Atypical Fast-Slow Atrioventricular Nodal Reentrant Tachycardia Using a Slow Pathway Extending to the Superoanterior Right Atrium.

We report a case of atypical fast-slow atrioventricular nodal reentrant tachycardia (AVNRT) using a slow pathway variant extending to the superoanterior right atrium. The AVNRT diagnosis was confirmed by using standard electrophysiological criteria that exclude a diagnosis of atrial tachycardia and atrioventricular reentrant tachycardia. The earliest atrial activation during tachycardia was found in the superoanterior right atrium adjacent to the tricuspid annulus, where the first delivery of radiofrequency energy terminated and eliminated the inducibility of the tachycardia.

Slow Potential at the Entrance of the Slow Conduction Zone in the Reentry Circuit of a Verapamil-Sensitive Atrial Tachycardia Originating From the Atrioventricular Annulus.

BACKGROUND: Slow conduction zone in a verapamil-sensitive reentrant atrial tachycardia originating from atrioventricular annulus is composed of calcium channel-dependent tissue. We examined whether there was a slow potential (SP) at the entrance of the slow conduction zone. METHODS AND RESULTS: We first identified the pacing site from where manifest entrainment and orthodromic capture of the earliest atrial activation site were demonstrated in 40 atrioventricular annulus patients with atrioventricular annulus. Radiofrequency energy was then delivered 2 cm proximal to the earliest atrial activation site in the direction of entrainment pacing site and gradually advanced toward the earliest atrial activation site until atrial tachycardia termination to localize the entrance of the slow conduction zone. Electrogram characteristics were analyzed at successful and unsuccessful ablation sites. During sinus rhythm, SP was observed at all 40 successful sites, but was observed at only 12 unsuccessful sites (P<0.0001). During sinus rhythm, there was no significant difference in electrogram amplitude nor width of atrial electrogram between successful and unsuccessful sites (0.407±0.281 versus 0.487±0.447 mV [P=0.1989] and 37.0±9.2 versus 38.9±8.0 ms [P=0.1773]); however, SP amplitude and width at successful sites were significantly greater than those at unsuccessful sites (0.110±0.049 versus 0.025±0.046 mV [P<0.0001] and 38.8±13.4 versus 8.1±13.2 ms [P<0.0001]). During atrial tachycardia, SP amplitude was significantly attenuated (0.088±0.042 versus 0.110±0.049 mV, P<0.001) and SP width was significantly prolonged (47.8±14.1 versus 38.8±13.4 ms, P<0.0001) at successful sites. CONCLUSIONS: SP was observed during sinus rhythm at the entrance of the slow conduction zone; however, SP amplitude was attenuated and SP width was prolonged during atrial tachycardia, suggesting that SP reflects the characteristics of calcium channel-dependent tissue involved in atrioventricular annulus reentry circuit.

Case report: an unstable wide QRS complexes tachycardia after ablation of a poster-septal accessory pathway: What is the mechanism?

INTRODUCTION: Differentiation of wide QRS complex tachycardia required repeated electrophysiological stimuli and mapping. However, instability of tachycardia would increase the difficulty in differential diagnosis. SYMPTOMS AND CLINICAL FINDINGS: In this paper, we reported a wide QRS tachycardia following ablation of an atrioventricular reentrant tachycardia participated by a poster-septal accessory pathway. Limited differentiation strategy was performed because the wide QRS tachycardia was self-limited and with unstable hemodynamics. We analyzed the mechanism of the wide QRS tachycardia by only 4 beats ventricular overpacing. On the basis of the last ventricular pacing, an atypical atrioventricular nodal reentrant tachycardia was confirmed. INTERVENTION AND OUTCOMES: After slow-pathway modification, the wide QRS tachycardia was eliminated. CONCLUSION: It was an atypical atrial-ventricular node reentrant tachycardia with right bundle branch block. Reasonable analysis based on electrophysiological electrophysiologic knowledge was the basis of successful diagnosis and treatment.

Therapy Of Cardiac Arrhythmias In Children: An Emerging Role Of Electroanatomical Mapping Systems.

