Postpacing Interval Research Articles

Upper turnaround point in a reentry circuit of the idiopathic left posterior fascicular ventricular tachycardia.

The anatomic extent of the reentry circuit in idiopathic left posterior fascicular ventricular tachycardia (LPF-VT) is yet to be fully elucidated. We hypothesized that entrainment mapping could be used to delineate the reentry circuit of an LPF-VT, especially including the upper turnaround point. Twenty-three consecutive LPF-VT patients (mean age, 29±9 years, 18 males) were included. We performed overdrive pacing with entrainment attempts at the left bundle branch (LBB) and the left His bundle (HB) region. Overdrive pacing from the LBB region showed concealed fusion in all 23 patients (post-pacing interval [PPI], 322.1±64.3ms; tachycardia cycle length [TCL], 319.0±61.6ms; PPI-TCL, 3.1±4.6ms) with a long stimulus-to-QRS interval (287.9±58.0ms, approximately 90% of the TCL). Pacing from the same LBB region at a slightly faster pacing rate showed manifest fusion with antidromic conduction to the LBB and minimal in-and-out time to the LBB potential (PPI-TCL, 21.3±13.7ms). Overdrive pacing from the left HB region showed manifest fusion with a long PPI-TCL (53.9±22.5ms). Our pacing study results suggest that the upper turnaround point in a reentry circuit of the LPF-VT may extend to the proximal His-Purkinje conduction system near the LBB region but below the left HB region. The LPF may constitute the retrograde limb of the reentry circuit.

Real-world performance of a fully automatic antitachycardia pacing algorithm

Abstract Background Antitachycardia pacing (ATP) found in most implantable cardioverter defibrillators (ICDs) is an important therapy for painless termination of ventricular tachycardias (VT). In ICDs programmed to guideline-recommended detection and therapy settings typical ATP success rates are 50-70%.[1-3] The first closed-loop, automated ATP (AATP) algorithm, introduced in 2021, applies an S1 train derived from the detected VT, followed by an S2 derived initially from a refractory period estimator and then adjusted using analysis of the post-pacing interval if ATP fails. The termination efficacy of AATP in the real-world population is unknown. Purpose To assess the effectiveness AATP in a large real-world population. Methods A database of de-identified ICD transmissions from subjects in the United States, Australia, Canada, and New Zealand was queried for AATP treated episodes. ICDs were randomly sampled, biased toward ICDs with multiple treated VT episodes. For rhythms classified as monomorphic ventricular tachycardia, each AATP pulse train was reviewed for: rhythm at delivery, effect of ATP, and any non-capturing pulses. Acceleration was defined as a post-ATP decrease in MVT cycle length (VTCL) of at least 10% and at least 30ms. Acceleration to polymorphic VT or ventricular fibrillation (PVT/VF) was assessed. Rates of termination and acceleration were calculated for all MVT and dichotomized using a 320ms VTCL cutoff. The method of generalized estimating equations (GEE) was used to correct event rates for multiple episodes from a single patient. Results There were 2281 episodes of MVT in 340 patients; 63% of patients had 2 or more episodes. There were 724 episodes with initial VTCL <320ms and 1557 episodes with VTCL ≥320ms. The rate of termination of MVT by AATP was 78% for all VTCL [95% CI: 74%-81%]. In 300 patients (88%) AATP terminated at least one MVT. For MVT with VTCL ≥320ms the termination rate was 80% [95% CI: 75%-83%] and for VTCL <320ms the termination rate was 75% [95% CI: 69%-80%]. The rate of acceleration was 3.6% [95% CI: 2.7%-4.9%], with a 0.8% rate of acceleration to PVT/VF [95% CI: 0.4%-1.8%]. Acceleration led to shock therapy in 63% of accelerated episodes. All MVT accelerated to PVT/VF either spontaneously terminated (4/14) or were successfully converted by a single shock therapy (10/14). All accelerations that remained MVT were successfully treated by the device with either subsequent ATP (35%) or shock therapy (61%), or spontaneously terminated (4%). Conclusion In this large, real-world cohort analysis, automated ATP’s termination rate exceeded the typical success rate of burst ATP, particularly for MVT <320ms. Acceleration to PVT/VF was low and effective first-shock defibrillation was consistent. Subsequent ATP for accelerated MVT had incremental benefit, leading to successful termination one-third of the time. Additional data are currently being prospectively collected in a separate post-approval study.

