Dual atrioventricular nodal pathways: a benign finding in arrhythmia-free children with heart disease

Dual atrioventricular nodal pathways physiology and high-grade heart block

We report of case of an 87 year old lady with preexisting RBBB who developed LBBB after transcatheter aortic valve replacement (TAVR) for the treatment of severe aortic stenosis. She underwent pacemaker implantation, and subsequently developed high-grade atrioventricular (AV) block. Dual chamber pacing in the setting of complete heart block with a long programmed AV delay showed retrograde P waves. Ventricular pacing showed intact retrograde conduction. Shortening the programmed AV delay resulted in loss of retrograde P waves during dual chamber pacing. These findings are discussed.

Arrhythmia diagnosis and management throughout life in congenital heart disease

Arrhythmias, covering bradycardia and tachycardia, occur in association with congenital heart disease (CHD) and as a consequence of surgical repair. Symptomatic bradycardia can occur due to sinus node dysfunction or atrioventricular block secondary to either unrepaired CHD or surgical repair in the area of the conduction system. Tachyarrhythmias are common in repaired CHD due to scar formation, chamber distension or increased chamber pressure, all potentially leading to abnormal automaticity and heterogeneous conduction properties as a substrate for re-entry. Atrial arrhythmias occur more frequently, but ventricular tachyarrhythmias may be associated with an increased risk of sudden cardiac death, notably in patients with repaired tetralogy of Fallot or aortic stenosis. Defibrillator implantation provides life-saving electrical therapy for hemodynamically unstable arrhythmias. Ablation procedures with 3D electroanatomic mapping technology offer a viable alternative to pharmacologic or device therapy. Advances in electrophysiology have allowed for successful management of arrhythmias in patients with congenital heart disease.

Multiple multisite low-temperature and low-power radiofrequency currents for the induction of atrioventricular nodal reentry tachycardia in non-inducible patients

AIMS

Some patients with documented episodes of paroxysmal supraventricular tachycardia (PSVT) do not have inducible tachycardia during the electrophysiological study. In this study, we describe how multiple low-temperature, low-power radiofrequency (RF) currents in the atrioventricular (AV) junction region can increase the rate of the induction of atrioventricular nodal reentrant tachycardia (AVNRT) in non-inducible cases.

METHOD

We enrolled 31 consecutive patients (mean age = 50.9 ± 11.9 years; 5 [16.1 %] male) who presented with documented clinical PSVT in superficial electrocardiography but had non-inducible arrhythmia in the electrophysiology laboratory despite applying different stimulation protocols. We delivered low-power (25 W), low-temperature (45 °C) RF currents into the AV junction region to induce AVNRT.

RESULTS

Arrhythmia was induced in 20 (64.5 %) patients, and it was non-sustained in 3 (9.6 %) patients. RF current was delivered into the posterior region near the coronary sinus ostium and midseptal region. RF ablation target in inducible patients was the non-inducibility of the AVNRT at the end of the procedure, while the target in the non-inducible patients was slow pathway ablation with no antegrade conduction over the slow pathway. During the follow-up period, none of the patients (either with inducible or non-inducible arrhythmia) had recurrence of AVNRT.

CONCLUSION

Multiple low-power, low-temperature RF current application into the AV junction region is a more effective method for the induction of AVNRT in comparison with a single current use into the slow pathway.

Dual atrioventricular nodal pathways physiology: a review of relevant anatomy, electrophysiology, and electrocardiographic manifestations

More than half a century has passed since the concept of dual atrioventricular (AV) nodal pathways physiology was conceived. Dual AV nodal pathways have been shown to be responsible for many clinical arrhythmia syndromes, most notably AV nodal reentrant tachycardia. Although there has been a considerable amount of research on this topic, the subject of dual AV nodal pathways physiology remains heavily debated and discussed. Despite advances in understanding arrhythmia mechanisms and the widespread use of invasive electrophysiologic studies, there is still disagreement on the anatomy and physiology of the AV node that is the basis of discontinuous antegrade AV conduction. The purpose of this paper is to review the concept of dual AV nodal pathways physiology and its varied electrocardiographic manifestations.

Approaches to empiric ablation of slow pathway: results from the Canadian EP web survey

AIM

Dual atrioventricular nodal physiology (DAVNP) is a frequent finding in patients with suspected or documented supraventricular tachycardia (SVT). Empiric slow pathway ablation (ESPA) is sometimes performed in patients with DAVNP without inducible SVT at the time of electrophysiological study. Evidence to guide this practice in the adult population is limited. This study was aimed to assess the practice of ESPA by adult electrophysiologists in Canada.

METHODS

All Canadian interventional electrophysiologists (n = 81) were invited to complete a web-based questionnaire assessing their practice of ESPA in patients with suspected and documented SVT. Operator experience, reimbursement models, diagnostic, and treatment decisions regarding ESPA were assessed with case scenarios.

RESULTS

Forty-one responses (50 %) were obtained. Ninety-five percent of the responders stated that the evidence for ESPA is lacking or limited. Responders were more likely to perform ESPA in the setting of non-inducible SVT when there was documentation of the clinical arrhythmia (64 vs. 31 % (p = 0.017)). The threshold to perform ESPA was highly variable. Longer time in practice (r = 0.38, p = 0.017) and less perceived complications with ESPA (r = 0.31, p = 0.05) were correlated with the practice of ESPA, whereas length of ablation waiting lists (r = -0.15, p = 0.38), number of procedures performed per day (r = 0.11, p = 0.51) and type of reimbursement (p = 0.24) were not associated with the practice of ESPA. The perceived complication rate with ESPA was <1 %.

CONCLUSION

Variability in the practice of ESPA in cases of non-inducible SVT exists. Documentation of the clinical arrhythmia, operator experience, and perceived low complication rates positively influence this practice.

Decremental Ramp Atrial Extrastimuli Pacing Protocol for the Induction of Atrioventricular Nodal Re-entrant Tachycardia and Other Supraventricular Tachycardias

AIM

The primary aim of this study was to evaluate the utility of decremental ramp atrial extrastimuli pacing protocol (PRTCL) for induction of atrioventricular nodal re-entrant tachycardia (AVNRT), and other supraventricular tachycardias (SVTs), compared to standard (STD) methods.

