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Second Degree AV Block - High grade - ECG

High grade 2nd degree AV block

I aVR V1 V4 II aVL V2 V5 III aVF V3 V6
12-lead ECG
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Smartwatch ECG

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Atrioventricular (AV) Node

SA node, AV node depolarisation vectors
  • During sinus rhythm, impulses are generated regularly (about 60/min) in the SA node
    • Each impulse spreads through the atria (P wave) to the AV node
  • In the AV node, the impulse slows down by about 0.1s
    • During this time, the atria pump blood into the ventricles
    • Then the impulse continues to the ventricles (QRS complex)

PQ Interval

AV junction delay, P wave, PR segment, PR interval, Q wave, R wave
  1. Impulse originates in the SA node
    • When it passes to the atrial myocardium, it begins to generate the P wave
    • Simultaneously, it spreads through the conduction system to the AV node
      • The impulse in the conduction system does not create a curve
  2. The impulse enters the AV node
    • The impulse spreads from the SA node
    • At the time of atrial activation (peak of the P wave)
      • It arrives through the conduction system to the AV node
  3. Slowed (decremental) conduction in the AV node
    • The impulse is delayed in the AV node for approx. 0.1s (no curve is created)
    • Then it passes into the His bundle (no curve is created)
  4. Activation of the ventricular septum
    • From the His bundle, the impulse travels through the Purkinje fibers
      • Begins to activate the myocardium of the ventricular septum
      • Begins to generate the Q wave

AV Block II Degree (Mobitz I, Mobitz II)

  • Woldemar Mobitz
    • He was a Russian physician who worked as a cardiologist in Germany
    • In 1924, he described AV block II degree on the ECG and divided it into 2 types (Mobitz I, II)

  • Mobitz I (Wenckebach)
    • Often referred to as Wenckebach
    • Because in the AV node there is the Wenckebach phenomenon
  • Mobitz II (Hay)
    • John Hay was an English physician who described this AV block II degree based on pulses (without ECG) in 1906
    • Later, it was described in more detail by Mobitz and is more commonly referred to as Mobitz II, rarely as Hay


AV junction conduction delay - 2nd AV block, Mobitz I
ECG 2nd AV block, Mobitz 1, narrow QRS

AV Block II Degree - Mobitz I (Wenckebach)



AV Mobitz 2, intermittent bundle of His block
ECG 2nd degree AV block, Mobitz 2, narrow QRS

AV Block II Degree, Mobitz II (QRS<0.12s)

  • The defect is infranodal (below the AV node)
    • The His bundle intermittently blocks impulses (P waves)
  • The PQ interval is constant (Wenckebach phenomenon is not present)
  • Mobitz II is an intermittent block in the AV junction (without lengthening of the PQ interval)
  • QRS complexes are narrow (<0.12s)
    • 25% of Mobitz II AV blocks have narrow QRS complexes
    • Because the intermittent block is in the His bundle
  • Conduction to the ventricles is (4:3)


2nd degree AV block, bundle branch block, Mobitz II
ECG second AV block, Mobitz 2, broad QRS complex

AV Block II Degree, Mobitz II (QRS>0.12s)


High-Degree AV Block

  • Sinus rhythm has a conduction to the ventricles of 1:1 (P:QRS)
  • In second-degree AV block, some P waves are blocked (in the AV junction), so conduction to the ventricles is not 1:1
  • Second-degree AV block most commonly has conduction to the ventricles: 3:2, 4:3, 5:4
  • Second-degree AV block with conduction to the ventricles (2:1) - can be either Mobitz I or Mobitz II
  • If conduction to the ventricles is 3:1 or higher
    • it is referred to as a high-degree AV block

  • High-degree AV block is almost always of the Mobitz II type
    • Hisian has narrow QRS complexes
    • Infrahisian has wide QRS complexes

ECG and High-Degree AV Block

ECG, laddergram, 2nd degree, high-grade AV block

High-Degree AV Block



ECG, laddergram 3rd, complete av block

Third-Degree AV Block (Complete AV Block)

  • In a third-degree AV block, the AV junction is disrupted
    • The atria and ventricles are electrically isolated from each other
  • PP interval is regular (the SA node generates impulses regularly - P waves)
  • PQ interval changes
    • The SA node generates impulses regularly (P waves)
    • An activated ventricular focus generates impulses independently of the SA node (wide QRS complexes)
    • Independence of the atria (P waves) and ventricles (QRS) is AV dissociation