INTRODUCTION: Cardiac arrhythmias are challenging diseases in childhood. Most of them in pediatric subjects (90.2%) are atrioventricular reentrant tachycardias and atrioventricular nodal reentrant tachycardias. The standard 12-lead ECG is a highly accurate diagnostic tool but an invasive electrophysiological study is often required. The main concern about this kind of procedures is their invasive nature and the need of radiations, so antiarrhythmic agents are currently the first line therapy. However, they often show side effects and can be insufficient for the rate control. MATERIALS AND METHODS: We performed a systematic research on Embase and PubMed. We found 563 articles and selected the most representative 50. DISCUSSION: Management of cardiac arrhythmias could be very difficult in several scenarios, especially in children with body weight <15 kg and age <4 years. In general, pediatric subjects show a cumulative risk of malignancy greater than adults, having greater life expectancy. On this basis the guiding principle during radiation delivery in electrophysiological procedures is "as low as reasonably achievable" (acronym: ALARA). The development of 3-dimensional (3D) electroanatomical mapping systems allowed significant reduction of exposure. The most recently reported experiences demonstrate safety and feasibility of fluoroless ablation in the most common arrhythmias in children, even in challenging conditions. CONCLUSION: The first reasonable approach in cardiac arrhythmias involving younger patients seems to be pharmacological. However antiarrhythmic drugs pose problems both in terms of side effects and often have poor efficacy. Expertise in electrophysiological techniques is constantly increasing and the development of new technologies allow us to encourage the use of electroanatomical mapping systems in order to reduce the radiation exposure in children undergoing to catheter ablation, especially for accessory pathways.

Management of supraventricular arrhythmias in adults with congenital heart disease.

Supraventricular arrhythmias are a frequent complication in adults with congenital heart disease (ACHD). The prevalence increases with time since surgery, complexity of the underlying defect, type of repair and older age at surgery. Arrhythmias are the most frequent reason for hospital admission and along with heart failure the leading cause of death. The arrhythmia-associated increase in morbidity and mortality makes their management a key task in patients with ACHD. Intra-atrial re-entry is the most frequent arrhythmia mechanism. Less common arrhythmia mechanisms are supraventricular tachycardias in the presence of an accessory pathway, atrioventricular nodal re-entrant tachycardia or focal tachycardias. Patient management includes stroke prevention, acute termination and prevention of arrhythmia recurrence. Acute treatment depends on patients' symptoms. In cases of haemodynamic instability, immediate cardioversion is warranted. For stable patients, acute treatment includes rate control and termination by antiarrhythmic drugs or electrical cardioversion. Following a symptomatic arrhythmia, catheter ablation or treatment with antiarrhythmic drugs is recommended to prevent recurrences. Advances in mapping and ablation technology are now associated with high success rates of catheter ablation. In patients with a complex substrate recurrence rates of 50% remain high. However, in the presence of side effects and complications associated with long-term antiarrhythmic drug therapy, redo procedures are encouraged by current guidelines.

Overdrive pacing from downstream sites on multielectrode catheters to rapidly detect fusion and to diagnose macroreentrant atrial arrhythmias.

BACKGROUND: Entrainment criteria for macroreentrant arrhythmias are based on detecting fusion between tachycardia and paced wavefronts, but this is often difficult for atrial tachycardias (AT) after ablation of atrial fibrillation. METHODS AND RESULTS: With the use of a multipolar catheter, pacing was performed from electrodes within the coronary sinus showing activation later than adjacent electrodes (downstream overdrive pacing) during 66 ATs in 62 patients: 20 cavotricuspid isthmus-dependent ATs, 20 perimitral ATs, 13 focal ATs with sequential coronary sinus activation, and 13 other macroreentrant left atrial ATs. The paced cycle length was 10 to 30 milliseconds below the tachycardia cycle length (TCL), and activation at the neighboring upstream electrodes was assessed. Downstream overdrive pacing at 48 sites close to a macroreentrant circuit (PPI-TCL <40 milliseconds, where PPI is postpacing interval) produced constant fusion demonstrated by a long stimulus to upstream atrial electrogram interval (S-Au) >75% TCL and was consistent with orthodromic activation of the upstream site despite its close proximity to the pacing site. In contrast, downstream overdrive pacing at 18 sites during focal AT or remote from the macroreentrant AT circuit (PPI-TCL >40 milliseconds) always demonstrated a comparatively short S-Au <25% of TCL (12±4% versus 89±4% of TCL; P<0.001), consistent with direct activation. CONCLUSIONS: Selection of a downstream activation site for overdrive pacing can facilitate rapid recognition of macroreentry and proximity to the reentry circuit using a single multielectrode catheter by recognizing a PPI-TCL <40 milliseconds and S-Au >75% of TCL. Recognition of intracardiac constant fusion with this method is a novel criterion for transient entrainment.

Demonstration of anatomic reentrant circuit in verapamil-sensitive atrial tachycardia originating from the atrioventricular annulus other than the vicinity of the atrioventricular node.

