Does ventricle generate it's own rhythm in mobitz type 2 and bundle branch block
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Searching PubMed
"atrioventricular block" AND "bundle branch block"
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Merck Manual Mobitz type II ventricular escape rhythm bundle branch block
The ventricular conduction system can generate its own escape rhythm, but not normally. The SA node normally suppresses these slower backup pacemakers.
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Mobitz type II AV block: Some atrial impulses fail to reach the ventricles, causing dropped QRS complexes. Between conducted beats, the ventricle usually does not start an independent rhythm if the pause is short. If conduction deteriorates to high-grade or complete heart block, a junctional or ventricular escape rhythm can take over.
- Junctional escape: about 40-60 bpm
- Ventricular escape: about 20-40 bpm, usually wide QRS
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Bundle branch block (BBB): The ventricles are still activated by the usual supraventricular impulse, but activation travels through the remaining functioning bundle and then spreads slowly to the other ventricle. Thus, BBB produces a wide QRS but does not itself mean the ventricle has generated its own rhythm.
So:
| Situation | Who sets the rhythm? |
|---|---|
| Mobitz II with intermittent dropped beats | Usually SA node, with intermittent failure of AV/His-Purkinje conduction |
| Mobitz II progressing to complete block | Escape pacemaker may take over, possibly ventricular |
| Isolated RBBB or LBBB | Usually SA node; ventricular activation is delayed, not ventricular-origin rhythm |
| Ventricular escape rhythm | Ventricle or distal His-Purkinje tissue becomes the pacemaker |
Mobitz II is concerning because it commonly reflects disease below the AV node, often in the His-Purkinje system, and can abruptly progress to complete heart block. A ventricular escape rhythm is slow and less reliable. Merck's AV-block review notes that Mobitz II may progress suddenly to complete block and that ventricular escape is typically 20-40 bpm.
Difference between junctional escape and ventricular ectope
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"junctional escape rhythm" AND "premature ventricular contractions"
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junctional escape rhythm versus premature ventricular complexes ECG features
Junctional escape rhythm vs ventricular ectopic beat (PVC)
| Feature | Junctional escape | Ventricular ectopic beat / PVC |
|---|---|---|
| Origin | AV junction, near AV node/His bundle | Ventricular myocardium or Purkinje tissue |
| Why it occurs | A backup beat after the sinus impulse is absent or delayed | An irritable ventricular focus fires early |
| Timing | Late: appears after a pause or slow underlying rhythm | Premature: comes earlier than the next expected sinus beat |
| Role | Protective, maintains cardiac output during bradycardia | Extra beat that interrupts the regular rhythm |
| QRS | Usually narrow, unless pre-existing BBB or aberrancy | Usually broad and bizarre, typically ≥120 ms |
| P wave | Often absent before QRS; may be retrograde/inverted P wave before, within, or after QRS | Usually no preceding P wave; a sinus P wave may be hidden in the PVC |
| Rate/pattern | May be a single escape beat or sustained regular rhythm at ~40-60 bpm | Isolated or repeated early beats; underlying sinus rate may be normal |
| Pause after beat | It terminates a preceding long pause | Often followed by a full compensatory pause |
Easy rule:
- Escape = late, rescue beat.
- Ectopic/PVC = early, extra beat.
Example:
- Sinus rhythm pauses for too long, then a narrow QRS occurs to prevent asystole: junctional escape beat.
- A wide QRS appears before the next expected normal beat, followed by a pause: PVC.
A junctional escape may be broad if there is a pre-existing bundle branch block, so timing relative to the expected sinus beat is often the key discriminator. Textbook descriptions place junctional escape rhythms around 40-60 bpm and commonly show a QRS without a preceding P wave; isolated junctional escape beats usually need no specific treatment. Frameworks for Internal Medicine and Tintinalli's Emergency Medicine describe these features. PVCs are ventricular-origin premature beats, commonly producing a broad, abnormal QRS. ECG PVC features summarize the typical early wide complex and compensatory pause.
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