AV nodal re-entrant tachycardia
Basic of normal conduction system of the heart
- AVNRT is the most common type of SVT meaning it originates above the bundle of his. The AVNRT is caused by reentry circuit in or around the AV node. Two circuits are formed the slow and fast pathway. The fast pathway is located along the septal portion of tricuspid annulus and the slow pathway is located on the posterior, close to the coronary sinus ostium.
- In most patients with this arrhythmia, the tachycardia is initiated when an atrial premature complex is blocked in the fast pathway with a longer refractory period and conducts in the slow pathway with a shorter refractory period. While the impulse conducts to the ventricle in the slow pathway (antegrade conduction), the fast pathway recovers so that the impulse can conduct retrograde up the fast pathway to the atrium and the atrial end of the slow pathway (retrograde conduction). AVNRT is induced by premature ventricular stimulation or ectopic atrial beats.
- Prognosis is good in the absence of structural heart disease. Most patients respond well to medication or radiofrequency ablation to prevent recurrence.
- Patients that have AVNRT is characterized by abrupt onset and termination. Symptoms include palpitaitons, nervousness, anxiety, lightheadedness, chest discomfort, dyspnea, neck pounding, and syncope. Heart rate is rapid and ranges from 150-250 bpm.
- EKG – P wave may not be seen due to being buried in the QRS complex, narrowed QRS complex less than .12 sec.
- To terminate AVNRT, try vagal maneuvers first, ex. Doing carotid sinus massage, expose the face to cold ice water, and valsalva maneuver before using drug tx.
- If the patient is hemodynamically unstable or if drug conversion fails and the patient continues to be symptomatic, then DC synchronized cardioversion is indicated to terminate an attack.
- Drug therapy. Adenosine is the first line drug used to terminate AVNRT. Adenosine is given 6 mg via IV push and followed by saline flush
- Radiofrequency catheter ablation of the reentrant circuit should be considered for patients that have frequent or highly symptomatic episodes in which drug therapy has failed. The ablation is done at the location of the slow AV nodal pathway in order to interrupt conduction via this pathway and therefore stop the circuit.
Atrioventricular reentrant tachychardia with an accessory pathway
Example of AVRT is Wolff Parkinson white syndrome
- WPW syndrome arises from a congenital abnormality involving the prescence of abnormal conductinve cardiac tissue between the atria and the ventricles called the accessory pathway or the bundle of kent that bypasses the AV node.
- Accessory pathways, connection between the atrium and ventricles are the result of congenital development of myocardial tissue bridging the fibrous tissues called the bundle of kent. This allows electrical conduction btwn. The atria and ventricles at sites other than the AV node. The patient then develops a tachydysrhytmia. The prescense of this AP causes a reentrant tachycardia circuit to occur.
- Once identified, there is excellent prognosis with RF catheter ablation.
- Patient will usually feel chest pain, palpitations, syncope or difficulty breathing
- EKG will show short PR interval < .12 s , wide QRS complex longer than .12 s with a slurred QRS waveform producing a delta wave in the early part of the QRS
- In stable patients, vagal maneuvers can be attempted.
- If vagal maneuvers fail, IV adenosine is the first line agent used and is effective. It is admistered via rapid IV bolus
- The definitive treatment of choice is radiofrequency ablation.
Ellis, C. (2014, August 1). Wolff-Parkinson-White Syndrome . Retrieved November 13, 2014, from http://emedicine.medscape.com/article/159222-overview
Oshansky, B. (2014, September 2). Atrioventricular Nodal Reentry Tachycardia . Retrieved November 13, 2014, from http://emedicine.medscape.com/article/160215-overview