METHODS

The study cohort of 121 patients (age 57.51 +/- 14.02 years) who presented with documented SVTs and/or symptoms of palpitations and dizziness, and underwent invasive electrophysiological evaluation was divided into Group I (AVNRT, n = 42) and Group II (Control, n = 79). The PRTCL involved a train of six atrial extrastimuli, delivered in a decremental ramp fashion. The STD methods included continuous burst and rapid incremental pacing up to atrioventricular (AV) block cycle length, and single and occasionally double atrial extrastimuli. Prolongation in the Atrio-Hisian (Delta-AH) intervals achieved by both methods were compared, as were induction frequencies.

RESULTS

In Group I, three categories of responses--(1) induction of AVNRT, (2) induction of echo beats only, and (3) none--were observed in 29 (69%), 11 (26%), and 2 (5%) patients with the PRTCL, when compared with 14 (33%), 16 (38%), and 12 (29%) patients with STD methods in the baseline state without the use of pharmacological agents. The Delta-AH intervals for each of these three categories were larger using PRTCL versus STD methods; 293.3 +/- 95.2 ms versus 192.9 +/- 61.4 ms (P < 0.005), 308.6 +/- 68.5 ms versus 189. 9 +/- 64.9 ms (P < 0.0005), and 203.0 +/- 86.3 ms versus 145.8 +/- 58.9 ms (P = NS), respectively. In Group II, in one patient with dual AV nodal physiology but no clinical tachycardia, the PRTCL induced nonsustained (12 beats) AVNRT. Additionally, in this group, both PRTCL and STD methods induced atrial tachycardia in two patients and orthodromic AV re-entrant tachycardia in one patient.

CONCLUSION

Decremental ramp atrial extrastimuli pacing PRTCL demonstrates a superior response for induction of typical AVNRT as compared to STD techniques. Because of easy and reliable induction of AVNRT and echo beats by the PRTCL, we recommend it as a method to increase the likelihood of induction of AVNRT. For induction of other SVTs, the PRTCL and the STD methods are comparable.

Sustained Slow Pathway Conduction: Superior to Dual Atrioventricular Node Physiology in Young Patients with Atrioventricular Nodal Reentry Tachycardia?

BACKGROUND

Young patients with atrioventricular nodal reentry tachycardia (AVNRT) frequently do not display discrete dual AV node physiology (DAVNP) as classically defined. The purpose of the study was to investigate the prevalence of sustained slow pathway conduction (SSPC; PR > RR during atrial pacing) in young patients with AVNRT and compare it to dual atrioventricular node physiology.

METHODS

The presence of SSPC and DAVNP was prospectively assessed before and after radiofrequency catheter ablation in 61 young patients (age 4-23 years) with typical AVNRT.

RESULTS

Prior to ablation, 32 (52%) displayed DAVNP, while 46 (75%) displayed SSPC; 7 patients (11%) had neither marker. Patients with DAVNP were older than those without (15 +/- 3 vs 13 +/- 4, P = 0.027) and the prevalence increased with age (38% <13 years, 50% 13-15, 70% >15, P = 0.041), while SSPC showed no age predilection. Patients under 13 years displayed SSPC more commonly than DAVNP (81% vs 38%, P = 0.004). DAVNP persisted after ablation in 10/32 (31%) patients, compared to 6/46 (13%) with persistent SSPC after ablation. The ability to use loss of the marker (present before, absent after ablation) as a surrogate for successful ablation was greater for SSPC than for DAVNP (66% vs 36%, P = 0.001).

CONCLUSION

SSPC is more common than DAVNP in young patients with AVNRT. SSPC is eliminated more frequently than DAVNP after acutely successful ablation, and appears to be a better indicator of the substrate for AVNRT. Elimination of SSPC may serve as a useful surrogate endpoint for slow pathway ablation.

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.

Radiofrequency Modification for Inducible and Suspected Pediatric Atrioventricular Nodal Reentry Tachycardia

INTRODUCTION

AV Node Reentry Tachycardia (AVNRT) is the second most common supraventricular tachycardia (SVT) undergoing pediatric radiofrequency ablation behind accessory pathway reentry tachycardias. AVNRT can be difficult to induce during electrophysiology study (EPS) and dual atrioventricular nodal (AVN) pathways physiology may not be demonstrated in young patients.

PURPOSE

This report is the largest single center long term pediatric experience of radiofrequency modification of slow AVN input fibers for inducible or suspected (non-inducible) AVNRT.

RESULTS

One hundred thirty-two patients underwent slow input AVN modification from 1993 to 2002. The mean patient age was 13.7 years (4-20 yrs) with 62M/70F. Outpatient tachycardia was documented by ambulatory monitoring in all patients. AVNRT was induced in 98/132 patients during EPS (group A) with mean SVT cycle length of 324 msec (230-570 msec). Initial AVN modification (group A) was successful in 97/98 patients (99%). During 34/132 EPS, AVNRT was non-inducible; dual AVN physiology was present in 19/34 (group B), and 15/34 did not show evidence for dual AVN physiology (group C). These 34 patients underwent empiric AVN modification following discussion with patients' families. Freedom of recurrence from SVT at 1 year was 96% for group A (94/98), 89% (17/19) for group B and 93% (14/15) for group C. 1 major and 6 minor complications occurred.

CONCLUSIONS

AVN modification for AVNRT can be performed safely and effectively in pediatric patients with good long-term results. Empiric slow pathway AVN modification for non-inducible SVT results in a high rate of freedom from recurrence of tachycardia.

Long-term efficacy of slow-pathway catheter ablation in patients with documented but noninducible supraventricular tachycardia

BACKGROUND

The long-term efficacy of radiofrequency catheter ablation of slow pathway in patients with dual atrioventricular node pathway and a documented but noninducible paroxysmal supraventricular tachycardia (PSVT) is not entirely clear.

