Case 1: Inferior ischemia or infarction
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EKG: The T wave is negative in leads II, III, and AVF, but positive in I and AVL (Figure 13.13).
Visualization: The T is pointing to the left and superiorly, away from the inferior wall
(Figure 13.14).
Critical Thinking: The T wave is pointing away from the inferior wall. The right coronary artery (RCA) supplies blood to the inferior and posterior walls. We expect a significant obstruction with either a plaque (or a plaque plus a clot) in that artery. Since we have no other information and only a single EKG, the First Rule of the T Waves applies (Table 13.1, middle row). This provides a differential diagnosis of three likely possibilities.
- These T waves could be old, unchanged from a previous non-ST elevation MI.
- These T waves could be new and changed from a previously normal EKG, but may reverse in the next (in 30 minutes or several hours) EKG. This would indicate a new reversible ischemic process called unstable angina.
- These T waves could be new but not reverse within 24 hours. They would then typically be associated with a positive blood test of biochemical markers such as Troponin. This would confirm an irreversible loss of myocardial cells called non-ST elevation myocardial infarction (NSTEMI).
Pattern to Memorize: The T waves point away (−105° to −165°) from leads I and AVF, giving an inverted T wave in these leads.
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Case 2: Lateral wall ischemia or infarction
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EKG: The T wave is negative in leads I and AVL, but positive in III and AVF (Figure 13.15).
Visualization: The T wave is pointing to the patient’s right side, away from the lateral wall (Figure 13.16).
Critical Thinking: Since the T wave is pointing away from the lateral wall, we locate the area of ischemia or infarction here. The left coronary artery supplies blood to the anterior and lateral walls. We expect a significant obstruction with either a plaque (or a plaque plus a clot) in the LAD or circumflex artery. Again, if we have no other information, we apply the First Rule of the T Waves. This provides a differential diagnosis of three likely possibilities.
- These T waves could be old, unchanged from a previous non-ST elevation MI.
- These T waves could be new and changed from a previously normal EKG, but may reverse in the next (in 30 minutes or several hours) EKG. This would indicate a new reversible ischemic process called unstable angina.
- These T waves could be new but not reverse within 24 hours. They would then typically be associated with a positive blood test of biochemical markers such as Troponin. This would confirm an irreversible loss of myocardial cells called non-ST elevation myocardial infarction (NSTEMI).
Pattern to Memorize: The T waves point away (+105° to +180°) from leads I and AVL, giving an inverted T wave in these leads.
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Case 3: Apical ischemia or infarction
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EKG: The T wave is negative in leads I and AVF (Figure 13.17).
Visualization: The T is pointing superiorly and to the patient’s right side, away from the apex (Figure 13.18).
Critical Thinking: Since the T wave is pointing away from the apex, we locate the area of ischemia or infarction here. The left coronary artery supplies blood to the apex. We expect
a significant obstruction with either a plaque (or a plaque plus a clot) in the LAD. Again, if we have no other information, we apply the First Rule of the T Waves. This provides a differential diagnosis of three likely possibilities.
- These T waves could be old, unchanged from a previous non-ST elevation MI.
- These T waves could be new and changed from a previously normal EKG, but may reverse in the next (in 30 minutes or several hours) EKG. This would indicate a new reversible ischemic process called unstable angina.
- Third, these T waves could be new but not reverse within 24 hours. They would then typically be associated with a positive blood test of biochemical markers such as Troponin. This would confirm an irreversible loss of myocardial cells called non-ST elevation myocardial infarction (NSTEMI).
Pattern to Memorize: The T waves point away (+105° to +180°) from leads I and AVL, giving an inverted T wave in these leads.
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Case 4: Septal and anterior ischemia or infarction
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EKG: The T wave is negative in leads V1, V2, V3, and V4 (Figure 13.19).
Visualization: The T is pointing posteriorly, away from the septum and anterior walls (Figure 13.20).
Critical Thinking: Since the T wave is pointing away from the septum and anterior walls, we locate the area of ischemia or infarction here. The left coronary artery supplies blood to
the septum and anterior walls. We expect a significant obstruction with either a plaque (or a plaque plus a clot) in the LAD. Again, if we have no other information, we apply the First Rule of the T Waves. This provides a differential diagnosis of three likely possibilities.
- These T waves could be old, unchanged from a previous non-ST elevation MI.
- These T waves could be new and changed from a previously normal EKG, but may reverse in the next (in 30 minutes or several hours) EKG. This would indicate a new reversible ischemic process called unstable angina.
- These T waves could be new but not reverse within 24 hours. They would then typically be associated with a positive blood test of biochemical markers such as Troponin. This would confirm an irreversible loss of myocardial cells called non-ST elevation myocardial infarction (NSTEMI).
Pattern to Memorize: The T waves point away (−22.5° to −60°) from leads V1, V2 and V3, giving an inverted T wave in these leads.
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