First Degree AV Heart Block

Atrioventricular (AV) Blocks

First degree AV heart block Rate= dependant on underlying rhythm Rhythm= regular P waves= uniform in appearance, positive in lead II, and one precedes each QRS complex PR interval= greater than 0.20 seconds QRS duration= 0.10 seconds or less, unless an intraventricular conduction delay exists

Second degree AV block, type I (Wenckebach) Rate= atrial rate is greater than the ventricular rate Rhythm= irregular P waves= uniform in appearance, positive in lead II, and one some P waves are not followed by a QRS complex (More P’s than QRS’s) PR interval= lengthens with each cycle until a P wave appears without a QRS complex; the PR interval after the nonconducted P wave is shorter than the interval preceding the nonconducted beat QRS duration= 0.10 seconds or less, unless an intraventricular conduction delay exists, is periodically dropped

Second degree AV block, type II Rate= atrial rate is greater than the ventricular rate; ventricular rate is often slow Rhythm= atrial regular, ventricular irregular P waves= uniform in appearance, positive in lead II, some P waves are not followed by a QRS complex (More P’s than QRS’s) PR interval= within normal limits or slightly prolonged but constant for the conducted beats QRS duration= 0.10 seconds or less, unless an intraventricular conduction delay exists, periodically absent after P waves

Third degree AV block, complete AV block Rate= atrial rate is greater than the ventricular rate Rhythm= atrial and ventricular rhythm are regular, there is no relationship between the atrial and ventricular rhythms P waves= uniform in appearance, positive in lead II PR interval= none, the atria and ventricles beat independently of each other; thus there is no true PR interval QRS duration= narrow or wide, depending on the location of the escape pacemaker and the condition of the intraventricular conduction system; narrow indicates junctional pacemaker; wide indicates ventricular pacemaker