non-conducted p-waves dDx

Blocked Premature Atrial Complexes

• P waves are irregular in rhythm, and ectopic with a different P wave morphology from normal sinus P waves

• The non-conducted P wave comes early and there is a compensatory atrial pause before the next normal sinus beat

• Commonly misdiagnosed as Mobitz II

2^nd degree AV Block: Mobitz I (Wenckebach)

• P waves are regular (P-P interval is constant)

• Progressive PR interval lengthening prior to a non-conducted P wave

• Clumped or grouped beats, regularly irregular rhythm

• Commonly misdiagnosed as atrial fibrillation

2^nd degree AV Block: Mobitz II

• P waves are regular (P-P interval is constant)

• Constant PR interval that remains unchanged prior to a non-conducted P wave (e.g., 3:2 conduction, 4:3 conduction, etc.)

2^nd degree AV Block: 2:1 conduction

• P waves are regular (P-P interval is constant)

• Every other P wave is a non-conducted P wave (2:1 conduction)

• It is difficult to differentiate Mobitz I vs. Mobitz II when 2:1 AV block is present

  • With a standard ECG, there is limited opportunity to observe for the constant PR interval characteristic of Mobitz II

  • Consider a long rhythm strip or repeat ECGs

2^nd degree AV Block: Advanced AV Block or “High-grade AV Block”

• P waves are regular (P-P interval is constant)

• Two or more consecutive P waves are non-conducted (P: QRS ³ 3:1)

• In contrast to 3^rd degree (complete) heart block, some P waves continue to be conducted to the ventricle

3^rd degree AV Block (Complete Heart Block) + AV dissociation

• P-P intervals and QRS complex intervals are regular but occur independently of each other

• No apparent communication between atrium and ventricle

• PR-interval is randomly changing

3^rd degree AV Block (Complete Heart Block) + Isorhythmic AV dissociation

• CHB where atrial rate and ventricular rate are approximately the same