Anterograde Conduction Research Articles

Efficacy of Electroanatomical Mapping for Radiofrequency Ablation of Right-sided Accessory Pathways

Introduction: Due to the difficulty in performing detailed mapping around the tricuspid annulus and the high occurrence of mechanical trauma during the procedure, the outcome of right‐sided accessory pathway (AP) ablation still has a relatively high primary failure and recurrence rate.Methods and Results: Six patients with right free‐wall APs underwent electroanatomical mapping. The AP had retrograde unidirectional conduction in 3 patients, anterograde unidirectional conduction in 1 patient, and bidirectional conduction in 2 patients. The right atrial (RA) activation map was constructed during right ventricular (RV) pacing (n = 5), and the RV activation map was constructed during RA pacing (n = 3). During mapping, the AP conduction was interrupted by catheter mechanical trauma in 3 patients. The first RF application successfully eliminated the AP conduction within 2 seconds in 3 patients with concealed pathways. In the remaining 3 patients, rescue RF energy was delivered at the tagged bump site on the map. The mean procedure time was 214 ± 77 minutes, and mean fluoroscopy time 63 ± 23 minutes. No recurrence occurred during 12 ± 3.2 months of followup in any of the patients.Conclusions: With the guidance of an electroanatomical mapping system, right‐sided accessory pathways can be satisfactorily eliminated without later recurrence.

Case Report of Atrio-Ventricular Reentry Tachycardia Due to Accessory Pathway Having Unidirectional Anterograde Conduction Block and Typical Atrio-Ventricular Nodal Reentry Tachycardia Both Clinically Cured by Ablation of the Only Atrio-Ventricular Nodal “Slow Pathway”

Introduction We report the case of a 49-year old male patient with recurrent palpitations and 2 different supraventricular tachycardias due to atrio-ventricular (AV) nodal reentry and orthodromic AV reentry sustained by a left-sided, unidirectional, AV accessory pathway (AP) evidenced during electrophysiological study. Method and Results During the baseline electrophysiological study, dual AV nodal conduction (90 ms A2H2 sudden jump at 320 ms A1A2 coupling interval), and non-decremental, eccentric, ventriculo-atrial conduction due to a left-sided, unidirectional, postero-septal AP were documented. Both typical AV nodal reentrant and orthodromic AV reentrant tachycardias were induced by programmed electrical stimulation several times. Intervals measured during each tachycardia are reported in the Table. The diagnosis of tachycardia mechanism was performed according to standard criteria. In both cases, shift and sustained conduction over the AV “slow pathway” were required for tachycardia inductions and maintenances, respectively. Accordingly, catheter ablation was performed by targeting the AV nodal “slow pathway” first with radiofrequency current applications delivered at the inferior portion of the Koch's triangle. Irritative, slow-rate junctional rhythm was observed during ablation. Afterward, programmed electrical stimulation demonstrated continuous AV nodal conduction curve, persistent conduction over the AP, and only single orthodromic AV echo beats inducible under baseline condition and pharmacological stress (atropine 0.02 mg/kg i.v. bolus and continuous isoprenaline i.v. administration). Sustained reentrant tachycardias were not inducible any more. For these reasons, the procedure was stopped without any attempt to ablate the AP. After a 18 month follow-up the patient is still asymptomatic without antiarrhythmic drug usage. Conclusion AV nodal “slow pathway” ablation may abolish both typical AV nodal reentry tachycardia and orthodromic AV reentry tachycardia induction when the latter arrhythmia is dependent from AV nodal “slow pathway” conduction for induction and maintenance. This ablation strategy resulted in a mid-term clinical success in the reported case, and it could be considered, under some instances (i.e. right antero-septal accessory pathways, older patients, etc), in order to reduce the procedure risks due to multiple arrhytmia substrates. ![Graphic][1] [1]: /embed/graphic-1.gif

Effect of Conduction Mode and Location on Electrophysiologic Characteristics of Accessory Pathways

The conduction properties of accessory pathways (APs) are independent of location and conduction mode (except in patients with multiple, Mahaim, and slowly conducting APs). Patients with right-sided APs show higher rates of atrial fibrillation and longer arrhythmia cycle length due to slower anterograde conduction over the atrioventricular node during atrioventricular reentrant tachycardia.

