Today's basic rhythm strip illustrates second-degree AV block, Type II. Even though there is fine baseline artifact present, it is easy to measure the P-to-P interval, and your students will be able to see that every third P wave falls in the T wave. The PR intervals are constant and the atrial rate is about 110/min. The ventricular rate results from a 3:1 conduction ratio, and is less than 30/min. For your students who have learned about bundle branch block, this strip shows a right bundle branch block, which is very common in second-degree Type II blocks, as they usually represent "intermittent tri-fascicular block" - that is, two of the three fascicles in the bundle branches are blocked, and one is intermittently blocked. Other combinations of complete block and intermittent block are possible, resulting in intermittent failure of conduction. This strip can start a lively classroom discussion about treatment of bradycardias. See comments below for discussion of terminology, second-degree AVB and high-grade AVB. This strip can be used as a good example of high-grade AVB.
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