Abstract 14364: Atrial Fibrillation With Rapid Ventricular Response Induced Ventricular Tachycardia Terminated by Intrinsic Anti-Tachycardia Pacing - A First in Literature Case Report

Background: Intrinsic anti-tachycardia pacing (iATP) is a novel tailored algorithm that has shown increased efficacy against ventricular tachycardia (VT), including fast VT. We describe a case of atrial fibrillation (AF) with rapid ventricular response (RVR) induced VT terminated by iATP. Case description: A 71-year-old male with coronary artery disease, heart failure (EF 30-35%), atrial fibrillation, VT status post biventricular implantable cardioverter defibrillator and failed renal transplant presented with syncope during dialysis. His home medications included amiodarone, metoprolol, apixaban. He was hemodynamically stable on presentation. He had bilateral pitting edema with a systolic murmur and bilateral basilar crackles on exam. His labs were consistent with anemia and end stage renal disease. His device interrogation (Figure) showed AFRVR which degenerated to VT with final cycle length (CL) of 290 msec. First round of ATP with S1x10 burst pulses (88%, CL 250msec) and S2 extra stimuli (CL 230 msec) failed to terminate the VT. Post pacing interval (PPI) was 450 msec. Given calculated remote distance, another five rounds of adaptive iATP with similar S1 pulses but faster S2 and addition of S3 extra stimuli were delivered but were unsuccessful in terminating VT. Finally, the seventh round of iATP (S1x10 at CL 260 msec, S2 at 240 msec) was successful at conversion to sinus rhythm briefly before reverting to AF with controlled ventricular pacing. Discussion: ATP decreases ICD shocks but is programmed empirically and there is less success with fast VT. iATP analyses the PPI of the prior failed sequence to adjust the subsequent ATP therapy by altering the number of burst pulses (S1) and addition of ramp extra stimuli. Computational models and early clinical experience have shown increased efficacy of iATP in terminating fast VT without concomitant increase in VT acceleration. To the best of our knowledge, this is first case report of AFRVR induced VT terminated by iATP.

Bidirectional rotating biatrial tachycardia.

A 72-year-old man was treated for recurrent atrial tachycardia (AT) and underwent ablation. The AT was diagnosed as bi-AT based on the activation map and the postpacing interval. Another AT appeared and was diagnosed as bi-AT by the same method. Surprisingly, the circuits of both ATs were perfectly matched and rotated in opposite directions. The left atrial anteroseptal wall was ablated during the AT. The AT was immediately stopped and was no longer induced.

Selective and non-selective right bundle pacing for the diagnosis of bundle branch reentry ventricular tachycardia.

Bundle branch reentry ventricular tachycardia (BBRVT) can be seen in patients with conduction disease. In this report, we describe the use of conduction system pacing for its diagnosis. BBRVT was induced in two patients with infra-nodal conduction disease. Bundle branch reentry ventricular tachycardia with a left bundle branch block morphology was observed in the first patient (type A), whereas the second patient had a right bundle branch block morphology (type C).The diagnosis of BBRVT was confirmed in both patients by ventriculo-atrial dissociation, and the interdependence of the conduction system and the ventricular tachycardia cycle length variations.Selective and non-selective RB pacing was observed in the two patients during apical right ventricular pacing for entrainment of BBRVT with evidence of manifest entrainment with non-selective RB capture in the first patient, and concealed entrainment by selective RB capture in the second patient. Other criteria for entrainment including a short post-pacing interval at the right bundle pacing site were noted. Right bundle pacing is feasible in patients with BBRVT and may be a helpful manoeuver for the diagnosis of BBRVT.