Torsade de Pointes in a Patient With Wolff-Parkinson-White Syndrome

A 17-year-old girl presented with syncope 1 year ago and complained of dizziness for 6 months. Her paternal aunt had died from sudden cardiac death at age 22. On the ECG, preexcitation was present, and Holter recording revealed recurrent wide QRS tachycardia with short cycle length. Episodes of atrial fibrillation with rapid anterograde conduction over the accessory pathway …

Mechanism of Induction of Atrioventricular Node Reentry by Simultaneous Anterograde Conduction Over the Fast and Slow Pathways

AV node reentry (AVNRT) is typically induced with anterograde (Ant) block over the fast pathway (FP) and conduction over the slow pathway (SP), with subsequent retrograde (Ret) conduction over the FP. Rarely, a premature atrial complex (PAC) conducts simultaneously over the FP and SP to induce AVNRT (2 for 1). This study investigates the mechanism of 2 for 1 induction. Of 192 consecutive patients (pts) undergoing posteroseptal radiofrequency ablation to treat AVNRT, 4 pts (2%) had 2 for 1 AVNRT induction. All needed isoproterenol for AVNRT initiation, and Ant conduction was over the SP during AVNRT. Controls (n = 15) were randomly selected from the remaining 188 pts and required isoproterenol to induce AVNRT with Ant block over the FP. For 2 for 1 versus control, respectively, there was no difference in mean age (55 vs. 46 yr), AVNRT cycle length (420 vs. 320 ms), or the Ant effective refractory period of the FP (320 vs. 344 ms). Of note, the PAC that induced AVNRT had a significantly longer AH interval over the SP in pts with 2 for 1 versus control (470 vs. 320 ms, P = 0.016), even though the A1A2 interval for induction was longer for 2 for 1 (315 vs. 260 ms, P = 0.003). Ret conduction over the SP was relatively poor in the 2 for 1 group as evidenced by 4/4 pts with induction of AVNRT during incremental ventricular pacing versus only 1/15 control pts (P < 0.001). The unique induction of AVNRT by a PAC with simultaneous conduction over the FP and SP is best explained by minimal to no retrograde invasion of the SP from the anterogradely conducted fast pathway impulse, and consistent with this observation is the initiation of slow/fast AVN reentry during incremental RV pacing.

The electrocardiogram during sinus rhythm and tachycardia in patients with Mahaim fibers: The importance of an “rS” pattern in lead III

The purpose of the study was to identify the electrocardiographic (ECG) characteristics of the Mahaim fiber. Mahaim fibers are slowly conducting accessory pathways reaching into the right ventricle. They often play a role in tachycardias. We retrospectively analyzed 40 patients with Mahaim fibers. Five patients had associated Wolff-Parkinson-White syndrome and were excluded from the study. Two patients had a short atrioventricular decremental accessory pathway and were also excluded. The remaining 33 patients had a tachycardia with anterograde conduction over a Mahaim fiber. Twenty were female. Their mean age was 24 +/- 10 years. The most common pattern of minimal preexcitation during sinus rhythm was an rS pattern in lead III. This was found in 20 patients. There was a match between the presence of rS in lead III during sinus rhythm and left axis deviation during tachycardia with anterograde conduction over the Mahaim fiber. After ablation, a different QRS pattern emerged in lead III, indicating the absence of conduction over the Mahaim fiber. To obtain information on the prevalence of an rS pattern in lead III in age-matched controls with palpitations and without structural heart disease, the 12-lead ECG of 200 young individuals were examined. An rS pattern in lead III was found in 6%. A narrow QRS with an rS pattern in lead III during sinus rhythm in a patient with a history of palpitations should alert the physician to the possibility of a Mahaim fiber. During tachycardia, these patients typically show a left bundle branch block-like QRS complex with left axis deviation.

Electrocardiogram during tachycardia in patients with anterograde conduction over a Mahaim fiber: Old criteria revisited

The aim of this study was to prospectively evaluate the sensitivity, specificity, and positive and negative predictive values of previously described ECG criteria to identify preexcited tachycardia due to decrementally conducting accessory pathways (QRS axis between 0 and -75 degrees , QRS width < or = 0.15 seconds, an R wave in lead I, an rS pattern in lead V(1), RS > 1 QRS transition > V(4), and cycle length between 220 and 450 ms). Preexcited tachycardia associated with decrementally conducting right-sided accessory pathways usually shows a rather "narrow" QRS complex and can be difficult to differentiate from supraventricular tachycardia (SVT) with left bundle branch block (LBBB) aberrant conduction. We analyzed three groups of patients: 32 patients with an atriofascicular pathway (group I); 8 patients with long (n = 3) or short (n = 5) decrementally conducting right-sided AV pathway (group II); and a control group that consisted of 35 patients with SVT and LBBB (group III). Presence of all six criteria had 87.5% sensitivity in group I and a 0% sensitivity in group II. There were four false negatives in group I. The negative predictive value was 82.5%, with six false positives in group III (five patients with an aberrant LBBB-shaped tachycardia with ventriculoatrial conduction over an accessory AV pathway). The criterion cycle length was not helpful. Criteria for identifying a tachycardia with anterograde conduction over a Mahaim fiber are helpful only in atriofascicular pathways, with a sensitivity of 87.5% and a negative predictive value of 82.5%. The major cause of false positives was a tachycardia with aberrant LBBB conduction and ventriculoatrial conduction over an accessory AV pathway.

