Index
Ep Defined | Getting Started | Working in the EP Lab
Right Atrium | Right Ventricle | Left Atrium | Left Ventricule | Cardiac Conduction | Cardiac Cell Properties | Action Potential | Sympathetic or Not | Med Page
Electrograms Defined | Recording Modes | Electrode Spacing | Filters | EGM Interpretation | Arrhythmia Analysis
The Physical Lab | Tools of the Trade
Setting Up | Catheter Placement | Baseline Measurement | SNRT | Conduction Study | Arrhythmia Induction | Pacing Protocols | Ablation | Tilt Table | Secrets to Success
Bradycardia | Atrial Tach | Atrial Flutter | Atrial Fibrillation | AVNRT | AVRT | Ventricular Tachycardia
Surface ECG's | Intracardiac Questions | Med Challenge | Advanced

Cardiac Arrhythmias - Atrial / Ventricular Reentry Tachycardia

AVRT

          AVRT - Atrial Ventricular Reentry Tachycardia is very similar to AVNRT with the exception that one or more of the two conduction channels exists outside the AV node. These extra conduction channels are called accessory bypass tracts and are present at birth in people who have AVRT. Most people are born without these bypass tracts and thus, can not have this type of tachycardia. If a person does have a bypass tract when they are born, it does not mean they will ever have problems with AVRT.
          Accessory bypass tracts may conduct signals antegrade, from the atrium to the ventricle, or retrograde, from the ventricle to the atrium. When a bypass tract conducts antegrade, it falls under the category of Wolf Parkinson White syndrome, or WPW. It is easy to identify patients with WPW due to the ventricular preexcitation that occurs when a patient has this type of bypass tract. The tissue of accessory bypass tracts behaves very similar to normal heart muscle, or myocardial, tissue. Mycocardial tissue conducts the electrical signals of the heart at a rapid rate where tissue of the AV Node conduct signals at a much slower rate. This slower conduction through the AV node helps prevent the heart from beating overly fast. When a bypass tract is present that conducts angtegrade, the AV node conducts part of the electrical activation through to the ventricles. Some elctrical activity reaches the ventricle through the bypass tract. Because most bypass tracts, also referred to as Bundles of Kent, do not have properties of decremental conduction, electrical depolarization of the ventricular tissue at the distal end of the fibers of the accessory bundle will start to show activation before the normal depolarization of the ventricle starts. This early depolarization may be visualized on the surface ECG as shown below.

WPW - Overt AVRT with visible Delta Waves

          The image below shows a 12 lead ECG with delta waves present in all the inferior (leads II, III and aVF) and precordial (V1 - V6) leads. Note the enlarged box showing a QRS from lead aVF with the delta wave highlighted in red.

When a bundle of Kent is present that has antegrade conduction, a delta wave will be present. This delta wave indicates areas of the ventricle that are starting to depolarize before conduction through the normal depolarization that arrives by way of the AV node / HIS Purkinjie network.

This type of pathway is identifiable on the surface ECG and is referred to as an overt bypass tract. If the pathway was not visible on the 12 lead and could only conduct retrograde, it would be referred to as a concealed bypass tract.

 

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