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A neonate admitted to the cardiac intensive care unit after cardiac surgery becomes acutely hypotensive on his first postoperative night; ST changes are noted on the monitor. A 12-lead electrocardiogram is performed.  

Of the following, based on the interpretation of the 12-lead electrocardiogram (Figure 1) and rhythm strip (Figure 2), perfusion is MOST acutely compromised in the distribution of: 

Figure 1:

Figure 2:

  • A. left anterior descending artery
  • B. left circumflex coronary artery
  • C. left main coronary artery
  • D. right coronary artery

The correct answer is: 

C. left main coronary artery 

Critique: 


For the patient described in the vignette, the 12-lead electrocardiogram (ECG) (Figure 3) and rhythm strip (Figure 4) show the following: 

  1. ST elevation > 2 mm in leads I, aVL, V2, V5, and V6 (highlighted with red circles in Figure 3 and Figure 4) 
  2. Reciprocal ST depression in the inferior leads III and aVF (highlighted with green squares in Figure 3 and Figure 4) 
  3. ST depression in aVR and V1 (highlighted with purple squares in Figure 3 and Figure 4) 

These findings are consistent with myocardial ischemia in the distribution of the left main coronary (LMCA) artery. As there are no wide Q waves visible, the ischemia has not progressed to irreversible cell damage or infarction. The patient had external compression of the left main coronary artery that developed during cardiac repair and needed immediate surgical revision. Complete acute occlusion of the LMCA in the absence of collateral circulation can result in cardiogenic shock with fatal outcome if not correctly recognized and managed immediately. 

Myocardial infarction (MI) happens when myocardial ischemia causes cardiac myocyte cell death. It is diagnosed by the presence of elevated biomarkers (cardiac troponin T or I) suggestive of myocyte necrosis associated with either ECG criteria of ischemia/infarction or ischemic symptoms or both. An ECG is an important noninvasive tool to assess for cardiac ischemia. The presence of dome-shaped or convex ST segment elevation alone indicates myocardial injury and impending infarction, and the presence of Q waves indicates progression to infarction. 

In order to localize the area involved, it is important to know the normal vascular supply of the myocardium. 

Right coronary artery (RCA): 

  1. Right atrium 
  2. Right ventricle 
  3. Inferior wall of the left ventricle (LV)  
    1. In 80%-90% of individuals, the RCA gives rise to the posterior descending artery, which supplies the inferior wall of the LV, ie, the right-dominant system 
  4. Atrioventricular node (if the right-dominant system) 
  5. Sinoatrial node (in 60% of individuals) 
  6. Posterior 1/3 of the interventricular system 

Left anterior descending coronary artery (LAD): 

  1. Anterior 2/3 of the interventricular system 
  2. Anterosuperior wall of the LV 
  3. Left ventricle apical region 

Left circumflex coronary artery (LCx): 

  1. Left atrium 
  2. Basal and mid-parts of the posterolateral wall of the LV 
  3. Inferior wall of LV  
    1. In 10%-20% of individuals, the LCx continues as the posterior descending artery, which supplies the inferior wall of the LV, ie, the left-dominant system) 
  4. Atrioventricular node (if left-dominant system) 

The ST segment vector is directed towards the area of ischemia/infarction, and manifests as ST elevation in the leads, representing the ischemic/infarcted area +/- reciprocal changes in opposite leads as shown: 

Based on this information, obstruction to the blood flow in each coronary artery results in a set of unique ECG findings: 

RCA occlusion: inferior MI (80%) 

  • ST elevation in inferior leads II, III, and aVF (lead III>II) 
  • ST depression in the lateral leads I, aVL, or both 
  • In proximal RCA occlusion, RV infarction may be seen with the addition of ST elevation in V1 and V4R 

LAD occlusion: anteroseptal MI, lateral MI 

  • ST elevation in V1-V3, +/- aVL, I 
  • Proximal LAD occlusion may also include:
  • ST elevation in aVL 
  • ST depression in II, III, and aVF 
  • ST elevation in V1 > 2.5 mm 
  • RBBB with Q wave in V1 

LCx occlusion: posterolateral MI, inferior MI in 20% 

  • ST elevation in I, aVL, V5, and V6
  • ST depression in V1-V3 
  • If a left-dominant system in addition causes inferior MI (20%); ST elevation in II, III, and aVF 

LMCA occlusion: anteroseptal and lateral MI 

  • ST elevation in V2-V3, I, aVL, and V5-V6 
  • ST depression in II, III, aVF, V1, and aVR 
  • ST elevation in V1 from LAD occlusion is masked by ST depression from LCx occlusion 

Myocardial ischemia can also affect the conduction system and result in both atrial and life-threatening ventricular arrhythmias. 

Identifying MI in children may be more difficult compared with adults due to normal pediatric ECG changes and ECG changes associated with some other pediatric disorders. Based on studies of MI in children, ECG criteria for diagnosis of acute MI in children are: 

  1. Wide Q waves (> 35 ms) with or without notching 
  2. ST segment elevation (> 2 mm) 
  3. Prolonged corrected QTc (> 440 ms) with accompanying Q-waves abnormalities 
  4. New T-wave inversion and reduction in R-wave amplitude associated with Q waves and ST segment changes 

Figure 3:

Figure 4:

Last Updated

02/14/2025

Source

American Academy of Pediatrics