The mechanism and tachycardia circuit of verapamil-sensitive atrial tachycardia originating from the atrioventricular annulus (AVA-AT) other than the atrioventricular node vicinity are not well clarified. In 23 patients, we examined the mechanism and anatomic tachycardia circuit of AVA-AT. While recording the atrial electrogram at the earliest atrial activation site (EAAS) during tachycardia, rapid atrial pacing at a rate 5 beats/min faster than the tachycardia rate was delivered from multiple sites of the right atrium (RA) to demonstrate manifest entrainment and define the direction of proximity of slow conduction area (SCA) of reentry circuit. When EAAS was orthodromically captured, radiofrequency energy was delivered starting at a site 2 cm away from the EAAS in the direction of entrainment pacing site. Then application site was gradually advanced toward the EAAS until termination of tachycardia to define the entrance of SCA of reentry circuit. Manifest entrainment was demonstrated in all AVA-ATs. The EAAS, distributed along the tricuspid annulus from 3- to the 12-o'clock position, was orthodromically captured by pacing delivered from high anterolateral RA (n = 6), high anteroseptal RA (n = 7), high posteroseptal RA (n = 3), low anterolateral RA (n = 6), and coronary sinus ostium (n = 1). Radiofrequency energy delivery to the site, 10.4 ± 2.4 mm proximal to the EAAS where the atrial electrogram was observed 13.9 ± 5.7 ms later than the EAAS, terminated AVA-AT immediately after the onset of energy delivery (2.9 ± 1.1 seconds). In conclusion, it was shown that the AVA-AT is organized as reentry involving the verapamil-sensitive SCA with its entrance and exit at different distinct locations.

His overdrive pacing during supraventricular tachycardia: a novel maneuver for distinguishing atrioventricular nodal reentrant tachycardia from atrioventricular reciprocating tachycardia.

BACKGROUND: Because the His bundle is intrinsic to the circuit in orthodromic reciprocating tachycardia and remote from that of atrioventricular nodal reentrant tachycardia (AVNRT), pacing the His bundle during supraventricular tachycardia (SVT) may be useful to distinguish these arrhythmias. OBJECTIVE: The purpose of this study was to test the hypothesis that His overdrive pacing (HOP) would affect SVT immediately for orthodromic reciprocating tachycardia and in a delayed manner for AVNRT. METHODS: Once SVT was induced, HOP was performed by pacing the His bundle 10-30 ms faster than the SVT cycle length. The maneuver was determined to have entered the tachycardia circuit when a nonfused His-capture beat advanced or delayed the subsequent atrial electrogram by ≥10 ms or when the tachycardia was terminated. The number of beats required to enter each tachycardia with HOP was recorded. RESULTS: HOP was performed during 66 SVTs (26 atrioventricular reciprocating tachycardia [AVRT] and 40 AVNRT). Entry into the tachycardia within 1 beat had sensitivity of 92%, specificity of 92%, positive predictive value (PPV) of 89% and negative predictive value (NPV) of 95% to confirm the diagnosis of AVRT. A cutoff ≥3 beats to enter the circuit had sensitivity of 90%, specificity of 92%, PPV of 95% and NPV of 86% to confirm the diagnosis of AVNRT. HOP had sensitivity, specificity, PPV, and NPV of 100% for distinguishing septal AVRT from atypical AVNRT. CONCLUSION: HOP during SVT is a novel technique for distinguishing orthodromic reciprocating tachycardia from AVNRT. It can reliably distinguish between these arrhythmias with high sensitivity and specificity.

Electroanatomically estimated length of slow pathway in atrioventricular nodal reentrant tachycardia.

The length of the slow pathway (SP-L) in atrioventricular (AV) nodal reentrant tachycardia (NRT) has never been measured clinically. We studied the relationship among (a) SP-L, i.e., the distance between the most proximal His bundle (H) recording and the most posterior site of radiofrequency (RF) delivery associated with a junctional rhythm, (b) the length of Koch's triangle (Koch-L), (c) the conduction time over the slow pathway (SP-T), measured by the AH interval during AVNRT at baseline, and (d) the distance between H and the site of successful ablation (SucABL-L) in 26 women and 20 men (mean age 64.6 ± 11.6 years), using a stepwise approach and an electroanatomic mapping system (EAMS). SP-L (15.0 ± 5.8 mm) was correlated with Koch-L (18.6 ± 5.6 mm; R 2 = 0.1665, P < 0.005), SP-T (415 ± 100 ms; R 2 = 0.3425, P = 0.036), and SucABL-L (11.6 ± 4.7 mm; R 2 = 0.5243, P < 0.0001). The site of successful ablation was located within 10 mm of the posterior end of the SP in 38 patients (82.6 %). EAMS-guided RF ablation, using a stepwise approach, revealed individual variations in SP-L related to the size of Koch's triangle and AH interval during AVNRT. Since the site of successful ablation was also correlated with SP-L and was usually located near the posterior end of the SP, ablating anteriorly, away from the posterior end, is not a prerequisite for the success of ablation procedures.

