High-density mapping of Koch's triangle during sinus rhythm and typical atrioventricular nodal re-entrant tachycardia, integrated with direct recording of atrio-ventricular node structure potential.

BACKGROUND: The mechanism of typical slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) and its anatomical and electrophysiological circuit inside the right atrium (RA) and Koch's Triangle (KT) are not well known. OBJECTIVE: To identify the potentials of the compact AV node and inferior extensions and to perform accurate mapping of the RA and KT in sinus rhythm (SR) and during AVNRT, to define the tachycardia circuit. METHODS: Consecutive patients with typical AVNRT were enrolled in 12 Italian centers and underwent mapping and ablation by means of a basket catheter with small electrode spacing for ultrahigh-density mapping and a modified signal-filtering toolset to record the potentials of the AV nodal structures. RESULTS: Forty-five consecutive cases of successful ablation of typical slow-fast AVNRT were included. The mean SR cycle length (CL) was 784.1 ± 6 ms and the mean tachycardia CL was 361.2 ± 54 ms. The AV node potential had a significantly shorter duration and higher amplitude in sinus rhythm than during tachycardia (60 ± 40 ms vs. 160 ± 40 ms, p < .001 and 0.3 ± 0.2 mV vs. 0.09 ± 0.12 mV, p < .001, respectively). The nodal potential duration extension was 169.4 ± 31 ms, resulting in a time-window coverage of 47.6 ± 9%. The recording of AV nodal structure potentials enabled us to obtain 100% coverage of the tachycardia CL during slow-fast AVNRT. CONCLUSION: Detailed recording of the potentials of nodal structures is possible by means of multipolar catheters for ultrahigh-density mapping, allowing 100% of the AVNRT CL to be covered. These results also have clinical implications for the ablation of right-septal and para-septal arrhythmias.

Pulmonary vein isolation in atrial fibrillation patients guided by a novel local impedance algorithm: 1-year outcome from the CHARISMA study.

BACKGROUND: Highly localized impedance (LI) measurements during atrial fibrillation (AF) ablation have recently emerged as a viable real-time indicator of tissue characteristics and durability of the lesions created. We report the outcomes of acute and long-term clinical evaluation of the new DirectSense algorithm in AF ablation. METHODS: Consecutive patients undergoing AF ablation were included in the CHARISMA registry. RF delivery was guided by the DirectSense algorithm, which records the magnitude and time-course of the impedance drop. The ablation endpoint was pulmonary vein isolation (PVI), as assessed by the entrance and exit block. RESULTS: 3556 point-by-point first-pass RF applications of >10 s duration were analyzed in 153 patients (mean age=59 ± 10 years, 70% men, 61% paroxysmal AF, 39% persistent AF). The mean baseline LI was 105 ± 15 Ω before ablation and 92 ± 12 Ω after ablation (p < .0001). Both absolute drops in LI and the time to LI drop (LI drop/τ) were greater at successful ablation sites (n = 3122, 88%) than at ineffective ablation sites (n = 434, 12%) (14 ± 8 Ω vs 6 ± 4 Ω, p < .0001 for LI; 0.73 [0.41-1.25] Ω/s vs. 0.35[0.22-0.59 Ω/s, p < .0001 for LI drop/τ). No major complications occurred during or after the procedures. All PVs had been successfully isolated. During a mean follow-up of 366 ± 130 days, 18 patients (11.8%) suffered an AF/atrial tachycardia recurrence after the 90-day blanking period. CONCLUSION: The magnitude and time-course of the LI drop during RF delivery were associated with effective lesion formation. This ablation strategy for PVI guided by LI technology proved safe and effective and resulted in a very low rate of AF recurrence over 1-year follow-up.

Early rhythm-control ablation therapy to prevent atrial fibrillation recurrences: Insights from the CHARISMA Registry.

