Specificity of Retrograde Conduction in Screening for Atrioventricular Nodal Reentrant Tachycardia

Baseline AV conduction properties (antegrade and retrograde) are often used to assess the presence of dual AV nodal physiology or concealed AV accessory pathways. Although retrograde conduction (RET) is assumed to be a prerequisite for AV nodal reentrant tachycardia (AVNRT), its prevalence during baseline measurements has not been evaluated. We reviewed all cases of AVNRT referred for radiofrequency ablation to determine the prevalence of RET at baseline evaluation and after isoproterenol infusion. Results: Seventy-three patients with AVNRT underwent full electrophysiological evaluation. Sixty-six patients had manifest RET and inducible AVNRT during baseline atrial and ventricular stimulation. Seven patients initially demonstrated complete RET block despite antegrade evidence of dual AV nodal physiology. In 3 of these 7 patients AVNRT was inducible at baseline despite the absence of RET. In the other four patients isoproterenol infusion was required for induction of AVNRT, however only 3 of these 4 patients developed RET. One of these remaining patients had persistent VA block after isoproterenol. Conclusions: The induction of AVNRT in the absence of RET suggests that this is not an obligatory feature of this arrhythmia. Therefore, baseline AV conduction properties are unreliable in assessing the presence of AVNRT and isoproterenol infusions should be used routinely to expose RET and reentrant tachycardia.     

Atrial Tachycardia Mimicking Atrioventricular Nodal Reentry Tachycardia

Background

The term supraventricular tachycardia (SVT) is used to describe tachydysrhythmias that require atrial or atrioventricular nodal tissue for their initiation and maintenance. SVT can be used to describe atrioventricular nodal reentry tachycardia, atrioventricular reentry tachycardia, and atrial tachycardia (AT). AT is the least common of these SVT subtypes, accounting for only 10% of cases. Although the suggested initial management of each SVT subtype is different, they all can present with similar symptoms and electrocardiographic findings.

Objective

Discuss the pathophysiology, diagnosis, and treatment of AT as compared with other types of SVT.

Case Report

We report a 56-year-old woman with symptoms and electrocardiographic findings consistent with SVT. Although standard treatment with intravenous adenosine failed to convert the SVT, it revealed AT as the cause of the tachydysrhythmia. The AT was successfully terminated with beta-blockade and the patient eventually underwent successful radioablation of three separate AT foci.

Conclusions

AT frequently mimics other more common forms of SVT. AT might be recognized only when standard treatment of SVT has failed. Identification of AT in this setting is crucial to allow for more definitive therapy.     

房室结双径路伴房室结折返性心动过速的室房传导探讨

根据电生理检查结果,将接受射频消融术患者62例分为房室旁道伴房室折返性心动过速(AVRT)32例,房室结双径路(DAVNP)伴房室结折返性心动过速(AVNRT)30例。以房室旁道伴AVRT室房(VA)传导特征为对照,探讨DAVNP伴AVNRT VA传导特征。结果表明DAVNP伴AVNRT其VA传导发生率为100％;室房逆传多经房室结快径;快径逆传具有房室旁道逆传特征。     

Characteristics of Ventriculoatrial Conduction in Patients with Enhanced Atrioventricular Nodal Conduction

To study the characteristics of the ventriculoatrial conduction system in palienfs capable of rapid antegrade atrioventricuiar conduction, eiectrophysiologic studies were performed in 23 subjects capable of 1:1 atrioventricular conduction at atrial cycle lengths < 300 ms (Group I). and in 23 subjects with normal 1:1 atrioventricular conduction (Group II). During venfricular pacing, ventriculoatrial block at all cycle lengths was seen in 5/23 (22%) in Group I and in 7/23 (30%) in Group II patients (p = NS). In the remainder, the minimum ventricuar pacing cycle length maintaining 1:1 ventriculoatrial conduction was 359 ± 85 ms in Group I, compared to 444 ± 118 ms in Group II (p < .02). Both flat and exponential VA conduction interval curves, drawn as a function of pacing cycle length, were observed in both groups. Discontinuous ventricuioatrial conduction curves were seen in 5/18 (28%) Group I and 1/16 (6%) Group II patients (p = NS). In conclusion, retrograde ventriculoatrial conduction, when present in patients capable of rapid 1:1 atrioventricular conduction, is maintained at shorter cycle lengths than in patients with normal atrioventricular conduction. Quantitative, rather than qualitative, differences distinguish the two groups.     