PO-04-186 ASSESSING PROXIMITY TO THE VENTRICULAR TACHYCARDIA CIRCUIT EARLY IN THE PACING TRAIN: NUMBER NEEDED TO RESET

When ventricular tachycardia (VT) continues after entrainment the post pacing interval (PPI) can be used to assess proximity to the circuit. It is not known if the initial beats of a pacing train can be used to assess reentry circuit proximity, which could be useful when pacing terminates or alters VT. We hypothesized that the number of stimuli with local electrogram(EGM) capture needed to reset (NNR) VT may provide an indication of proximity to the reentry circuit as has been shown in atrial flutter. During stable scar-related VT, pacing trains 10 – 40ms faster than the VT cycle length with the first stimulus synchronized to a ventricular electrogram were delivered. We included sites with stable VT cycle length(TCL) and without perturbation of VT post pacing to allow comparison with the PPI-TCL. Of 102 trains at 92 sites in 28 VTs in 17 patients the first capturing stimulus was earlier than 30 ms in prematurity relative to local activation, such that NNR could be artificially short. NNR was analyzed in the remaining 23 trains at 21sites in 10 VTs (457ms +/- 85ms CL). The PPI-TCL ranged from 0-100ms and the NNR ranged from 1-6. PPI-TCL was correlated with NNR (r=0.67, p=0.006) (figure). When the first or second stimulus reset VT (NNR = 1 or 2) the PPI-TCL was < 30ms and 3-6 with a PPI-TCL of >30ms. The NNR provides an indication to the proximity to the circuit with NNR <2 indicating a PPI-TCL of <30ms that can potentially be applied if pacing terminates VT. Application of NNR requires attention to synchronization of the pacing train that is not straight forward in areas of fractionated electrograms.

PO-05-056 FAILURE OF INTRINSIC ANTI-TACHYCARDIA PACING TO TERMINATE VENTRICULAR TACHYCARDIA AND POTENTIAL PROARRHYTHMIC EFFECTS

Intrinsic anti-tachycardia pacing (iATP™) is a novel, automated ATP algorithm that provides individualized therapy to terminate ventricular tachycardia (VT). If the first ATP attempt is unsuccessful, the algorithm analyzes the tachycardia cycle length and the post-pacing interval (PPI) and adjusts the subsequent sequence to successfully terminate VT. This algorithm was effective in a single clinical study without a comparator arm and case reports have corroborated this success in clinical practice. Despite the previously presented data, iATP™ failure has not been well documented in the literature. We present the first case series of iATP™ failure in routine clinical practice with detailed episode analysis and the apprise the electrophysiology community of the potential proarrhythmic effect of the algorithm. We retrospectively evaluated 262 patients with Medtronic Cobalt XT defibrillators followed at Mayo Clinic campuses in Minnesota, Florida, and Arizona. 119 patients had devices with the iATP™ feature turned on. 4 out of 119 patients (3.36%) had an acceleration of their ventricular arrhythmias within our cohort. Illustrative Case: A 74-year-old male with a history of idiopathic, non-ischemic cardiomyopathy (LVEF) 21%) status post-cardiac resynchronization therapy (CRT)-defibrillator for primary prevention, subsequent VT, and atrial fibrillation presented to our heart rhythm clinic for evaluation of syncope. The patient was riding an all-terrain vehicle when he felt a sudden onset of dyspnea and pre-syncope. His device interrogation revealed a presenting rhythm of VT at 200 beats per minute (bpm). The patient underwent four unsuccessful rounds of ATP. The 4th round of ATP resulted in acceleration (figure 1A) and degeneration into ventricular fibrillation (VF), followed by a successful 39.5 J shock (figure 1B). Figure 1C shows the dot plot for the entire episode with the blue box highlighting the acceleration in ventricular rate after the 4th ATP sequence. Given concern for a proarrhythmic effect, iATP™ was turned off. The patient was treated with amiodarone and mexiletine and underwent endocardial ablation with substrate modification in the inferolateral LV. He is currently doing well without a subsequent need for VT therapies. While the novel adaptive algorithm and its underlying concepts are intriguing, clinicians should be aware of the potential for acceleration and degeneration of VT by iATP™ and prepared to turn off the feature when this occurs.

