Internodal pathways (anterior, middle, posterior)
Atrial conduction
Three preferential routes through right atrial myocardium — anterior, middle (Wenckebach) and posterior (Thorel, along the crista terminalis) — carrying the sinus impulse to the AV node in about 30–50 ms. They are functional pathways defined by fibre orientation, not insulated bundles.
Traced from the start
- Sinoatrial node
- Internodal pathways (anterior, middle, posterior)
Detail
- Conduction velocity
- ~1 m/s, the fastest atrial tissue; the impulse reaches the AV node about 40 ms after sinus discharge
- Supplies
- Ordered delivery of the impulse to the AV node's superior (fast pathway) and inferior (slow pathway) inputs
- Anatomy
- The anterior pathway gives off Bachmann's bundle to the left atrium; the posterior pathway runs in the crista terminalis and passes the coronary sinus ostium
When it goes wrong
Ectopic focus or micro-re-entry along the crista terminalis
Focal atrial tachycardia: abnormal P wave morphology before every QRS, 'warm-up' onset; adenosine-induced AV block unmasks but does not terminate it
Practise this structure
2 questions in the bank tagged Cardiac Conduction.
A 24-year-old man presents with two hours of palpitations. He is alert, has no chest pain, and his blood pressure is 124/76 mmHg. The radial pulse is regular at…
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