Regular tachycardia terminated by ventricular anti-tachycardia pacing in an ICD recipient. What is the mechanism?

This is the case of a misdiagnosed atrioventricular nodal reentry tachycardia (AVNRT) with occasionally 2:1 atrioventricular block terminated by delivery of an inappropriate ventricular antitachycardia pacing scheme, in an ICD recipient. The detailed analysis of stored electrograms facilitated the revelation of the arrhythmic mechanism.

Differential sequential septal pacing: a simple maneuver to differentiate nodal versus extranodal ventriculoatrial conduction.

BACKGROUND: Distinguishing retrograde nodal conduction from extranodal conduction using an accessory pathway (AP) can sometimes be challenging. OBJECTIVE: To distinguish nodal from extranodal ventriculoatrial (VA) conduction regardless of AP location by proposing a simple method. This method is based on the principle that moving the pacing site progressively from the basal region toward the entrance of the His-Purkinje system should shorten VA time for nodal but not for AP conduction. METHODS: Sixty-seven patients with supraventricular tachycardia were prospectively recruited. Quadripolar catheters were placed at the right ventricular (RV) apex, right atrium, and His and coronary sinus. The RV septum was sequentially paced at 4 sites: (1) basal, (2) high midventricle, (3) low midventricle, and (4) apex at a cycle length 100 ms shorter than the resting cycle length. The stimulus-to-atrial (SA) interval was measured by using the proximal coronary sinus atrial electrogram. RESULTS: Group 1 (n = 33) had nodal VA conduction; all patients had typical atrioventricular nodal reentrant tachycardia. Group 2 (n = 34) had extranodal VA conduction via an AP: 19 left-sided, 6 right-sided, and 9 posteroseptal. In group 1, the SA interval decreased significantly as pacing site moved closer toward the apex (site 1: 166 ± 35 ms, site 2: 153 ± 32 ms, site 3: 149 ± 32 ms, site 4: 154 ± 33 ms, P < .001, respectively, at sites 2-4 compared with site 1). In contrast, in group 2, the SA interval increased significantly toward the apex (site 1: 149 ± 45 ms, site 2: 158 ± 43 ms, site 3: 161 ± 43 ms, and site 4: 163 ± 40 ms, P < .001, respectively, at sites 2-4 compared with site 1). The SA interval at the high midventricular site (site 2) - SA interval at the base (site 1) ≤ 0 ms for nodal and > 0 ms for extranodal conduction had optimal sensitivity and specificity (nodal: selectivity = 97.0% and specificity = 85.3%; extranodal: selectivity = 85.3% and specificity = 97.0%). CONCLUSIONS: Differential sequential pacing of the RV septum reliably distinguishes retrograde atrioventricular nodal conduction from AP conduction.

Electrophysiology and ablation of arrhythmias.

Major advances in diagnosis and treatment of arrhythmias have created the subspecialty of cardiac electrophysiology. This article reviews supraventricular and ventricular arrhythmias and outlines the indications and process of electrophysiological testing, arrhythmia mechanism and their treatment by catheter ablation.

Resetting criteria during ventricular overdrive pacing successfully differentiate orthodromic reentrant tachycardia from atrioventricular nodal reentrant tachycardia despite interobserver disagreement concerning QRS fusion.

BACKGROUND: The beginning of ventricular overdrive pacing (VOP) during supraventricular tachycardia (SVT) accurately distinguishes orthodromic reentrant tachycardia (ORT) from atrioventricular nodal reentrant tachycardia (AVNRT) even when pacing terminates tachycardia. Tachycardia resetting most often occurs during this transition zone (TZ) of QRS fusion in ORT and after this TZ in AVNRT. The end of the TZ is marked by the first beat with a stable QRS morphology but is a subjective assessment. Disagreement concerning this beat may change tachycardia diagnosis. OBJECTIVE: The purpose of this study was to assess interobserver agreement for identifying the TZ and whether disagreement affected diagnosis. METHODS: Seventy-nine consecutive patients with inducible ORT and AVNRT were included. Resetting of tachycardia was evaluated by (1) atrial timing perturbation and (2) fixed stimulation-atrial activation timing (SA). Two blinded observers identified the end of the TZ and used the two resetting criteria to establish a diagnosis. Diagnostic results were compared with standard criteria for SVT diagnosis. The diagnosis was considered correct if both electrophysiologists' TZ assessment resulted in a correct diagnosis. RESULTS: Agreement on the TZ occurred in 80% (148/186) of VOP trains. In ORT patients, tachycardia resetting occurred during the TZ and correctly diagnosed ORT based on atrial timing perturbation and fixed SA in 91% and 98% of VOP trains, respectively. In AVNRT patients, tachycardia resetting occurred after the TZ and correctly diagnosed AVNRT based on atrial timing perturbation and fixed SA in 93% and 94% of VOP trains, respectively. CONCLUSION: Resetting criteria used during the VOP TZ accurately differentiate between ORT and AVNRT despite interobserver disagreement concerning identification of the TZ.

