ST segment elevation in lead aVR and coronary artery lesions in patients with acute coronary syndrome

INTRODUCTION: Recently, the prognostic value of ST segment elevation in lead aVR in acute coronary syndrome (ACS) and its relationship with significant stenosis of the left main coronary artery (LMCAS) and three-vessel disease have been highlighted. AIM: Analysis of the relationship between ST segment elevation observed in aVR lead and angiographic severity of coronary artery disease in patients with ACS. METHODS: The study involved 134 patients with ACS, including 54 subjects with ST elevation in aVR (group A) and 80 patients without elevation of ST in the same lead (group B), aged 33-78 years, mean 59.9+/-9.7 years. The severity of coronary artery disease was compared between the two groups. The logistic regression model was used for the analysis of factors affecting ST segment in aVR, as well as LMCAS and three-vessel disease probability. RESULTS: In patients with ST elevation in aVR, three-vessel disease prevalence was two times higher (61.1% vs 35.0%; p <0.01), and LMCAS - three times higher (55.6% vs 17.5%; p <0.000001) than in those without ST elevation in aVR. Factors independently associated with ST elevation in aVR were LMCAS (OR 6.1; 95% CI 2.62-14.23; p <0.00005), ST segment elevation in V1 (OR 3.03; 95% CI 1.34-6.86; p <0.01) and diabetes (OR 2.89; 95% CI 1.17-7.15; p <0.05). The predictors of LMCAS were three-vessel disease and ST elevation in aVR, while the predictors of three-vessel disease were: LMCAS, diabetes, male gender and history of myocardial infarction. CONCLUSIONS: Elevation of the ST segment in aVR in the setting of acute coronary syndrome identifies patients with severe coronary artery disease. Only left main coronary artery disease, however, remains independently associated with ST segment elevation in aVR. Three-vessel disease and the left main coronary artery stenosis equivalent are not independent predictors of ST segment elevation in aVR of standard electrocardiograms recorded in patients with acute coronary syndrome.     

冠状动脉前降支闭塞致急性心肌梗死的心电图ST段偏移特点分析

目的探讨冠状动脉前降支(LAD)单支闭塞所致急性心肌梗死(AMI)的心电图(ECG)特点。方法回顾性分析51例LAD急性闭塞所致AMI患者心电图ST段改变与冠状动脉造影结果。结果 V_2导联ST段抬高<0.2 mV预测LAD远段闭塞敏感度为52.9%,特异度为88.2%,在胸导联ST段抬高的情况下,特异度增高(96.2%)。V_6导联ST段压低预测LAD近段闭塞敏感度为26.5%,特异度100%,在胸导联ST段抬高的情况下,V_1导联ST段抬高≥0.2 mV预测LAD近段闭塞敏感度53.8%,特异度88.9%。下壁导联Ⅱ、Ⅲ、aVF ST段压低预测LAD近段闭塞特异度较高,Ⅲ、aVF导联组合较Ⅱ、Ⅲ、aVF导联组合判断LAD近段闭塞特异度及阳性预测值高。结论 V_1导联ST段抬高、V_6导联ST段压低、下壁导联ST段压低有助于判断LAD近段闭塞,V_2导联ST段抬高<0.2 mV有助于判断LAD远段闭塞。     

aVR 导联 ST 段抬高对冠脉左主干和／或3支血管病变的诊断价值

严重的冠脉病变包括冠脉左主干（left main coronary artery,LMCA）急性完全闭塞、次全闭塞以及3支血管病变（3-vessel disease,3-vd）。尽管 LMCA 急性完全闭塞患者能生存到达医院者很少,但 aVR 导联 ST 段抬高对其诊断的特异性和准确率均超过80％。对 LMCA 急性次全闭塞及3-vd 患者,aVR 导联 ST 段抬高的诊断价值高于心电图的任何其他单一或多个导联。aVR 导联 ST 段抬高幅度越大、持续时间越长,患者的病情就越重。本文对 aVR 导联 ST段抬高的诊断标准、电生理机制及国外研究进展进行综述。     

Correlation of the location of coronary arterial spasm with the lead distribution of ST segment elevation during variant angina