METHODS

Forty nine patients (Group A) with documented but noninducible PSVT and dual atrioventricular node pathway were prospectively studied. Programmed electrical stimulation induced a single atrioventricular node echo beat in 13 patients, and double echo beats in 9 at baseline or during isoproterenol infusion. Clinical and electrophysiological characteristics of Group A patients were compared with that of age- and gender-matched patients with dual atrioventricular node pathway but inducible PSVT (Group B).

RESULTS

There was no significant difference in the electrophysiological properties of the fast and slow pathways between the two groups. Catheter ablation eliminated the slow pathway in all patients. There was no recurrence of PSVT in either Group A or Group B during the follow-up of 38 +/- 5 months.

CONCLUSIONS

In patients with dual atrioventricular node pathway and a documented but noninducible PSVT, catheter ablation of slow pathway is highly effective in preventing tachycardia in long term.

Inducible atrioventricular nodal reentry tachycardia in infants with a history of neonatal orthodromic reciprocating tachycardia

Atrioventricular nodal reentry tachycardia (AVNRT) is an uncommon mechanism of supraventricular tachycardia in neonates in whom orthodromic reciprocating tachycardia (ORT) predominates. We report three patients with structurally normal hearts who presented with neonatal ORT, documented by transesophageal electrophysiology studies at 2 to 3 weeks of age. At follow-up study at 8-12 months of age, no infant had inducible ORT, suggesting spontaneous regression of congenital accessory pathways; however, each had inducible tachycardia consistent with the typical form of AVNRT. The clinical significance of this finding is unknown and warrants further study.

AV nodal pathways in the R-R interval histogram of the 24-hour monitoring ECG in patients with atrial fibrillation

BACKGROUND

Patients with more than one AV nodal pathway show two and more peaks in the histogram of the R-R intervals of the Holter monitoring ECG during atrial fibrillation. It was the purpose of the present study to determine the number of patients showing more than one AV nodal pathway in a larger patient group with permanent atrial fibrillation by analyzing the Holter monitoring ECG.

METHODS

250 patients with permanent atrial fibrillation during Holter monitoring ECG were studied; 203 patients had structural heart disease. The number of peaks in the R-R interval histogram of each patient was determined. The distribution of the number of peaks in the R-R interval histogram in different patient groups was analyzed.

RESULTS

153 patients (61%) had one peak, 80 patients (32%) two peaks, 13 patients (5%) three peaks, and four patients (2%) four peaks, reflecting the number of different AV nodal pathways. In the different patient groups, in the patients with or without structural heart disease, with coronary heart disease, with a history of syncope, and in patients with a mean heart rate of more than 100/min, there was no significant difference in the distribution of the number of peaks in the R-R interval histogram.

CONCLUSIONS

In more than one third of all patients with permanent atrial fibrillation there are two, three, or four AV nodal pathways. It is suggested that this number of different AV nodal pathways found in the studied group can be applied to all humans. 38.8% of all patients with permanent atrial fibrillation have more than one AV nodal pathway; 6.4% of all patients with atrial fibrillation would benefit from an ablation of AV nodal pathways with shorter refractory periods for reduction of the heart rate.

Multiple AV nodal pathways with multiple peaks in the RR interval histogram of the Holter monitoring ECG during atrial fibrillation

Two or more peaks on the 24-hour electrocardiogram (ECG) RR interval histogram of patients with atrial fibrillation suggests the presence multiple AV nodal pathways. The prevalence of multiple AV nodal pathways in this population is unknown. The study included 250 patients with permanent atrial fibrillation during 24-hour ECG. The number of peaks on the RR interval histogram was measured in each patient. A single peak was present in 153 patients (61%), 80 patients (32%) had two peaks, 13 patients (5%) had three, and 4 patients (2%) had four peaks. Among the 97 patients (39%) with > 1 AV nodal pathway, the estimated mean heart rate reduction by hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods was 16 beats/min, from 82 to 65 beats/min. Among the overall population, 16 patients (6%) with > 1 AV nodal pathway had a mean heart rate > 100 beats/min. In this subgroup, modulation of AV node conduction by hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods yielded an estimated reduction in mean heart rate of 26 +/- 15 beats/min, from 110 +/- 9 beats/min to 84 +/- 14 beats/min (P < 0.01), a 23% decrease. The presence of > 1 AV nodal pathway was suspected in 39% of all patients with permanent atrial fibrillation. The hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods resulted in a clinically significant reduction in heart rate in 6% of patients in this population.

Supraventricular tachycardia in the neonate and infant

Supraventricular tachycardia (SVT) is the most common sustained arrhythmia to present in the neonatal and infancy age group. Predisposing factors (congenital heart disease, drug administration, illness and fever) occur only in 15% of infants. The presentation of SVT in the neonate is frequently subtle, and may include pallor, cyanosis, restlessness, irritability, feeding difficulty, tachypnea, diaphoresis and grunting. Congestive heart failure is more common in infants under 4 months of age (35% incidence). Age-related differences in the distribution of SVT mechanisms occur in different age groups. In infants under 1 year of age, the mechanisms underlying SVT are atrial tachycardia (15%), AV nodal re-entry tachycardia (5%), and AV reciprocating tachycardia (80%). Options for acute management include: use of the diving reflex, intravenous adenosine, transesophageal pacing, and cardioversion. Intravenous administration of verapamil should be avoided. Data regarding freedom from recurrence of untreated SVT in the first year of life are limited, and may be in the range of 25-60%. Chronic therapy with digoxin, beta-blockers, flecainide, sotalol and amiodarone has proved effective in controlling recurrent episodes of SVT. Radiofrequency ablation can be employed successfully in medically refractory cases, but should be avoided in this age group (increased complication rate).

