Clinical and electrophysiologic features and role of catheter ablation techniques in adult patients with automatic atrioventricular junctional tachycardia

Diagnosis and management of junctional ectopic tachycardia in children

Junctional ectopic tachycardia (JET) is more common in its postoperative form. A thorough understanding of its etiology, pathophysiology, and management strategies is essential. Classically, postoperative JET is considered to arise from surgical trauma. Genetic susceptibility and an intrinsic morphologic/functional defect in the conduction system inherent in congenital heart diseases likely play a significant role. The devastating effects on postoperative hemodynamics warrant prompt attention. A multipronged management approach with general measures, pharmacotherapy, and pacing has decreased morbidity and mortality. Amiodarone and procainamide remain the preferred drugs, while ivabradine appears promising. Carefully planned randomized trials can go a long way in developing a systematic management protocol for postoperative JET.

Afterdepolarizations and triggered activity as a mechanism for clinical arrhythmias

Afterdepolarizations cause triggered arrhythmias. One kind occurs after repolarization is complete, delayed afterdepolarizations (DADs). Another occurs as an interruption in repolarization, early afterdepolarizations (EADs). Afterdepolarizations initiate arrhythmias when they depolarize membrane potential to threshold potential for triggering action potentials. DADs usually occur mostly when Ca2+ in the sarcoplasmic reticulum (SR) is elevated. The SR leaks some of the Ca2+ into the myoplasm through Ca2+ release channels controlled by ryanodine receptors (RyR2) during diastole. The Na+ -Ca2+ exchanger extrudes elevated diastolic Ca2+ from the cell in exchange for Na+ (1 Ca2+ for 3 Na+ ) generating inward current causing DADs. DAD amplitude increases with decreasing cycle length, causing triggered activity during an increase in heart rate or during programmed electrical stimulation (PES). Coupling interval of the first triggered impulse is directly related to initiating cycle length. EADs are associated with an increased action potential duration (APD) causing long QT (LQT). EADs are caused by net inward currents (ICaL , INCX ) as a consequence. Hundreds of mutations can cause congenital LQT by altering repolarizing ion channels. Acquired LQT results from drug interaction with repolarizing ion channels. EAD-triggered ventricular tachycardia is polymorphic and called "torsade de pointes." Effects of PES on EAD-triggered activity is related to effects of cycle length on APD. Shortening cycle length prevents EADs by accelerating repolarization. Typical PES protocols inhibit formation of EADs which can be therapeutic.

Human His-Purkinje System: Abnormalities of Conduction, Rhythm Disorders and Case Studies

This review covers many of the arrhythmias and conduction abnormalities related to His-Purkinje System. These include junctional premature complexes, junctional and fascicular tachycardias, bundle branch reentry (BBR), and the role of apparent conduction in various forms of supraventricular tachycardias (SVT) with or without involvement of accessory pathways (AP).

The 12-lead electrocardiogram in supraventricular tachycardia

The 12-lead electrocardiogram (ECG) is an invaluable tool for the diagnosis of supraventricular tachycardia (SVT). Most forms of SVT can be distinguished with a high degree of certainty based on specific ECG characteristics by using a systematic, stepwise approach. This article provides a general framework with which to approach an ECG during SVT by describing the salient characteristics, ECG findings, and underlying electroanatomical relationships of each specific type of SVT encountered in adults. It concludes by providing a systematic algorithm for diagnosing SVT based on the findings of the 12-lead ECG.

Classification and differential diagnosis of atrioventricular nodal re-entrant tachycardia

Recent evidence on atrioventricular nodal re-entrant tachycardia has identified several types of this common arrhythmia, with potential therapeutic implications. This article reviews the relevant new information, discusses the differential diagnosis of atrioventricular nodal re-entrant tachycardia, and summarizes the electrophysiological criteria for classification of the various forms of the arrhythmia.

