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Tachycardia: Difference between revisions
→Pathophysiology:
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[[file:OCT_ACT.svg|thumb|400px|'''Figure 4.''' An example of orthodrome AVRT and antidrome AVRT. Note the differences in the direction of the arrhythmia.<cite>ECGPedia</Cite>]] | [[file:OCT_ACT.svg|thumb|400px|'''Figure 4.''' An example of orthodrome AVRT and antidrome AVRT. Note the differences in the direction of the arrhythmia.<cite>ECGPedia</Cite>]] | ||
====Pathophysiology:==== | ====Pathophysiology:==== | ||
AVRT are tachycardias with a re-entry circuit comprising the entire heart. The atria, AV-node, ventricles and an extra bundle are the essential parts of this circuit. The pre-requisite for an AVRT is the existence of an extra bundle between the atrium and the ventricle. This bundle can bypass the AV-node and connect directly to the His bundle, ventricular myocardium or one of the fascicles. Bundles have variety of anatomical locations and can even run epicardially.<cite>Cosio</cite> The conduction direction of these bundles can be anterograde (atrium-ventricle), retrograde (ventricle-atrium) or bidirectional. Some of the bundles exhibit AV-nodal like conduction properties, these are also known as Maheim bundles. If a bundle can conduct anterograde at a high rate (a refractory period of <260ms), then a risk of VF exists if the patients develops AF due to fast conduction of fibrillatory activity. Depending on the conduction characteristics of the bundle and the direction of conduction two different AVRT circuits can manifest: | AVRT are tachycardias with a re-entry circuit comprising the entire heart. The atria, AV-node, ventricles and an extra bundle are the essential parts of this circuit. The pre-requisite for an AVRT is the existence of an extra bundle between the atrium and the ventricle. This bundle can bypass the AV-node and connect directly to the His bundle, ventricular myocardium or one of the fascicles. Bundles have variety of anatomical locations and can even run epicardially.<cite>Becker,Cosio</cite> The conduction direction of these bundles can be anterograde (atrium-ventricle), retrograde (ventricle-atrium) or bidirectional. Some of the bundles exhibit AV-nodal like conduction properties, these are also known as Maheim bundles. If a bundle can conduct anterograde at a high rate (a refractory period of <260ms), then a risk of VF exists if the patients develops AF due to fast conduction of fibrillatory activity. Depending on the conduction characteristics of the bundle and the direction of conduction two different AVRT circuits can manifest: | ||
* Orthodrome AV re-entry tachycardia: The impulse travels through the normal conduction system in the standard direction and returns to the atria via the accessory bundle. | * Orthodrome AV re-entry tachycardia: The impulse travels through the normal conduction system in the standard direction and returns to the atria via the accessory bundle. | ||
* Antidrome AV re-entry tachycardia: The impulse travels antrograde through the accessory bundle and activates the ventricles. The impulse returns through the normal conduction system to the atria. | * Antidrome AV re-entry tachycardia: The impulse travels antrograde through the accessory bundle and activates the ventricles. The impulse returns through the normal conduction system to the atria. | ||