared T2-weighted CMR to CMR ESA calculations in measuring the MaR and found that the CMR ESA calculations underestimated the MaR compared to T2-weighted CMR. Based on these findings it could be concluded that it is possible that the CMR ESA calculations underestimate the MaR as compared to 99mTc-sestamibi SPECT. Predictive value of an ECG-based Acute Ischemia Index for 3-month prognosis of myocardial salvage and infarct healing Hassell et al. [24] performed a study in which the combined ECG score was used to create the Acute Ischemia Index—[Aldrich ST score ECG1/(Aldrich ST score
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ECG1 + Selvester QRS score ECG1)] × 100%. This index represents the ischemic component of the MaR that could potentially be salvaged with reperfusion therapy. To determine how successful reperfusion therapy was the portion of the MaR that has remained viable 3 months after the intervention was determined using the Chronic Salvage Index—[(Aldrich ST score ECG1 + Selvester QRS score ECG1 − Selvester QRS score ECG2)/(Aldrich ST score ECG1 + Selvester QRS score ECG1)] × 100%. It was hypothesized that 1) there would be a significant positive relationship between the Acute Ischemia Index and the Chronic Salvage Index and 2) delay in performing reperfusion therapy would cause the Chronic Salvage Index to be lower than predicted by the Acute Ischemia Index. The study population consisted of 59 patients with an acute inferior STEMI. To determine the scores, the same methods were used as described by van Hellemond et al. [10,11]. Two ECGs were analyzed; the first ECG was recorded on admission (ECG1) and the second ECG was recorded approximately 3 months after discharge (ECG2). The found measurements were input in the formulas for the Acute Ischemia Index and Chronic Salvage Index. Subgroups were created based on the relationship between the Acute Ischemia Index and the Chronic Salvage Index: 1) The concordance group, represented those patients whose Chronic Salvage Index was consistent with the prediction made using the Acute Ischemia Index (− 30%–+30%). 2) The Salvage and Healing (S&H) underestimated group
represented those patients whose Chronic Salvage Index was larger than was predicted by the Acute Ischemia Index (N+30%). 3) The S&H overestimated group represented those patients whose Chronic Salvage Index was smaller than predicted by the Acute Ischemia Index (b−30%) (Fig. 3). The mean measured amount of salvaged MaR was less after 3 months (Chronic Salvage Index: 53.8%) than initially expected (Acute Ischemia Index: 74.6%) and the correlation between the two scoring systems was not significant (r = 0.253, p = 0.053). It was also shown that the time between admission and PCI did not have a significant (p = 0.130) effect on the relationship between the two indexes. In the analysis of the subgroups, it was found that in the S&H overestimated group 6 patients had a Chronic Salvage Index b 0, showing that the ECG-estimated infarct size was larger 3 months after discharge than the total MaR that was estimated at admission. These results show that the Acute Ischemia Index can provide a modest contribution to the prediction of the amount of viable MaR 3 months postreperfusion. Furthermore it was shown that patients with a high acute ischemia index had the potential to retain more viable MaR than patients with lower index scores, giving the clinician an indication of how much myocardium can be saved by reperfusion therapy. This score is however not accurate enough to influence the decision making as regards the reperfusion therapies in the acute setting.
Conclusions It has been shown that combining the Aldrich ST score and the initial Selvester QRS score increases the accuracy of estimating the MaR in the acute phase, especially in the acute inferior STEMI, as compared to the Aldrich ST score. One study [15] did find that the combined ECG score actually overestimated the MaR at onset, whereas other studies did not [10,11]. Explanations for this different finding are the ECGs analyzed and the method the ECG score was compared to. Finally it was reported that there was a moderate relation between the Acute Ischemia Index and the Chronic Salvage Index, representing the MaR expected to be viable after 3 months and the MaR that was actually still viable 3 months post-discharge. These results show that the combined ECG score does improve the accuracy of measuring the MaR in the acute phase. However the correlations found and associated variances are still not high enough to influence decision making with regard to reperfusion therapy in the acute setting and further validation of the combined ECG score. Better alternatives for measuring the MaR are required.
Future studies
Fig. 3. Scatterplot depicting the relationship between the Acute Ischemia Index and the Chronic Salvage Index (Pearson's r = 0.253, p = 0.05) [24]. The regression line is depicted as the continuous line and the middle dashed line represents the identity line. The subjects located between the two outer dashed lines are defined as the concordance group.
It would be interesting to see whether the combined ECG score will remain stable over time. Bouwmeester et al. [25] have already shown that the Aldrich ST score alone is not sufficiently stable over time. A study is currently being performed to see whether the combined ECG score will remain stable over time. If the scores are correct the MaR
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should remain stable—the Aldrich ST score declining and the Selvester QRS score increasing over time. Another important aspect that needs further validation is the use of the Selvester QRS score in the acute phase of myocardial infarction. The Selvester QRS score has only been validated for use after the acute phase, although studies have used it during the acute phase [9]. A method for testing the Selvester QRS score in the acute phase would be to determine the score before and after successful reperfusion. If the Selvester QRS score represents infarcted myocardium, then the scores should not differ. Finally, an important limitation of the combined ECG score is the Aldrich ST score. The Aldrich ST score was created based on the assumption that the MaR would be equal to final infarct size if no reperfusion occurs. However it is known that in some patients, even if no reperfusion occurs, the final infarct size will be reduced due to protection of the myocardium through collaterals and metabolic conditioning [26]. These statements make it clear that additional research regarding the combined ECG score can still be performed.
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[13]
[14]
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