Provocation of Atrioventricular Reentry Tachycardia: A Paradoxical Effect of Adenosine

Adenosine has been used to diagnose latent preexcitation in patients with the Wolff-Parkinson-White syndrome. A case is reported in which intermittent preexcitation had been previously observed, however only retrograde accessory pathway conduction was documented at the time of invasive eiectrophysiological study, Administration of intravenous adenosine during sinus rhythm resulted in provocation of orthodromic atrioventricular reentry tachycardia.     

Differential Entrainment Distinguishes Atrioventricular Nodal Reentry Tachycardia from Atrioventricular Reentrant Tachycardia

Background: Entrainment from the right ventricular (RV) apex and the base has been used to distinguish atrioventricular reentrant tachycardia (AVRT) from atrioventricular nodal reentry tachycardia (AVNRT). The difference in the entrainment response from the RV apex in comparison with the RV base has not been tested. Methods: Fifty‐nine consecutive patients referred for ablation of supraventricular tachycardia (SVT) were included. Entrainment of SVT was performed from the RV apex and base, pacing at 10–40‐ms faster than the tachycardia cycle length. SA interval was calculated from stimulus to earliest atrial electrogram. Ventricle to atrium (VA) interval was measured from the RV electrogram (apex and base) to the earliest atrial electrogram during tachycardia. The SA‐VA interval from apex and base was measured and the difference between them was calculated. Results: Thirty‐six AVNRT and 23 AVRT patients were enrolled. Mean age was 44 ± 12 years; 52% were male. The [SA‐VA]apex–[SA‐VA]base was demonstrable in 84.7% of patients and measured ?9.4 ± 6.6 in AVNRT and 10 ± 11.3 in AVRT, P < 0.001. The difference was negative for all AVNRT cases and positive for all septal accessory pathways (APs). Conclusion: The difference between entrainment from the apex and base is readily performed and is diagnostic for all AVNRTs and septal APs. (PACE 2010; 1335–1341)     

三磷酸腺苷在房室结折返性心动过速消融终点判定中的意义

【目的】探讨三磷酸腺苷（adenosine triphosphate,ATP）在射频消融（radiofrequency cather abalation,RFCA）慢径治疗慢-快型房室结折返性心动过速（atrioventricular nodal reentrant tachycardia,AVNRT）消融终点判定中的意义。【方法】40例慢-快型AVNRT患者RFCA前经股静脉快速（2S内）注射ATP（0．15mg／kg起始量及每次增加0．1mg／kg）,直至出现房室结双径路（dua atrioventricular nodal pathways,DAVNP）现象、Ⅱ度或Ⅲ度房室传导阻滞等。对ATP试验诊断有房室结双径路现象者RFCA慢径阻断成功后重复原ATP剂量,连续记录体表心电图和心内电图。【结果】RFCA前行ATP实验29例（72．5％）出现DAVNP现象,该29例患者RFCA慢径阻断成功后重复注射原ATP剂量,均无DAVNP现象。【结论】ATP是诊断DAVNP的一个判定指标,如若RFCA术前ATP试验诊断有DAVNP现象,术后ATP试验诊断无DAVNP现象意味着慢径阻断成功。     

Successful Radiofrequency Energy Ablation of Automatic Junctional Tachycardia Preserving Normal Atrioventricular Nodal Conduction

Automatic junctional tachycardia is frequently refractory to medical management and difficult to treat with nonpharmacoJogical methods. A 12-year-old female with symptomatic, refractory automatic junctional tachycardia is reported. Earliest atrial activation during supraventricular tachycardia was in the posterior portion of the intraatrial septum. The patient underwent electrophysiological study and successful radiofrequency current ahiation of the ectopic automatic focus within the atrioventricuiar junction. Normal atrioventricular junctional conduction was maintained, and at 7-month foJlow-up the patient has been free of tachycardia.     

Discordant Effects of Carotid Sinus Massage and Intravenous Adenosine in Atypical (Fast-Slow) Atrioventricular Nodal Reentrant Tachycardia

The precise mechanism underlying supraventricular tachycardia with a long R-P interval is often difficult to assess noninvasively. Carotid sinus massage has been used traditionally to produce transient AV nodal conduction delay at the bedside, and may be of diagnostic or therapeutic benefit. More recently, adenosine has also been shown to be useful in this situation. We report the case of a patient with an incessant long R-P tachycardia in whom the response to CSM was misleading while the response to adenosine was diagnostic. The electrophysiologic responses to both maneuvers are displayed, and a mechanism for the discordant responses is proposed.     