ECG av block, fixed ratio 2:1

Second-Degree AV Block with 2:1 Conduction



2nd degree, high-grade AV block
Second degree AV block - Mobitz II, high grade, 3:1

High-Grade AV Block (3:1)



High-grade AV block
2nd AV block - Mobitz II, high degree, 4:1

High-Grade AV Block



3rd AV block, junctional escape rhythm
ECG 3rd degree, complete av block, av dissociation

Third-Degree AV Block (Complete AV Block)

  • PP interval is constant
  • PQ interval varies
    • The SA node generates impulses regularly (P waves)
    • A secondary pacemaker has activated in the AV junction
  • Third-Degree AV Block
    • Conduction through the AV junction is interrupted
    • The atria (P waves) and ventricles (QRS) are independent of each other (AV dissociation)


2nd AV block, Mobitz 2, RBBB
ecg ecg infra hisian block, 2nd degree av block, mobitz II

High-Grade AV Block (5:1)




Sources

  • ECG from Basics to Essentials Step by Step
  • litfl.com
  • ecgwaves.com
  • metealpaslan.com
  • medmastery.com
  • uptodate.com
  • ecgpedia.org
  • wikipedia.org
  • Strong Medicine
  • Understanding Pacemakers





Home /

Second Degree AV Block - High grade - ECG

High grade 2nd degree AV block

I aVR V1 V4 II aVL V2 V5 III aVF V3 V6
12-lead ECG
OR
Smartwatch ECG

Have a doctor’s or smartwatch ECG?

Upload your 12-lead, smartwatch or smart device ECG.
Get a physician’s report within 24 hours.

Get my ECG reviewed →

Reviewed by a physician · Your questions answered · Not AI

Atrioventricular (AV) Node

  • During sinus rhythm, impulses are generated regularly (about 60/min) in the SA node
    • Each impulse spreads through the atria (P wave) to the AV node
  • In the AV node, the impulse slows down by about 0.1s
    • During this time, the atria pump blood into the ventricles
    • Then the impulse continues to the ventricles (QRS complex)
SA node, AV node depolarisation vectors

PQ Interval

  1. Impulse originates in the SA node
    • When it passes to the atrial myocardium, it begins to generate the P wave
    • Simultaneously, it spreads through the conduction system to the AV node
      • The impulse in the conduction system does not create a curve
  2. The impulse enters the AV node
    • The impulse spreads from the SA node
    • At the time of atrial activation (peak of the P wave)
      • It arrives through the conduction system to the AV node
  3. Slowed (decremental) conduction in the AV node
    • The impulse is delayed in the AV node for approx. 0.1s (no curve is created)
    • Then it passes into the His bundle (no curve is created)
  4. Activation of the ventricular septum
    • From the His bundle, the impulse travels through the Purkinje fibers
      • Begins to activate the myocardium of the ventricular septum
      • Begins to generate the Q wave
 AV junction delay, P wave, PR segment, PR interval, Q wave, R wave

AV Block II Degree (Mobitz I, Mobitz II)

  • Woldemar Mobitz
    • He was a Russian physician who worked as a cardiologist in Germany
    • In 1924, he described AV block II degree on the ECG and divided it into 2 types (Mobitz I, II)

  • Mobitz I (Wenckebach)
    • Often referred to as Wenckebach
    • Because in the AV node there is the Wenckebach phenomenon
  • Mobitz II (Hay)
    • John Hay was an English physician who described this AV block II degree based on pulses (without ECG) in 1906
    • Later, it was described in more detail by Mobitz and is more commonly referred to as Mobitz II, rarely as Hay


ECG 2nd AV block, Mobitz 1, narrow QRS

AV Block II Degree - Mobitz I (Wenckebach)

  • The defect is in the AV node
    • Conduction in the AV node through the AV node gradually lengthens (Wenckebach phenomenon)
  • Mobitz I has the Wenckebach phenomenon:
    • The PQ interval gradually lengthens
    • until the 5th P wave is blocked, then the cycle repeats
  • QRS complexes are narrow (<0.12s)
  • Conduction to the ventricles is (5:4), from 5 P waves, 4 QRS complexes are produced
 AV junction conduction delay - 2nd AV block, Mobitz I


ECG 2nd degree AV block, Mobitz 2, narrow QRS

AV Block II Degree, Mobitz II (QRS<0.12s)

