AUTHOR AND EDITOR INFORMATION

Section 1 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

INTRODUCTION

Section 2 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

Background

Atrioventricular node reentrant tachycardia (AVNRT) is a reentrant rhythm within the atrioventricular (AV) node. Reentrant rhythms account for most episodes of supraventricular tachycardia (SVT) in children. A reentrant rhythm involves the presence of 2 distinct pathways with unidirectional block in one limb, allowing an electrical impulse to travel down the second limb and reenter the blocked pathway from the other direction. Reentrant rhythms usually can be initiated and terminated by pacing. During AVNRT, the circuit involves the fast and slow pathways within the AV node, allowing the impulses to reenter the node retrogradely as depolarization proceeds simultaneously to the ventricles. The relative incidence of AVNRT appears to increase in children aged approximately 5-10 years, and AVNRT is the predominant mechanism of SVT in adults. It occurs somewhat more commonly in females than in males and usually is not associated with structural heart disease.

Pathophysiology

Often, 2 or more functionally and (usually) anatomically distinct pathways are located within the AV node; they are known as the fast and slow pathways and have different electrophysiologic characteristics. The fast pathway is identified by its short conduction time and long effective refractory period (ERP), whereas the slow pathway has longer conduction time and an ERP that typically is relatively short compared to fast pathway ERP.

Conduction during sinus rhythm usually occurs over the fast pathway, and the PR interval is normal. A premature atrial beat may block in the fast pathway (because of its longer ERP) and conduct down by the slow pathway. The slow pathway has longer conduction time than the fast pathway, providing sufficient delay of the impulse. When it reaches the insertion site of the fast pathway (which already has recovered from its longer ERP), the impulse is conducted fast in a retrograde fashion. After traversing a short portion of the low septal right atrium, it reenters the slow pathway again, creating a circus movement tachycardia.

The 2 forms of AV node reentry (AVNR) that usually are described are the typical form (ie, slow-fast) and the atypical form (ie, fast-slow), referring to the characteristic of antegrade-retrograde conduction during tachyarrhythmia. In the typical form, which represents 90% of clinical AVNRT episodes, the conduction moves in antegrade direction through the slow pathway and in retrograde direction through the fast pathway. In the atypical form, the conduction moves antegradely in the fast pathway and retrogradely in the slow pathway, resulting in a long RP interval. A third form also has been identified in which the conduction appears to be antegrade and retrograde through 2 slow pathways.

The natural history of AVNR is unknown, but some infants appear to exhibit spontaneous resolution.

Frequency

United States

AVNR is the most common cause of paroxysmal supraventricular tachycardia (PSVT). Approximately 89,000 new cases are reported each year, and 570,000 persons with PSVT live in the United States.

International

PSVT has a prevalence of 2.25 per 1000 population and an incidence of 35 per 100,000 person-years.

Mortality/Morbidity

Episodes of SVT caused by any mechanism, including AVNRT, have a minimal impact on mortality rates in children, although SVT may lead to some degree of morbidity. Rare cases of AVNRT in young infants may be associated with more significant morbidity and possible mortality. The presence of dual AV node physiology per se does not necessarily indicate morbidity. Discontinuous AV nodal conduction curves on the electrophysiologic study that suggest the presence of dual AV nodal pathways have been encountered in patients without SVT and occur in approximately 63% of children. However, the presence of dual AV node physiology with associated AVNR is a common mechanism for SVT in children and adults. Thapar and Gillette's publication showed that dual AV node physiology was the mechanism in 46% of children who presented for evaluation of arrhythmias.

Sex

Prevalence of AVNRT is slightly more common in females than in males.

Age

AVNR is uncommon in newborns and increases in prevalence throughout childhood. The relative incidence of AVNRT appears to increase in children with age, and AVNRT is the predominant mechanism (accounting for 40-50% of cases) of SVT in adults.

