Atrioventricular Node Reentry Supraventricular Tachycardia Treatment & Management
- Author: Glenn T Wetzel, MD, PhD; Chief Editor: Stuart Berger, MD more...
Patients with known supraventricular tachycardia (SVT) who are presenting with recurrence and receiving effective therapy usually do not require admission. New patients are frequently 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).
Emergency treatment of patients with hemodynamic instability such as atrioventricular node reentrant tachycardia (AVNRT) is directed at converting the rhythm to sinus through a brief episode of atrioventricular (AV) block.
Perform synchronized electrical cardioversion if patients have a deteriorating condition or if there is no response to the initial attempts of conversion (see below).
As in any other mechanism of supraventricular tachycardia (SVT), the use of vagal maneuvers can be very helpful in the acute setting. In the infant, 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 intravenous site as close as possible to the heart. Importantly, 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.
Esophageal overdrive atrial pacing is also quite safe and effective in converting to sinus rhythm.
Recording of a long 3- or 12-lead rhythm strip during attempts to terminate the tachycardia may be invaluable in subsequent efforts to define the mechanism of SVT and should be routinely performed.
Ideally, as with most tachycardias in children, transfer should take place after successful conversion has been achieved.
Patients with AVNRT should avoid caffeine-containing items so that SVT is not provoked by caffeine-induced premature beats.
Knowledge of the anatomy of the Koch triangle (ie, where the AV node is located) is needed to understand how atrioventricular node reentry (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 generally located posterior-inferiorly, along the tricuspid annulus, near the ostium of the coronary sinus. However, less common variations have been described.[4, 20]
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.
Cryothermal energy has allowed catheter mapping of specific ablation targets. This is especially advantageous in children with AVNRT because it allows greater reversibility of conduction block, decreasing the risk of complete AV block. The cryolesion becomes irreversible at temperatures below -70ºC. 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.
In a survey of physicians who were largely invasive pediatric electrophysiologists (94%) who practice at mid- to high-volume centers (>50 ablation procedures/year), 41% of responders use cryoablation as first-line therapy for atrioventricular nodal reentrant tachycardia.
Success rates of 83% were achieved for pediatric AVNRT cryoablation in a multicenter study. No complications were reported, and, subsequently, the success rate for radiofrequency ablation in the 4 AVNRT cryoablation failures was 100% with the combined approach.
In one single center study, acute success was obtained in 95% of RF (42 patients) and 97% of cryo cases (38 patients). There was one confirmed recurrence of tachycardia in each group, with a 2% recurrence rate.
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.
Another study 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.[27, 28]
One study of pediatric patients showed a trend toward improved initial success rates (98% vs 93%) and lower early recurrence rates (9% vs 18%) using a 6-mm tip cryoablation catheter as compared with a 4-mm tip catheter.
One study in adult patients emphasized the importance of eliminating AH jumps with retrograde atrial (echo) beats in reducing the recurrence rate. The applicability of this finding to the pediatric population is unclear as the typical findings of dual AV nodal physiology described in adult patients are less common in pediatric patients. Pediatric patients also exhibit an increased prevalence of inducible atypical arrhythmias.
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 reinduce 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. A recent meta-analysis concluded that cryoablation is a safe and effective treatment. Late recurrences were more common with cryoablation; however, avoidance of AV nodal block was noted.
Postcatheterization complications include hemorrhage, pain, nausea and vomiting, rhythm abnormalities, and arterial or venous obstruction from thrombosis or spasm. Although the long-term sequelae of AVNRT ablation are unknown, one study of pediatric patients has described changes in atrial size and electrophysiology 2-5 years following ablation.
Cyroablation has been shown to be more successful with increased individual experience in one study. This showed a decreased recurrence rate from 28% in the first 25 cases to 8.9% in the last 45 cases.
Current electroanatomic mapping systems have led to a significant decrease in fluoroscopy use and thus radiation exposure during electrophysiology studies and ablation. Intracardiac echocardiography has also been used in conjunction with electroanatomic mapping to lower radiation exposure.
Some authors have suggested that cryoablation has a lower recurrence rate when performed at a younger age.
One study showed early transient AV block following cryotherapy in 18% of patients; however, in all patients, there was no evidence of AV nodal dysfunction 24 hours following the procedure.
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