Why there is re entry phenomenon in PSVT ?
Paroxysmal Supraventricular Tachycardia (PSVT) is a type of abnormal heart rhythm characterized by sudden, rapid heart rates originating above the heart’s ventricles (supraventricular), typically in the atria or the atrioventricular (AV) node. The underlying mechanism of PSVT often involves reentry circuits, which contribute to the onset and continuation of the tachycardia.
Reentry is a fundamental mechanism in many types of arrhythmias, including PSVT. It occurs when there is a circular or circuitous electrical pathway within the heart that allows electrical impulses to travel in a loop, continuously stimulating the heart to beat at a rapid rate.
Here’s how reentry contributes to PSVT:
- Dual Pathways or Circular Pathways:
- In PSVT, there are typically two pathways or a circular pathway within the heart that allow the electrical impulse to circulate.
- One pathway is usually the normal conduction pathway (e.g., AV node, His-Purkinje system), and the other is an abnormal pathway, often involving accessory pathways (e.g., Wolff-Parkinson-White syndrome).
- Unidirectional Block:
- Within this circular pathway, there is often a region of unidirectional block, meaning the electrical impulse can travel in one direction but not the other.
- This unidirectional block is crucial for establishing the reentry circuit.
- Retrograde and Anterograde Conduction:
- The electrical impulse circulates through the abnormal pathway (e.g., accessory pathway) in a retrograde (backward) direction and through the normal pathway in an anterograde (forward) direction.
- The impulse reaches the area of unidirectional block and is unable to travel through the block in the retrograde direction but can pass in the anterograde direction.
- Reentry Loop:
- The impulse reenters the abnormal pathway through the unidirectional block, completing the circuit or loop.
- This continuous circular electrical activation in the heart leads to the rapid, regular heartbeat observed in PSVT.
Reentry pathways in PSVT can be influenced by factors such as the refractory period of the pathways, the timing of impulses, and the conduction properties of the AV node and accessory pathways.
Understanding the reentry phenomenon is essential for diagnosing and managing PSVT. Various treatments, including medications and certain procedures like catheter ablation, aim to interrupt or eliminate these reentry circuits, ultimately restoring a normal heart rhythm.