The lead distribution of ST segment elevation produced by severe “spasm” of major coronary arteries was correlated with the specific artery involved in a group of 110 cases of variant angina with single vessel coronary arterial spasm made up from eight cases personally observed and 102 cases abstracted from published literature.The most sensitive and specific lead for ST elevation during anterior descending (LAD) coronary arterial spasm was V₃; V₂ was almost as good. For spasm of either the right (RCA) or circumflex coronary artery (CMFX), Leads 3 and aV_F showed ST elevation most frequently; electrocardiographically it was difficult to distinguish between spasm of these two vessels. ST elevation in Leads V₅ and V₆ was not specific, occurring in some cases of spasm of each of the three major coronary arteries. ST elevation in Lead V₁ occurred in either RCA or LAD spas, but never in CMFX spasm. ST elevation in Lead 1 was never seen with isolated RCA spasm.No single lead can detect all cases of transient ST elevation. Simultaneous monitoring of Leads 3 and V₃ would have detected 98.2% of 333 cases of ST elevation reviewed, and addition of Lead aV_L would have detected most of the remainder. These findings should be considered in lead selection for monitoring to detect ST elevation, and in using the ECG to identify spastic coronary arteries.     

急性心肌梗死aVR导联ST段抬高的临床意义

目的 探讨体表心电图aVR导联ST段抬高对急性心肌梗死患者梗死相关血管(IRA)诊断及临床预后的意义.方法 收集2010年10月至2012年12月因急性心肌梗死入住我院的患者共240例,根据患者入院时心电图aVR导联ST段有无抬高,分为A组(AVR导联ST段抬高)80例和B组(aVR导联ST段无抬高)160例,对两组患者临床资料、冠状动脉造影结果及主要不良心血管事件进行对比.结果 ①两组患者性别、糖尿病病史、PCI病史等一般临床资料对比差异无统计学意义(P＞0.05).②两组冠状动脉造影结果比较:IRA为左主干(LM),A组9例,B组3例,两组比较差异有统计学意义(P＜0.01);IRA左主干和(或)三支血管(LM/3VD),A组46例,B组15例,两组比较差异有统计学意义(P＜0.01).③aVR导联ST抬高对IRA为左主干的敏感性及特异性分别为75％和69％,对IRA为左主干和(或)三支病变的敏感度及特异度分别为73％和81％.④住院期间主要不良心血管事件(MACE),A组36例,B组25例,两组比较差异有统计学意义(P＜0.01).⑤在住院期间,aVR导联ST段抬高(OR=10.03,95％CI=5.36～18.77,P＜0.01)是急性心肌梗死患者发生不良心血管事件的独立危险因素.结论 aVR导联ST段抬高提示急性心肌梗死患者梗死相关血管为左主干和(或)三支血管病变及住院期间不良心血管事件发生率增高.aVR导联ST段抬高对急性心肌梗死患者梗死相关血管判断及临床预后具有一定的临床指导意义.     

Acute myocardial infarction with significant left main coronary artery stenosis, significant 3-vessel coronary artery disease and elevated troponin-I at admission

Exercise-induced ST-segment elevation in lead aVR accompanied by ST-segment elevation in lead V1 might be a specific finding of left main coronary artery (LMCA) stenosis. Lead aVR and lead v1 ST segment elevation has been reported, during an attack of chest pain, in patients with LMCA disease with ST segment depression in leads V3, V4 and V5 (with maximal depression in V4). ST-segment elevation in lead aVR in patients with angina at rest can be related to transmural ischemia of the basal part of the interventricular septum, frequently due to LMCA or multivessel coronary disease too. 3-vessel coronary artery disease (CAD) and LMCA disease show a frequent combination of leads with abnormal ST segments during chest pain with ST-segment depression in leads I II V4-V6, and ST-segment elevation in lead aVR. When ST-segment status in lead aVR combines with troponin T, ST-segment elevation in lead aVR and positive troponin T on admission are useful predictors of LMCA or 3-vessel CAD. We present a case of acute myocardial infarction with significant left main coronary artery stenosis, significant 3-vessel coronary artery disease and elevated troponin I at admission in an 83-year-old Italian woman. Also this case focuses attention on the importance of the recognition of the patterns suspected for LMCA and/or 3-vessel coronary disease.     