Exploration électrophysiologique endocavitaire: Étude de la fonction sinusale et de la conduction auriculoventriculaire

The different steps of intracardiac electrophysiological investigations are addressed in this chapter, except for those concerning tachycardias (analyzed in other chapters). Conduction is considered at all levels: the sinus node function, anterograde AV nodal conduction, intrahisian and infrahisian conduction, and retrograde conduction.

Taquicardia recíproca de la unión auriculoventricular: características electrofisiológicas en un paciente con la variedad paroxística. Caso clínico

Junctional reciprocating tachycardia is an atrioventricular reentrant tachycardia whose anterograde conduction occurs via the His Purkinje and the retrograde conduction via an accessory pathway with slow conduction. The most common form is incessant tachycardia but a paroxysmal form also exists. We report a 35 years old female with recurrent paroxysmal tachycardia, that underwent electrophysiological evaluation. A left posterolateral accessory pathway was documented. Reciprocating paroxysmal tachycardia was induced by electrical stimulation and a successful pathway ablation was performed.

Termination of paroxysmal supraventricular tachycardia by tecadenoson (CVT-510),a novel A1-adenosine receptor agonist

ObjectivesThe aim of this study was to evaluate tecadenoson safety and efficacy during conversion of paroxysmal supraventricular tachycardia (PSVT) to sinus rhythm. BackgroundTecadenoson (CVT-510), a novel adenosine receptor (Ado R) agonist, selectively activates the A1Ado R and prolongs atrioventricular (AV) nodal conduction at doses lower than those required to cause A2Ado R-mediated coronary and peripheral vasodilation. Unlike adenosine, which non-selectively activates all four Ado R subtypes and produces unwanted effects, tecadenoson appears to terminate AV node-dependent supraventricular tachycardias without hypotension and bronchoconstriction. MethodsIn this open-label, multicenter, dose escalation study, tecadenoson was administered to 37 patients (AV node re-entrant tachycardia, n = 29; AV re-entrant tachycardia, n = 8) with inducible PSVT sustained for ≥1 min during an electrophysiology study. Seven regimens (0.3 to 15 μg/kg) of up to two identical tecadenoson intravenous bolus doses were administered. ResultsAfter the first or second bolus, PSVT converted to sustained sinus rhythm for ≥5 min in 86.5% (32/37) of the patients, with 91% (29/32) of the conversions occurring after the first bolus (most within 30 s), coincident with anterograde conduction block in the AV node. No effects on sinus cycle length (SCL) or systolic blood pressure were observed. The atrial-His (AH), but not the His-ventricular (HV) interval was prolonged up to 5 min after the final tecadenoson bolus, returning to baseline by 10 min. Tecadenoson was generally well tolerated. ConclusionsIn this study, tecadenoson rapidly terminated sustained PSVT by depressing AV nodal conduction without causing hypotension. After sinus rhythm restoration, there was minimal AH interval prolongation without HV interval or SCL prolongation.

Electrophysiological features of orthodromic atrioventricular reentry tachycardia in patients with wolff-Parkinson-white syndrome and atrial fibrillation.