BACKGROUND: An early, comprehensive rhythm-control therapy is needed in order to treat atrial fibrillation (AF) effectively and to improve ablation outcomes. METHODS: A total of 153 consecutive patients from the CHARISMA registry undergoing AF ablation at eight centers were included. Patients with de novo PVI were classified as having undergone early treatment (ET) if the procedure was performed within 6 months after the first AF episode, and as having undergone delayed treatment (DT) if ablation was performed over 6 months after the first AF episode. RESULTS: One-hundred fifty-three patients were enrolled (69.9% male, 59 ± 10 years, 61.4% paroxysmal AF, 38.6% persistent AF). The time from the first AF episode to the ablation procedure was 1034 ± 1483 days. The ET group comprised 36 patients (25.3%), the DT group 60 (39.2%) and Redo cases were 57 (37.3%). During a mean follow-up of 366 ± 130 days, 18 patients (11.8%) suffered an AF/AT recurrence. More DT patients than ET patients suffered recurrences (15.7% vs. 2.2%, p = 0.0452) and the time to AT/AF recurrence was shorter in the group of patients who received an ablation treatment after 6 months (HR = 6.19, 95% CI: 1.7 to 21.9; p = 0.0474). On multivariate Cox analysis, only hypertension (HR = 4.86, 95% CI: 1.6 to 14.98, p = 0.0062) was independently associated with recurrences. Beyond the hypertension risk factor, ET was associated with a low risk of recurrence; recurrence rate ranged from 0% (ET patients without hypertension) to 25.0% (DT patients with hypertension). CONCLUSIONS: An early rhythm-control ablation therapy in the absence of common risk factors was associated with the lowest rate of recurrences.

Reasons for successful clinical outcome following pulmonary vein isolation despite lack of persistent LA-PV conduction block.

The mechanisms of atrial fibrillation (AF) induction and maintenance, including those involved in paroxysmal atrial fibrillation, are not completely known; this limits our ablation strategies and prevents us from understanding what we are actually doing when performing pulmonary vein isolation. In this report, we focus on the commonly used ablation strategies for AF and question the importance of complete pulmonary vein isolation in achieving lasting success in the ablation of AF. We also discuss in detail the absence of durable pulmonary vein isolation in patients without arrhythmic recurrences after AF ablation and the possibility to cure paroxysmal AF without concomitant pulmonary vein isolation, provocatively questioning the dogma of pulmonary vein isolation as the cornerstone of AF ablation. Finally, a prospective personalized approach in the individual patient is advocated.

Multichannel system based on a high sensitivity superconductive sensor for magnetoencephalography.

We developed a multichannel system based on superconducting quantum interference devices (SQUIDs) for magnetoencephalography measurements. Our system consists of 163 fully-integrated SQUID magnetometers, 154 channels and 9 references, and all of the operations are performed inside a magnetically-shielded room. The system exhibits a magnetic field noise spectral density of approximatively 5 fT/Hz(1=2). The presented magnetoencephalography is the first system working in a clinical environment in Italy.

Relevance of Anatomical Significance of AV Nodal Structures within Koch's Triangle and Pyramid.

The exploration of the cardiac conduction system evolved over a century, marked by groundbreaking discoveries in atrioventricular (AV) nodal physiology. Atrioventricular nodal re-entrant tachycardia (AVNRT), the most prevalent regular tachycardia in humans, remains enigmatic despite extensive research. Detailed examinations of AV nodal anatomy and histology reveal variations in location and shape, influencing electrophysiological properties. Variability in AV nodal extensions and their embryological origins contribute to the complexity of the conduction system. Physiologically, the AV node plays a crucial role in modulating AV conduction, introducing delays for ventricular filling and filtering atrial impulses. Dual-pathway physiology involving fast and slow pathways further complicates AVNRT circuitry. Integrated approaches combining pre-procedural imaging with electroanatomical mapping enhance our understanding of AV nodal structures and high-definition mapping improves precision in identifying ablation targets. Electrophysiological-anatomical correlations may unveil the specific roles of conduction axis components, aiding in the optimization of ablation strategies. This review traces the historical journey from Tawara's pioneering work to recent integrated approaches aimed at unraveling the intricacies of AV nodal structures while emphasizing the importance of a multidimensional approach, incorporating technological advancements, anatomical understanding, and clinical validation in human mapping studies.

Case Report: Epi-endocardial bridges in refractory cavotricuspid isthmus-dependent atrial flutter: technical analysis of epi-endocardial breakthrough.

