Author + information
- J.Willis Hurst, MDa
The report by Matetzky et al. (1) stimulates the following thoughts. There are two ways to interpret electrocardiograms (ECGs). One is to memorize patterns and the other is to use basic principles of electrocardiography, including the use of vector concepts, as described by Grant (2–6).
The tracing in Figure 1A of the report by Matetzky et al. reveals a left atrial abnormality; a mean spatial QRS vector that is directed at about +20° in the frontal plane (it changes direction during inspiration and expiration) and about 45° posteriorly; a mean spatial ST segment vector that is directed at +115° in the frontal plane and at least 90° posteriorly, indicating epicardial injury of the posterior wall of the left ventricle; a mean spatial T-wave vector that is directed at +90° in the frontal plane and 80° to 90° anteriorly, indicating posterior myocardial ischemia; and a large U wave in lead I.
The point is, the ST segment vector points toward an area of posterior epicardial injury. Furthermore, one can suspect that the ST segment vector is directed toward an obstruction in the circumflex coronary artery or its branches. It should be no surprise that the ST segment is elevated in leads V7–9, because the transitional pathway was just beyond electrode position V6. The ST segment abnormality is not hidden.
The follow-up discharge tracing in Figure 1B is also interesting. The left atrial abnormality has disappeared; an S1, S2 and S3 conduction defect has developed; and the first half of the QRS complex is directed at about +40° in the frontal plane and markedly anterior, producing large abnormal R waves in leads V1 and V2. This abnormality is due to a true posterior infarction. Electrodes located anywhere on the front half of the chest would record large R waves, and electrodes located anywhere on the back half of the chest would record Q waves. The abnormal initial portion of the QRS is not hidden.
The ECG shown in Figure 2 also reveals an S1, S2 and S3 conduction defect and abnormal ST segment displacement. Some would argue that the ST segment displacement in the extremity leads is an artifact due to downsloping of the recording. If that is true, the mean ST segment vector points toward epicardial injury surrounding a true posterior infarction, which is usually caused by obstruction of the circumflex coronary artery, the distal right coronary artery, or their branches. If the ST segment displacement in the extremity leads is real, the mean ST segment vector is directed at 30° to 60° in the frontal plane and about 45° posteriorly, indicating epicardial injury of the left lateral and posterior portion of the left ventricle. This could be caused by obstruction in the obtuse marginal branch of the circumflex coronary artery or a diagonal branch of the left anterior descending coronary artery. The ST segment abnormality is not hidden.
None of the abnormalities are hidden, and true posterior infarction should be considered in both of the 12-lead tracings.
- American College of Cardiology
- Matetzky S.,
- Hod H.,
- Kaplinsky E.
- Grant R.P.
- Grant R.P.
- Hurst J.W.,
- Woodson G.C. Jr.
- Hurst J.W.
- Hurst JW. Examination of the electrocardiogram. In: Cardiac Puzzles. St. Louis: Mosby, 1995:33–87.