The aim of this study was to compare the electrophysiological features of tachycardia between WPW patients with and without AF. The study population consisted of 114 patients with WPW syndrome and reciprocating tachycardia during electrophysiological study. Two groups were selected: group I with AF during the procedure(n = 42)and the control group n = 72 without AF (group II). Cycle length (V-V interval), antero A-V, retrograde V-A conduction time during tachycardia and indexes V-A/V-V were analyzed. In addition, the relation between antero-, retrograde conduction time, and V-V was evaluated. Selection of the most predictive factor for AF presence was performed using regression analysis. Significant differences between the two groups were observed. These included a higher rate of tachycardia, shorter anterograde conduction time, A-V/V-V-indexes, longer retrograde conduction time, and V-A/V-V-indexes in group I compared with group II. Significant, positive correlations between anterograde conduction time and V-V were present in both groups, but retrograde conduction correlated significantly with the V-V-interval only in group II and group I (r = 0.37 vs r =-0.01, respectively). Significant, negative correlations between A-V and V-A conduction time in all analyzed points has been found to exist in group I (r =-0.45 for the point of maximal preexcitation [PMP]), whereas there were no significant correlations between these parameters in group II (r = 0.04). The most powerful AF predictor has been identified as the V-A/V-V index. The presence of AF in WPW syndrome may be associated with discrete patient characteristics. Ventricular activation occurs earlier, and atrial later, in the tachycardia cycle in AF than in patients free of AF. The different ability of the accessory pathway for adaptation to tachycardia rate changes in group I causes prolonged retrograde conduction over the pathway while the tachycardia rate increases.

Optimal ventricular rate slowing during atrial fibrillation by feedback AV nodal-selective vagal stimulation.

Although the beneficial effects of ventricular rate (VR) slowing during atrial fibrillation (AF) are axiomatic, the precise relationship between VR and hemodynamics has not been determined. We hypothesized that selective atrioventricular node (AVN) vagal stimulation (AVN-VS) by varying the nerve stimulation intensity could achieve precise graded slowing and permit evaluation of an optimal VR during AF. The aims of the present study were the following: 1) to develop a method for computerized vagally controlled VR slowing during AF, 2) to determine the hemodynamic changes at each level of VR slowing, and 3) to establish the optimal anterograde VR during AF. AVN-VS was delivered to the epicardial fat pad that projects parasympathetic nerve fibers to the AVN in 14 dogs. Four target average VR levels, corresponding to 75%, 100%, 125%, and 150% of the sinus cycle length (SCL), were achieved by computer feedback algorithm. VR slowing resulted in improved hemodynamics and polynomial fit analysis found an optimum for the cardiac output at VR slowing of 87% SCL. We conclude that this novel method can be used to maintain slow anterograde conduction with best hemodynamics during AF.

Late Breaking Science Abstracts

### A New Apolipoprotein Influencing Plasma Triglyceride Levels in Humans and Mice Len Pennacchio, Lawrence Berkeley National Laboratory, Berkeley, CA; Michael Olivier, Medical College of Wisconsin, Milwaukee, WI; Jaroslav A Hubacek, Jonathan C Cohen, UT Southwestern Medical Center, Dallas, TX; David R Cox, Stanford Human Genome Center, Palo Alto, CA; Jamilla Fruchart, Pasteur Institute, Lille, France; Ronald M Krauss, Edward M Rubin, Lawrence Berkeley National Laboratory, Berkeley, CA The apolipoprotein gene cluster on human chromosome 11q23 (apoAI/CIII/AIV) represents a well-studied region that influences a variety of plasma lipid parameters and atherosclerosis susceptibility in humans. To facilitate the identification of evolutionarily conserved sequences with potential function near this cluster, we determined the sequence of ∼200 kbp of orthologous mouse DNA and compared the mouse and human sequences. The presence of a stretch of inter-species sequence conservation approximately 30 kbp proximal to the apoAI/CIII/AIV gene cluster, led us to an interval that upon further analysis was shown to encode a new member (apoAV) of the chromosome 11 apolipoprotein gene cluster. ApoAV transcripts were identified predominantly in liver tissue from mice and humans. To assess the function of apoAV, we generated mice over-expressing a human apoAV transgene as well as apoAV knockout mice. We observed dramatic but opposite effects on plasma triglyceride in these two groups of animals; a 3-fold decrease in plasma triglycerides in the apoAV transgenics and a 4-fold increase in the knockout mice. To explore the relationship between apoAV and lipid parameters in humans, several single nucleotide polymorphisms (SNPs) across the apoAV locus were identified and genotyped in two independent patient populations of normo-lipidemics. A common haplotype was found to be significantly associated with increased plasma triglycerides in the two large independent studies each employing different study designs. These findings in humans and mice illustrate the utility of comparative sequence analysis as a means to prioritize regions of the genome for further …

Pacemapping of the triangle of Koch: a simple method to reduce the risk of atrioventricular block during radiofrequency ablation of atrioventricular node reentrant tachycardia.