Ventriculatrial Block During Atrioventricular Nodal Reentrant Tachycardia Suggesting Existence of an Upper Common Pathway

Studies on the mechanisms of atrioventricular nodal reentrant tachycardia (AVNRT) have yet to clarify whether the slow and fast pathways connect directly with the atria or via an upper common pathway. Although a "final common pathway" connecting the slow and fast pathways to the proximal His bundle was thought to be part of the reentrant circuit, debate on the presence of an upper common pathway continues. We report a case of AVNRT continuing despite the occurrence of ventriculoatrial block, thus supporting the existence of an upper common pathway.

Radiofrequency catheter ablation of junctional ectopic tachycardia with preservation of atrioventricular conduction

Junctional ectopic tachycardia is a relatively rare disorder, frequently refractory to drug therapy, and with a poor prognosis in childhood. This report describes a successful radiofrequency catheter ablation of the focus of this arrhythmia in a 9-year-old girl with preservation of normal atrioventricular conduction, using precise catheter navigation with the LocaLisa system and carefully titrated RF delivery.

Influence of isoproterenol on the accelerated junctional rhythm observed during radiofrequency catheter ablation of atrioventricular nodal slow pathway conduction

BACKGROUND

Accelerated junctional rhythm (AJR) has been considered as a sensitive but rather nonspecific marker of successful radiofrequency (RF) ablation of slow pathway in patients with atrioventricular nodal reentrant tachycardia (AVNRT). However, AJR also occurs commonly during isoproterenol infusion. We therefore investigated the effect of isoproterenol on the significance of AJR while attempting slow pathway ablation.

METHODS

Forty patients with AVNRT underwent slow pathway ablation. Sixty-nine RF applications accompanied by AJR were observed and were separated into 2 groups: applications performed without (group I, n = 26) and with (group II, n = 43) isoproterenol infusion. The specificity of AJR for successful ablation for each group was calculated.

RESULTS

The specificity of AJR in groups I and II was 73% (19/26) and 49% (21/43), respectively (P <.05). There was no significant difference between the groups in the atrial electrogram width, atrial/ventricular electrogram amplitude ratio, the time from application onset to AJR emergence, or AJR cycle length. The catheter-tip temperature at AJR emergence was significantly lower (47 degrees C +/- 3 degrees C vs 52 degrees C +/- 3 degrees C, P <.001) and the ratio of junctional beats to total heart beats during RF application was significantly greater (46% +/- 24% vs 33% +/- 18%, P <.05) in group II compared with group I.

CONCLUSIONS

Isoproterenol lowers the threshold of AJR emergence during RF application and thereby lowers the specificity of AJR for successful ablation. Complete washout of isoproterenol may therefore improve the specificity of AJR during RF ablation in patients with AVNRT.

Atrial pacing during radiofrequency ablation of junctional ectopic tachycardia--a useful technique for avoiding atrioventricular bloc

Radiofrequency catheter ablation (RFCA) was performed on a 5-year-old boy with congenital junctional ectopic tachycardia (JET) that was refractory to medical management. Because of the lack of retrograde atrial depolarization during tachycardia, radiofrequency energy was delivered during atrial overdrive pacing to confirm the presence of preserved atrioventricular (AV) conduction. Although the procedure was complicated by complete right bundle branch block after ablation of the para-Hissian region, the patient regained sinus rhythm accompanied by normal AV conduction. Rapid atrial pacing during RFCA of JET may be safely used to avoid AV block.

Supraventricular tachycardia: implications for the intensivist

The critical care physician must have a keen awareness of supraventricular tachycardia patterns, mechanisms, precipitants, and treatment. Although long-term management of most forms of supraventricular tachycardia lies primarily in the realm of the cardiac electrophysiologist, the intensivist must be proficient at acute arrhythmia therapy. Expertise in electrocardiography, pharmacokinetics, and pharmacodynamics is essential. Careful assessment of hemodynamics and prudent bedside clinical acumen help assure optimal patient outcomes.

