Tachycardia: Difference between revisions

AVRT are tachycardias with a re-entry circuit compromising the entire heart. Atria, AV-node, ventricle and an extra bundle are an essential part of this circuit. The pre-requisite of an AVRT is the existence of an extra bundle between the atria and 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 location and can even run epicardially. 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 there exists a risk of VF if the patients develops AF due to fast conduction of fibrillatory activation. Depending on the conduction characteristics of the bundle and the direction of conduction two different AVRT circuits can manifest:

If an accessory bundle excites the ventricle earlier than normal AV-conduction can activate the ventricles, pre-exitation is visible on the ECG. This is a can be visible on the ECG by a shortned PQ interval and a widened QRS complex >120ms due to slurring of the QRS complex (delta wave). This is also called Wolf-Parkison-White symptom and can occur intermittently. If a patient has pre-exitation and traces of a AVRT the combination of these two is called the Wolf-Parkinson-White syndrome. Some patient have an AVRT, but no traces of pre-exitation. The bundle is then a concealed bundle.