aVR导联ST段抬高对急性心肌梗死预后的价值

目的探讨心电图aVR导联ST段抬高对急性前壁心肌梗死患者预后的价值。方法首次入院急性前壁心肌梗死患者57例，对其心电图和冠状动脉造影及临床资料进行对比分析。根据心电图aVR导联ST段变化分为抬高组、无偏移组。结果梗死相关血管为左主干病变的ST段抬高组、ST段无偏移组分别为5例（21．7％）、1例（2．9％），两组统计有显著性差异（p〈0．01）；病变范围为多支病变ST段抬高组、ST段无偏移组分别为10例（43．4％）、8例（23．5％），两组统计有显著性差异（p〈0．05）；发生心脏事件ST段抬高组、ST段无偏移组分别为8例（34.8％）、3例（8．8％），两组有显著性差异（p〈0．01）。结论aVR导联ST段抬高对预测急性前壁心肌梗死患者的预后有重要的价值，应高度重视。     

左主干闭塞所致急性心肌梗死的心电图特点

目的分析急性左主干(LM)闭塞的常规心电图(ECG)表现,总结其ECG特点。方法1999年1月至2004年8月,10例急性心肌梗死(AMI)患者经急诊冠状动脉造影证实为急性LM闭塞(LM组),回顾性分析其急诊ECG表现。并选取同时期30例经急诊造影证实为左前降支(LAD)近段闭塞的AMI患者(LAD组),比较两组造影前的急诊ECG表现,以求总结急性LM闭塞的常规ECG特点。结果LM组心率快于LAD组,在心律失常发生率方面两组差异无统计学意义。LM组中9例患者存在aVR导联ST段抬高(≥0·05mV),发生率明显高于LAD组(分别为90%和36·7%,P=0·002),同时LM组aVR导联ST段抬高幅度亦明显大于LAD组。而LM组胸前导联V1-3的ST段抬高程度则明显低于LAD组。aVR导联ST段抬高>0·05mV诊断急性LM闭塞的敏感性为90%,特异性为63·3%。如果同时再满足V1 V2 V3导联ST段抬高程度<0·5mV,其诊断急性LM闭塞的敏感性为90%,特异性达到86·7%。结论aVR导联ST段抬高>0·05mV,同时伴有V1~V3导联ST段抬高不明显、甚至压低是急性LM闭塞区别于LAD闭塞的ECG特点,结合临床表现,分析ECG特点可能有助于造影术前预测此类患者和风险评价。     

Wellens' syndrome and other electrocardiographic changes in a patient with a left anterior descending artery subocclusion associated with a left main coronary artery subocclusion

Changing axis deviation has been reported also during atrial fibrillation or atrial flutter. Changing axis deviation has been also reported during acute myocardial infarction associated with atrial fibrillation too or at the end of atrial fibrillation during acute myocardial infarction. Patients with unstable angina have a higher incidence of left main coronary artery (LMCA) and proximal left anterior descending (LAD) coronary artery disease compared to patients with stable angina pectoris. In 1982, Wellens and colleagues described two electrocardiographic patterns that were predictive of critical narrowing of the proximal LAD artery, and were subsequently termed Wellens' syndrome. The criteria were: a) prior history of chest pain, b) little or no cardiac enzyme elevation, c) no pathologic precordial ST segment elevation, d) no loss of precordial R waves, and e) biphasic T waves in leads V2 and V3, or asymmetric, often deeply inverted T waves in leads V2 and V3. The ECG changes are best recognized outside the episode of anginal pain. Lead aVR and lead v1 ST segment elevation, during chest pain, has been reported in patients with LMCA disease with ST segment depression in leads V3, V4 and V5 (with maximal depression in V4).We present a case of changing axis deviation in a 37-year-old Italian man with a LAD coronary artery subocclusion associated with a LMCA subocclusion. This case focuses attention on the importance of the recognition of the patterns suspected for LAD coronary artery disease or for LMCA disease.     