CLINICAL

Section 3 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

History

Presenting symptoms vary with factors such as age, heart rate, duration, and underlying heart condition. Tachycardia rates can be very dependent on the adrenergic state. Children presenting with tachycardia during exercise may have much faster rates.

• Patients with AVNRT may be more symptomatic than those with other mechanisms of SVT; this is because of the simultaneous depolarization of atrial and ventricular myocardium, causing the occurrence of atrial contraction against a closed AV valve and loss of the atrial contribution to a complete diastolic filling.
• Symptoms of congestive heart failure in the infant may include restlessness, feeding problems, and diaphoresis. Shock may occur when a tachyarrhythmia goes unrecognized during variable amounts of time, from a few hours to days.
• In the older child, symptoms may include chest pain, palpitations, shortness of breath, lightheadedness, and fatigue.
• Occasionally, the patient may present with syncope or severe presyncope. A pounding sensation in the neck (ie, neck pulsations) is fairly unique to the presence of AVNRT and considered to be the result of cannon waves when the atrium contracts against a simultaneously contracting ventricle.

Physical

Promptly evaluate the hemodynamic state of children presenting with tachyarrhythmia. As stated above, the degree of compromise usually is determined by a number of factors, including age, heart rate, duration of the arrhythmia, and the presence or absence of structural heart disease.

• Evaluate infants for signs of congestive heart failure, such as tachypnea, retractions, rales, liver enlargement, decreased pulse, and perfusion.
• Cardiogenic shock with hypotension, metabolic acidosis, ventricular dysfunction, and pulmonary edema may occur.
• Physical examination findings of the older child without underlying heart disease may be normal except for the fast heart rate.
• The patient may exhibit tachypnea, pallor, and evidence of jugular venous pulsations caused by asynchrony of atrial and ventricular contractions (ie, the atrium contracting against a closed AV valve).
• Patients with structural heart disease and ventricular dysfunction may have more severe hemodynamic compromise upon presentation because they have limited myocardial reserves and do not tolerate the absence of AV synchrony for long periods.

Causes

The incidence of AVNRT appears to be increased in the setting of congenital heart disease. In addition, related conditions, such as AV node-to-node reentry with a Mönckeberg sling, may occur in the setting of complex congenital heart disease. Finally, dual AV nodal physiology may be a bystander to accessory pathways, and accessory pathways, including Mahaim fibers, may be bystanders to AVNRT. A recent report shows evidence that AVNRT may have a familial inheritance in some cases, which is suggestive of an involved genetic mechanism.

DIFFERENTIALS

Section 4 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

Other Problems to be Considered

The permanent form of junctional reciprocating tachycardia (PJRT) is difficult to distinguish from atypical (fast-slow) AVNRT.

WORKUP

Section 5 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

Lab Studies

• Upon initial presentation, assessments of serum electrolyte levels, thyroid function, and hemoglobin often are performed. Other lab studies may be performed to monitor serum levels and adverse effects in children receiving antiarrhythmic medications.

Imaging Studies

• A chest x-ray and echocardiogram often are performed to evaluate the degree of cardiopulmonary dysfunction associated with the tachyarrhythmia and to assess for structural abnormalities.
• Recent clinical and experimental studies utilizing electrophysiological and electroanatomical mapping are adding to the understanding of the anatomy and physiology of this disorder.
• It has been suggested that the coronary sinus, imaged at the time of electrophysiologic study, may have a broader opening in patients with AVNRT. This has not been confirmed.