Age related changes in dual AV nodal physiology

Dual atrioventricular nodal (DAVN) physiology has been reported in up to 63% of pediatric patients with anatomically normal hearts, yet atrioventricular nodal reentrant tachycardia (AVNRT) accounts for only 13%-16% of supraventicular tachycardia (SVT) in childhood. The incidence of AVNRT increases with age and becomes the most common form of SVT by adolescence. We investigated the age related electrophysiological responses to programmed atrial and ventricular stimulation in 14 pediatric patients who underwent intracardiac electrophysiological study prior to radiofrequency catheter ablation for AVNRT and who exhibited DAVN physiology. Single atrial and ventricular extrastimuli were placed following drive trains with cycle lengths of 400-700 ms and 350-500 ms, respectively. Six children (mean age 8.2 years, range 5.2-11.5 years) were compared to eight adolescents (mean age 16.6 years, range 13.3-20.7 years). Adolescents were found to have a significantly longer fast pathway effective refractory period (ERP) (median 375 vs 270 ms, P = 0.03), slow pathway ERP (median 270 vs 218 ms, P = 0.04), atrio-Hisian (AH) during AVNRT (median 300 vs 225 ms, P = 0.007), and AVNRT cycle length (median 350 vs 290 ms, P = 0.03). There was a strong trend for the AH measured at the fast pathway ERP to be longer in adolescents than in children (median 258 vs 198 ms, P = 0.055). The AH at the fast pathway ERP was more strongly correlated with baseline cycle length than with age (r = 0.7, P = 0.01 vs r = 0.5, P = 0.7). There was no significant difference in the retrograde VA conduction between adolescents and children. These results demonstrate an age related difference in AV nodal response to programmed atrial stimuli in pediatric patients with DAVN physiology and AVNRT. These differences are consistent with mechanisms that may explain the increased incidence of AVNRT in adolescents compared to children.

Radiofrequency catheter ablation of tachycardia in children with and without congenital heart disease: indications and limitations

From 1993 to 1998, a total of 100 consecutive pediatric patients with tachycardia (45 male and 55 female, aged 1 year 10 months to 17 years, 11+/-4 year) who underwent electrophysiological study were reviewed. Eleven of them were younger than 5 years. Two had tachycardia-related cerebrovascular accident. Congenital heart disease was found in 12 patients. After propofol anesthesia, the clinical tachycardia could not be induced in three (two atrial tachycardia and one AV nodal re-entrant tachycardia) and became nonsustained in five (atrial tachycardia). Mechanical ablation occurred in three and two had subsequent recurrences. Among the 85 cases who received radiofrequency ablation, the overall final success rate of RF ablation for all diagnoses was 94% with a diagnosis-specific success rate ranging from 100 to 57%. Tachycardia cardiomyopathy was noted in four (three atrial tachycardia and one junctional ectopic tachycardia) and all regressed after successful ablation. Success in two patients with left posterioseptal accessory pathway could only be achieved by delivering the energy at the middle cardiac vein. Two patients with right atrial isomerism had an 'AV nodal-to-AV nodal tachycardia' which was eliminated by ablation. Total recurrence rate was 13% but final success was achieved in all during re-study except the three patients who refused re-intervention. The atrial tachycardia developed in postoperative congenital heart disease was associated with the lowest success rate (57%) and highest recurrence rate (25%). Procedure-related complications occurred in four; two with transient brachial palsy, one with first-degree AV block and one with blood loss requiring blood transfusion. In conclusion, the experience of this single center confirmed the efficacy and safety of radiofrequency catheter ablation in treating pediatric arrhythmias, but the limitations in postoperative arrhythmias and the effects of propofol on tachycardia induction (especially the atrial tachycardia) need to be improved.

Progressive anterior ablation in the coronary sinus region: evidence to support the presence of a 'slow pathway' input in normal patients?

BACKGROUND

AV node modification is an emerging approach to rate control in patients with medically refractory atrial fibrillation. The mechanism of benefit of this procedure is not completely understood.

METHODS AND RESULTS

Twenty-two patients (age, 65+/-11 years; 16 women) with medically refractory paroxysmal atrial fibrillation referred for complete AV node ablation underwent serial ablations beginning at the level of the coronary sinus os progressing in a superior and anterior direction toward the His bundle. Serial atrial extrastimulus testing was performed to determine the effect of the progressive posteroseptal ablation in the region of the coronary sinus on the AV node antegrade refractory curve. Two of 22 patients had antegrade dual AV node pathways before ablation. Three patterns of response to serial ablation were noted. In 10 patients (45%), loss of the terminal portion of the AV node antegrade refractory curve occurred without evidence of fast pathway injury. In 7 patients (32%) the curve was shifted upward and to the left, consistent with nonspecific AV node damage. In 5 patients (23%), no effect could be attained before induction of complete AV block at superior and anterior ablation sites. Clinical variables and site of ablation did not predict response to serial ablations.

CONCLUSIONS

These data suggest that the mechanism of benefit of AV node modification in this population may be through elimination of "slow pathway" tissue in half of patients and nonspecific injury in the remainder. Modification without complete AV block may not be possible in a minority of patients, as the response to progressive ablation appears to be "all or none" conduction.

Spontaneous accelerated junctional rhythm: an unusual but useful observation prior to radiofrequency catheter ablation for atrioventricular node reentrant tachycardia in young patients

Between May 1990 and March 1995, 5 of 29 young patients (ages 4.2-25 years; median 14.1 years) undergoing RF ablation for atrioventricular node reentrant tachycardia (AVNRT) presented with spontaneous accelerated junctional rhythm (AJR) (CL = 500-750 ms), compared to 0 of 58 age matched controls undergoing RF ablation for a concealed AV accessory pathway (P = 0.004). In 3 of the 5 patients with AVNRT and AJR, junctional beats served as a trigger for reentry. During attempted slow pathway modification in the five patients with AVNRT and AJR, AVNRT continued to be inducible until the AJR was entirely eliminated or dramatically slowed. These 5 patients are tachycardia-free in followup (median 15 months; range 6-31 months) with only 1 of the 5 patients continuing to experience episodic AJR at rates slower than observed preablation. Episodic spontaneous AJR is statistically associated with AVNRT in young patients and can serve as a trigger for reentry. Successful modification of slow pathway conduction may be predicted by the elimination of AJR or its modulation to slower rates, suggesting that the rhythm is secondary to enhanced automaticity arising near or within the slow pathway.