  • The defect is infranodal (below the AV node)
    • The His bundle intermittently blocks impulses (P waves)
  • The PQ interval is constant (Wenckebach phenomenon is not present)
  • Mobitz II is an intermittent block in the AV junction (without lengthening of the PQ interval)
  • QRS complexes are narrow (<0.12s)
    • 25% of Mobitz II AV blocks have narrow QRS complexes
    • Because the intermittent block is in the His bundle
  • Conduction to the ventricles is (4:3)
 AV Mobitz 2, intermittent bundle of His block


ECG second AV block, Mobitz 2, broad QRS complex

AV Block II Degree, Mobitz II (QRS>0.12s)

  • The defect is infrahisian (below the His bundle)
    • The bundle branch or fascicle intermittently blocks impulses (P waves)
  • There is a pre-existing bundle branch block (LBBB, RBBB)
  • QRS complexes are wide (>0.12s)
    • 75% of Mobitz II AV blocks have wide QRS complexes
    • because of a pre-existing bundle branch (fascicular) block
  • The PQ interval is constant (Wenckebach phenomenon is not present)
  • Mobitz II is an intermittent block in the AV junction (without lengthening of the PQ interval)
  • Conduction to the ventricles is (3:2)
 2nd degree AV block, bundle branch block, Mobitz II

High-Degree AV Block

  • Sinus rhythm has a conduction to the ventricles of 1:1 (P:QRS)
  • In second-degree AV block, some P waves are blocked (in the AV junction), so conduction to the ventricles is not 1:1
  • Second-degree AV block most commonly has conduction to the ventricles: 3:2, 4:3, 5:4
  • Second-degree AV block with conduction to the ventricles (2:1) - can be either Mobitz I or Mobitz II
  • If conduction to the ventricles is 3:1 or higher
    • it is referred to as a high-degree AV block

  • High-degree AV block is almost always of the Mobitz II type
    • Hisian has narrow QRS complexes
    • Infrahisian has wide QRS complexes

ECG and High-Degree AV Block

ECG, laddergram, 2nd degree, high-grade AV block

High-Degree AV Block



ECG, laddergram 3rd, complete av block

Third-Degree AV Block (Complete AV Block)

  • In a third-degree AV block, the AV junction is disrupted
    • The atria and ventricles are electrically isolated from each other
  • PP interval is regular (the SA node generates impulses regularly - P waves)
  • PQ interval changes
    • The SA node generates impulses regularly (P waves)
    • An activated ventricular focus generates impulses independently of the SA node (wide QRS complexes)
    • Independence of the atria (P waves) and ventricles (QRS) is AV dissociation


ECG av block, fixed ratio 2:1

Second-Degree AV Block with 2:1 Conduction



Second degree AV block - Mobitz II, high grade, 3:1

High-Grade AV Block (3:1)

 2nd degree, high-grade AV block

2nd AV block - Mobitz II, high degree, 4:1

High-Grade AV Block

  • PP interval is constant
  • PQ interval is constant at 0.2s
  • Conduction to the ventricles is 4:1
    • This indicates a High-Grade AV Block
  • This is a Hisian second-degree AV block - Mobitz II
 High-grade AV block


ECG 3rd degree, complete av block, av dissociation

Third-Degree AV Block (Complete AV Block)

  • PP interval is constant
  • PQ interval varies
    • The SA node generates impulses regularly (P waves)
    • A secondary pacemaker has activated in the AV junction
  • Third-Degree AV Block
    • Conduction through the AV junction is interrupted
    • The atria (P waves) and ventricles (QRS) are independent of each other (AV dissociation)
 3rd AV block, junctional escape rhythm


ecg ecg infra hisian block, 2nd degree av block, mobitz II

High-Grade AV Block (5:1)

  • PP interval is constant
  • PQ interval is constant 0.2s
  • Conduction to the ventricles is 5:1
    • Out of five P waves, one is conducted to the ventricles (blue arrow)
    • This is a High-Grade AV Block
  • This is a Infra-Hisian AV Block II Degree - Mobitz II
    • QRS complexes are wide (>0.12s)
    • And have the shape of RBBB — note the V1 lead
 2nd AV block, Mobitz 2, RBBB



Sources

  • ECG from Basics to Essentials Step by Step
  • litfl.com
  • ecgwaves.com
  • metealpaslan.com
  • medmastery.com
  • uptodate.com
  • ecgpedia.org
  • wikipedia.org
  • Strong Medicine
  • Understanding Pacemakers