Other Tests

• The ECG obtained during normal sinus rhythm shows a normal PR interval and the absence of preexcitation. Some patients may exhibit a slightly shortened PR interval or increased beat-to-beat variability of the PR interval, reflecting conduction through the fast or slow pathways. The typical AVNRT is characterized as a narrow complex regular tachycardia with rates that vary from 150-300 beats per minute.
• • Slow-fast form of AVNRT
    • The slow-fast form of AVNRT is typical.
    • Initiation of tachycardia usually occurs suddenly with a premature atrial beat. Sometimes, sudden sinus slowing is followed by a junctional escape beat as a trigger for the tachyarrhythmia.
    • The termination usually occurs with AV block, which is spontaneous or induced by vagal maneuvers or medications.
    • The rhythm may terminate with a P wave or QRS complex, depending on the site of block.
    • Little variability in RR intervals usually exists.
    • The time that the impulse takes to reach the atrium and the ventricle from the distal node is approximately the same, which causes the retrograde P waves to be buried within the QRS or appear at the terminal end of the QRS.
    • The RP interval is usually less than 70 milliseconds, which often results in the P wave being hidden in the QRS complex.
    • When the P wave is visible at the end of the QRS, it exhibits a characteristic late-positive component in ECG lead V₁ (ie, pseudo-r' wave), or the retrograde P waves may simulate an S wave in the inferior leads.
  • Fast-slow form of AVNRT
    • The fast-slow form of AVNRT is atypical.
    • The trigger is usually a premature ventricular beat that blocks in the fast pathway and is conducted up through the slow pathway and down through the fast pathway.
    • In this form, conduction to the atria takes longer than conduction to the ventricles, and the RP interval is longer than the PR interval.
    • Another characteristic is that the P wave axis is superior (ie, negative P waves in inferior leads), because it is retrograde and originates in the AV node.
    • Distinguishing this tachycardia from PJRT is difficult, although PJRT usually presents with a more incessant rather than paroxysmal pattern.

Procedures

• The electrophysiological characteristics of AVNRT include its initiation and termination by extrastimulus or rapid pacing; normal antegrade and retrograde AV conduction (with earliest retrograde activation at the His bundle); and termination with AV block that, although uncommon, may allow the AVNRT to persist. These characteristics can be evaluated in patients through the electrophysiological study (EPS), which may be semi-invasive (eg, esophageal electrode behind the heart) or intracardiac.
• • During the EPS, the presence of the 2 functional pathways can usually be demonstrated with atrial extrastimulus testing.
  • As the atrial extrastimulus-coupling interval (A1-A2) is shortened by 10-millisecond decrements, the AV nodal conduction time following the atrial extrastimulus (A2-H2) increases gradually.
  • At a critical atrial-coupling interval, a 10-millisecond decrease in A1-A2 results in a marked increase (>40-50 ms) in A2-H2. This abrupt increase in AV nodal conduction time is termed a jump in conduction (discontinuous AH conduction curve), and it often is associated with the appearance of atrial echo beats or initiation of AVNR tachycardia.
  • Further 10-millisecond decreases in the A1-A2 interval result in small additional increases ( <50 ms) in the A2-H2 interval, or, less commonly, additional AH jumps are evident.
• Some data indicate that AV nodal physiology in children is different than in adults. Based on the traditional definition of a 50 ms AH jump after a decrement of 10 ms in the extrastimulus coupling interval, only 62% of the children in one study met criteria for dual AV node physiology. However, all patients had inducible AVNRT, and most of them successfully ablated. The clinical importance of this finding is that children may not always fit the classic electrophysiologic criteria as it applies to adults; therefore, the endpoints for catheter ablation need to be readdressed and redefined in the pediatric population.
• Another, more recent study has demonstrated that the fast pathway effective refractory period (ERP) prolongs during AV node modification by cryotherapy, and this can be used as a marker of success. This study indicates that prolongation of more than 20 ms in the fast pathway ERP during cryotherapy application is 70% sensitive and 72% specific for predicting successful slow pathway modification. Subsequent to the procedure, the fast pathway ERP shortens to below baseline levels.

TREATMENT

Section 6 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

Medical Care

Emergency treatment of patients with hemodynamic instability is directed at converting the rhythm to sinus through a brief episode of AV block.

