Lead Thirteen Electrocardiography

Abstract

To the Editor.— In a LETTER TO THE EDITOR (224:1533, 1973) entitled " `Lead Thirteen' Electrocardiography," Dr. Sanford Lewis makes a plea for the routine recording of lead III during deep inspiration to differentiate between abnormal Q waves indicating diaphragmatic infarction and benign Q waves. Q waves persisting during inspiration are regarded as due to diaphragmatic infarction. We disagree with this recommendation. In our experience this maneuver has not been helpful in distinguishing abnormal Q waves due to diaphragmatic myocardial infarction from benign Q waves. A Q wave is considered abnormal if it is 0.04 seconds or more in duration and at least 25% of the QRS voltage (amplitude) It is true that in many individuals a Q wave in lead III may disappear or become insignificant on deep inspiration. This, however, does not always establish the benign nature of the Q wave, since a marked number of patients with well-established