ECG rhythms AV blocks
Third-degree AV block with a ventricular escape ECG
Third-degree AV block with a wide ventricular escape. Regular P waves run independently of a very slow, regular, wide escape rhythm.
A 30-second recording of the heart model, played in real time. Run live starts the engine itself with this rhythm.
Computed by the TracingsMD heart model (Junkers engine): simulated for education, not a patient recording and not for diagnosis.
Measured on this recording
| Ventricular rate | 34/min |
|---|---|
| PR | — |
| QRS | 153 ms |
| QT | 503 ms |
| QTc (Bazett) | 378 ms |
| QTc (Fridericia) | 416 ms |
What it is
Complete AV block with a ventricular escape rhythm: the block lies low in the conduction system, and a slow (usually 20–40/min), wide escape rhythm from the ventricles takes over. The P waves run independently.
How to read this strip
| Rate | Atrial faster than ventricular; ventricular very slow. |
|---|---|
| Rhythm | P–P regular; R–R regular; the two are independent. |
| P waves | Regular, none conducted. |
| PR | Varies (no true PR). |
| QRS | Wide (≥120 ms): ventricular escape. |
| QT | Long in absolute terms because the rate is slow. |
Causes
- Degenerative conduction system disease.
- Anterior myocardial infarction.
- Infiltrative disease (sarcoidosis, amyloidosis).
- After cardiac surgery or valve replacement.
- Hyperkalemia.
What to consider
- A ventricular escape is slow and unreliable: it can slow further or stop (asystole). This is an emergency.
- Pacing pads should go on early. If the patient is unstable, follow the bradycardia algorithm: atropine is unlikely to work and must not delay transcutaneous pacing; an epinephrine or dopamine infusion can bridge to transvenous pacing.
- Check potassium, drugs and ischemia; most patients need a permanent pacemaker.
Key point
A slow, wide escape in complete block is unreliable: get pads on early, because atropine often fails and pacing may be needed within minutes.
Not to be confused with
- Second-degree AV block, Mobitz I — No PR lengthening pattern; P waves and QRS complexes are unrelated.
- Sinus bradycardia — There are more P waves than QRS complexes, and the QRS is wide.
- Third-degree AV block with a junctional escape — A junctional escape is narrow. Here the escape QRS is wide, so it starts in the ventricles.