The Incidence of Retrograde Conduction in Children

With the increasing use of "physiological" pacemakers in the pediatric age group, retrograde conduction in children has become of clinical importance. Pacemakers which sense atrial depolarization may sense "retrograde" P waves. The pacemaker may then act as the antegrade limb of a reciprocating tachycardia circuit, while the patient's own conduction system acts as the retrograde limb. We reviewed the data of 127 patients who underwent antegrade and retrograde electrophysiologic study at Texas Children's Hospital, with regard to retrograde conduction. Sixty percent of the patients had ventriculo-atrial conduction through the A-V node; the incidence of retrograde conduction in patients after surgical correction of a tetralogy of Fallot was significantly lower (33%). None of the patients with third-degree A-V block had retrograde conduction. The mean retrograde conduction time was 162 ms (range 70-335 ms) at the slowest pacing rate and 257 ms (range 80-475 ms) at the fastest pacing rate. This high incidence of retrograde conduction and the variability of conduction times must be taken into account when "physiological" pacemakers are to be implanted.     

Delayed Termination of Re-Entrant Atrioventricular Nodal Tachycardia

Termination of atriovontricular nodal (A VN) re-entrant tachycardia by one or two induced premature beats generally occurs within one tachycardia cycle from the last premature beat. Two cases are described in which programmed stimulation during sustained re-entrant AVN tachycardia caused delayed termination in the second or third tachycardia cycle following the extrastimuli. The site of block was the antegrade pathway in one case and the retrograde pathway in the other. The most likely mechanism was induced second degree block in one limb of the tachycardia circuit. Delayed termination provided evidence for concealed penetration of the tachycardia circuit in one case. We conclude that delayed termination of tachycardia is not an indicator of the underlying mechanism of tachycardia. Delayed termination may reveal concealed penetration of the tachycardia circuit. Lastly, in unusual cases programmed stimulation may fail to cause immediate termination of re-entrant tachycardia but may perturb the tachycardia circuit enough to cause termination in subsequent tachycardia cycles.     

Retrograde Supernormal Conduction, Gap Phenomenon in Concealed Accessory Atrioventricular Pathways

We present four patients with the Wolff-Parkinson-White syndrome who exhibited retrograde supernormal conduction or gap phenomenon in concealed accessory pathways. In the first patient, ventricular extrastimulus testing revealed retrograde block at the coupling interval of 520 msec and reappearance of conduction at the coupling interval of 370 msec. In a second patient, 1:1 retrograde conduction was not present but supernormal conduction was demonstrated at coupling intervals of 360 msec to 310 msec during the ventricular extrastimulus testing when the basic drive consisted of atrioventricular (AV) simultaneous pacing. In a third patient, ventricular extrastimulus testing demonstrated retrograde conduction through the accessory pathway only at coupling intervals of 400 msec to 360 msec. In a fourth patient, retrograde block occurred at the coupling interval of 340 msec and retrograde "slow" conduction reappeared at coupling intervals of 300 msec to 250 msec (gap phenomenon) only when the basic drive consisted of AV simultaneous pacing. Thus, concealed accessory pathways may exhibit retrograde supernormal conduction or gap phenomenon. Ventricular extrastimulus testing consisting of AV simultaneous pacing during the basic drive may facilitate demonstration of these unusual properties.     

Effects of Pharmacological Autonomic Blockade on Dual Atrioventricular Nodal Pathways Physiology in Patients with Slow-Fast Atrioventricular Nodal Reentrant Tachycardia

