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Interatrial Block

Interatrial conduction delay (IACD), Interatrial block

Interatrial Block

• Occurs due to an interruption in Bachmann's Bundle
• The left atrium is activated with a delay
• Occurs in 88% of cases with left atrial hypertrophy (P mitrale)
• It is common in men over 60 years old
• Isolated interatrial block occurs with
• atrial fibrosis
• after an atrial infarction
• It is a risk factor for the development of
• Atrial fibrillation
• Atrial flutter
• Sick sinus syndrome

Types of Interatrial Block

Normal P Wave

Partial Block

Complete Block

• Partial Interatrial Block (Type 1)
• The most common type
• Conduction through the Bachmann's bundle is prolonged (not interrupted)
• The P wave is broad > 0.12s (notched in the middle)
  
  
• Alternating Type (Type 2)
• Intermittently alternates between Type 1 and Type 3
  
  
• Complete Interatrial Block (Type 3)
• Bachmann's bundle is interrupted
• The left atrium is activated retrogradely from the AV node area
• The P wave is broad (> 0.12s) and biphasic
• The vector of the right atrium (1) points down
• Then the vector of the left atrium (2) points up

Interatrial Block

• This is an ECG recording from a previous patient
• ECG voltage is set to 20mm
• The amplitude of the ECG waveform is thus 2x higher
• P waves (V3-V4) are broad > 0.12s and have a low amplitude (red arrows)
• This indicates a partial interatrial block (type 1)
• which was unmasked by the change in ECG calibration

Interatrial Block and STEMI

• Acute Inferior Wall STEMI
• ST elevations (II, III, aVF)
• Interatrial Block (type 1)
• Low and broad P wave > 0.12s (red arrows) (indicated notch)

Interatrial Block and Pacemaker

• The patient has an implanted pacemaker
• Atrial pacing at a rate of 60/min (red arrows)
• Following the pacing artifacts, there is a wide P wave (more difficult to evaluate)
• Low and wide P wave > 0.12 (lead II) - (green arrows)
• This indicates an interatrial block (type 1)
• The P wave would be better evaluated with a 20mm calibration