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Atrioventricular block.

Atrioventricular block.
Atrioventricular block.

For 1st-degree block, conduction is slowed without skipped beats. All normal P waves are followed by QRS complexes, but the PR interval is longer than normal ( > 0.2 sec). For 3rd-degree block, there is no relationship between P waves and QRS complexes, and the P wave rate is greater than the QRS rate.