Escape rhythm
An escape rhythm is a "backup rhythm" produced by the heart if the SA node fails to conduct impulses, either temporarily or permanently. To maintain cardiac output, another pacemaker focus in the heart takes over, and the resulting rhythm is called an escape rhythm.
The focus with the highest frequency will be the dominant focus. Many foci can be the origin of an escape rhythm, usually
The rate and morphology of the escape rhythm depends on where it originates from. Atrial escape rhythms originate in the atria, have a narrow QRS complex, and a rate of more than 60 bpm. Junctional or AV nodal escape rhythms have narrow QRS and have a rate of about 40 to 60 bpm. Ventricular escape rhythms, also called idioventricular rhythms, have no P-waves, wide QRS and a rate of less than 40 bpm, which may be result in an insufficient cardiac output, causing symptoms.
| Type of rhythm | P wave morphology | QRS complex morphology | Frequency | Symptoms? |
|---|---|---|---|---|
| Atrial escape rhythm | P wave present but different than sinus rhythm P wave | Narrow | > 60 bpm | Rare |
| Junctional or AV nodal escape rhythm | P wave may be present after the QRS complex, or may be absent | Narrow | 40 - 60 bpm | May have |
| Ventricular escape rhythm or idioventricular rhythm | No P waves | Wide | 25 - 40 bpm | Usually |
Etiology
Escape rhythms occur when the SA node fails to function properly:
- Severe sinus bradycardia
- Sick sinus syndrome
- High-degree AV block