PO-05-155 A CASE OF ALCOHOL LEADING TO ISOLATION IN THE ELECTROPHYSIOLOGY LABORATORY

Ligament of Marshall alcohol ablation is a treatment for refractory atrial fibrillation and left atrial flutter. Left atrial appendage (LAA) isolation resulting from LOM ablation has not been described. To describe a case of LOM alcohol ablation which resulted in left atrial appendage isolation and dissociation of a left atrial appendage reentrant atrial flutter from the atria. A middle aged man with a history of atrial fibrillation and multiple left atrial flutters was referred for repeat ablation after multiple prior unsuccessful ablations. He previously underwent surgical MAZE and 3 endocardial ablations including an anterior mitral line and endocardial and epicardial mitral isthmus line without achieving bidirectional block. He had recurrent, symptomatic atrial flutter despite therapy with dofetilide and metoprolol. The patient presented in an atypical flutter. The ligament of Marshall was cannulated and alcohol was sequentially injected for a total of 3.8 mL. After the first alcohol injection, the tachycardia abruptly terminated on the coronary sinus (CS) catheter and sinus rhythm resumed (Figure, blue arrows), though the surface ECG showed ongoing small atrial flutter waves (Figure, red arrows). Subsequent left atrial mapping confirmed that the left atrial appendage (LAA) was isolated from the remaining left and right atrium and remained in atrial flutter (Figure C). Overdrive pacing from a multipolar catheter in the LAA demonstrated a post-pacing interval within 20 ms of the tachycardia-cycle length (Figure C). Adenosine administration resulted in AV block but no alteration in tachycardia cycle-length. These findings were highly suggestive of a reentrant mechanism. Because 3D mapping was limited by dissociated CS and LAA rhythms, manual activation mapping was performed with earliest activation at the anterior superior LAA. RF ablation at this site resulted in atrial flutter slowing and termination. In a patient with LAA flutter and prior anteroseptal and lateral linear endocardial ablation, LOM alcohol ablation may isolate the LAA. This should be recognized when counseling patients and planning procedures.

PO-05-222 NOVEL APPROACHES FOR THE DIAGNOSIS OF CONCEALED NODO-VENTRICULAR AND HIS-VENTRICULAR PATHWAYS

Concealed nodo-ventricular (cNV) or His-ventricular (cHV) pathways are rare accessory pathway variants that represent important challenges for the clinician to separate from the more common supraventricular tachycardia arrhythmias. To describe novel observations to aid in diagnosing cNV or cHV pathways. We present a case series of seven patients with re-entrant arrhythmias involving cNV (5 cases) or cHV (2 cases) pathways. We focus on several laboratory observations: (1) differential ventricular overdrive pacing (VOD) from the right ventricular base vs. apex, (2) response to His refractory premature ventricular complexes (PVCs), (3) paradoxical atriohisian (AH) response in long RP tachycardia, and (4) the role of adenosine to aid in the diagnosis. (1) Three cases underwent differential basal vs. apical VOD during tachycardia. All demonstrated a shorter post-pacing interval minus tachycardia cycle length during basal pacing than apical pacing with one case exhibiting apical VOD results compatible with atrioventricular nodal reentrant tachycardia (AVNRT). In one case with a cHV pathway, basal VOD was useful for localizing the ventricular connection and guiding the ablation site. (2) In 3 cases, His refractory PVCs reset the tachycardia without conduction the atrium, which excluded atrioventricular reentry, atrial tachycardia, or AVNRT alone. One case had His refractory PVCs followed by subsequent constant AA and HH intervals and then tachycardia termination, suggesting a bystander cNV pathway involvement. (3) Two cNV pathway cases presented with long RP tachycardia had shorter AH intervals during tachycardia than those during sinus rhythm of >15ms, suggesting parallel activation of the atrium and the atrioventricular node. (4) Low-dose adenosine (3 and 6 mg) terminated the tachycardia with a retrograde block in 2 cases with cNV pathways, while high dose adenosine titrated up to 18 mg failed to convert in a case with a HV pathway. cNV and cHV pathways mediated tachyarrhythmias can present with variable clinical presentations. We emphasized (1) the role of differential VOD and the importance of the basal VOD for a proper diagnosis and pathway localization (Figure, Panel A), (2) the importance of His refractory PVCs that reset or terminate the tachycardia without conducting the atrium (Panel B), (3) the importance of paradoxical AH response in long RP tachycardia (Panel C), and the use of adenosine for possibly distinguishing cNV from cHV pathways (Panel D).