• As in any other mechanism of SVT, the use of vagal maneuvers can be very helpful in the acute setting.
• • In the infant, it is worthwhile to apply a plastic bag containing ice cubes and water to the face for 25-30 seconds to induce the diving reflex, a vagal stimulus. In older children, other vagal maneuvers can be attempted, such as breathholding or Valsalva maneuver.
  • If this is not successful, the next step is to administer medication. The drug of choice is adenosine, administered from an IV site as close as possible to the heart. Importantly, recent data have indicated low efficacy of recommended doses of adenosine, therefore suggesting the need to redefine current guidelines. Use of esmolol, a short-acting beta-blocker, also has been successful.
• Perform electrical cardioversion if patients have a deteriorating condition or if there is no response to the initial attempts of conversion.
• Esophageal overdrive atrial pacing is also quite safe and effective in converting to sinus rhythm.

Surgical Care

Knowledge of the anatomy of the Koch triangle (ie, where the AV node is located) is needed to understand how AVNR ablation is performed. The Koch triangle is defined by the ostium of the coronary sinus posteriorly. The apex of the triangle is defined anteriorly by the His bundle. The tendon of Todaro and the tricuspid valve annulus comprise the sides of the triangle. In the electrophysiology laboratory, landmarks of the Koch triangle are identified by one catheter recording the His deflection and by a second catheter placed in the ostium of the coronary sinus. The Koch triangle is located between these 2 catheters.

The fast pathway is anteriorly located, along the tendon of Todaro. The slow pathway is posterior-inferiorly located, along the tricuspid annulus, near the ostium of the coronary sinus.

The electrophysiologic signal is equally important to the anatomic location for determination of appropriate ablation targets.

Ablation of AVNR is accomplished by delivering either radiofrequency or cryothermal energy over the slow pathway. Because its location is more posterior and, thus, distant from the AV node, incidence of complete heart block with the use of radiofrequency energy is low (1.2%). The overall success rate of radiofrequency ablation on AVNRT has been more than 98% over the past several years.

More recently, cryothermal energy has allowed catheter mapping of specific ablation targets. This is especially advantageous in children with AVNRT, because it allows reversibility of conduction block, decreasing the risk of complete AV block. The cryolesion becomes irreversible at temperatures below -70 degrees C. The use of cryothermal energy to map and ablate arrhythmia substrates has been shown to be safer than radiofrequency energy; however, this safety comes at the expense of acutely lower success rates and higher recurrence rates at midterm follow-up.

Success rates of 83% were achieved for pediatric AVNRT cryoablation in a recently published multicenter study. No complications were reported, and, subsequently, the success rate for RF ablation in the 4 AVNRT cryoablation failures was 100% with the combined approach.

In another series, 14 pediatric patients with AVNRT had cryoablation success rates of 92.8%, with no complications and a recurrence rate of 30% for AVNRT in 22 months of follow-up.

With the use of radiofrequency energy, the AV node can be modified, usually at the slow pathway, with a large-tipped catheter in the same procedure as the electrophysiologic study. The approaches to AV node slow pathway modification are generally anatomical (ie, creating a line or lines of block across the usual site of the slow-pathway entrance) or guided by slow-pathway potentials. Successful deliveries of energy often are associated with a smooth and gradual acceleration of junctional tachycardia. AV conduction must be assessed carefully during energy application to ensure that heart block is not created. Successful ablation usually is associated with a loss of the jump in conduction, fewer or no AV nodal echo beats, and failure to re-induce tachycardia.

With cryothermal energy, the advantage of creating a map for subsequent ablation has been partly obscured by the finding that, in some patients, the mapped location does not predict the actual successful spot, with a reported negative predictive value of 66% in some series. Also, transient AV block was noted in other patients, where the map has previously shown to be a safe location. So far, no permanent AV block has been described with cryomapping/ablation; however, the patient numbers are still small.

Postcatheterization complications include hemorrhage, pain, nausea and vomiting, rhythm abnormalities, and arterial or venous obstruction from thrombosis or spasm.

Diet

It is prudent for patients with AVNRT to avoid caffeine-containing items so that SVT is not provoked by caffeine-induced premature beats.

