- Third-degree AV block or complete heart block is the most clinically significant AV block associated with ACLS
- Complete heart block occurs when the electrical impulse generated in the SA node in the atrium is not conducted to the ventricles
When the atrial impulse is blocked, an accessory pacemaker in the ventricles will typically activate a ventricular contraction. This accessory pacemaker impulse is called an escape rhythm.
Because two independent electrical impulses occur (SA node impulse & accessory pacemaker impulse), there is no apparent relationship between the P waves and QRS complexes on an ECG.
Characteristics that can be seen on an ECG include:
- P waves with a regular P to P interval
- QRS complexes with a regular R to R interval
- The PR interval will appear variable because there is no relationship between the P waves and the QRS Complexes
- P-waves are independent of the QRS complexes.
Common Causes: The most common cause of complete block is coronary ischemia and myocardial infarction. Reduced blood flow or complete loss of blood flow to the myocardium damages the conduction system of the heart, and this results in an inability to conduct impulses from the atrium to the ventricles.
Possible Symptoms of third-degree AV block:
- Bradycardia
- Hypotension
- Hemodynamic instability
Treatment: Transcutaneous pacing