Radiofrequency catheter ablation of the anterosuperior and posteroinferior atrial approaches to the AV node for treatment of AV nodal reentrant tachycardia: techniques for selective ablation of "fast" and "slow" AV node pathways

Radiofrequency catheter ablation has been established as a first-line curative treatment modality in patients with symptomatic AV nodal reentrant tachycardia (AVNRT). The successful sites of stepwise catheter ablation approaches of the so-called fast and slow pathways strongly suggest that AVNRT involves the atrial approaches to the AV node. The typical fast pathway ablation sites are located anterosuperior toward the apex of the triangle of Koch, which also contains the compact AV node, whereas the usual slow pathway ablation sites are located posteroinferior toward the base of the triangle of Koch at a greater distance to the compact AV node and bundle of His. Accordingly, ablation studies with large patient cohorts have demonstrated that fast pathway ablation carries a higher risk of inadvertent complete AV block. Thus, the slow pathway is clearly the primary target site, and fast pathway ablation is rarely necessary. Different approaches for slow pathway ablation have been elaborated: anatomically oriented stepwise techniques, ablation guided by double potentials recorded within the area of the slow pathway insertion, and combined techniques. The modern concept of AVNRT suggests that this arrhythmia involves the highly complex three-dimensional nonuniform anisotropic AV junctional area. Accordingly, mapping and ablation studies demonstrated that the anterior approach is not identical with fast pathway ablation, and the posterior approach is not identical with slow pathway ablation. Therefore, it is essential for interventional electrophysiologists to familiarize themselves with the anatomic and electrophysiologic details of this complex and variable specialized AV junctional region. In this review, the anatomic and pathophysiologic aspects of the AV junctional area as they relate to interventional therapy are summarized briefly, and the catheter techniques for ablation of the so-called fast and slow AV nodal pathways for the treatment of AVNRT are described.

Comparison of atrial-His intervals in patients with and without dual atrioventricular nodal physiology and atrioventricular nodal reentrant tachycardia

The purpose of this study was to compare the atrial-His intervals generated during programmed atrial stimulation in patients with and without dual atrioventricular nodal physiology and with and without inducible atrioventricular nodal reentrant tachycardia. Programmed atrial stimulation at a basic-drive cycle length of 500 to 600 msec was performed in 180 patients. The minimum atrial-His interval was defined as the atrial-His interval of the basic-drive beats. The maximum atrial-His interval was defined as the longest A2H2 interval. The criterion for dual atrioventricular nodal physiology was an increment of 50 msec in the A2H2 interval in association with a 10 msec decrement in the A1A2 interval. The minimum atrial-His interval was significantly shorter (106 +/- 34 msec vs 116 +/- 29 msec; p < 0.05) and the maximum atrial-His interval significantly longer (304 +/- 101 msec vs 222 +/- 56 msec; p < 0.001) in the 87 patients who had atrioventricular nodal reentry than in the 93 patients who did not. Among the 87 patients who had atrioventricular nodal reentry, the maximum atrial-His interval was significantly longer in 53 patients who had dual atrioventricular nodal physiology than in 34 patients who did not (340 +/- 105 msec vs 249 +/- 62 msec; p < 0.001). Among the 66 patients who had dual atrioventricular nodal physiology, the maximum atrial-His interval was significantly longer in 53 patients who had atrioventricular nodal reentry than in 13 patients who did not (340 +/- 105 msec vs 268 +/- 61 msec; p < 0.01). The insensitivity of the conventional dual atrioventricular nodal physiology criterion for the detection of dual atrioventricular nodal pathways is in part attributable to a lesser degree of slowing of conduction in the slow pathway relative to the fast pathway in some patients who have atrioventricular nodal reentry. The inability to demonstrate atrioventricular nodal reentry despite the presence of dual atrioventricular nodal physiology in some persons may be attributable in part to an inadequate degree of conduction delay in the slow pathway.

Slow pathway ablation in patients with documented but noninducible paroxysmal supraventricular tachycardia

OBJECTIVES

The purpose of this study was to assess the clinical efficacy of radiofrequency ablation of the slow pathway in patients with documented but noninducible paroxysmal supraventricular tachycardia (PSVT) who have evidence of dual atrioventricular (AV) node pathways.

BACKGROUND

Patients with a documented history of PSVT at times do not have inducible PSVT in the electrophysiology laboratory. Because dual AV node pathways serve as the substrate for AV node reentrant tachycardia (AVNRT), ablation of the slow pathway potentially may be useful in these patients.

METHODS

The subjects in this prospective study were seven consecutive patients who underwent an electrophysiologic procedure because of documented PSVT and were found to have dual AV node physiology or inducible single AV node echo beats, but no inducible PSVT despite the administration of isoproterenol and atropine. Their mean (+/- SD) age was 33 +/- 13 years, and they had been symptomatic for 12 +/- 12 years. The frequency of the episodes of PSVT ranged from > or = 1/day to 1/month. The rate of the documented episodes ranged from 170 to 260 beats/min, and discrete P waves were not apparent. Slow pathway ablation was performed with 9 +/- 4 applications of radiofrequency energy using a combined anatomic and electrogram mapping approach.

RESULTS

All evidence of dual AV node pathways was eliminated in six patients, and dual AV node physiology remained present in one patient. During a mean follow-up period of 15 +/- 10 months (range 8 to 27), no patient had a recurrence of symptomatic tachycardia (success rate 95% confidence interval 65% to 100%).

CONCLUSIONS

Slow pathway ablation may be clinically useful in patients with documented but noinducible PSVT who have evidence of dual AV node pathways.

Efficacy and risks of medical therapy for supraventricular tachycardia in neonates and infants

To assess the efficacy and safety of current pharmacologic therapy for supraventricular tachycardia (SVT) in infants, we reviewed 112 infants treated between July 1985 and March 1993. The SVT mechanism was determined by esophageal electrophysiologic study and involved an accessory pathway in 86, atrioventricular (AV) node reentry in 10, atrial muscle reentry in 11, and an ectopic atrial tachycardia in 5 patients. Of six infants not treated, none had clinical recurrences of SVT. Of the 106 patients treated, 70% remained free of tachycardia while receiving digoxin, propranolol, or both. Class I antiarrhythmic agents were necessary for 13 patients, and class III agents were required for another 13 infants. Verapamil was used in one infant with AV node reentry tachycardia. Nine infants with complex clinical presentations were believed to have failed medical management and underwent radiofrequency ablation. Five patients died, four of complications related to structural heart disease and one shortly after radiofrequency ablation was performed. No deaths appeared to be related to antiarrhythmic medications. No drug-related side effects requiring medication change occurred, and no proarrhythmia was observed. Thus medical therapy appears to be effective and safe in infants with SVT. Radiofrequency ablation should be reserved for rare infants who fail aggressive medical regimens or when the situation is complicated by ventricular dysfunction, severe symptoms, or complex congenital heart disease.