Slow pathway ablation in common AVNRT can be complicated by total AV block. When radiofrequency energy is delivered to the posterior aspect of the triangle of Koch, total AV block may be the consequence of the absence of anterograde conduction along the fast pathway or of inadvertent damage to a fast pathway abnormally located close to the slow pathway. To localize the anterogradely conducting fast pathway, the triangle of Koch was pacemapped in 72 patients who underwent the ablation of common AVNRT. In all cases, before ablation the St-H interval was calculated by stimulating the anteroseptal (AS), mid-septal (MS), and posteroseptal (PS) aspect of the triangle of Koch at a rate slightly faster than the sinus rate. In all patients, common AVNRT was induced. In 64 (89%) of 72 patients (group A) the shortest St-H interval was recorded on stimulating the AS region. In six (8%) patients (group B) the shortest St-H interval was recorded on stimulating the MS region. Finally, in two (3%) patients (group C) the shortest St-H interval was recorded stimulating in the PS region. In group C, AH interval, calculated on stimulating in the AS region, was significantly longer than in patients of groups A and B (200 +/- 99 ms vs 64 +/- 18 and 62 +/- 3, respectively). In group A, on stimulating in the AS, MS, and PS regions, the AH interval remained constant in all patients. In contrast, in groups B and C on stimulation in the MS and PS regions, AH interval shortened (in group B from 56 +/- 8 to 27 +/- 37 and 37 +/- 14, respectively; in group C from 200 +/- 99 to 170 +/- 100 and to 137 +/- 109, respectively). In groups A and B, a posteroseptal slow pathway, and in group C, an anteroseptal retrograde fast pathway were successfully ablated without AV block. Pacemapping of the triangle of Koch can help to recognize patients in whom the anterograde conducting fast pathway is abnormally located far from the anteroseptal region or in whom anterograde conduction of the fast pathway is absent. In these cases the risk of AV block can be reduced by performing slow pathway ablation in a site sufficiently far from the site of the anterograde fast pathway or ablating the retrogradely conducting fast pathway.

Atrioventricular conduction: a determinant for the manifestation of ventricular preexcitation in patients with Wolff-Parkinson-White syndrome.

The relation between the atrioventricular conduction properties of the atrioventricular node and the anterograde conduction ability over the accessory pathway in the Wolff-Parkinson-White syndrome has never been studied. Atrioventricular nodal characteristics were studied in 285 patients with manifest and 204 with concealed accessory pathway who underwent radiofrequency ablation, and compared with 146 controls. First and second degree atrioventricular block was observed in 13 (5%) preexcitation patients after ablation, compared with none in concealed accessory pathway (P=0.001) and control patients (P=0.006). The atrial-His intervals in preexcitation patients (88 +/- 20 ms) was significantly longer than in concealed accessory pathway (76 +/- 15 ms, P<0.0001) and control patients (77 +/- 15 ms, P=0.0007), as was PR intervals (165 +/- 25 versus 149 +/- 20 and 150 +/- 21 ms, P<0.0001, respectively) even after excluding those with atrioventricular block. Significant differences in PR and atrial-His intervals were not observed between concealed accessory pathway and control patients. More preexcitation patients had ventriculoatrial dissociation than had patients in the other groups. The results indicate that atrioventricular block is not uncommon in preexcitation patients and a relatively long atrioventricular conduction time is an electrophysiological prerequisite for the manifestation of preexcitation in the Wolff-Parkinson-White syndrome.

Mechanisms underlying the reentrant circuit of atrioventricular nodal reentrant tachycardia in isolated canine atrioventricular nodal preparation using optical mapping.

The reentrant pathways underlying different types of atrioventricular (AV) nodal reentrant tachycardia have not yet been elucidated. This study was performed to optically map Koch's triangle and surrounding atrial tissue in an isolated canine AV nodal preparation. Multiple preferential AV nodal input pathways were observed in all preparations (n=22) with continuous (73%, n=16) and discontinuous (27%, n=6) AV nodal function curves (AVNFCs). AV nodal echo beats (EBs) were induced in 54% (12/22) of preparations. The reentrant circuit of the slow/fast EB (36%, n=8) started as a block in fast pathway (FP) and a delay in slow pathway (SP) conduction to the compact AV node, then exited from the AV node to the FP, and rapidly returned to the SP through the atrial tissue located at the base of Koch's triangle. The reentrant circuit of the fast/slow EB (9%, n=2) was in an opposite direction. In the slow/slow EB (9%, n=2), anterograde conduction was over the intermediate pathway (IP) and retrograde conduction was over the SP. Unidirectional conduction block occurred at the junction between the AV node and its input pathways. Conduction over the IP smoothed the transition from the FP to the SP, resulting in a continuous AVNFC. A "jump" in AH interval resulted from shifting of anterograde conduction from the FP to the SP (n=4) or abrupt conduction delay within the AV node through the FP (n=2). These findings indicate that (1) multiple AV nodal anterograde pathways exist in all normal hearts; (2) atrial tissue is involved in reentrant circuits; (3) unidirectional block occurs at the interface between the AV node and its input pathways; and (4) the IP can mask the existence of FP and SP, producing continuous AVNFCs.