The purpose of this study was to investigate the atrioventricular AV nodal physiology and the inducibility of AV nodal reentrant tachycardia (AVNRT) under pharmacological autonomic blockade (AB). Seventeen consecutive patients (6 men and 11 women, mean age 39 ± 17 years) with clinical recurrent slow-fast AVNRT received electrophysiological study before and after pharmacological AB with atropine (0.04 mg/kg) and propranolol (0.2 mg/kg). In baseline, all 17 patients could be induced with AVNRT, 5 were isoproterenol-dependent. After pharmacological AB, 12 (71 %) of 17 patients still demonstrated AV nodal duality. AVNRT became noninducible in 7 of 12 nonisoproterenol dependent patients and remained noninducible in all 5 isoproterenol dependent patients. The sinus cycle length (801 ± 105 ms vs 630 ± 80 ms, P < 0.005) and AV blocking cycle length (365 ± 64 ms vs 338 ± 61 ms, P < 0.005) became shorter after AB. The antegrade effective refractory period and functional refractory period of the fast pathway (369 ± 67 ms vs 305 ± 73 ms, P < 0.005; 408 ± 56 ms vs 350 ± 62 ms, P < 0.005) and the slow pathway (271 ± 30 ms vs 258 ± 27 ms, P < 0.01; 344 ± 60 ms vs 295 ± 50 ms, P < 0.005) likewise became significantly shortened. However, the ventriculoatrial blocking cycle length (349 ± 94 ms vs 326 ± 89 ms, NS) and effective refractory period of retrograde fast pathway (228 ± 38 ms vs 240 ± 80 ms, NS) remained unchanged after autonomic blockade. Pharmacological AB unveiling the intrinsic AV nodal physiology could result in the masking of AV nodal duality and the decreased inducibility of clinical AVNRT.     

Entrainment to Distinguish Orthodromic Reciprocating Tachycardia from Atrioventricular Nodal Reentry Tachycardia in Children

Background : Studies in adults suggest that after entrainment from the right ventricle, a post‐pacing interval (PPI) minus tachycardia cycle length (TCL), when corrected for atrioventricular node delay (cPPI‐TCL), is useful to distinguish atrioventricular nodal reentry tachycardia (AVNRT) from orthodromic reciprocating tachycardia (ORT), but this has not been evaluated in children. Methods : In 100 children undergoing catheter ablation, entrainment of ORT or AVNRT was performed from the right ventricular apex. The atrial‐His (AH) interval was measured on the return cycle (post‐AH) and during tachycardia just prior to pacing (pre‐AH). The cPPI‐TCL was calculated as (PPI‐TCL) ? (post‐AH ? pre‐AH). In the first 50 children, the best cutoff was identified and then validated in the next 50 children. Results : In the first 50 children, cPPI‐TCL was longer in AVNRT compared with ORT (122 ± 19 ms vs 63 ± 23 ms, P < 0.001). Furthermore, cPPI‐TCL exceeded 95 ms in all AVNRT patients, but was less than < 95 ms in 28 of 29 ORT patients. In the next 50 children, a cPPI‐TCL < 95 ms was 100% specific for ORT; a cPPI‐TCL > 95 ms was 95% specific for AVNRT. There was even greater separation of cPPI‐TCL values comparing AVNRT with ORT utilizing a septal accessory pathway. Conclusions : The cPPI‐TCL is a useful technique to distinguish AVNRT from ORT in children. Our data suggest that in children a cPPI‐TCL < 95 ms excludes AVNRT, while a value > 95 ms is rarely observed in ORT. This technique is particularly useful to distinguish AVNRT from ORT utilizing a septal accessory pathway. (PACE 2010; 469–474)     

Intravenous Adenosine During Atrioventricular Reentrant Tachycardia: Induction of Atrial Fibrillation with Rapid Conduction Over an Accessory Pathway

Adenosine is considered to be a safe agent for termination of orthodromic atrioventricular reentrant tachycardia in patients with accessory pathways. A case with initially successful accessory pathway ablation and without preexcitation during sinus rhythm is presented, in which intravenous adenosine (6 mg) during orthodromic tachycardia was followed by atrial fibrillation and sudden onset of preexcitation with subsequent rapid ventricular response with moderate hemodynamic compromise.     

Occurrence of Atrial Fibrillation in Patients With Paroxysmal Supraventricular Tachycardia Due to Atrioventricular Nodal Reentry

The occurrence of atrial fibrillation in patients with paroxysmal supraventricular tachycardia (PSVT) has been well documented when PSVT is secondary to atrioventricular reentry, but not when PSVT is secondary to atrioventricular nodal reentry (AVNRT). Seventeen patients with AVNRT were followed using transtelephonic electrocardiogram monitoring to document symptomatic tachycardias. The median length of telephone monitor surveillance was 357 days. Fifteen of 17 patients transmitted electrocardiograms that showed PSVT. Three of 17 patients (18%) transmitted electrocardiograms that showed atrial fibrillation. A transition from PSVT into atrial fibrillation was not recorded, but all three did have PSVT recorded on other days of follow-up. We report the occurrence of atrial fibrillation in patients with AVNRT and that its incidence is higher than expected for the general population.     