Supraventricular tachyarrhythmias. Pharmacologic versus nonpharmacologic approaches

Nonpharmacologic approaches to the long-term management of SVTs have evolved rapidly and now offer to patients a safe, effective alternative for symptomatic relief from many SVTs. By far, radiofrequency catheter ablation, a technology less than 10 years old, offers the least invasive and most cost-effective nonpharmacologic alternative for many SVTs. Knowledge gained through electrophysiologic and ablation studies has enlarged the understanding of SVTs and may enable electrophysiologists to approach the more common and morbid condition of atrial fibrillation. From a societal standpoint, catheter ablation can remain a cost-effective mode of treatment if patient selection is stringent. The next 10 years should see further refinement in technique and in understanding of SVTs, improved technology, and enlarging applications of radiofrequency energy to cure or modify cardiac arrhythmias.

The architecture of the atrioventricular conduction axis in dog compared to man: its significance to ablation of the atrioventricular nodal approaches

AV Node in Dog and Man.

INTRODUCTION

Advances in treating patients with dual atrioventricular nodal pathways have called for a better understanding of the morphology of the approaches to the atrioventricular node. In this respect, it has recently been suggested that, in dog, anatomically discrete muscle bundles originating from the sinus node represent the substrate of the dual pathways recognized electrophysiologically in patients with atrioventricular nodal reentrant tachycardia. This concept is at odds with most anatomic studies of the human specialized atrioventricular junctional area. In this study, therefore, we studied histologically the junctional area in dog hearts, comparing them with our own findings in human heart and the descriptions of the earliest investigators.

METHODS AND RESULTS

Five dog and six human hearts were prepared for histology and sectioned serially in different planes. Reconstructions were then made from each of three dog and two human hearts sectioned in orthogonal planes. Gross differences in the anatomy of the atrioventricular junctional area and in the structure of the conduction system were obvious between dog and human hearts. The penetrating portion of the conduction axis was longer in the dog, being much more extensively embedded in the central fibrous body. The atrioventricular node, in both dog and man, was composed of a zone of transitional cells overlying a compact region. The zone of transitional cells in the dog was more extensive posteriorly than anteriorly. No bundles insulated anatomically by fibrous tissue were found either in the internodal atrial myocardium or in the approaches to the atrioventricular node. Our findings in both dog and man are comparable with the initial descriptions of the atrioventricular junctional area.

CONCLUSION

Although the disposition of the conduction system in dog and man is basically similar, there are important differences which relate to the gross anatomy. The anatomic substrate for functional duality of the inputs to the atrioventricular node remains unclear, since our study confirms that the concept of insulated atrionodal tract has no morphologic basis.

Mechanisms of AV node reentrant tachycardia in young patients with and without dual AV node physiology

Recent advances in electrophysiological mapping and radiofrequency catheter ablation have demonstrated the participation of perinodal atrial tissue or pathways in atrioventricular node reentrant tachycardia (AVNRT). Current concepts of the role of these pathways in the genesis of the various forms of AVNRT continue to evolve. In view of these recent advances, this study investigated the electrophysiology of AVNRT in young patients, and factors potentially associated with variant forms of this arrhythmia. Detailed programmed stimulation and catheter mapping were performed in 35 consecutive young patients with AVNRT. This group consisted of 15 male and 20 female patients, with a mean age of 12.1 +/- 4.2 years (range 3-18 years). Of the 35 patients, 23 demonstrated dual AV node physiology, either in response to a critically timed extrastimulus (n = 17) or to rapid pacing (n = 6). The common form (antegrade slow-retrograde fast) of AVNRT was demonstrated in 21 of these 23 patients. Antegrade fast-retrograde slow (n = 1) and antegrade slow-retrograde slow (n = 1) forms of AVNRT were identified in the 2 other patients. In contrast, only 5 of the 12 patients who did not demonstrate dual AV node physiology had the common form of AVNRT (P = 0.03). Five of these patients also had the slow-slow form of AVNRT, while 1 patient each had a fast-slow and fast-fast form of AVNRT.(ABSTRACT TRUNCATED AT 250 WORDS)

Atypical forms of supraventricular tachycardia due to atrioventricular node reentry in children after radiofrequency modification of slow pathway conduction

OBJECTIVES

This study was performed to investigate the prevalence, mechanisms and clinical significance of supraventricular tachycardias inducible in children or adolescents after radiofrequency modification of slow pathway conduction for the treatment of atrioventricular (AV) node reentrant tachycardia.

BACKGROUND

Limited data have been reported with regard to the physiology of AV node reentrant tachycardia in young patients. Radiofrequency catheter ablation allows evaluation of the effects of selective modification of the different pathways involved in AV node reentrant tachycardia.

METHODS

Selective modification of slow pathway conduction was performed in 18 young patients (12.9 +/- 3.4 years old) with typical (anterograde slow-retrograde fast) AV node reentrant tachycardia. Radiofrequency energy was applied across the posteromedial or midseptal tricuspid annulus, guided by slow pathway potentials and anatomic position. Programmed stimulation was performed after modification of slow pathway conduction defined as noninducibility of typical AV node reentrant tachycardia.