Novel Approaches for the Diagnosis of Concealed Nodo-Ventricular and His-Ventricular Pathways

Confirming the presence and participation of concealed nodo-ventricular (cNV) or concealed His-ventricular (cHV) pathways in tachyarrhythmias is challenging. We describe novel observations to aid in diagnosing cNV or cHV pathways. We present 7 cases of cNV and cHV pathway-mediated arrhythmias and focus on several laboratory observations: (1) differential ventricular overdrive pacing (VOD) from the base versus apex, (2) response to His refractory premature ventricular complexes, (3) paradoxical atriohisian response (shorter atriohisian interval during tachycardia than that during sinus rhythm) in long RP tachycardia, and (4) the role of adenosine to aid in the diagnosis. Three cases underwent differential VOD during tachycardia. All demonstrated a shorter postpacing interval minus tachycardia cycle length during basal pacing than apical pacing with one case exhibiting apical VOD results compatible with atrioventricular nodal reentrant tachycardia. Basal VOD was useful for localizing the ventricular connection in a case with cHV pathway. In 3 cases, His refractory premature ventricular complexes reset the tachycardia without conduction to the atrium, which excluded the involvement of an atrioventricular pathway or atrial tachycardia, or atrioventricular nodal reentrant tachycardia alone. One case had His refractory premature ventricular complexes followed by subsequent constant AA interval and then tachycardia termination, suggesting a bystander cNV pathway involvement. Two cNV pathway cases presented with long RP tachycardia had paradoxical atriohisian shortening of >15 ms, suggesting parallel activation of the atrium and the atrioventricular node. Adenosine terminated the tachycardia with retrograde block in 2 cases with cNV pathways but had no response on a cHV pathway. cNV and cHV pathways mediated tachyarrhythmias can present with variable clinical presentations. We emphasize the important role of differential VOD sites, His refractory premature ventricular complexes that reset or terminate the tachycardia without conduction to the atrium, paradoxical atriohisian response in long RP tachycardia, and the use of adenosine for diagnosing cNV and cHV pathways.

A macroreentrant atrial tachycardia ablated within the superior vena cava

A 75-year-old man was referred for the treatment of a narrow QRS tachycardia. Electrophysiological testing demonstrated that the narrow QRS tachycardia was an atrial tachycardia. Catheter ablation of the tachycardia was performed using the Rhythmia mapping system (Boston Scientific, Marlborough, MA). By mapping the superior vena cava (SVC) using a mini-electrode basket catheter (Orion, Boston Scientific), a reentry circuit around the points traced by Lumipoint algorithms (Boston Scientific) was demonstrated (Figure 1A and Online Supplemental Video 1). The activation map of the SVC encompassed 100% of the tachycardia cycle length. Extrastimulus pacing in the vicinity of the highlighted points reset the tachycardia with a postpacing interval identical to the tachycardia cycle length.

Effect of stimulation parameters on entrainment.