MEDICATION

Section 7 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

Emergency treatment in the patient with hemodynamic instability is directed at immediate cardioversion. If the patient is stable, the goal is to convert the rhythm to sinus through a brief episode of AV block. Adenosine is the drug of choice for short-term termination of AVNRT. Esmolol, other beta-adrenergic blockers, verapamil, and digoxin also have been used with some success.

Drugs used for long-term therapy that have some effect in AV node reentrant tachycardia include digoxin, beta-blockers, and verapamil. Avoid intravenous verapamil use in infants because of its negative inotropic effects and avoid its use in combination with beta-blockers.

Drug Category: Antiarrhythmic agents

These agents alter the electrophysiologic mechanisms responsible for arrhythmia.

FOLLOW-UP

Section 8 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

Further Inpatient Care

• Patients with known SVT who are presenting with recurrence and receiving effective therapy usually do not require admission. New patients frequently are admitted for a period of observation and to provide teaching and reassurance to the parent or child. Often, certain antiarrhythmic medications are initiated in the hospital while the patient is monitored for adverse effects (eg, proarrhythmia).

Transfer

• Ideally, as with most tachycardias in children, transfer should take place after successful conversion has been achieved.

Prognosis

• The diagnosis of AV node reentrant tachycardia is associated with random unpredictable occurrences that pose a nuisance and interfere with quality of life more than they are life-threatening.

Patient Education

• Patients beyond infancy usually are informed that their condition, despite the severity of symptoms, is not significantly life threatening. Vagal maneuvers are taught, and the options of intermittent treatment (eg, vagal maneuvers, ED visits), long-term drug therapy, and AV node modification with RF or cryocatheter energy are discussed.
• For excellent patient education resources, visit eMedicine's Heart Center. Also, see eMedicine's patient education article Supraventricular Tachycardia.