A novel approach to differentiating orthodromic reciprocating tachycardia from atrioventricular nodal reentrant tachycardia.

BACKGROUND: Various diagnostic maneuvers have been proposed to help differentiate orthodromic reciprocating tachycardia (ORT) from atrioventricular nodal reentrant tachycardia (AVNRT) prior to ablation. However, not all criteria are applicable in every situation as each has limitations. OBJECTIVE: The purpose of this study was to determine whether the behavior of tachycardia during onset of right ventricular (RV) pacing would help differentiate ORT from AVNRT. METHODS: We retrospectively reviewed 72 cases (42 typical AVNRT, 7 atypical AVNRT, 15 left free-wall pathways, 6 septal pathways, 2 right free-wall pathways). We assessed the number of beats required to accelerate the tachycardia cycle length (TCL) to the paced cycle length (PCL) once a fully RV paced complex was achieved during supraventricular tachycardia. RESULTS: In the AVNRT group, delta cycle length (DCL = PCL-TCL) was 29 +/- 16 ms compared to 29 +/- 10 ms in ORT group (P = NS). In the AVNRT group, the average number of fully RV paced beats required to reset the tachycardia was 3.7 +/- 1.1 compared to 1 +/- 0 in the ORT group (P <.0001). Using a cutoff >1 beat yielded both positive and negative predictive values of 100% for diagnosing AVNRT versus ORT. During entrainment attempts, AVNRT terminated 51% of the time and ORT terminated 65% of the time but still allowed application of the new criterion. CONCLUSION: Assessing timing and type of response of supraventricular tachycardia to RV pacing can help differentiate ORT from AVNRT with high certainty and prevent the need for other pacing maneuvers and measurements.

Tilting at windmills.

A 69-year-old man had numerous episodes of syncope over three years. A head-up tilt test had shown a mixed response and he was labeled as having neurocardiogenic syncope. Lifestyle, dietary and pharmacologic measures were ineffective. At electrophysiology study, an easily inducible, self-terminated AV nodal re-entrant tachycardia was induced. At 1 year follow-up after radiofrequency ablation, he is asymptomatic.

Clinical and electrophysiological characteristics, and relatively benign outcome, of typical atrioventricular nodal reentrant tachycardia in children and adolescents.

BACKGROUND: Atrioventricular nodal re-entrant tachycardia is an uncommon arrhythmia in children. The natural history of this disturbance is poorly known in young patients. METHODS: We analyzed the clinical and electrophysiological features, and the final outcome, in 19 children affected by typical atrioventricular nodal re-entrant tachycardia diagnosed by a transoesophageal electrophysiological study. RESULTS: Of the cohort, 12 patients were female and 7 male, with a mean age of 11 years. Dual atrioventricular nodal physiology was demonstrated in 14 children (73%). The mean length of the tachycardia cycle was 297 milliseconds, with periods of 2 to 1 atrioventricular block during tachycardia noted in 5 children (26%). The mean cycle length was significantly shorter in the children who presented episodes of 2 to 1 atrioventricular block than in those who did not. After diagnosis, 12 children were not treated, 6 were treated with medical therapy, and 1 was submitted to radiofrequency transcatheter ablation. During a mean follow-up period of 41 months, 2 children with rare, but sustained, episodes of tachycardia that initially had not been treated were submitted to radiofrequency transcatheter ablation. Among children treated pharmacologically, 1 teenager was submitted to radiofrequency transcatheter ablation on the basis of parental choice, 3 children have discontinued medical therapy recording only sporadic episodes of tachycardia, and 2 children are still treated with antiarrhythmic drugs. At the last follow-up visit, 13 children (68%) were without any treatment, 4 had been successfully ablated, and 2 were still on medical treatment. CONCLUSIONS: Our data indicates a relatively benign outcome in this group of children and adolescents with atrioventricular nodal re-entrant tachycardia.