急性心肌梗死左主干与前降支近段病变心电图ST段压低的对照分析

目的探讨12导联心电图ST段压低在急性心肌梗死左主干与前降支近段病变鉴别中的价值。方法选取因急性心肌梗死住院的患者,依冠状动脉造影结果,分为冠状动脉左主干病变(LM组)和左前降支近端病变(LAD组)。回顾性分析患者入院即刻的12导联心电图,比较两组ST段压低改变的特点。结果入选符合标准的患者共74例,LM组15例,LAD组59例。LM组Ⅰ、Ⅲ、aVL和aVF导联ST段压低比例显著高于LAD组(P均<0.05),V2～6ST段压低比例两组亦有差异(P均<0.01)。同时,V2～6导联ST段改变值两组亦有差异。多元分析表明Ⅲ、V2和V6导联ST段压低对急性左主干病变有预测价值(P均<0.001),其诊断的敏感度为26.7%、特异度100%、阳性预测值100%和准确度85.1%。结论Ⅲ、V2和V6导联ST段压低有助于鉴别急性左主干与左前降支近段病变。     

aVR 导联 ST 段改变对不同冠脉血管病变的诊断及鉴别诊断意义

冠状动脉左主干及其主要分支病变均可引起心电图 aVR 导联 ST 段的抬高或压低,但不同血管病变所致心肌缺血或梗死的危险分层及临床预后却相差甚远,因此对不同冠脉血管病变的诊断及鉴别诊断非常重要。这其中 aVR 导联 ST 段的改变具有重要的临床意义,其诊断及鉴别诊断价值高于其他任何单一或多个导联。本文就 aVR 导联 ST 段的抬高或压低对不同冠脉血管病变的诊断及鉴别诊断意义、诊断标准及国外近年来的研究进展进行综述。     

Right and left ventricular ejection fraction in acute inferior wall infarction with or without ST segment elevation in lead V4R

To detect right ventricular involvement, lead V4R was recorded within 10 hours of the onset of chest pain in 42 consecutive patients admitted with acute inferior wall myocardial infarction. One week after the acute infarction, multigated equilibrium radionuclide ventriculography was performed to assess right and left ventricular ejection fraction. Two weeks after the acute infarction, coronary angiography was performed to determine the site and location of the obstruction leading to the infarction. Seventeen patients had an obstruction in the right coronary artery proximal to the first branch to the right ventricular free wall (group 1); all of these had ST segment elevation in lead V4R. Fourteen patients had an obstruction in the right coronary artery distal to the first branch to the right ventricular free wall (group 2); only two of these patients had ST segment elevation in lead V4R. In 11 patients, the obstruction was located in the circumflex coronary artery (group 3); none of these had ST segment elevation in lead V4R. Nineteen patients had ST segment elevation of 1 mm or greater in lead V4R (group 4). Left ventricular ejection fraction was not different among the four groups of patients, although the right ventricular ejection fraction was significantly lower in group 1 and group 4 patients. It is concluded that ST segment elevation in lead V4R reliably identifies the group of patients with inferior wall myocardial infarction with depressed right ventricular function. This phenomenon persists for at least 1 week after infarction.     

急性下壁心肌梗死患者心电图胸前导联ST段改变的临床意义

目的探讨急性下壁心肌梗死患者心电图胸前导联ST段改变与冠状动脉造影(CAG)所见冠状动脉病变部位的关系及其临床意义。方法 187例急性下壁心肌梗死患者,按入院时18导心电图胸前导联ST段改变分为3组,ST段无变化组(47例),ST段抬高组(16例),ST段压低组(124例);所有患者均行CAG。结果急性下壁心肌梗死伴胸前导联ST段抬高时多为右冠状动脉(RCA)近段闭塞(14例,82.3%),尤其是伴圆锥支动脉闭塞,与RCA中远端闭塞(2例,5.9%)比较差异有统计学意义(P0.01),且14例(73.7%)伴有右心功能不全和血流动力学障碍。下壁心肌梗死胸前导联ST段压低者可见于RCA、回旋支(LCX)闭塞及RCA、LCX闭塞与前降支(LAD)、对角支(D)病变的不同组合,其中LCX闭塞伴RCA病变者多表现为朐前ST V_4～V_6的压低,RCA闭塞伴LAD近端病变多有胸前ST V_1～V_6的压低,RCA伴D病变胸前ST V_1～V_3压低,与对照组比较差异有统计学意义(P0.05)。结论急性下壁心肌梗死合并胸前导联ST段抬高表明为RCA近段或丌口闭塞且多伴右心室心肌梗死和心功能不全;下壁心肌梗死伴胸前导联ST段压低提示为多支病变,ST V_1～V_3压低多伴有对角支严重狭窄,STV_1～V_6压低多伴有前降支的严重狭窄。     