Background: Typical isthmus-dependent atrial flutter (AFL) is traditionally treated through radiofrequency (RF) ablation to create a bidirectional conduction block across the cavo-tricuspid isthmus (CTI) in the right atrium. While this approach is successful in many cases, certain anatomical variations can present challenges, making CTI ablation difficult. Methods: We enrolled four patients with typical counter-clockwise AFL who displayed an epicardial bridge at the CTI. Patients underwent high-resolution mapping of the right atrium and CTI ablation. Results: Post-mapping identified areas of early focal activation outside the lesion line which suggested the presence of an epi-endocardial bridge with an endocardial breakthrough, confirmed by recording a unipolar rS pattern on electrograms at that site. A stable CTI block was achieved in all patients only after ablation at the site of the epi-endocardial breakthrough. Conclusions: The presence of an epicardial bridge at the CTI, allowing conduction to persist despite endocardial ablation, should be considered in challenging cases of CTI-dependent AFL. Understanding this phenomenon and utilizing appropriate mapping and ablation techniques are essential for achieving successful and lasting CTI block.

Prevention and Risk Assessment of Cardiac Device Infections in Clinical Practice.

The implantation of cardiac electronic devices (CIEDs), including pacemakers and defibrillators, has become increasingly prevalent in recent years and has been accompanied by a significant rise in cardiac device infections (CDIs), which pose a substantial clinical and economic burden. CDIs are associated with hospitalizations and prolonged antibiotic therapy and often necessitate device removal, leading to increased morbidity, mortality, and healthcare costs worldwide. Approximately 1-2% of CIED implants are associated with infections, making this a critical issue to address. In this contemporary review, we discuss the burden of CDIs with their risk factors, healthcare costs, prevention strategies, and clinical management.

New insights into atrioventricular nodal anatomy, physiology, and immunochemistry: A comprehensive review and a proposed model of the slow-fast atrioventricular nodal reentrant tachycardia circuit in agreement with direct potential recordings in the Koch's triangle area.

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most frequent regular tachycardia in humans. In this review, we describe the most recent discoveries regarding the anatomical, physiological, and molecular biological features of the atrioventricular junction that could underlie the typical slow-fast AVNRT mechanisms, as these insights could lead to the proposal of a new theory concerning the circuit of this arrhythmia. Despite several models have been proposed over the years, the precise anatomical site of the reentrant circuit and the pathway involved in the slow-fast AVNRT have not been conclusively defined. One possible way to evaluate all the hypotheses regarding the nodal tachycardia circuit in humans is to map this circuit. Thus, we tried to identify the slow potential of nodal and inferior extension structures by using automated mapping of atrial activation during both sinus rhythm and typical slow-fast AVNRT. This constitutes a first step toward the definition of nodal area activation in sinus rhythm and during slow-fast AVNRT. Further studies and technical improvements in recording the potentials of the atrioventricular node structures are necessary to confirm our initial results.

Navx-guided Cryoablation of Atrial Tachycardia Inside the Left Atrial Appendage.

Radiofrequency ablation procedures inside the left atrial appendage (LAA) are likely to involve dangerous complications because of a high thrombogenic effect. Cryoablation procedures are supposed to be safer. We describe two cases of successful cryoablation procedures. Two NavX-guided cryoablations of permanent focal atrial arrhythmias arising from the LAA were performed. Left atrial reconstruction and mapping allowed the zone of the earliest atrial potential to be recorded; the entire course of the ablation catheter was monitored. The arrhythmias were successfully ablated; no thrombotic complications were observed.

High-density mapping of Koch's triangle during sinus rhythm and typical AV nodal reentrant tachycardia: new insight.

