Prolonged Arterial Occlusion Case Studies

Home » MEDCLIN530 » EKG » 12-Lead EKG Confidence » V. Ischemic Disorders: EKG changes related to ischemia and myocardial infarction » 15. Prolonged Arterial Occlusion: Q Waves and Equivalents » Prolonged Arterial Occlusion Case Studies
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Chris Anderson
MD · Clinical Education Director, Pediatrics
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Table of Contents

Case 1: Inferior Q wave infarction

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EKG: The first 0.04 seconds of the QRS are entirely negative in leads II, III, and AVF. These are significant Q waves (Figure 15.7).
Visualization: The beginning of the QRS is pointing to the left and superiorly away from the inferior wall.
Critical Thinking: The beginning of the QRS is pointing away from the inferior wall (Figure 15.7). We expect an infarction to be present in the inferior wall of the left ventricle. This is permanent loss of cells. 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.
Timing of the infarction can be suggested but not proven. Since there are inverted T waves, this suggests that the Q waves may be relatively acute or recent. Additionally, if this is the only EKG, the First Rule of the T Waves still applies. These T waves may be related to the Q wave infarction, and time it as recent. Or these T waves may represent new ischemia or infarction.
Pattern to Memorize: Q waves point away (–45° to –90°) from leads II, III, and AVF.
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Case 2: Septal and anterior wall infarction

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EKG: The first 0.04 seconds of the QRS are on average negative in leads V1, V2, and V3. These are Q wave equivalents (Figure 15.8).
Visualization: The beginning of the QRS is pointing to the left and posteriorly away from the septal and anterior walls.
Critical Thinking: The beginning of the QRS is pointing away from the septal and anterior walls. We expect an infarction to be present in the septal and anterior walls of the left ventricle. This is permanent loss of cells. The left anterior descending branch (LAD) of left coronary artery (LCA) supplies blood to the septal and anterior walls. We expect a significant obstruction with either a plaque (or a plaque plus a clot) in that artery. Timing of the infarction can be suggested but not proven. Since there are normal T waves, this suggests that the Q waves may be old, and the exact age indeterminate.
Pattern to Memorize: Q waves point away (–22.5° to –60°) from leads V1, V2, and V3.
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Case 3: Septal infarction with RBBB and LAHB

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Septal infarctions are sometimes complicated by conduction disturbances. The right and left bundle branches are located within the myocardial layer of the ventricular septum. When the septum is damaged, the bundle branches or parts of them may be damaged as well. Importantly, RBBB does not affect the initial part of the QRS. Examine the example (Figure 15.9a).
  1. The initial QRS shows significant Q waves in leads V1 through V4, indicating septal and anterior Q wave infarction.
  2. The last part of the QRS points anterior and rightward, indicating RBBB.
  3. The mean QRS in the frontal plane is upward (–90°), indicating LAHB.
  4. A single lesion in the LAD caused the infarction that resulted in all the above.
  5. This EKG is one of the most complicated in the entire book. Taking one's time, and going through it step by step in an organized fashion, can provide a very sophisticated cardiac diagnosis!
The most common conduction problems associated with septal infarctions are RBBB, LBBB, RBBB and LAHB, RBBB and LPHB, 2° AV block, and complete heart block. Except for isolated RBBB, the above conduction diseases may require a temporary ventricular pacemaker.
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Case 4: Septal infarction causing LBBB

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There is no reliable way to diagnose infarction or ischemia on the EKG in a patient with LBBB. The patient in Figure 15.10 may have had a septal infarction as the cause of the LBBB. There is just no useful way to figure that out from the EKG. LBBB is LBBB. It indicates likely significant underlying pathology, but creates a “fog of war” that prevents the use of the EKG to help diagnose its cause. The EKG below should not be read as septal infarction. It should not be read as transmural ischemia. It should be read as LBBB.
Less Specific Patterns of Infarction—Poor R wave progression: As in the inferior and lateral leads, leads V1, V2, and V3 can have an initial QRS that is intermediate between clearly abnormal and definitely normal. This borderline appearance is shown in Figure 15.11. There are several causes. Septal infarction can cause it, as can anything that decreases the ability of a sensor on the chest wall to record voltage. Some other clinical conditions that cause poor R wave progression are chronic lung disease, pericardial effusion, pneumothorax, and a large amount of breast tissue.
The Q wave equivalent—Inferior and lateral leads: Normal and abnormal Q waves were already discussed and illustrated in Figure 15.5. The QRS can still begin abnormally, even without the presence of a Q wave, as shown in Figure 15.12. Although the last QRS on the chart (Letter E) has no Q wave, the initial 0.04 seconds of the QRS is clearly negative. This is a Q wave equivalent and conveys the same information as a regular Q wave.
The Q wave equivalent—Posterior infarction: Figure 15.13 demonstrates a tall wide R wave in leads V1 and V2. The beginning of the QRS (as seen in leads AVF and V2) points away from the posterior wall. This is analogous to a Q wave for the posterior wall. Usually, as in this case, an inferior infarction is present on the EKG as well.
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