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Can It Wait until after X-Mas?
By Ken Grauer, MD, Professor, Department of Community Health and Family Medicine, University of Florida. Dr. Grauer reports that he is the sole proprietor of KG-EKG Press,and publisher of an ECG pocket brain book.
|Figure. 12-lead ECG and lead II rhythm strip obtained from an older woman with weakness. Can treatment of this rhythm wait?|
Clinical Scenario: The ECG in the Figure was obtained from an older woman who was seen in the Emergency Department with a chief complaint of weakness of several days duration. No chest pain. As it was "the season", she asked her physician, "Can it wait until after Christmas?" How would you respond?
Interpretation/Answer: Attention to the lead II rhythm strip at the bottom of this tracing shows an underlying sinus arrhythmia. Only every other P wave is conducted. That this rhythm is not 3° (complete) AV block is evident from the constant PR interval preceding each QRS complex. Thus, the rhythm is 2° AV block with 2:1 AV conduction.
There are three types of 2° AV block. Mobitz I (AV Wenckebach) is by far the most common form. This form of 2° AV block is often transient. It occurs at a higher level in the conduction system (usually at or around the AV node), and as a result the QRS complex most often is narrow. Because the right coronary artery is most often responsible for vascularizing the AV node, Mobitz I is usually seen in association with acute inferior myocardial infarction. Atropine may be helpful in improving AV conduction.
Mobitz II is a much more severe form of AV block than Mobitz I. This conduction defect usually occurs in association with acute anterior infarction, and generally occurs at a lower level in the conduction system. As a result, the QRS complex tends to be wide. The importance of recognizing this much less common form of 2° AV block is that a pacemaker will almost always be needed if the patient has Mobitz II.
The third form of 2° AV block is 2:1 AV conduction. Because you never see two beats conducted in a row, it is impossible to tell if the PR interval is increasing until the beat is dropped (as it would with Mobitz I) — or not increasing (as occurs with Mobitz II). This is the case for the rhythm seen here. However, the fact that the QRS complex in the Figure is clearly widened strongly suggests that the conduction defect is Mobitz II. Thus, this patient should not try to wait until after Christmas — but rather requires immediate evaluation to determine if a cardiac pacemaker is needed.