QRS波宽度及aVR导联ST段抬高对NSTE-ACS左主干或三支病变的预测作用

目的研究非ST段抬高型急性冠脉综合征(NSTE-ACS)患者心电图的QRS波宽度及aVR导联抬高幅度对冠状动脉左主干/三支病变的诊断价值。方法分析106例NSTE-ACS患者的体表心电图QRS波宽度及aVR导联ST段抬高幅度,通过与冠状动脉造影结果对比,研究其对诊断左主干/三支病变的敏感性、特异性和相关性。结果 QRS波宽度及aVR导联ST段抬高是左主干/三支病变的独立预测因子,OR值分别为9.04(95%CI,4.88～16.7)、7.10(95%CI,4.91～76.2);QRS间期≥90ms和aVR导联ST段抬高≥0.5mm预测左主干/三支病变的敏感性及特异性分别为88%、76%及88%、86%。结论 QRS波增宽及aVR导联ST段抬高是NSTE-ACS患者左主干/三支病变较为灵敏的预测因子。     

Value of lead aVR in the detection of significant left main coronary artery stenosis in acute coronary syndrome

BACKGROUND: Electrocardiographic lead aVR is usually ignored in patients with chest pain. ST segment elevation in aVR may have diagnostic value in patients with acute coronary syndrome (ACS) and significant stenosis or obstruction of the left main coronary artery (LMCAS), especially when accompanied by ST segment elevation in lead V(1). AIM: To asses the value of lead aVR and V1 for the detection of LMCAS in patients with ACS. METHODS: The study group consisted of 150 patients (mean age 60.6+/-9.5 years, range 33-78 years) with ACS, including 46 with LMCAS and 104 without LMCAS. ECG recordings obtained on admission were compared between these two groups. RESULTS: In patients with LMCAS, ST segment elevation in lead aVR was two times more frequent than in remaining patients (69.6% vs 34.6% p=0.0001) whereas there were no differences in lead V(1). Sensitivity of ST elevation in aVR in detection of LMCAS was 69.6%, specificity - 65.4%, positive predictive value - 47.1%, and negative predictive value - 82.9%. In patients with LMCAS, ST segment depression was significantly more often present in ECG leads other than aVR (45.6% vs 23.1% p<0.01). Patients with LMCAS more often had hypertension (95.6% vs 77.9% p<0.05) and three-vessel disease (78.3% vs 31.8%, p<0.0001). CONCLUSIONS: The assessment of lead aVR in patients with ACS may indicate LMCAS. Additional analysis of lead V(1) does not improve diagnostic accuracy.     

Significance of exercise-induced ST changes in leads aVR,V5, and V1. Discrimination of patients with single- or multivessel coronary artery disease

BACKGROUND: It is known that exercise-induced ST-segment elevation in lead V1 (V1-E) detects left anterior descending (LAD) stenosis. It was also postulated that ST elevation in aVR and simultaneous ST depression in V5 (aVR-E + V5-D) is a marker of ischemia due to significant stenosis of the LAD in patients with single-vessel disease. HYPOTHESIS: This study was undertaken to investigate the significance of the concomitant appearance of both electrocardiographic (ECG) ischemic markers, and of each of them alone during exercise, to detect either LAD stenosis as single-vessel coronary artery disease (CAD), or multivessel CAD involving LAD stenosis. METHODS: A total of 196 consecutive patients (152 men and 44 women, mean age 54 +/- 7 years) with at least one of these ECG markers, who underwent treadmill exercise testing with the Bruce protocol and coronary arteriography, were studied. RESULTS: Patients were divided into three groups. In Group A (83 patients with V1-E + aVR-E & V5-D), 93% of patients with single-vessel disease had significant LAD stenosis (p<0.001), whereas 75% of patients with double-vessel disease had significant stenoses of the LAD and the left circumflex (LCx) coronary arteries (p<0.01). In Group B (97 patients with aVR-E & V5-D but without V1-E), 43% of patients with single-vessel disease had significant LAD stenosis (p<0.08), whereas 85% of patients with double-vessel disease had significant stenoses of the LAD and the right coronary artery (RCA) (p<0.01). In Group C (16 patients with only V1-E), 60% of patients with single-vessel disease had significant LAD stenosis (p<0.05), whereas 75% of patients with double-vessel disease had significant LAD and LCx stenoses (p<0.05). CONCLUSIONS: The concomitant appearance of exercise-induced ST elevation in lead V1, ST elevation in lead aVR, and ST depression in lead V5, as well as the isolated appearance of ST elevation in lead V1 detect significant LAD stenosis as single-vessel disease, or significant stenoses of LAD and LCx arteries in patients with double-vessel disease, whereas the appearance of ST elevation in aVR & ST depression in V5 but without ST elevation in V1 correlates strongly with significant LAD and RCA stenoses and usually indicates double-vessel disease.     