RESULTS

Modification of slow pathway conduction was achieved in each patient, with a median of four applications of radiofrequency energy. However, atypical forms of supraventricular tachycardia were inducible in 9 of 18 young patients after slow pathway modification: AV node reentrant tachycardia with 2 to 1 AV block (seven patients); anterograde fast-retrograde slow AV node reentrant tachycardia (five patients); and sustained accelerated junctional tachycardia (two patients). In comparison, atypical forms of tachycardia were inducible in only 2 of 59 adult patients with AV node reentrant tachycardia undergoing slow pathway modification in the same laboratory (p = 0.01). Additional applications of radiofrequency energy to the posteromedial tricuspid annulus rendered AV node reentrant tachycardia with 2 to 1 block and the fast-slow form of AV node reentrant tachycardia noninducible. Junctional tachycardia terminated spontaneously in both patients. During 9.8 +/- 3 months of follow-up, slow-fast AV node reentrant tachycardia has recurred in one patient, whereas fast-slow AV node reentrant tachycardia has occurred in two patients, both with inducible fast-slow tachycardia after the initial modification of slow pathway conduction.

CONCLUSIONS

Initial applications of radiofrequency energy may selectively modify the anterograde conduction of slow pathway fibers in young patients with AV node reentrant tachycardia. This may result in AV node reentrant tachycardia with 2 to 1 AV block or a reversal of the reentrant circuit (fast-slow tachycardia). Induction of these tachyarrhythmias indicates that further applications of radiofrequency energy are required for the successful modification of slow pathway conduction in young patients. The increased prevalence of inducible atypical arrhythmias among young patients suggests differences in the anatomic or electrophysiologic substrate of AV node reentrant tachycardia that may evolve as a function of age.

"AV nodal" reentry: Part I: "AV nodal" reentry revisited

This review is the first of a two-part series of articles on "atrioventricular [AV] nodal reentry." The early clinical literature as well as the experimental studies are reviewed, and more recent morphologic data are presented, with the aim of clarifying whether the reentrant circuit is confined to the AV node, or consists in part of extranodal components. Most of the evidence supports the concept that atrial tissue is an essential link in the reentrant pathway. Arguments will be presented to indicate that within the AV node, the separation between antegrade and retrograde pathways is functional, not anatomical, and that both pathways are in electrotonic contact.

Morphology of the cardiac conduction system in patients with electrophysiologically proven dual atrioventricular nodal pathways

INTRODUCTION

Although the electrophysiologic criteria for dual atrioventricular nodal pathways are well established, the anatomical substrate is still unclear.

METHODS AND RESULTS

We examined the hearts from 10 patients who had been studied electrophysiologically prior to cardiac transplantation. All 10 patients were male, aged 22 to 60 years. Nine of the 10 patients had dual atrioventricular nodal pathways according to accepted criteria. Histologic studies of the atrioventricular conduction system showed normal structure of the atrioventricular node in all 10 hearts, with minor variations within the node in 3 cases, within the penetrating bundle in 3 cases, and within the nonbranching bundle in 3 cases. The atrial approaches to the atrioventricular node were generally scanty in 6 hearts. The solitary case that was shown electrophysiologically to lack dual pathways had no obvious difference in the structure of the nodal area other than sparsity of transitional cells. We were unable to locate any extranodal atrial tracts as described by other investigators.

CONCLUSION

The anatomical substrate for conduction over dual pathways may be too subtle to be detected by gross morphologic studies. Since dual pathways were unmasked in all patients but one during electrophysiologic studies, it may be that the potential for these pathways is ubiquitous.

Role of intravenous isoproterenol in the electrophysiologic induction of atrioventricular node reentrant tachycardia in patients with dual atrioventricular node pathways

To assess the role of intravenous isoproterenol for the facilitation of electrophysiologic induction of atrioventricular (AV) node reentrant tachycardia, 20 patients with dual AV node pathways who lacked inducible AV node reentrant tachycardia at control study had a constant isoproterenol infusion administered and underwent repeat study. Six (30%) of 20 patients (group I) had inducible AV node reentrant tachycardia during isoproterenol infusion whereas the other 14 (70%) patients (group II) did not. Paroxysmal supraventricular tachycardia was clinically documented in all 6 group I patients compared to 3 (21%) of 14 group II patients (p = 0.002). The sensitivity and specificity of isoproterenol-facilitated induction of AV node reentrant tachycardia were 67 and 100%, respectively. The isoproterenol-facilitated induction of sustained AV node reentry was mediated by resolution of the weak link in anterograde slow pathway in 2 (33%) patients, in retrograde fast pathway in 3 (50%) and in both anterograde slow and retrograde fast pathways in 1 (17%) patient. Four group I patients were given intravenous propranolol, 0.2 mg/kg body weight, and had complete suppression of isoproterenol-facilitated induction of AV node reentry. Thus, intravenous isoproterenol is a rather sensitive and highly specific adjunct to electrophysiologic induction of AV node reentrant tachycardia in patients with dual AV node pathways but without inducible sustained AV node reentry.

Nonsustained atrial flutter in a child without congenital heart disease

An 8 1/2-year-old child without heart disease developed nonsustained atrial flutter by programmed atrial stimulation. Atrial re-entry was the underlying mechanism.

Multiple anterograde and retrograde AV nodal pathways: demonstration by multiple discontinuities in the AV nodal conduction curves and echo time intervals

Programmed electrical cardiac stimulation was performed in a 40-year-old man with documented recurrent, sustained ventricular tachycardia which was refractory to standard medical therapy. Both the presence of several discontinuities in the AV nodal conduction curves during atrial and ventricular stimulation and the time intervals of the AV nodal echo phenomena suggested the presence of multiple AV nodal pathways. The results of this study are of interest in further increasing our understanding of the electrophysiologic behavior of the human AV node.

