UNCONTROLLED WHEN PRINTED

Group of arrythmias raised from failed or delayed transmission of impulses above the AV node to the ventricles. This is usually from ischemia or conduction system degeneration. Some AV blocks recovery overtime, however, some AV blocks may require temporary or permanent pacing.

1st Degree AV block

1

2

Difficulty transmitting impulse through AV node (where SA node is normal) – Due to this delay, the PR interval is longer – Once this travels through AV node, the impulse travels normally.

QRS Complex P Wave PR Interval Rate (bpm)
0.08        – 0.10s (2 – 2.5 small boxes) Present >0.20s (> 5 small boxes) 50 – 100 bpm
Causes
  • AMI
  • Congenital abnormalities
  • Degenerative changes
  • Drug toxicity
  • Ischaemic heart disease
  • Vagal activity
Signs & Symptoms
  • Nausea & Vomiting
  • Related to ‘causes’ symptoms
2nd Degree AV Block / Mobitz-Type I (Wenchkebach)

5

4

Represents a delayed transmission impulse through the AV node – However the time it takes to reach the ventricles increase for every impulse. This results in gradual PR interval increase. This continues until SA node intervenes with a sinus beats which resets the cycle again to prevent a fall in blood pressure.

  • RR interval shortens with each beat of the cycle
  • P-P interval remains constant
QRS Complex P Wave PR Interval Rate (bpm)
0.08 – 0.10s (2 – 2.5 small boxes) Present (more than QRS complex) Progressive Prolongation 50 – 100 bpm
Causes
  • AMI
  • Cardiac infections
  • Drug toxicity
  • Ischaemic heart disease
  • Increase vagal tone
  • Lightheaded / dizzy
Signs & Symptoms
  • Chest pain
  • Regularly has irregular heartbeat
  • Bradycardia
  • Hypotension
2nd Degree AV block / Mobitz-Type II

6

Severe 2nd degree block resulting in a dropped beat – Due to SA node impulse not being transmitted to the ventricles, without progressive prolongation of the PR interval. If 2 or more impulses are blocked at the AV node before reaching the ventricles, it is called 2:1 or 3:2 block.

Can develop into 3rd degree AV block or ventricular standstill.

QRS Complex P Wave PR Interval Rate (bpm)
0.08 – 0.10s (2 – 2.5 small boxes)
Can sometimes widened
Present Normal when P-wave & QRS are together Can be slow
Causes
  • AMI
  • Degenerative changes
  • Drug toxicity
  • Ischaemic heart disease
Signs & Symptoms
  • Fall in blood pressure from dropped beat
  • Syncope
  • Chest pain
  • Regularly has irregular heartbeat
  • Bradycardia
3rd Degree AV block / Complete Heart Block

7

8

9

No communication through AV node resulting in separate atrial & ventricle transmission by their own branches. The SA node fires at 60-100 where the ventricles are at about 20-40bpm from nearby impulses from AV node or; within the ventricles.

Perfusion is through junctional or ventricular escape rhythm – Can result to ventricle standstill.

Hypotension is displayed due to inability of atria to intervene resulting in diminished cardiac output.

QRS Complex P Wave PR Interval Rate (bpm)
0.08 – 0.10s (2 – 2.5 small boxes)
Can sometimes widened
Normal but more than QRS complex Dissociated relationship Variable Atria (60-100bpm) and Ventricle (20-40bpm) rates.
Causes
  • AMI
  • Degenerative changes
  • Drug toxicity
  • Ischaemic heart disease
  • From other AV blocks
Signs & Symptoms
  • Lightheaded / dizzy
  • Syncope
  • Chest pain
  • Bradycardia
  • •Hypotension

References

College of Pre-Hospital Care. (2015). 12-Lead ECG Analysis: Self-Directed Learning Package. Version 3. St John Ambulance Ltd.  

Curtis, K., & Ramsden, C. (2016). Emergency and trauma care for Nurses and Paramedics (2nd ed.). Elsevier Australia.

DeLaune, S. C., Ladner, P. K., McTier, L., Tollefson, J., & Lawrence, J. (2016). Australian and New Zealand fundamentals of nursing (1st ed.). Cengage Learning Australia Pty Limited.

ECG & ECHO Learning. (2020). Clinical ECG Interpretation. https://ecgwaves.com/topic/ecg-normal-p-wave-qrs-complex-st-segment-t-wave-j-point/

Life in the Fast Lane. (2020). ECG Library. https://litfl.com/ecg-library/

St John WA Ltd. (2017). Electrocardiography (ECG). Clinical Resources. https://clinical.stjohnwa.com.au/clinical-skills/assessment/vital-signs/electrocardiography-(ecg)

WikiEM. 2020. The Global Emergency Medicine Wiki. https://www.wikem.org


Page contributors:

60825Thanh Bui, AP60825
Event Medic, Emergency Medical Technician &
Volunteer Development Officer

 

16790

Andrew Moffat, AP16790
Volunteer Training Manager & Volunteer Development Officer

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