BACKGROUND: Atrial activation during typical atrioventricular nodal reentrant tachycardia (AVNRT) exhibits anatomic variability and spatially heterogeneous propagation inside the Koch's triangle (KT). The mechanism of the reentrant circuit has not been elucidated yet. Aim of this study is to describe the distribution of Jackman and Haïssaguerre potentials within the KT and to explore the activation mode of the KT, in sinus rhythm and during the slow-fast AVNRT. METHODS: Forty-five consecutive cases of successful slow pathway (SP) ablation of typical slow-fast AVNRT from the CHARISMA registry were included. RESULTS: The KT geometry was obtained on the basis of the electroanatomic information using the Rhythmia mapping system (Boston Scientific) (mean number of points acquired inside the KT = 277 ± 47, mean mapping time = 11.9 ± 4 min). The postero-septal regions bounded anteriorly by the tricuspid annulus and posteriorly by the lateral wall toward the crista terminalis showed a higher prevalence of Jackman potentials than mid-postero-septal regions along the tendon of Todaro and coronary sinus (CS) (98% vs. 16%, p < 0.0001). Haïssaguerre potentials seemed to have a converse distribution across the KT (0% vs. 84%, p < 0.0001). Fast pathway insertion, as located during AVNRT, was mostly recorded in an antero-septal position (n = 36, 80%), rather than in a mid-septal (n = 6, 13.3%) or even postero-septal (n = 3, 7%) location. During typical slow-fast AVNRT, two types of propagation around the CS were discernible: anterior and posterior, n = 31 (69%), or only anterior, n = 14 (31%). During the first procedure, the SP was eliminated, and acute procedural success was achieved (median of 4 [3-5] RF ablations). CONCLUSION: High-density mapping of KT in AVNRT patients both during sinus rhythm and during tachycardia provides new electrophysiological insights. A better understanding and a more precise definition of the arrhythmogenic substrate in AVNRT patients may have prognostic value, especially in high-risk cases. TRIAL REGISTRATION: Catheter Ablation of Arrhythmias With High Density Mapping System in the Real World Practice (CHARISMA) URL: http://clinicaltrials.gov/ Identifier: NCT03793998.

Clinical and arrhythmic outcomes after implantation of a defibrillator for primary prevention of sudden death in patients with post-myocardial infarction cardiomyopathy: The Survey to Evaluate Arrhythmia Rate in High-risk MI patients (SEARCH-MI).

AIMS: To evaluate clinical and arrhythmic outcomes in post-infarction cardiomyopathy patients implanted with a defibrillator (ICD) for primary prevention of sudden death. METHODS AND RESULTS: The SEARCH-MI registry is a European multi-centre, prospective, observational study enrolling patients after myocardial infarction, chronic left ventricular dysfunction and an ICD implanted for primary prevention of sudden death. Data on 556 patients with at least one recorded follow-up are presented. Survey to Evaluate Arrhythmia Rate in High-risk MI (SEARCH-MI) patients were sicker than those enrolled in MADIT-II with higher New York Heart Association class and left bundle branch block. Total mortality was 10.4%. Close to one-third (30%) of patients experienced episodes of sustained ventricular arrhythmia. One-quarter (23%) received at least one appropriate therapy and 10% inappropriate therapy. Gender (25% males vs. 5% females, P = 0.0009) and history of non-sustained ventricular tachycardia (24% with vs. 18% without P = 0.037) were predictive of appropriate ventricular therapy. CONCLUSION: SEARCH-MI represents the current clinical management of post-MI patients with left ventricular dysfunction indicated to defibrillator implant for primary prevention. European routine clinical practice was influenced by landmark trials and guidelines which impacted on the implantation of cardiac resynchronization therapy in over 25% of such patients. Non-sustained ventricular tachycardia identifies subjects with a higher incidence of appropriate ICD therapy.

Mapping of ventricular tachycardia in patients with ischemic cardiomyopathy: Current approaches and future perspectives.

Despite the technical improvements made in recent years, the overall long-term success rate of ventricular tachycardia (VT) ablation in patients with ischemic cardiomyopathy remains disappointing. This unsatisfactory situation has persisted even though several approaches to VT substrate ablation allow mapping and ablation of noninducible/nontolerated arrhythmias. The current substrate mapping methods present some shortcomings regarding the accurate definition of the true scar, the modality of detection in sinus rhythm of abnormal electrograms that identify sites of critical channels during VT and the possibility to determine the boundaries of functional re-entrant circuits during sinus or paced rhythms. In this review, we focus on current and proposed ablation strategies for VT to provide an overview of the potential/real application (and results) of several ablation approaches and future perspectives.

Is dual defibrillator better than conventional DDD pacing in brady-tachy syndrome? Results of the ICARUS Trial (Internal Cardioversion Antitachypacing and Prevention: Resource Utilization Study).

