Atrioventricular Block Differential Diagnoses

Updated: Jul 13, 2022
  • Author: Chirag M Sandesara, MD, FACC, FHRS; Chief Editor: Jose M Dizon, MD  more...
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Diagnostic Considerations

Mobitz I and Mobitz II atrioventricular (AV) block must be differentiated from sinus node dysfunction and increased vagal tone. AV block generally occurs with a constant PP interval. Blocked premature atrial beats must be differentiated from Mobitz II AV block. Blocked atrial beats will occur earlier than expected compared with the fixed PP interval in Mobitz II AV block. Atrial fibrillation with a slow heart rate may indicate second-degree AV block. If the ventricular rate is slow and regular during atrial fibrillation, third-degree AV block is likely present.

Important considerations in the differential diagnosis

AV dissociation due to sinus bradycardia with a junctional escape rhythm is not AV block. Severely prolonged first-degree AV block may appear to be a junctional rhythm. The P waves may be buried in the preceding QRS complex and suggest retrograde activation. However, in junctional rhythm, the retrograde P waves are inverted and they are upright in sinus rhythm with first-degree AV block. Variations in rate start with changes in timing of the PP interval rather than the RR interval.

The irregularity of the RR intervals in Mobitz I AV block may appear to be sinus rhythm with premature atrial complexes or multifocal atrial tachycardia. The presence of distinct, similar P waves and the grouped beating of the QRS complexes can help to distinguish Mobitz type I AV block from the aforementioned arrhythmias.

Differential Diagnoses