Heart Block’s

First degree AV block rate

Dependent on underlying rhythm

First degree AV block rhythm

Dependent on underlying rhythm

First degree AV block P-wave

Upright and uniform

First degree AV block PRI

Prolonged, > 0.20 seconds

First degree AV block QRS

< 0.12 seconds

First degree AV block etiology

May occur for no apparent reason, sometimes associated with myocardial ischemia or infarction, increased vagal tone, digitalis toxicity

How should a first degree AV block be considered?

More as a characteristic of a rhythm, not a rhythm itself

Example of a first degree AV block description

Sinus Bradycardia with a First Degree AV Block

Second degree type I (Wenckebach) rate

Normal to slow

Second degree type I (Wenckebach) rhythm

Irregular

Second degree type I (Wenckebach) P-wave

Upright and uniform, may have more than one for each QRS

Second degree type I (Wenckebach) PRI

Progressively lengthens before dropping a beat

Second degree type I (Wenckebach) QRS

< 0.12 seconds

Second degree type I (Wenckebach) etiology

Often occurs in acute MI or myocarditis, increased vagal tone, ischemia, drug toxicity, head injury, electrolyte imbalance

Second degree type II rate

Often bradycardic

Second degree type II rhythm

Regular or irregular

Second degree type II P-wave

Upright and uniform, more P-waves than QRS complexes

Second degree type II PRI

Constant for conducted beats

Second degree type II QRS

Normal or wide

Second degree type II etiology

May be associated with septal wall MI, normally does not result from increased parasympathetic tone or drug toxicity

Third degree (complete heart block) rate

Bradycardic

Third degree (complete heart block) rhythm

Regular

Third degree (complete heart block) P-wave

Upright and uniform, more P-waves than QRS complexes

Third degree (complete heart block) PRI

No correlation with QRS, completely chaotic

Third degree (complete heart block) QRS

Normal or wide

Third degree (complete heart block) etiology

Inferior wall MI, drugs that block AV node conduction, chronic degeneration of conduction system, electrolyte imbalance