REFERENCES

Section 9 of 9

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• References

• Benson DW Jr, Dunnigan A, Benditt DG, et al. Transesophageal study of infant supraventricular tachycardia: electrophysiologic characteristics. Am J Cardiol. Nov 1 1983;52(8):1002-6. [Medline].
• Calkins H, Yong P, Miller JM, et al. Catheter ablation of accessory pathways, atrioventricular nodal reentrant tachycardia, and the atrioventricular junction: final results of a prospective, multicenter clinical trial. The Atakr Multicenter Investigators Group. Circulation. Jan 19 1999;99(2):262-70. [Medline].
• Cohen MI, Wieand TS, Rhodes LA, Vetter VL. Electrophysiologic properties of the atrioventricular node in pediatric patients. J Am Coll Cardiol. Feb 1997;29(2):403-7. [Medline].
• Dixon J, Foster K, Wyllie J, Wren C. Guidelines and adenosine dosing in supraventricular tachycardia. Arch Dis Child. Nov 2005;90(11):1190-1. [Medline].
• Drago F, De Santis A, Grutter G, Silvetti MS. Transvenous cryothermal catheter ablation of re-entry circuit located near the atrioventricular junction in pediatric patients: efficacy, safety, and midterm follow-up. J Am Coll Cardiol. Apr 5 2005;45(7):1096-103. [Medline].
• Epstein MR, Saul JP, Fishberger SB, et al. Spontaneous accelerated junctional rhythm: an unusual but useful observation prior to radiofrequency catheter ablation for atrioventricular node reentrant tachycardia in young patients. Pacing Clin Electrophysiol. Jun 1997;20(6):1654-61. [Medline].
• Etheridge SP. Cryoablation for supraventricular tachycardia in children: is it okay to trade success for decreased risk?. J Cardiovasc Electrophysiol. Sep 2005;16(9):967-8. [Medline].
• Figa F, Chiu C, Gow RM. Unusual electrophysiological findings in atrioventricular node reentrant tachycardia. Pacing Clin Electrophysiol. Jun 1995;18(6):1324-6. [Medline].
• Goldberger J, Brooks R, Kadish A. Physiology of "atypical" atrioventricular junctional reentrant tachycardia occurring following radiofrequency catheter modification of the atrioventricular node. Pacing Clin Electrophysiol. Dec 1992;15(12):2270-82. [Medline].
• Hayes JJ, Sharma PP, Smith PN, Vidaillet HJ. Familial atrioventricular nodal reentry tachycardia. Pacing Clin Electrophysiol. Jan 2004;27(1):73-6. [Medline].
• Josephson ME, Wellens HJ. Differential diagnosis of supraventricular tachycardia. Cardiol Clin. Aug 1990;8(3):411-42. [Medline].
• Kirsh JA, Gross GJ, O'Connor S, et al. Transcatheter cryoablation of tachyarrhythmias in children: initial experience from an international registry. J Am Coll Cardiol. Jan 4 2005;45(1):133-6. [Medline].
• Kriebel T, Broistedt C, Kroll M, et al. Efficacy and safety of cryoenergy in the ablation of atrioventricular reentrant tachycardia substrates in children and adolescents. J Cardiovasc Electrophysiol. Sep 2005;16(9):960-6. [Medline].
• Miyazaki A, Blaufox AD, Fairbrother DL, Saul JP. Prolongation of the fast pathway effective refractory period during cryoablation in children: a marker of slow pathway modification. Heart Rhythm. Nov 2005;2(11):1179-85. [Medline].
• Okumura Y, Watanabe I, Yamada T, et al. Comparison of coronary sinus morphology in patients with and without atrioventricular nodal reentrant tachycardia by intracardiac echocardiography. J Cardiovasc Electrophysiol. Mar 2004;15(3):269-73. [Medline].
• Rhodes LA, Wieand TS, Vetter VL. Low temperature and low energy radiofrequency modification of atrioventricular nodal slow pathways in pediatric patients. Pacing Clin Electrophysiol. Jul 1999;22(7):1071-8. [Medline].
• Silka MJ, Halperin BD, Hardy BG, et al. Safety and efficacy of radiofrequency modification of slow pathway conduction in children < or = 10 years of age with atrioventricular node reentrant tachycardia. Am J Cardiol. Nov 15 1997;80(10):1364-7. [Medline].
• Silka MJ, Kron J, Halperin BD, et al. Mechanisms of AV node reentrant tachycardia in young patients with and without dual AV node physiology. Pacing Clin Electrophysiol. Nov 1994;17(11 Pt 2):2129-33. [Medline].
• Silka MJ, Kron J, Park JK, et al. Atypical forms of supraventricular tachycardia due to atrioventricular node reentry in children after radiofrequency modification of slow pathway conduction. J Am Coll Cardiol. May 1994;23(6):1363-9. [Medline].
• Teixeira OH, Balaji S, Case CL, et al. Radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia in children. Pacing Clin Electrophysiol. Oct 1994;17(10):1621-6. [Medline].
• Thapar MK, Gillette PC. Dual atrioventricular nodal pathways: a common electrophysiologic response in children. Circulation. Dec 1979;60(6):1369-74. [Medline].
• Van Hare GF, Chiesa NA, Campbell RM, et al. Atrioventricular nodal reentrant tachycardia in children: effect of slow pathway ablation on fast pathway function. J Cardiovasc Electrophysiol. Mar 2002;13(3):203-9. [Medline].
• Wolff GS, Sung RJ, Pickoff A, et al. The fast-slow form of atrioventricular nodal reentrant tachycardia in children. Am J Cardiol. Jun 1979;43(6):1181-8. [Medline].
• Wu D, Denes P, Amat-Y-Leon F, et al. An unusual variety of atrioventricular nodal re-entry due to retrograde dual atrioventricular nodal pathways. Circulation. Jul 1977;56(1):50-9. [Medline].

Article Last Updated: Jun 26, 2006