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.
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 |
- AMI
- Congenital abnormalities
- Degenerative changes
- Drug toxicity
- Ischaemic heart disease
- Vagal activity
- Nausea & Vomiting
- Related to ‘causes’ symptoms
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 |
- AMI
- Cardiac infections
- Drug toxicity
- Ischaemic heart disease
- Increase vagal tone
- Lightheaded / dizzy
- Chest pain
- Regularly has irregular heartbeat
- Bradycardia
- Hypotension
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 |
- AMI
- Degenerative changes
- Drug toxicity
- Ischaemic heart disease
- Fall in blood pressure from dropped beat
- Syncope
- Chest pain
- Regularly has irregular heartbeat
- Bradycardia
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. |
- AMI
- Degenerative changes
- Drug toxicity
- Ischaemic heart disease
- From other AV blocks
- Lightheaded / dizzy
- Syncope
- Chest pain
- Bradycardia
- •Hypotension
Page contributors:
 | Thanh Bui, AP60825 Event Medic, Emergency Medical Technician & Volunteer Development Officer
|
 | Andrew Moffat, AP16790 |
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