AIM OF THE STUDY: To compare the impact of dual defibrillator versus conventional DDD pacing on quality of life and hospitalizations in patients with sinus node disease and recurrent symptomatic atrial fibrillation. STUDY DESIGN: Prospective, parallel, controlled trial. METHODS: Sixty-three patients (41 M, mean age 71 +/- 8 years) with sinus node disease and at least three symptomatic episodes of atrial fibrillation during the last year were enrolled. Thirty-one consecutive patients received a dual defibrillator (group A) and 32 standard DDD pacing (group B). In group A, 12 patients received an external remote-control device in order to shock themselves in case of atrial fibrillation, while 19 were scheduled for early in-hospital manual shock. Seventy-five percent had been hospitalized during the last year and 57% had required electrical cardioversion. Atrial fibrillation was persistent in 63.5% and paroxysmal in 37.5%. The follow-up lasted 1 year. RESULTS: Atrial fibrillation recurred in 83.3% in group A and 79.3% in group B (p = ns). Electrical cardioversion was applied in 54.8% in group A and in 21.9% in group B (p < 0.05). On the whole, 89.5% of electrical cardioversions were delivered in the defibrillator group (p < 0.0001). In the whole population 27.0% patients had cardiac-related hospitalization (31.2% in the pacemaker group and 22.6% in the defibrillator group, p = n.s.). In patients with persistent atrial fibrillation, cardiac-related hospitalization rate was significantly lower in the group A (0% vs. 30%, p < 0.05). Considering Symptom Check List, symptoms significantly improved in the whole population, but symptom number and frequency improved significantly only in the group A. Similarly, SF-36 questionnaire scores showed a little higher quality of life improvement in the group A. CONCLUSIONS: Dual defibrillator showed consistent trends toward a higher effectiveness when compared with standard DDD pacing. Dual defibrillator was associated to reduced in-patient cardioversions and to better quality of life. All-cause hospitalizations were reduced only in patients with persistent atrial fibrillation.

[Treatment of arrhythmias and syncope in the elderly with heart failure]. / Valutazione e trattamento della sincope nell'anziano con scompenso cardiaco.

A review of the huge literature on syncope and arrhythmias has been conducted with special regard to older subjects with heart failure. All the available data show that aging is a risk factor for syncope spells and that the risk is almost doubled in patients with heart failure. In older patients as well, syncope may be classified as non-cardiac, cardiac and unknown in origin and in the aging cardiac syncope has been clearly demonstrated to have a worse prognosis. Syncope, whatever the mechanism involved in, may hardly impair the quality of life. The diagnostic algorithm in spells of unknown origin is extensively discussed and the troubling problem related to vasovagal (and carotid sinus hypersensitivity) syncope and to iatrogenic episodes (very frequent in patients often treated with multiple drugs acting on pressure regulation) is highlighted. A review of the management options is performed with special emphasis on the difficulties due to the scarce relevance of the older groups in clinical trials regarding the treatment strategies of syncope and arrhythmias. Finally, the authors suggest a brief decision-making protocol extrapolated by their experience to manage these difficult clinical conditions.

[Temporary emergency cardiac pacing under continuous echocardiographic control. Feasibility and safety of the procedure without using fluoroscopy]. / Posizionamento ecoguidato di elettrostimolatore temporaneo endocavitario in emergenza. Fattibilità e sicurezza della procedura senza impiego di fluoroscopia.

BACKGROUND: Cardiac pacing often turns out to be the only effective treatment of severe brady-arrhythmias. Several invasive and noninvasive temporary pacing procedures are known, whose application is sometimes difficult or time-consuming. An alternative temporary cardiac pacing procedure is described in this article, which is based on echocardiographic control. METHODS: Fifty-four nonconsecutive patients were studied; they all were needing urgent cardiac pacing. A first choice attempt to perform an ultrasound-guided temporary cardiac pacing, by using a right jugular venous approach, was done. The catheter pathway was monitored by means of echocardiography performed by another operator. All data concerning time of execution, pacing parameters, acute or chronic complications and the in situ time duration of the catheter without needing to be repositioned were obtained. RESULTS: Ultrasound-guided cardiac pacing was not feasible in 3 patients (6%), because of a high thoracic acoustic impedance or failing to perform right jugular venous catheterization. Mean execution time was 680 +/- 179 s. Echocardiographic monitoring was performed in 50 patients by a cardiologist, in 1 patient by a non-cardiologist physician, and in 3 patients by a nurse, who had been previously trained to keep the transducer in the right position. No serious complications occurred. On 4 occasions (8%) the catheter had to be repositioned during the following hours. On 25 occasions (46%) permanent cardiac pacing was finally performed. CONCLUSIONS: Temporary ultrasound-guided cardiac pacing seems to be a safe and easy procedure; it can be performed in a broad range of clinical and logistic scenarios and does not require fluoroscopic monitoring. A limited number of human resources is needed, but technical skills in central venous catheterization are required. Further studies are needed to validate this procedure; however it shows several potential benefits as compared to the other temporary cardiac pacing techniques.