The postpacing interval (PPI) may be longer (>30 ms) or even shorter (<0 ms) than the tachycardia cycle length (TCL) when entrainment pacing is performed within the isthmus of the circuit.1,2 In this study, we aimed to evaluate whether stimulation parameters can affect the PPI in typical (cavotricuspid isthmus–dependent) atrial flutter (AFL).

Peculiarities of surgical treatment of atrial macro reentry tachyarrhythmia in elderly patients with implanted pacemaker

Atrial macro reentry tachycardias are the most common tachyarrhythmias in the structure of cardiac arrhythmias in the elderly. Catheter ablations are the gold standard for the treatment of atrial macro reentry arrhythmias, but in the elderly group, the risks of complex ablations often outweigh the benefits. Aim: to determine the optimal volume of catheter ablation in atrial tachyarrhythmia using an implanted pacemaker in elderly patients. Materials and methods. The work is based on a retrospective analysis of the results of surgical treatment of (n = 45) elderly patients (75–90 years) with atrial macro reentry tachycardia, who were previously identified as an artificial pacemaker at the National M. Amosov Institute of Cardiovascular Surgery Affiliated to National Academy of Medical Sciences of Ukraine. Patients were divided into 3 groups depending on the response of the reentry tachycardia to electrical pacing (assessed by the difference between postpacing interval (PPI) and tachycardia cycle lens (CL): group І – PPI-CL 20–40 ms; group ІІ – PPI–CL 20–40 ms; group ІІІ – PPI-CL 60 ms and more. Results. In the group I (n = 20) in 100 % of the patients isthmus-dependent reentry tachyarrhythmia was diagnosed and cava-tricuspid isthmus was ablated. In the group ІІ (n = 12) 4 (33 %) patients were diagnosed with reentry tachycardia around the right pulmonary veins, in 8 (67 %) patients – reentrant tachycardia around the mitral valve. In the group ІІІ (n = 13) in 8 (62 %) patients macro reentry around the mitral valve was found, in 3 (23 %) – reentry around the left pulmonary veins, in another 2 (15 %) of the patients – reentry of the left atrial roof. Conclusions. Non-invasive electrophysiological study with pacemaker can be an effective way to study atrial macro reentry tachyarrhythmias. Electrophysiological PPI-SI criteria less than 20 ms can be used as an additional diagnostic criterion for the selection of patients for surgical treatment. Catheter ablation is recommended for elderly patients when the reentry circle is located in the right atrium.

Entrainment of ventricular tachycardia with V-shaped diastolic activation pattern: Is the pacing site in or out?

The use and interpretation of entrainment mapping, or continuous resetting, of a reentrant ventricular tachycardia, has been regarded as the gold standard for delineation of the components of a reentrant circuit. However, there are both inherent limitations and interpretative pitfalls to entrainment mapping. Beyond the far-field (FF) signals, the multiple near-field (NF) components may also be recorded at a given site and pacing typically interacts and captures only one component of the local activation. In the evaluation of the entrainment response, it is crucial to distinguish the NF electrogram captured from FF or other NF components to accurately measure the post-pacing interval, particularly in the presence of multiple NF signals This article is protected by copyright. All rights reserved.

Abstract 10194: Pacing Site- and Rate-Dependent Shortening of Retrograde Conduction Time Over the Slow Pathway After Atrial Entrainment of Fast-Slow Atrioventricular Nodal Reentrant Tachycardia

