Figure 15-1. Electrocardiogram. (Reproduced, with permission, from Stead LG. Stead SM. Kaufman MS. First aid for the medicine clerkship, 2nd ed. New York: McGraw-Hill, 2006:46.)

ANSWERS TO CASE 15: Syncope-Heart Block

Summary: An older man presents with a witnessed syncopal episode, which was brief and not associated with seizure activity. He has experienced decreasing exercise tolerance recently because of weakness and presyncopal symptoms. He is bradycardia with third-degree atrioventricular (AV) block on ECG. Arrows in Figure 15-1 point to P waves.

♦ Most likely diagnosis: Syncope as a consequence of third-degree AV block.

^ Next step: Placement of temporary transcutaneous or transvenous pacemaker and evaluation for placement of a permanent pacemaker.



1. Know the major causes of syncope and important historical clues to the diagnosis.

2. Understand the basic evaluation of syncope based on the history.

3. Recognize vasovagal syncope and carotid sinus hypersensitivity.

4. Be able to diagnose and know the management of first-, second-, and third-degree AV block.


There are two major considerations to the management of this patient: the cause and the management of his AV block. He should be evaluated for myocardial infarction and structural cardiac abnormalities. If this evaluation is negative, he may simply have conduction system disease as a consequence of aging. Regarding temporary management, atropine or isoproterenol can be used when the conduction block is at the level of the AV node, but in this case, the heart rate is less than 40 bpm, and the QRS borderline is widened, suggesting the defect is below the AV node, in the bundles of His. A pacemaker likely is required.

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