Although in most infarctions significant Q waves persist for the lifetime of the patient, this is not necessarily true with inferior infarcts. Within half a year, as many as 50% of these patients will lose their criteria for significant Q waves. The presence of small Q waves inferiorly may therefore suggest an old inferior infarction. Remember, however, that small inferior Q waves also may be seen in normal hearts. The clinical history of the patient must be your guide.
P.226 A fully evolved inferior infarction. Deep Q waves can be seen in leads II, III, and AVF. Lateral Infarction Lateral infarction may result from occlusion of the left circumflex artery. Changes may be seen in leads I, AVL, V5, and V6. Reciprocal changes may be seen in the inferior leads.
P.227 An acute lateral wall infarction. ST elevation can be seen in leads I, AVL, V 5 , and V 6 . Note also the deep Q waves in leads II, III, and AVF, signifying a previous inferior infarction. Did you notice the deep Q waves in leads V 3 through V 6 ? These are the result of another lateral infarction that occurred years ago. Anterior Infarcts Anterior infarction may result from occlusion of the LAD. Changes are seen in the precordial leads (V 1 through V 6 ). If the left main artery is occluded, an anterolateral infarction may result, with changes in the precordial leads and in leads I and AVL. Reciprocal changes are seen inferiorly. The loss of anterior electrical forces in anterior infarction is not always associated with Q wave formation. In some patients, there may be only a loss or diminishment of the normal pattern of precordial R wave progression. As you already know, under normal circumstances, the precordial leads show a progressive increase in the height of each successive R wave as one moves
P.228 from V 1 to V 5 . In normal hearts, the amplitude of the R waves should increase at least 1 mV per lead as you progress from V 1 to V 4 (and often V 5 ). This pattern may vanish with anterior infarction, and the result is called poor R wave progression. Even in the absence of significant Q waves, poor R wave progression may signify an anterior infarction. Poor R wave progression is not specific for the diagnosis of anterior infarction. It also can be seen with right ventricular hypertrophy, in patients with chronic lung disease, and—perhaps most often—with improper lead placement. An anterior infarction with poor R wave progression across the precordium. Posterior Infarction Posterior infarction typically results from an occlusion of the right coronary artery. Because none of the conventional leads overlie the posterior wall, the diagnosis requires finding reciprocal changes in the anterior leads. In other words, because we can't look for ST segment elevation and Q waves in nonexistent posterior leads, we have to look for ST segment depression and tall R waves in the anterior leads, notably lead V 1 . Posterior infarctions are the mirror images of anterior infarctions on the EKG.
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- Summer '16
- Electrical conduction system of the heart, QRS complex, Electrocardiography, WAV