Atrioventricular reciprocating tachycardia (AVRT) is a macroreentrant tachycardia that needs an accessory pathway to bypass the regular conduction system.
Atrioventricular reentry tachycardia has a circuit that consists of two different pathways consisted of the regular conduction system through the AV node and an accessory pathway that enables communication between the atrium with the ventricle. After an extra beat of ectopic atrial or ventricular origin, these two pathways enable a difference between the refractory period and conduction time to allow tachycardia to persist
Atrioventricular reentry tachycardia and Wolf-Parkinson-White syndrome are often used interchangeably. However, to be specific, AVRT is the most common type of arrhythmia associated with the Wolf Parkinson White syndrome. Other examples of arrhythmia include AVNRT, atrial fibrillation with preexcitation, and atrial flutter.
AVRT or atrioventricular reentry tachycardia is a type of supraventricular tachycardia that requires an accessory pathway to initiate and maintain the tachyarrhythmia. The accessory pathway connects the atrium to the ventricle bypassing the AV node and has electrophysiologic properties that are different than those of the AV node as well as the His-Purkinje system. Yet, the accessory pathway resembles more the properties of the Purkinje fibers. The accessory pathway forms one of the two limbs required for the reentrant circuit; the other limb is the AV node, His-Purkinje system. Thus, the accessory pathway may conduct the impulse in the antegrade or retrograde fashion, resulting in orthodromic AVRT or antidromic AVRT:
Orthodromic Atrioventricular Reentry Tachycardia
This form compromises 90 to 95% of the reentrant tachycardia and can initiate from atrial premature beats or ventricular premature beats. Atrial premature beats initiating the atrioventricular reentry tachycardia will be blocked in the accessory pathway and conducted to the ventricles in an antegrade fashion through the AV node, His-Purkinje system; after the conduction, the impulse travels back to the atria through the accessory pathway to complete the circuit. While ventricular premature beats initiating the AVRT will be blocked in the His-Purkinje system and conducted to the atria through the accessory pathway in a retrograde fashion, after the conduction, the impulse with travel to the ventricles through the His-Purkinje system to complete the circuit. In both cases, the impulse will travel through the AV node His-Purkinje system in an antegrade fashion and through the accessory pathway in a retrograde fashion.
Antidromic Atrioventricular Reentry tachycardia
This type of reentrant tachycardia represents around 5 to 10% of AVRTs. As with orthodromic AVRT, the tachyarrhythmia initiates by either an atrial premature beat (APB) or a ventricular premature beat (VPB). When initiated with an ABP, the impulse is blocked in the AV node/His-Purkinje system but will conduct to the ventricles through the accessory pathway in an anterograde fashion, and then, will travel back to the atria through the AV node/His-Purkinje system in a retrograde fashion. In case the reentrant tachycardia was initiated by a VPB, the impulse will be blocked in the accessory pathway but will conduct in a retrograde fashion through the AV node, His-Purkinje system to the atria, and then back to the ventricles in an antegrade fashion through the accessory pathway. In both cases, the impulse will travel through the AV node His-Purkinje system in a retrograde fashion and through the accessory pathway in an antegrade fashion.
The prevalence of atrioventricular reentry tachycardia is rare and estimated to be less than 1%. In a study of 432166 individuals in Taipei surveying citywide elementary and high school students, the prevalence of Wolf-Parkinson-White was 0.067. Atrioventricular reentry tachycardia is likely even more infrequent as the presence of the WPW pattern in an ECG does not necessitate the development of an arrhythmia. In a study that followed 238 consecutive military aviators with WPW, with a mean age of 34.3 for a mean of 21.8 years, only 42 (17%) of the individuals devolved any form of SVT.
Vital signs are critical in the evaluation of atrioventricular reentry tachycardia. Clearly when would expect tachycardia with normal or elevated blood pressure. Respiratory and oxygen saturation will usually be within normal ranges. Like other SVTs, the symptoms of atrioventricular reentry tachycardia depends on other comorbidities, How fast the heart is beating and the resultant blood pressure, and how sensitive the individual is to their symptoms. Although the most commonly reported symptoms are palpitations, syncope or presyncope, dizziness, and chest pain, the remainder of the physical exam including cardiac auscultation will usually be unremarkable, which is not surprising given that symptoms of AVRT usually start at a mean age of 23 plus, minus 14 years.
The ideal method to evaluate atrioventricular reentry tachycardia is to obtain a 12 leads EKG during the time of arrhythmia, enabling one to differentiate between orthodromic vs. antidromic types of atrioventricular reentry tachycardia.
In orthodromic AVRT the QRS complexes would be narrow with an RR rate between 150 to 250 beats per minutes, and a retrograde P wave would follow the QRS complexes as the activation of the atria would be reversed, and the duration of the RP interval will be less than half of the RR intervals.
In antidromic AVRT, the QRS complexes should be wide, as the impulse is traveling to the ventricles through the accessory pathway making the QRS complexes fully pre-excitable, the rate is usually between 150 to 250, with a retrograde P wave following the QRS complexes. The duration of the RP intervals will be more than half of those of RR intervals.
Surface EKG when the individual is not in the tachyarrhythmia might demonstrate the characteristic delta wave with a short PR interval that results from the early depolarization of the ventricles through the accessory pathway.
Management of atrioventricular reentry tachycardia includes the termination of the acute arrhythmia and other treatments to prevent the recurrence of the arrhythmia.
In the case of a tachyarrhythmia patient who is hemodynamically unstable or symptomatic such as with altered mentation or ischemic chest pain, immediate electrical cardioversion is necessary.