Non-invasive diagnosis of concealed Wolff-Parkinson-White syndrome by detection of concealed anterograde pre-excitation.

Electrophysiological findings suggest that concealed anterograde conduction through accessory pathways may exist even during sinus rhythm in patients with so-called concealed Wolff-Parkinson-White (WPW) syndrome. To evaluate the pre-excitation characteristics in various types of WPW syndrome, high-resolution electrocardiograms were analyzed in 81 consecutive WPW syndrome patients and 50 age-matched normal subjects. The WPW group consisted of 30 cases of concealed WPW diagnosed by electrophysiological study, 38 cases of manifest WPW in which apparent delta waves were constant, and 13 cases of intermittent WPW in which the delta waves appeared periodically. The duration of the low-amplitude, high-frequency components of the signal-averaged filtered QRS complex that preceded the earliest upstroke of the surface QRS, including any delta waves (preceding potential duration, PPD), and the duration of low amplitude signals less than 10 microV (I-LAS10) or 20 microV (I-LAS20) were measured as parameters of pre-excitation. The PPDs in concealed and intermittent WPW were both significantly longer than in manifest WPW or in control subjects (6.8+/-2.7 ms, 7.9+/-3.5 ms vs 2.3+/-3.2 ms, 1.0+/-1.6 ms, both p<0.0001). Abnormally prolonged PPDs (>4 ms) were observed in 90% of concealed WPW cases and 76.9% of intermittent WPW, but in only 4% of normal subjects and 31.6% of manifest WPW. Both I-LAS10 and I-LAS20 in the 3 types of WPW syndrome were significantly longer than in normal subjects. The initial portion of the filtered QRS in concealed WPW closely resembled that of intermittent WPW. These results strongly suggest that in concealed WPW anterograde conduction through accessory pathways does occur and produces small amounts of pre-excitation even during sinus rhythm. The study concluded that, despite its name, concealed WPW is not completely concealed, and that non-invasive diagnosis during sinus rhythm is possible by using high-resolution electrocardiography to detect the concealed anterograde pre-excitation.

Ablation of atriofascicular accessory pathways with slow anterograde conduction — left-sided fibers shall be also considered

Ablation of atriofascicular accessory pathways with slow anterograde conduction — left-sided fibers shall be also considered

Ablation of atriofascicular accessory pathways with slow anterograde conduction - left-sided fibers shall be also considered

Ablation of atriofascicular accessory pathways with slow anterograde conduction - left-sided fibers shall be also considered

Electrophysiologic characteristics of diverse accessory pathway locations of antidromic reciprocating tachycardia

This study assessed antidromic reciprocating tachycardia (ART) in patients with paraseptal accessory pathways (APs). Previous clinical experience suggests that paraseptal APs are unable to serve as the anterograde limb during ART. Based on the reentry wavelength concept, we hypothesized that anatomic location of a paraseptal AP may not preclude occurrence of ART. If wavelength criteria were met due to prolonged conduction time retrogradely in the atrioventricular node or anterogradely in the AP, ART may be sustained. All patients who had ART in the electrophysiologic laboratory at our institution (1991 to 1998) were studied. Based on fluoroscopically guided electrophysiologic mapping and radiofrequency ablation, AP location was classified as paraseptal, posterior, or lateral. Conduction time and refractoriness measurements were made for all components of the ART circuit. Of 24 patients with ART, 5 (21%) had ART utilizing a paraseptal AP. Anterograde conduction time through the AP and retrograde atrioventricular nodal conduction time were significantly longer in patients with paraseptal versus lateral pathways. Isoproterenol was required for ART induction in 38% of patients with a posterior AP, 36% with lateral AP location, but not in patients with a paraseptal AP. There were no significant differences in tachycardia cycle length or refractoriness of anterograde and/or retrograde components of the macroreentry circuit between the 3 pathway locations. Thus, ART can occur in patients with a paraseptal AP. Slower anterograde pathway conduction, or retrograde atrioventricular nodal conduction renders the wavelength critical for completion of the antidromic reentrant circuit.