STaVR抬高对急性冠状动脉综合征预后评估的价值

目的探讨心电图STaVR抬高对急性冠状动脉综合征预后评估的价值。方法回顾性分析68例急性冠状动脉综合征患者的心电图和冠状动脉造影资料、临床资料。根据STaVR抬高是否≥0.05mV分为抬高组（n=23）和非抬高组（n=45）。结果病变血管涉及左主干和左前降支近段的分别为抬高组13例（56.5％）和非抬高组1例（2.2％）,病变范围为多支病变的分别为9例（39.1％）和8例（17．8％）,发生心脏事件分别为7例（30.4％）和4例（8.9％）,两组差异均有非常显著性意义（P〈0．01）。结论急性冠状动脉综合征患者STaVR抬高提示左主干和左前降支近段病变、多支病变的可能,对判断预后有参考价值。     

Precordial ST segment elevation in acute ischemia caused by right coronary artery occlusion.

The purpose of this study is to determine why precordial ST elevation (V1 lead) occurs during acute occlusion of the right coronary artery (RCA). Nineteen patients with vasospastic angina, in whom ergonovine administration into RCA provoked spasms, were divided into 2 groups by precordial ST change during spasms. Group I (n = 6) had precordial ST elevation; group II (n = 13) had no precordial ST elevation. A subgroup, IIA was comprised 6 patients in group II with spasms in the RCA proximal segment (segment number less than 2 of AHA coronary classification). None had left coronary dominancy. There was no difference in collateral flow during spasms. Location of spasms in group I was in the RCA proximal segment, and was significantly more proximal compared to group II. There was no difference in sigma ST in II, III, aVF between group I and II or IIA. Max ST elevation time by which duration of ischemia was estimated was significantly longer in group I than in group IIA. Three patients in group I displayed precordial ST depression before elevation, in all of whom in sigma ST in II, III, aVF was higher during precordial ST elevation than during depression. During acute occlusion in the RCA proximal segment, precordial ST elevation is caused by ischemia of the right ventricular anterior wall. Furthermore, precordial ST elevation can occur in a patient with RCA dominance, even if ischemic injury in the left ventricular infero-posterior wall increases progressively.     

ST-segment elevation in lead augmented vector right may also be caused by diffuse left main coronary artery vasospasm without fixed stenosis

ST-segment deviation in lead augmented vector right (aVR) is useful for evaluating patients with acute coronary syndrome (ACS). The ST-segment elevation in this aVR in the patient with clinically suspected acute coronary syndrome suggests a strong possibility of left main coronary artery (LMCA) obstruction due to fixed stenosis. In this article, we report the first case, to our knowledge, of ST-segment elevation in lead aVR due to diffuse LMCA spasm.     

Electrocardiographic discrimination of infarct-related artery between left circumflex and right coronary artery: comparison of ST elevation between leads II and III

OBJECTIVES: Admission electrocardiography was evaluated to discriminate left circumflex artery (LCX) versus right coronary artery (RCA) as the cause of acute myocardial infarction. METHODS: Electrocardiographic findings were assessed in patients with RCA (n = 60) and LCX (n = 60) occlusion. RESULTS: ST segment elevation in the inferior leads or right precordial leads was more common in the RCA group. ST segment depression or negative T wave was more common in leads I, aVL in the RCA group. ST segment elevation was more common in leads V5, V6 in the LCX group. ST segment was elevated in inferior leads in 55 patients in the RCA group and 27 patients in the LCX group. Mean ST level was higher in lead III than in lead II in the RCA group, but not in the LCX group. The ST level was higher in lead III than in lead II in 78% of the RCA group, but only 44% of the LCX group (p < 0.01). CONCLUSIONS: Comparison of ST levels between leads II and III, and a three-dimensional analysis in 12-lead electrocardiography is useful for discriminating the left circumflex artery from the right coronary artery as the cause of acute myocardial infarction.