Acute Termination of Orthodromic AVRT
In a case where the patient is hemodynamically stable, vagal maneuvers should be attempted first. A Valsalva maneuver involves asking the patient to bear down against a closed glottis for 10 to 30 seconds. Carotid massage also can be performed, but the absence of carotid bruit should be confirmed first, Carotid massage requires applying steady pressure over the left and right carotid sinuses, one at a time. In one study that examined at the effects of vagal maneuvers in terminating SVT in 148 individuals, the success rate was 27.7%.
IV adenosine should be the next intervention to terminate the tachycardia. The dosage of adenosine is 6 mg (0.1 mg/k for children with a maximum dose of 6 mg). Adenosine can be repeated in a dosage of 12 mg if the initial dosage is ineffective. Adenosine, in a dosage of up to 12 mg is 91% effective in terminating paroxysmal supraventricular tachycardia with minimal and brief side effects.
IV verapamil is also effective in terminating atrioventricular reentry tachycardia when used at a dosage of 5 mg every two to three minutes and a maximum dosage of 15 mg. However it should be used with caution in patients with heart failure and a reduced ejection fraction.
If the above treatment fails to terminate orthodromic AVRT, either IV procainamide or IV beta blockers are the next attempts. IV procainamide should be used at a dosage of 20 to 50 mg per minute until the arrhythmia stops, hypotension occurs, or the QRS widen by more than 50 percent with a maximum dosage of 17mg/kg. IV metoprolol can be dosed at a dosage of 5 mg pushed IV over 2 minutes and can be repeated every 10 minutes for a total dosage of 15 mg.
Acute Termination of Antidromic AVRT
In case the diagnosis is certain, the same management used for the acute termination of orthodromic AVRT can be used. In practice, since antidromic AVRT is a wide QRS complex tachycardia, confirmation of the diagnosis can be difficult in the acute setting. Thus, AV node blockade agents should be avoided, and IV procainamide should be tried, in the same dosage as mentioned above, to acutely terminate the arrhythmia.
Treatment to Prevent Recurrence of the Arrhythmia
In symptomatic individuals, and in select asymptomatic individuals particularly younger patients, radiofrequency ablation of the accessory pathway is the treatment of choice to prevent the recurrent arrhythmia. In a study that looked at 166 subjects who underwent radiofrequency ablation of the accessory pathway, AVRT recurred in 9% of patients after a mean follow up of 8 months; all of the subjects that had a recurrent arrhythmia underwent a second successful ablation. In another study, catheter ablation was successful in 94% of 654 patients with an accessory pathway.
In symptomatic individuals who are not candidates for ablation or refuse, initiate therapy with antiarrhythmic medication. Class 1C antiarrhythmics like flecainide are the drugs of choice to prevent the recurrence of the arrhythmia.
The differential diagnosis of orthodromic atrioventricular reentry tachycardia includes all regular narrow complex SVT such as AVNRT, sinus tachycardia, and a flutter. The differential diagnosis of antidromic tachycardia should include regular wide complex tachycardia including ventricular tachycardia.
Patients with atrioventricular reentry tachycardia generally enjoy a favorable prognosis as the arrhythmia usually can be terminated when it persists. Similarly, the prognosis of WPW syndrome is also generally good; however, in less than 1% of patients with preexcitation, sudden cardiac death can occur. In a meta-analysis that included 20 studies involving 1869 patients with preexcitation that did not undergo ablation, the rate of SVT was 16 events per 1000 person-years, and the rate of sudden cardiac death was 1.25 per 1000 person-years.
Complications of atrioventricular reentry tachycardia itself are rare and are similar to the complications of any rapid tachycardia resulting in pre-syncope or syncope, chest pain or shortness of breath. As discussed above, the most dreaded complication of an individual with an accessory pathway is sudden cardiac death, but thankfully this is rare. Complications from radiofrequency ablation of the accessory pathway occur in 2 to 4 percent of cases. Information gathered from a national registry that reported 3357 patients, of those who underwent accessory pathway ablation, found that complications include cardiac tamponade, acute MI, femoral artery pseudoaneurysms, AV block, pneumothorax, and pericarditis. In this registry, all of these complications occurred less than 2% of the time.
Like every other disease, patient education plays a significant role in management. Patients should be educated about the signs and symptoms of tachyarrhythmia, risks, and benefits of radiofrequency ablation and long term utility and effects of antiarrhythmic drugs when appropriate.
Atrioventricular reentry tachycardia is a supraventricular tachyarrhythmia that requires an accessory pathway that bypasses the AV node. Atrioventricular reentry tachycardia and Wolf-Parkinson-White syndrome are often used interchangeably. However, to be specific, AVRT is the most common type of arrhythmia associated with Wolf-Parkinson-White syndrome. Other examples of arrhythmia include AVNRT, atrial fibrillation with preexcitation, and atrial flutter.
Recognizing patients with atrioventricular reentry tachycardia and including the appropriate specialist is vital in better managing this condition. A cardiologist, specifically one who specialized in electrophysiology should evaluate the patient to determine the need for accessory pathway ablation as this can provide a definitive cure and prevent the patient from long term antiarrhythmic medication that can bear a lot of unwanted side effects. Patients managed with antiarrhythmic drugs are usually followed by the primary care provider and nurse practitioner, but they should never make changes to these medications without first consulting with the cardiologist. All patients need regular ECGs to ensure that the arrhythmia has resolved. (Level I) A comprehensive approach to each patient, taking into consideration patient age, other comorbidities, underlying structural heart disease and involving the appropriate specialist should be the standard of care to manage atrioventricular reentry tachycardia.
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