Which Is the Key Lead?
By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
The patient whose ECG appears in the figure is a middle-aged man who presented to the emergency department (ED)with new chest pain. Should the cath lab be activated?
Interpretation: Today’s ECG is challenging to interpret. The rhythm is sinus, with a normal axis and normal intervals (PR-QRS-QTc). There is no chamber enlargement.
• There are no Q waves (i.e., there is a definite positive initial component to the QRS complex in lead III). Although transition is slightly delayed, there is no loss of anterior forces (i.e., there are relatively tall R waves in leads V2,V3,V4).
The key lead for concern is lead V3.
• A slight amount of ST segment elevation is normally seen in anterior leads V2 and V3. The shape of this common and benign ST segment elevation in these leads is characteristic in that it is gently upsloping with smooth transition from the end of the ST segment to the upright T wave.
• This is not what we see in today’s tracing. The ST segment in lead V3 is more elevated than should be seen normally. In addition, the ST segment “takeoff” is straighter than it should be. Contrast this ST segment shape in lead V3 with the normal, gentle upsloping ST segment seen in lead V5.
• To emphasize: The fact that today’s patient presented to the ED with new chest pain immediately places him in a higher-risk group for having an acute infarction. As a result, any deviation from normal ST segment morphology is indication for a high index of suspicion for an acute event until proven otherwise.
Key Point: The clinical course of an acute evolving infarction is often “dynamic” and subject to changing ST-T wave morphology that sometimes evolves over the course of minutes rather than hours. As a result, in a patient such as the one presented here, serial ECGs should be repeated often, until such time that a definite determination can be made that an acute event is (or is not) in progress. In this patient with ongoing chest pain, this initial ECG should be repeated within 10 to 20 minutes, looking for evidence of actively evolving ST-T wave changes.
Summary: Despite the fact that there is no loss of anterior R wave forces and that ST-T wave changes in other leads on today’s tracing are nonspecific, the worrisome history of today’s patient and the clearly abnormal ST-T wave appearance in lead V3 indicates the need to consider an acute ongoing event until proven otherwise. Subsequent tracings confirmed there was acute occlusion of the left anterior descending coronary artery.
Note: For additional information about this case, please see: https://tinyurl.com/KG-Blog-418
The patient whose ECG appears in the figure is a middle-aged man who presented to the emergency department with new chest pain. Should the cath lab be activated?
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