Effect of adenosine and verapamil in catecholamine-induced accelerated atrioventricular junctional rhythm: insights into the underlying mechanism

Accelerated AV junctional rhythm is postulated to be due to enhanced automaticity of a high AV junctional focus. The adenosine response of this rhythm was tested in 17 patients (7 males, 12-83 years). The indications of electrophysiology study were nonspecific palpitation (n = 5), unexplained syncope (n = 6), postablation of accessory pathways (n = 4), and postmodification of AV nodal reentry tachycardia (n = 2). The sinus node and AV nodal functions were normal. Pacing and programmed electrical stimulation failed to induce any arrhythmia at baseline. The accelerated junctional rhythm (cycle length = 553 +/- 134 ms) was initiated spontaneously in all patients after isoproterenol infusion (1-2 micrograms/min). It was not suppressible by overdrive pacing. Cessation of isoproterenol infusion terminated the rhythm in all patients. Adenosine (6 mg) reproducibly terminated the accelerated junctional rhythm in all patients. In six patients, adenosine suppressed the junctional rhythm without producing AV nodal block. In the other 11 patients, the junctional rhythm was terminated prior to the occurrence of AV nodal block. Verapamil was tested in ten patients and 5 mg of intravenous verapamil terminated the junctional rhythm in all patients. In conclusion, the mechanism of catecholamine-induced accelerated AV junctional rhythm is most likely enhanced automaticity, and catecholamine-induced accelerated AV junctional automaticity is sensitive to adenosine and verapamil. Adenosine appears to have differential effects on catecholamine-enhanced AV junctional automaticity and AV nodal conduction. This suggests that, under catecholamine stimulation, adenosine may have different mechanisms of action on AV nodal conduction and automaticity.

Successful radiofrequency catheter ablation of congenital junctional ectopic tachycardia with preservation of atrioventricular conduction in a 9-month-old infant

An infant with congenital junctional ectopic tachyardia required frequent hospitalizations due to tachycardia acceleration despite multiple antiarrhythmic medications. At 9 months of age, he underwent successful radiofrequency catheter ablation of the tachycardia with preservation of AV conduction.

Narrow complex tachycardia with VA block: diagnostic and therapeutic implications

To review our experience with cases of narrow complex tachycardia with VA block, highlighting the difficulties in the differential diagnosis, and the therapeutic implications. Prior reports of patients with narrow complex tachycardia with VA block consist of isolated case reports. The differential diagnosis of this disorder includes: automatic junctional tachycardia, AV nodal reentry with final upper common pathway block, concealed nodofascicular (ventricular) pathway, and intra-Hissian reentry. Between June 1994 and January 1996, six patients with narrow complex tachycardia with episodes of ventriculoatrial block were referred for evaluation. All six patients underwent attempted radiofrequency ablation of the putative arrhythmic site. Three of six patients had evidence suggestive of a nodofascicular tract. Intermittent antegrade conduction over a left-sided nodofascicular tract was present in two patients and the diagnosis of a concealed nodofascicular was made in the third patient after ruling out other tachycardia mechanisms. Two patients had automatic junctional tachycardia, and one patient had atrioventricular nodal reentry with proximal common pathway block. Attempted ablation in the posterior and mid-septum was unsuccessful in patients with nodofascicular tachycardia. In contrast, those with atrioventricular nodal reentry and automatic junctional tachycardia readily responded to ablation. The presence of a nodofascicular tachycardia should be suspected if: (1) intermittent antegrade preexcitation is recorded, (2) the tachycardia can be initiated with a single atrial premature producing two ventricular complexes, and (3) a single ventricular extrastimulus initiates SVT without a retrograde His deflection. The presence of a nodofascicular pathway is common in patients with narrow complex tachycardia and VA block. Unlike AV nodal reentry and automatic junctional tachycardia, the response to ablation is poor.

