Robin Naples1, Alvin Wang2, and William J. Brady3 1 Thomas Jefferson University, Philadelphia, PA, USA 2 Division of EMS, Jefferson Health System, Philadelphia, PA, USA 3 Departments of Emergency Medicine and Medicine, University of Virginia School of Medicine, Charlottesville, VA, USA Cardiac rhythm monitoring and interpretation has evolved from single‐lead rhythm strips to advanced multilead ECGs, which can now be rapidly performed, interpreted, and digitally transmitted to specialists and transfer centers. Accurate interpretation of the ECG enables medical providers to rapidly diagnose and treat cardiac arrhythmias, myocardial ischemia, and infarction and an array of metabolic emergencies. Adjuncts to the standard 12‐lead ECG may further aid the clinician during the care of the patient, including additional ECG leads and serial electrocardiography. Two anatomic regions of the heart, the posterior wall of the left ventricle and the entire right ventricle, are less well imaged by the standard 12‐lead ECG (Table 19.1). Both of these anatomic regions of the heart are susceptible to infarction. The clinician should consider evaluating these regions in selected situations, including high clinical suspicion for acute myocardial infarction (AMI) with a non‐diagnostic 12‐lead ECG and certain ST segment depression patterns (Box 19.1). Posterior leads are particularly useful in the diagnosis of posterior wall myocardial infarction; the posterior ECG leads consist of leads V7–V9. Lead V8 is placed on the patient’s back at the lower pole of the left scapula and lead V9 is placed half‐way between lead V8 and the left paraspinal muscles. Lead V7 is placed on the posterior axillary line (Figure 19.1). In most instances, leads V8 and V9 are used and are adequate; lead V7 is less commonly employed. ECG lead findings suggestive of acute posterior infarction include ST segment elevation in leads V7, V8, and/or V9 (Figure 19.2). The degree of elevation can be minimal because of the relative distance from the surface electrode to the infracting myocardium. ECG findings other than ST segment elevation in these additional leads have not been defined. Indirect signs of posterior wall infarction can be present on the standard 12‐lead ECG (Figure 19.3). Leads V1–V4 indirectly image the posterior LV from an anterior perspective; thus, the clinician must consider the ECG findings in a “reciprocal manner.” In other words, when leads V1–V4 show ST segment depression that is flat or horizontal in configuration and accompanied by a positive QRS complex (i.e. R wave) and upright T wave on a standard 12‐lead ECG, the reciprocal perspective from the posterior wall is ST segment elevation with a Q wave and T wave inversion. If one considers all patients suspected of acute coronary syndrome (ACS) who have ST segment depression in leads V1–V4 distribution, approximately 50% of these individuals will be diagnosed with posterior wall ST segment elevation myocardial infarction (STEMI) and the rest with anterior wall ischemia. The most appropriate indication for obtaining posterior leads is ST segment depression in leads V1, V2, and/or V3 in a patient who is suspected of experiencing an ACS event. Patients with ST segment depression in leads V1–V3 resulting from bundle branch block or other instances of abnormal intraventricular conduction are not included in this indication. Posterior wall infarction is not infrequently associated with inferior and/or lateral wall STEMI, which will present with typical ST segment elevation in these regions. Posterior leads may be helpful in this instance to define the full extent of myocardial involvement. Table 19.1 ECG leads, anatomic segment, and coronary anatomy.
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Electrocardiographic Tools in Clinical Care
Additional Electrocardiographic Leads
Posterior Electrocardiographic Leads – Posterior Wall (of the Left Ventricle) Electrocardiographic Imaging
Primary chamber
Cardiac segment
ECG leads
Coronary artery
Left ventricle
Posterior wall
V1–V4 indirectly
V8 and V9 directly
Posterior descending branch (RCA) or left circumflex artery
Right ventricle
Right ventricle
RV4 (RV1–RV4)
Right ventricular branch (RCA)
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