• ECG and Electrical Impulse
• Laddergram
• Sinus Rhythm and Laddergram
• Laddergram and Atria

ECG and Electrical Impulse

• ECG curve illustrates the propagation of impulses through the heart
• Impulse propagates
• Quickly through the conduction system
• Slowly through the working myocardium
  
  
• The ECG curve mainly displays:
• Slow propagation of the impulse in the working myocardium
• The impulse creates a cardiac vector in the working myocardium
  
  
• Electrical activity in the atrial myocardium creates:
• P wave (atrial depolarization)
• Ta wave (atrial repolarization)
• is hidden within the QRS complex
  
  
• Electrical activity in the ventricular myocardium creates:
• QRS complex (ventricular depolarization)
• T wave (ventricular repolarization)

Laddergram

• The laddergram is located below the ECG recording
• It has 3 bands:
• A (Atria): shows the conduction of the impulse in the atria
• AV (AV node): shows the conduction of the impulse in the AV node
• V (Ventricles): shows the conduction of the impulse in the ventricles

• The red dot on the 2nd line indicates the beginning of AV node depolarization (the peak of the P wave)
• The atria are activated at the time when the P wave reaches its peak
• Then, the impulse from the atria enters the AV node (red dot on the 2nd line)
• The red line in the A segment of the laddergram represents the propagation of the impulse through the atria
• The time for atrial depolarization is approximately 0.03s

• The red dot on the 4th line indicates ventricular depolarization
• Ventricular depolarization begins and ends with the QRS complex, lasting about 0.1s
• Ventricular repolarization (the T wave) is not shown on the laddergram

First-Degree AV Block (Laddergram)

• A: impulse propagation through the atria
• AV: impulse propagation through the AV node
• Impulse conduction through the AV node is prolonged (>200ms): 280ms
• This is First-Degree AV Block
• V: impulse propagation through the ventricles

Second-Degree AV Block - Mobitz II (Laddergram)

• A: impulse propagation through the atria
• AV: impulse propagation through the AV node
• Impulse conduction through the AV node, only every 3rd impulse is conducted to the ventricles
• This is Second-Degree AV Block (Mobitz II)
• V: impulse propagation through the ventricles

Ventricular Extrasystole - Complete Compensatory Pause (Laddergram)

• A: The SA node generates impulses regularly (P1-P2 interval: 700ms)
• AV: impulses from the atria are conducted to the ventricles
• V: Ventricular extrasystole (VES) occurs in the ventricles earlier than the expected impulse from the atria
• VES retrogradely propagates to the atria through the AV node
• In the AV node, the VES meets the impulse from the SA node, and the impulses are reset (refractory period)
• A complete compensatory pause follows the VES
• The RR interval with VES (1400ms) is exactly twice the RR interval without VES (2x700ms)
• Because there was no reset of the SA node (The impulse from the VES did not pass to the atria to the SA node)

Atrial Fibrillation (Laddergram)

• A: In atrial fibrillation, impulses originate in the atria with a frequency of 350-600/min
• AV: Impulses from the atria bombard the AV node, but the AV node does not conduct every impulse to the ventricles
• The bombarded AV node changes the conduction speed - concealed conduction (concealed conduction)
• V: The ventricles are activated by impulses from the AV node irregularly

Laddergram and Atria

• 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 (Transport cells)
  • Carry impulses from P cells to the atria and internodal pathways
  • If the impulse does not pass through T cells, then P wave does not occur

SA Block II Degree - Type II (Laddergram)

• S: The SA node generates impulses regularly (670ms)
• SA: Some impulses are blocked in the SA junction (S3)
• When the impulse exits the SA node to the atria (P wave does not appear)
• This is SA block II Degree - Type II