Neonatal radiofrequency catheter ablation of junctional tachycardias

Junctional tachycardias comprise several arrhythmia types with differing mechanisms, principally involving the region of the atrioventricular (A-V) junction. Neonatal radiofrequency catheter ablation has typically been reserved for life-threatening, drug-refractory cases due to the unique concerns regarding patient size and development. We performed radiofrequency catheter ablation on two neonates with incessant, rapid junctional tachycardias and hemodynamic compromise after failing conventional medical therapy. This report describes 2 neonates who underwent emergent radiofrequency catheter ablation, and compares these two patients to a larger pediatric catheter ablation patient cohort. Both neonates had an acutely successful outcome and were able to be discharged within a week of the ablation procedure. Fluoroscopy time and total procedure time were shorter in these two patients than in the course of the average pediatric catheter ablation. Though long-term developmental consequences of neonatal catheter ablation are yet unknown, in unique extreme situations, radiofrequency catheter ablation can be performed in neonates, as in older children and adults, without excessive acute morbidity.

Diagnostic approach to narrow complex tachycardia with VA block

Narrow complex tachycardia with VA block is rare. The differential diagnosis usually consists of (1) junctional tachycardia (JT) with retrograde block; (2) AV nodal reentrant tachycardia (AVNRT) with proximal common pathway block; and finally (3) nodofascicular tachycardia using the His-Purkinje system for antegrade conduction and a nodofascicular pathway for retrograde conduction. Analysis of tachycardia onset and termination, the effect of bundle branch block on tachycardia cycle length, and the response to atrial and ventricular premature depolarization must be carefully done. Making the correct diagnosis is crucial as the success rate in eliminating the tachycardia will depend on tachycardia mechanism.

[Congenital ectopic junctional tachycardia: long-term remission after cryoablation of the bundle of His]

Congenital junctional ectopic tachycardia is an uncommon and potentially fatal arrhythmia that does not usually respond to medical therapy. We report a two month old infant with severe ventricular failure. The diagnosis was confirmed by electrophysiologic study. She underwent endocardial cryoablation of the His bundle during extracorporeal circulation and a ventricle epicardial-lead pacemaker was implanted. Eight years later the patient is still symptom-free without needing medical treatment.

Selective catheter ablation of the tachycardia focus in patients with nonreentrant junctional tachycardia

We describe a technique for ablation of junctional tachycardia focus by means of examining the earliest atrial activation sequence during tachycardia. The procedure was successful in 7 of 9 patients, and 1 developed complete atrioventricular block.

Experience with moricizine HCl in children with supraventricular tachycardia

Eight children, age between 4.5 and 19 years were treated with moricizine for supraventricular tachycardia during the last 3 years. The tachycardia was documented by surface electrocardiogram (ECG), and/or by ambulatory ECG in all the children and the mechanism of tachycardia was determined by previously published surface ECG and electrophysiologic criteria in all but one child. Of the eight children, three had atrial ectopic tachycardia, three had automatic junctional ectopic tachycardia, one had atrioventricular (AV) nodal reentry tachycardia and one had atrial reentry. All the children except one had failed trial of two or more antiarrhythmic drugs prior to moricizine therapy. The duration of moricizine therapy ranged from 4 days to 25 months. In three of the eight children (patients 3, 5 and 7), who presented with AV nodal reentrant tachycardia, automatic junctional ectopic tachycardia and atrial ectopic tachycardia, respectively, moricizine therapy was effective in restoring sinus rhythm and controlling the clinical tachycardia. Only one child (patient 1) developed proarrhythmia, an episode of fast, narrow-QRS supraventricular tachycardia lasting for 30 s, on the third day of therapy. This was subsequently confirmed by electrophysiologic study to be AV nodal reentrant tachycardia. The other side effects noted were non-cardiac, not dose-dependant and did not require dis-continuation of therapy. Based on our small series and those of others, moricizine, a newer class I anti-arrhythmic agent, has a limited but useful role in the management of recalcitrant type of supraventricular tachycardia, such as ectopic atrial and junctional tachycardia in children.