Use of Indicative and Reciprocal Electrocardiographic Changes to Help Localize the Site of Coronary Occlusion

A61-year-old man came to the emergency department complaining of chest pain, and an electrocardiogram was recorded (Figure ​(Figure11). Acute inferior myocardial infarction is indicated by ST-segment elevation and broad upright T waves in leads II, III, and aVF. These changes are mirrored perfectly by reciprocal ST depression and T-wave inversion in leads I and aVL. Both indicative and reciprocal changes are striking in this electrocardiogram, but at times, reciprocal or mirrorimage changes are more easily recognized than indicative changes and are the clue to the correct diagnosis (1). Reciprocity works both ways, and reciprocal ST depression may be seen in the inferior leads in high lateral myocardial infarction when ST elevation occurs in leads I and aVL. Figure 1 The electrocardiogram recorded when the patient arrived in the emergency department The standard 12-lead electrocardiogram does not record from the back of the chest or the right side of the chest, and as a consequence, important information may go undetected (2, 3). The anterior chest leads (V1 through V3), however, are the reciprocals of leads on the back of the chest. Thus, early in posterior myocardial infarction when ST elevation and broad upright T waves would be recorded on the back of the chest, ST depression and T-wave inversion can be recorded in the anterior precordial leads (4). Such a reciprocal change is seen in lead V2 of this electrocardiogram. Why is there no ST depression or T inversion in lead V1? In fact, there is ST elevation with an upright T in V1 because right ventricular infarction coexists. Its anteriorly directed current of injury obscures the changes of posterior infarction. This patient's right ventricle lies more squarely beneath lead V1 than V2, and the reverse is true for the posterior wall of the left ventricle. In the presence of changes of acute inferior myocardial infarction, ST elevation in V1 with depression in V2 is a quite specific (virtually pathognomonic), but rather insensitive, marker of right ventricular as well as posterior infarction (5). Other electrocardiographic signs of right ventricular infarction in patients with acute inferior infarction are ST elevation in lead III exceeding that in lead II (6) and a ratio of ST depression in V2 to ST elevation in aVF of ≲50% (7). The best electrocardiographic guide to right ventricular infarction is an electrocardiogram with right precordial leads (Figure ​(Figure22). The electrocardiogram recorded at 12:34, after initiation of thrombolytic therapy, shows ST elevation in right precordial leads V3Rthrough V6R, indicating right ventricular infarction, and further evolution of the changes of inferior myocardial infarction in leads II, III, and aVF. Persistent ST depression is seen in V1R (left-sided V2), and T waves are upright. These reciprocal changes of ST elevation and T inversion on the back of the chest indicate further evolution of posterior infarction. Figure 2 The electrocardiogram recorded 2 hours later during thrombolytic therapy. The precordial leads were recorded on the right side of the chest. Small portions of the right ventricle may receive blood supply from the left anterior descending and/or left circumflex coronary arteries, but most right ventricular blood supply is from the right coronary artery. Consequently, all clinically significant right ventricular infarcts are due to occlusion of the right coronary artery, usually in its proximal portion. Such is the case in this patient, whose right coronary arteriogram, performed a week later, reveals severe narrowing proximal to any right ventricular branch except the conus branch (Figure ​(Figure33). The right coronary artery also gives rise to the posterior descending artery and left ventricular branches, accounting for the inferior and posterior distributions, respectively, of this patient's infarction. Figure 3 Right coronary cinearteriograms recorded a week later in the cranial (a) left anterior and (b) right anterior oblique projections. In each, the culprit lesion is seen as an irregular, hazy narrowing (arrow) just proximal to the first of 3 right ventricular ...