Electrical And Hemodynamic Evalution Of Ventricular And Supraventricular Tachycardias With An Implantable Dual-Chamber Pacemaker.

The discrimination between ventricular (VT) and supraventricular tachycardia (SVT) and the evaluation of their hemodynamic impact are essential issues in the arrhythmia management. A new pacing device features a tachycardia diagnostic system relying on simultaneous recording of the transvalvular impedance (TVI) and a special integrated electric signal derived by the whole set of endocardial electrodes (iECG). The iECG waveform is sensitive to the pattern of ventricular activation, similarly to the surface ECG. The TVI increases in systole and decreases in diastole and the amplitude of this cyclic fluctuation is an expression of the effectiveness of the pump function. In order to test the value of these signals in the analysis of a tachycardia, we have assessed the iECG and TVI modifications induced by different SVTs and tolerated and non-tolerated VTs, during electrophysiological (EP) studies. In case of SVT, the ventricular component of the iECG maintained the same morphology as in sinus rhythm. The peak-peak amplitude of the TVI fluctuation was reduced to 66 ± 11 % of the individual sinus rhythm reference, but the signal was present at every beat and showed a remarkable stability (variation coefficient 0.19 ± 0.01). In case of VT, the ventricular component of the iECG was strikingly different than in sinus rhythm. Regular TVI fluctuation was observed with tolerated VTs (peak-peak amplitude 74 ± 6 %; variation coefficient 0.21 ± 0.04). In contrast, with non-tolerated VTs the TVI amplitude was depressed below 40%, and the signal was virtually absent in the event of very fast VT or VF. Our results confirm that the iECG is a reliable tool to quickly discriminate VTs from SVTs and that TVI can provide information on the severity of the hemodynamic impairment produced by a tachycardia, with potential clinical benefit in the follow-up of pacemaker patients. Furthermore, the application of these signals to automatic algorithms of arrhythmia recognition might improve the specificity of therapy administration by an implantable defibrillator (ICD).

Noncompacted ventricular myocardium: characterization by intracardiac echo.

We report a patient with clinical manifestation of arrhythmias and evidence of noncompacted myocardium in both left and right ventricular apex. The diagnosis was made with intracardiac echo performed during the electrophysiologic study. This method has allowed the diagnosis of noncompaction of the ventricular myocardium due to its high resolution. Color Doppler showed trabecular recesses in communication with the ventricular cavity that could not be identified with transthoracic echocardiography.

Propagation of the sinus impulse into the Koch triangle and localization, timing, and origin of the multicomponent potentials recorded in this area.

BACKGROUND: The presence of a conduction block at the level of the Koch triangle (KT) and the origin of the multicomponent potentials inside this area are controversial issues. We investigated the propagation of the sinus impulse into the KT and the characteristics of multicomponent potentials recorded in that area in patients with and without atrioventricular nodal reentrant tachycardia (AVNRT). METHODS AND RESULTS: Thirty-two patients (16 with AVNRT, 16 without AVNRT) underwent a sinus rhythm electroanatomic mapping of the right atrium (RA). Conduction velocities in the RA and in the KT were evaluated quantitatively on activation maps and qualitatively on isochronal and propagation maps. The presence, location, and timing of different types of multicomponent potentials were evaluated. A mean of 149±44 points were sampled in the RA, whereas a mean of 79±21 points were collected inside the KT. Propagation block at the level of crista terminalis was not found in any patient, whereas slow conduction inside the KT was found in all (median conduction velocity, 122 cm/s [110 to 135 cm/s] outside KT versus 60 cm/s [48 to 75 cm/s] inside KT; P<0.0001). Jackman potentials were identified inside KT in almost all the patients and were invariably found on the line of collision between the wavefronts activating the KT in opposite directions. CONCLUSIONS: No conduction block was detected inside the KT in patients with and without AVNRT. Conduction slowing was demonstrated during propagation of the sinus impulse inside the KT. The genesis of the Jackman potential may be related to the collision of the wavefronts activating KT in opposite directions.