Retrograde (Ventriculoatrial) Conduction

Ľinterêt dans la conduction VA rétrograde a été renouvelé depuis la découverte de tachycardies induites par les stimulateurs cardiaques de type physiologique qui incorporent le recueil des potentiels auriculaires. Seule ľétude de la conduction VA rétrograde associée à une parfaite connaissance de son comportement électrophysiologique dans dif-ferents cos, permettra de dépister les malades susceptibles de faire une tachycardie induite par le stimulateur.
Interest in retrograde VA conduction has been renewed with the advent of tachycardias induced by physiologic pacemakers with atrial sensing capabilities. Accurate representation of ventriculoatrial conduction requires detailed electrophysiologic analysis during sinus rhythm, during tachycardias whether or not associated with accessory pathways, and during ventricular pacing studies. Retrograde conduction should be assessed in patieifts considered for implantation of atrial sensing and tracking pacemakers (VAT, VDD, DDD), until technologic advances overcome the problems of endless loop tachycardias.     

Abnormal Atrioventricular Node Conduction and Atrioventricular Nodal Reentrant Tachycardia in Patients Older Versus Younger Than 65 Years of Age

Study Objective: We examined the possible role of atrioventricular node (AVN) conduction abnormalities as a cause of AVN reentrant tachycardia (RT) in patients >65 years of age.
Study Population: Slow pathway radiofrequency catheter ablation (RFCA) was performed in 104 patients. Patients in group 1 (n = 14) were >65 years of age and had AV conduction abnormalities associated with structural heart disease. Patients in group 2 (n = 90) were <65 years of age and had lone AVNRT.
Results: Patients in group 1 versus group 2 (66% vs. 46% men) had a first episode of tachycardia at an older age than in group 2 (68 ± 16.8 vs 32.5 ± 18.8 years, P = 0.007). The history of arrhythmia was shorter in group 1 (5.4 ± 3.8 vs 17.5 ± 14, P = 0.05) and was associated with a higher proportion of patients with underlying heart disease than in group 2 (79% vs 3%, P < 0.001). The electrophysiological measurements were significantly shorter in group 2: atrial-His interval (74 ± 17 vs 144 ± 44 ms, P = 0.005), His-ventricular (HV) interval (41 ± 5 vs 57 ± 7 ms, P = 0.001), Wenckebach cycle length (329 ± 38 vs 436 ± 90 ms, P = 0.001), slow pathway effective refractory period (268 ± 7 vs 344 ± 94 ms, P = 0.005), and tachycardia cycle length (332 ± 53 vs 426 ± 56 ms, P = 0.001). The ventriculoatrial block cycle length was similar in both groups. The immediate procedural success rate was 100% in both groups, and no complication was observed in either group. One patient in group 2 had recurrence of AVNRT. One patient with a 98-ms HV interval underwent permanent VVI pacemaker implantation before RFCA procedure.
Conclusion: In patients undergoing RFCA for AVNRT at >65 years of age had a shorter history of tachycardia-related symptoms than patients with lone AVNRT. The longer AVN conduction intervals and refractory period might explain the late development of AVNRT in group 1.     

Alternate Ventriculo-Atrial Wenckebach Conduction during Ventricular Tachycardia

Although pacing-induced ventriculo-atrial (VA) Wenckebach conduction has been previously described, the occurrence of this phenomenon during ventricular tachycardia has received little attention. The latter is defined as 2:1 VA block in which the conducted beats show progressive lengthening of VA conduction until the sequence is terminated by two or three blocked ventricular beats. This phenomenon was observed in a 16-year-old boy who underwent electrophysiologic study for ventricular tachycardia as a late complication of surgical correction of tetralogy of Fallot. During pacing-induced ventricular tachycardia with a morphology similar to that of the spontaneous tachycardia, 8:4 alternating VA block was observed. This sequence suggested that the AV node was the site of block, the 2:1 block being located at the upper level, and the VA Wenckebach block at the lower level. Alternate VA Wenckebach conduction appears as a possible cause of variation in atrial depolarization intervals during ventricular tachycardias with short cycle lengths.