Introduction: The entrainment rule by which the site of entrainment has no effect on the orthodromic conduction time across the reentry circuit immediately after cessation of pacing has not been unequivocally verified in atypical atrioventricular nodal reentrant tachycardia (AVNRT). We have recently observed a unique electrophysiological response upon atrial induction of fast-slow (F/S-) AVNRT, characterized by a shortening of the retrograde conduction time across the slow pathway (SP) (retro-SP-time). Hypothesis: Atrial entrainment pacing (EP) of a) the common-type (com-) F/S-AVNRT using a typical SP, or b) the superior-type (sup-) F/S-AVNRT using a superior SP, both might modify the retro-SP-time immediately after termination of EP. Methods: In 16 patients of com-F/S-AVNRT and 11 patients of sup-F/S-AVNRT in whom successful EP from the high right atrium (EP-HRA) and the proximal coronary sinus (EP-CS) was obtained at 2±2 rates, we evaluated the difference in the His-atrial (HA) interval measured immediately after cessation of each EP attempt (HA difference) between EP-HRA and EP-CS (HA[1]-HRA and HA[1]-CS, respectively) and also measured atrial-His and HA intervals in the 1st and 2nd cycles immediately after the EP, and during tachycardia stabilized. Results: &gt;20 ms HA difference, defined as an atypical difference, at ≥1 rates of EP was observed in 16 patients (56%), including 7 with com- and 9 with sup-F/S-AVNRT. Irrespective of the EP rate, the atypical response of com-F/S-AVNRT was always due to a shorter HA[1]-CS than HA[1]-HRA, with a 39±22 ms HA difference, whereas the atypical response of sup-F/S-AVNRT was always due to a longer HA[1]-CS than HA[1]-HRA, with a 51±26 ms HA difference. Moreover, the atypical response disappeared within 2 cycles after the cessation of EP. The atypical difference, although its exact mechanism remains unclear, might attribute to a shortening of the retro-SP-time according to decremental properties of the SP with deeper antidromic penetration during EP provoked depending on the site and rate of pacing. Conclusions: We have identified a little-known pacing site- and pacing rate-dependent shortening of the retro-SP-time. This phenomenon may affect an interpretation of post-pacing interval after EP of F/S-AVNRT.

Abstract 9796: Atypical Right Atrial Flutter with Double Loop Reentry Involving the Cavotricuspid Isthmus and Superior Vena Cava with Successful Ablation

Introduction: Atrial flutter (AFL) with figure-of-eight reentry (FOER) is effectively terminated by catheter ablation (CA) of the shared isthmus. Case: A 50-year-old man with prior mitral valve (MV) repair presented to our hospital with palpitations for 9 months refractory to metoprolol. ECG showed coarse atrial fibrillation at 61 bpm. Echocardiography showed left ventricular LVEF of 45%. Electrophysiology study revealed AFL (cycle length, TCL 290 msec) with a concentric activation pattern on the coronary sinus (CS) catheter, and a chevron pattern on the Halo catheter placed against the lateral tricuspid annulus (TA). Entrainment map revealed a near equal post-pacing interval and TCL in proximal CS, low lateral right atrium (RA), and CTI. Incomplete line of block was noted in the anterior wall of RA near the superior vena cava (SVC), likely from prior atriotomy scar. Double loop reentry (DLR) was demonstrated with one wavefront (WV) traveling counterclockwise around the TA using the CTI, and the other WV traveling posteriorly around the SVC (Figure). After CTI ablation, TCL changed from 290 msec to 330 msec suggesting blocked CTI. Now, the WV was a single loop around the SVC, confirmed by repeat activation mapping. Linear ablation from anterior TA to the anterior aspect of the SVC terminated the AFL. Differential pacing from either side of the anterior line and the CTI demonstrated a conduction time of &gt; 200 msec and 150 msec in either direction, respectively. Decremental atrial pacing was unable to induce any arrhythmias. Discussion: FOER in this case is suggested by fusion of WVs in the lateral RA. The 2 circuits each had their own conduction gap, in the CTI and anterior RA wall near the SVC, respectively. DLR was proven by entrainment as well as activation mapping. The faster CTI-dependent AFL was entraining the upper loop reentry circuit. Conclusion: Atypical right AFL with DLR mimicking FOER was successfully terminated by CA of CTI and anterior line of ablation from TA to SVC.

Interatrial septal tachycardias following atrial fibrillation ablation or cardiac surgery: Electrophysiological features and ablation outcomes.

