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Second Degree SA Block - Type I (Wenckebach)

2nd degree Sinoatrial (SA) block, type I (Wenckebach)

SA Node (P and T Cells)

SA node, P and T cells, second SA block, type I, Wenckebach
  • The SA node consists of 2 types of cells
  • P cells (Pacemaker cells)
    • Generate impulses in the SA node, and determine the heart rate
  • T cells (Transitional cells)
    • Transmit impulses from the P cells to the atria and the internodal pathways
    • If the impulse does not pass through the T cells, a P wave does not occur

Wenckebach Phenomenon


SA Block II Degree - Type I (Wenckebach)

  • The SA node generates impulses regularly
    • P cells are intact
  • Upon impulse exit from the SA node (in T cells), the Wenckebach phenomenon occurs
    • Impulse conduction at the exit from the SA node progressively lengthens
    • until the impulse is blocked, and the cycle repeats

ECG and SA Block II Degree - Type I (Wenckebach)


ECG 2nd degree SA block, exit block, Wenckebach

SA Block II Degree - Type I (Wenckebach)



Laddergram normal sinus rhythm, pp interval

Sinus Rhythm

  • Laddergram illustrates the propagation of impulses through the conduction system
    • S - P cells (SA node), S-A - T cells (Sinoatrial junction), A - atrium
  • In sinus rhythm, the SA node (P cells) generates impulses regularly (green dots)
  • Each impulse quickly reaches the T cells (S-A), where conduction slows down
  • Then, the impulse from the T cells (S-A) moves to the atrium (A - start of the P wave)
  • PP interval is consistent on the ECG


ECG and Laddergram 2nd degree sinoatrial (SA) block, Wenckebach

SA Block II. Degree - Type I (Wenckebach)



SA node and Sinoatrial first degree block
ECG sinus rhythm vs. 1st sinoatrial SA block

Sinus Rhythm



SA node 2nd degree SA block, Type I
ECG second degree sa block, type I, wenckebach

SA Block II. Degree, Type I (Wenckebach)



Sinoatrial exit block
ECG 2nd degree SA block, type II, PP interval

SA Block II. Degree - Type II

  • PP interval is constant (970ms)
  • PP interval with a dropped P wave (1940ms) is equal
    • to twice the PP interval without a pause (2 x 970 = 1940)
  • PQ interval is constant
  • SA Block II. Degree - Type II
    • SA node generates impulses regularly
    • Impulse conduction from the SA node does not prolong
    • Impulses from the SA node intermittently block (PP pause)


SA node 2nd degree Wenckebach
ECG and Laddergram, 2nd degree sinoatrial block, wenckebach

SA Block II. Degree, Type I (Wenckebach)




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





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Second Degree SA Block - Type I (Wenckebach)

2nd degree Sinoatrial (SA) block, type I (Wenckebach)

SA Node (P and T Cells)

  • The SA node consists of 2 types of cells
  • P cells (Pacemaker cells)
    • Generate impulses in the SA node, and determine the heart rate
  • T cells (Transitional cells)
    • Transmit impulses from the P cells to the atria and the internodal pathways
    • If the impulse does not pass through the T cells, a P wave does not occur

SA node, P and T cells, second SA block, type I, Wenckebach

Wenckebach Phenomenon


SA Block II Degree - Type I (Wenckebach)

  • The SA node generates impulses regularly
    • P cells are intact
  • Upon impulse exit from the SA node (in T cells), the Wenckebach phenomenon occurs
    • Impulse conduction at the exit from the SA node progressively lengthens
    • until the impulse is blocked, and the cycle repeats

ECG and SA Block II Degree - Type I (Wenckebach)


ECG 2nd degree SA block, exit block, Wenckebach

SA Block II Degree - Type I (Wenckebach)



Laddergram normal sinus rhythm, pp interval

Sinus Rhythm

  • Laddergram illustrates the propagation of impulses through the conduction system
    • S - P cells (SA node), S-A - T cells (Sinoatrial junction), A - atrium
  • In sinus rhythm, the SA node (P cells) generates impulses regularly (green dots)
  • Each impulse quickly reaches the T cells (S-A), where conduction slows down
  • Then, the impulse from the T cells (S-A) moves to the atrium (A - start of the P wave)
  • PP interval is consistent on the ECG


ECG and Laddergram 2nd degree sinoatrial (SA) block, Wenckebach

SA Block II. Degree - Type I (Wenckebach)



ECG sinus rhythm vs. 1st sinoatrial SA block

Sinus Rhythm


SA node and Sinoatrial first degree block


ECG second degree sa block, type I, wenckebach

SA Block II. Degree, Type I (Wenckebach)

  • PP interval shortens (1000ms...820ms)
  • PP interval with a dropped P wave (1580ms) is shorter
    • than twice the shortest PP interval (2 x 820 = 1640ms)
  • PQ interval is constant
SA node 2nd degree SA block, Type I


ECG 2nd degree SA block, type II, PP interval

SA Block II. Degree - Type II

  • PP interval is constant (970ms)
  • PP interval with a dropped P wave (1940ms) is equal
    • to twice the PP interval without a pause (2 x 970 = 1940)
  • PQ interval is constant
  • SA Block II. Degree - Type II
    • SA node generates impulses regularly
    • Impulse conduction from the SA node does not prolong
    • Impulses from the SA node intermittently block (PP pause)
Sinoatrial exit block


ECG and Laddergram, 2nd degree sinoatrial block, wenckebach

SA Block II. Degree, Type I (Wenckebach)

  • Laddergram
  • SA node generates impulses regularly S1-S6 (672ms)
  • Impulse conduction to the atrium through the SA junction gradually prolongs
    • PP intervals shorten P1-P4 (820...700ms)
  • A PP pause (1080ms) occurs, which is shorter
    • than twice the shortest PP interval
      (2 x 700 = 1400ms)
SA node 2nd degree Wenckebach



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