A 64-year-old man presents to the emergency room with a history of 2 hours of substernal chest discomfort that radiates to his lower jaw and left arm. The discomfort is associated with severe diaphoresis. Physical examination demonstrates a blood pressure of 150/90 mm Hg, bibasilar rales, and an S4. Initial cardiac biomarkers are normal. However, based on the clinical presentation and the initial ECG (ECG A) the patient undergoes an urgent cardiac catheterization and an intervention is performed. On the following day a second ECG is obtained (ECG B).
ECG A: There is a regular rhythm at a rate of 120 bpm. There is a P wave before each QRS complex (+) with a stable PR interval (0.20 sec). The P waves are positive in leads I, II, aVF, and V4–V6. Hence this is a sinus tachycardia. The QRS complex duration is normal (0.08 sec). There are beat to beat changes in the axis (ie, a normal axis between 0° and +90°, ^; positive QRS complex in leads I and aVF) alternating with an extreme leftward axis between −30° and −90° (▴; positive QRS complex in leads I and negative QRS complex in leads II and aVF). There are 2 causes for an extreme left axis (ie, an inferior wall myocardial infarction in which there is a deep initial Q wave in leads II and aVF or a left anterior fascicular block in which the QRS complex in leads II and aVF has an rS morphology). This extreme leftward axis is a left anterior fascicular block. There is J point and ST segment elevation in leads V2–V6 (↓), consistent with an extensive ST segment elevation myocardial infarction of the anterior wall. The QT/QTc intervals are normal (280/400 ms). Also noted are beat to beat changes in the amplitude of the QRS complexes in leads V5–V6 (→), which is QRS or electric alternans. QRS or electric alternans is seen in several conditions including an acute ST elevation myocardial infarction, any rapid supraventricular tachycardia, decompensated heart failure, and a severe cardiomyopathy. In these situations the cause is beat to beat changes in calcium fluxes. QRS alternans is also seen in a large pericardial effusion or tamponade and the cause is shifting of the heart in a fluid filled pericardial sac. The beat to beat change in axis is possibly a manifestation of the QRS alternans, although it may also reflect an intermittent left anterior fascicular block resulting from the acute myocardial infarction.
ECG B: The ECG obtained a day after the cardiac catheterization shows a regular rhythm at a rate of 64 bpm. There is a P wave before each QRS complex (+) with a stable PR interval (0.20 sec). The P wave is positive in leads I, II, aVF, and V4–V6, hence this is a normal sinus rhythm. The QRS complex duration is normal (0.08 sec), and there is an extreme left axis between −30° and −90° (positive QRS complex in lead I and negative QRS complex in leads II and aVF). This is a left anterior fascicular block which is now persistent. There is a QS complex in leads V1–V2 (↓), consistent with an anteroseptal myocardial infarction and T wave inversions in leads I, II, aVR (positive T wave in aVR is actually inverted), aVL, aVF, and V2–V6 (^). The T waves are symmetrically inverted, consistent with the recent ischemic event.
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- © 2013 American Heart Association, Inc.