Initiation of atrioventricular nodal reentrant tachycardia in patients with discontinuous anterograde atrioventricular nodal conduction curves with and without documented supraventricular tachycardia: observations on the role of a discontinuous retrograde conduction curve

To evaluate factors playing a role in initiation of atrioventricular (AV) nodal reentrant tachycardia utilizing anterogradely a slow and retrogradely a fast conducting AV nodal pathway, 38 patients having no accessory pathways and showing discontinuous anterograde AV nodal conduction curves during atrial stimulation were studied. Twenty-two patients (group A) underwent an electrophysiologic investigation because of recurrent paroxysmal supraventricular tachycardia (SVT) that had been electrocardiographically documented before the study. Sixteen patients (group B) underwent the study because of a history of palpitations (15 patients) or recurrent ventricular tachycardia (one patient); in none of them had SVT ever been electrocardiographically documented before the investigation. Twenty-one of the 22 patients of group A demonstrated continuous retrograde conduction curves during ventricular stimulation. In 20 tachycardia was initiated by either a single atrial premature beat (18 patients) or by two atrial premature beats. Fifteen of the 16 patients of group B had discontinuous retrograde conduction curves during ventricular stimulation, with a long refractory period of their retrograde fast pathway. Tachycardia was initiated by multiple atrial premature beats in one patient. Thirteen out of the remaining 15 patients received atropine. Thereafter tachycardia could be initiated in three patients by a single atrial premature beat, by two atrial premature beats in one patient, and by incremental atrial pacing in another patient. In the remaining eight patients tachycardia could not be initiated. Our observations indicate that the pattern of ventriculoatrial conduction found during ventricular stimulation is a marker for ease of initiation of AV nodal tachycardia in patients with discontinuous anterograde AV nodal conduction curves.

Induction of nonsustained atrial flutter by programmed atrial stimulation in children: incidence, mechanisms, and clinical implications

Nonsustained atrial flutter was induced by programmed atrial extrastimulation in 6 (4%) of 137 children with preoperative congenital heart defects, who underwent electrophysiologic evaluation as part of cardiac catheterization. None of these patients had ECG or clinical evidence of arrhythmias. Atrial reentry was induced by programmed atrial extrastimulation in these six patients at coupling intervals slightly longer than the coupling interval at which flutter was induced. The flutter cycle length was similar to the atrial refractory periods. The duration ranged between 0.4 second and 60 seconds. The PA interval and the duration of the P wave were normal in all of the patients. Five of the six had normal PR intervals. It is concluded that nonsustained atrial flutter may be induced by programmed atrial extrastimulation in dysrhythmia-free children. The cycle length is determined by atrial refractoriness and, contrary to adults with clinical atrial flutter, prolonged PA and P wave duration are not predisposing factors.

Maturational changes in ventriculoatrial conduction in the intact canine heart

This study reports on the changes in ventriculoatrial (VA) conduction that occur with maturation. Programmed atrial and ventricular premature extra-stimulation (coupled to a fixed paced cycle length) and rapid atrial pacing were performed in three groups of dogs: Group I = 8 neonates aged 5 to 14 days, Group II = 9 young dogs aged 6 to 9 weeks and Group III = 10 adult dogs. High right atrial, His bundle and right ventricular electrograms were recorded. There were no differences in the AH intervals at rest. In all but five animals, atrioventricular conduction was limited by the atrial functional refractory period (Group I, 109 +/- 12 ms; Group II, 152 +/- 22 ms; Group III, 167 +/- 19 ms). As expected, with rapid atrial pacing, Wenckebach conduction developed at a shorter cycle length in the younger animals (Group I, 145 +/- 20 ms; Group II, 153 +/- 15 ms; Group III, 200 +/- 25 ms, p less than 0.01). Ventriculoatrial conduction was documented in 87% of Group I puppies and 100% of Group II, but only 40% of Group III dogs. The effective and functional refractory periods of the VA conduction system were significantly shorter in the more immature groups of dogs (effective/functional: Group I, 124 +/- 27/168 +/- 22 ms; Group II, 139 +/- 23/202 +/- 13 ms; Group III, 270 +/- 28/326 +/- 25 ms; p less than 0.01). Relative to the adult dog, the immature heart showed a greater incidence of VA conduction and shorter VA refractory periods. This enhanced VA conduction may be of physiologic importance in the initiation and perpetuation of certain supraventricular arrhythmias.

Multiple atrioventricular nodal pathways--a new electrophysiological phenomenon in children

Multiple atrioventricular (A-V) nodal pathways are described in five dysrhythmia-free children with congenital heart defects. The five were some (2.9%) of 175 children who underwent diagnostic cardiac catheterization and electrophysiological evaluation over a three year period. Supraventricular tachycardia was not induced during the electrophysiological evaluation. Medical follow-up is recommended since multiple A-V nodal pathways have been demonstrated in adults with A-V nodal reentrant tachycardia.

Hemodynamics and intracardiac conduction after operative repair of tetralogy of Fallot

Electrophysiologic studies were performed in 47 children aged 3 to 18 years, 15 of whom had cardiac arrhythmias 1 to 15 years after repair of tetralogy of Fallot. Six exhibited sinus or atrioventricular nodal dysfunction, 8 had ventricular extrasystoles, and 1 had supraventricular tachycardia. Hemodynamic and electrophysiologic data were obtained at postoperative catheterization. Although electrophysiologic responses were abnormal in a proportion of both the children with and those without arrhythmia, hemodynamic values were similar. Three of 6 children with impaired sinus impulse generation or atrioventricular nodal conduction had a prolonged A-H interval, and in 3 Wenckebach heart block developed at low pacing rates. Ventricular ectopic rhythm was not associated with any particular abnormality of basic intracardiac conduction intervals. Thus, arrhythmias and conduction abnormalities are not consistently related to residual right ventricular hypertension. Abnormalities in electrophysiologic function are common after repair of tetralogy of Fallot in patients with sinus rhythm and may have prognostic implications for these patients.

Sudden sinus slowing with junctional escape: a common mode of initiation of juvenile supraventricular tachycardia

After noting bradycardia-induced supraventricular tachycardia (SVT) in two successive children with SVT, we analyzed Holter monitor recordings done on 66 children with suspected or proved SVT. Ten children had apparent reentry SVT. The most common mode of initiation (eight of 10 patients) was not premature atrial beats, but sudden sinus pause with a junctional escape beat (JEB), usually fused with the delayed sinus P wave, initiating the tachycardia. Electrophysiologic studies in five children who had this mode of initiation showed evidence of reentry in four, possibly by dual atrioventricular nodal (AVN) pathways. Since sudden sinus pause and JEB are relatively uncommon in adults, the disappearance of this phenomenon with age may be the most significant reason why children often have less tachyarrhythmia as they get older. Both propranolol and digoxin significantly increased the numbers of episodes of SVT in the three patients tested with serial Holter monitoring.