An idioventricular rhythm is an escape rhythm produced by an escape beat. The escape beat is caused by a failure of one of the higher pacemaker sites, causing a ventricular focus to take over. Idioventricular rhythms typically have rates of 20–40 bpm. An accelerated idioventricular rhythm is present when the rate is > 40 bpm (see Figure 6.7). 

Idioventricular rhythms are sometimes called agonal rhythms because the patient’s heart is on the brink of death.

Figure 6.7. Accelerated Idioventricular Rhythm

Accelerated Idioventricular Rhythm ECG

Because the impulse in an idioventricular rhythm is generated from the ventricles, there are no P waves: the escape mechanism has taken over for the atrial pacemaker sites that have failed. Very slow ventricular complexes with a regular rhythm may also be seen. 

Occasionally, this rhythm may discharge in an irregular manner. The ventricular complex is at least 120 milliseconds (0.12 seconds) in duration and sometimes longer.

Characteristics of Idioventricular Rhythms

1. Usually, regular
2. Rate typically 20–40 bpm but may be < 20 bpm or > 40 bpm (accelerated idioventricular rhythm)
3. No P waves
4. No PR interval
5. QRS complex: wide and unusual looking, ≥ 120 milliseconds

Related Video – ECG Rhythm Review – Idioventricular Rhythm