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Tachycardia: Difference between revisions
→AV Re-entry Tachycardia (AVRT)
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===AV Re-entry Tachycardia (AVRT)=== | ===AV Re-entry Tachycardia (AVRT)=== | ||
[[file:OCT_ACT.svg|thumb|400px|'''Figure 4.''' An example of | [[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.]] | ||
====Pathophysiology:==== | ====Pathophysiology:==== | ||
AVRT are tachycardias with a re-entry circuit | 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. 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 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. | ||
====Clinical diagnosis:==== | ====Clinical diagnosis:==== | ||
If an accessory bundle excites the ventricle earlier than normal AV-conduction can activate the ventricles, pre- | If an accessory bundle excites the ventricle earlier than normal AV-conduction can activate the ventricles, pre-excitation is visible on the ECG. This is a can be visible on the ECG by a shortened PQ interval and a widened QRS complex of >120ms due to slurring of the QRS complex (delta wave). This is also called the Wolf-Parkison-White symptom and can occur intermittently. If a patient has pre-excitation and complaints of arrhythmia caused by an AVRT the combination of these two is called the Wolf-Parkinson-White syndrome. Some patient have an AVRT, but no traces of pre-excitation. The bundle is then called a concealed bundle. Patients can be asymptomatic if they only have pre-exitation and this ECG pattern is commonly an incidental finding. When an arrhythmia develops using the accessory bundle, both types of AVRT can develop depending on the conduction characteristics of the bundle: | ||
* Orthodrome AV re-entry tachycardia: There is a P-wave (other morphology than sinus rhythm) followed by small QRS-complex | * Orthodrome AV re-entry tachycardia: There is a P-wave (other morphology than sinus rhythm) followed by small QRS-complex | ||
* Antidrome AV re-entry tachycardia: | * Antidrome AV re-entry tachycardia: This is a broad-complex tachycardia, where the broad QRS copmlex is followed by a retrograde P-wave originating from the AV-node. | ||
====Management:==== | ====Management:==== | ||
The circuit of the arrhythmia uses the AV node, therefore vagal manoeuvres are able to terminate the AVRT. Anti-arrhythmic drugs can be usueful to prevent paroxysms of arrhythmia, but drugs like digitalis and calcium antagonist should be avoided. Catheter ablation can target the accessory pathway and destroy the bundle. The success of the procedure is dependent on the location of the bundle as not all anatomical positions are easily targeted with ablation. It is controversial if patients with an asymptomatic WPW ECG pattern should have an ablation. The characteristics of the bundle and the life-style\proffession of the patient should guide treatment in these cases. | The circuit of the arrhythmia uses the AV node, therefore vagal manoeuvres are able to terminate the AVRT. Anti-arrhythmic drugs can be usueful to prevent paroxysms of arrhythmia, but drugs like digitalis and calcium antagonist should be avoided. Catheter ablation can target the accessory pathway and destroy the bundle. The success of the procedure is dependent on the location of the bundle as not all anatomical positions are easily targeted with ablation. It is controversial if patients with an asymptomatic WPW ECG pattern should have an ablation. The characteristics of the bundle and the life-style\proffession of the patient should guide treatment in these cases. | ||