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First-Degree Heart Block (for Professionals) First-degree atrioventricular block (prolonged AV conduction)A prolonged PR interval (greater than 200 msec) is called first-degree AV block. The PR interval of the surface ECG can be subdivided into intra-atrial, AV nodal and His-Purkinje system conduction times. An increase in the PR interval can result from conduction delays in any of these areas. However, first-degree AV block most commonly results from prolonged AV nodal conduction time, particularly in the presence of a narrow QRS complex. Drugs such as digitalis, beta-blockers and calcium channel blockers, which prolong AV nodal conduction, can also produce first-degree AV block. Atropine and isoproterenol can shorten the PR interval by enhancing AV nodal conduction. Less commonly, first-degree AV block can result from delay distal to the AV node such as the His-Purkinje system. Treatment This content is reviewed regularly. Last updated 12/5/08. |
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