Interatrial septal tachycardias (IAS-ATs) following atrial fibrillation (AF) ablation or cardiac surgery are rare, and their management is challenging. The purpose of this study was to investigate the electrophysiological features and outcomes associated with catheter ablation of IAS-AT. We screened 338 patients undergoing catheter ablation of ATs following AF ablation or cardiac surgery. Diagnosis of IAS-AT was based on activation mapping and analysis of response to atrial overdrive pacing. Twenty-nine patients (9%) had IAS-AT (cycle length [CL] 311 ± 104 ms); 16 (55%) had prior AF ablation procedures (median 3; range 1-5), 3 (10%) had prior surgical maze, and 12 (41%) had prior cardiac surgery (including atrial septal defect surgical repair in 5 and left atrial myxoma resection in 1). IAS substrate abnormalities were documented in all patients. Activation mapping always demonstrated a diffuse early IAS breakout with centrifugal biatrial activation, and atrial overdrive pacing showed a good postpacing interval (equal or within 25 ms of the AT CL) only at 1 or 2 anatomically opposite IAS sites in all cases. Ablation was acutely successful in 27 patients (93%) (from only the right IAS in 2, only the left IAS in 9, both IAS sides with sequential ablation in 13, and both IAS sides with bipolar ablation in 3). After median follow-up of 15 (6-52) months, 17 patients (59%) remained free from recurrent arrhythmias. IAS-ATs are rare and typically occur in patients with evidence of IAS substrate abnormalities and prior cardiac surgery. Catheter ablation can be challenging and may require sequential unipolar ablation or bipolar ablation.

Characteristics of macroreentrant atrial tachycardias using an anatomical bypass: Pseudo-focal atrial tachycardia case series.

Human atria comprise distinct layers. One layer can bypass another, and lead to a downstream centrifugal propagation at their interface. We sought to characterize anatomical substrates, electrophysiological properties, and ablation outcomes of "pseudo-focal" atrial tachycardias (ATs), defined as macroreentrant ATs mimicking focal ATs. We retrospectively analyzed left atrial ATs showing centrifugal propagation with postpacing intervals (PPIs) after entrainment pacing suggestive of a macroreentrant mechanism. A total of 22 patients had pseudo-focal ATs consisting of 15 perimitral and 7 roof-dependent flutters. A low-voltage area was consistently found at the collision site and colocalized with distinct anatomical structures like the: (1) coronary sinus-great cardiac vein bundle (27%),(2) vein of Marshall bundle (18%),(3) Bachmann bundle (27%),(4) septopulmonary bundle (18%), and (5) fossa ovalis (9%). The mean missing tachycardia cycle length (TCL) was 65 ± 31 ms (22%) on the endocardial activation map. PPI was 0 [0-15] ms and 0 [0-21] ms longer than TCL at the breakthrough site and the opposite site, respectively. While feasible in 21 pseudo-focal ATs (95%), termination was better achieved by blocking the anatomical isthmus than ablating the breakthrough site [20/21 (95%) vs. 1/5 (20%); p < .001]. Perimitral and roof-dependent flutters with centrifugal propagation are favored by a low-voltage area located at well-identified anatomical structures. Comprehensive entrainment pacing maneuvers are crucial to distinguish pseudo-focal ATs from true focal ATs. Blocking the anatomical isthmus is a better therapeutic option than ablating the breakthrough site.

B-PO02-176 ENTRAINMENT OF IDIOPATHIC LEFT VENTRICULAR TACHYCARDIA FROM LEFT VENTRICULAR SEPTUM INDICATED NEGATIVE PARTICIPATION OF DISTAL LEFT POSTERIOR FASCICLE

As a macro-reentrant tachycardia, the circuit of idiopathic left ventricular tachycardia (ILVT) is mainly described by activation mapping. Evidence from entrainment in left ventricle (LV) is limited. To investigate the reentrant circuit ILVT by entrainment at LV septum. In 4 patients with ILVT from left posterior fascicle (LPF) area, a decapolar catheter placed at LV septum was used to delineate activation pattern of Purkinje potentials (PP) during tachycardia. Entrainment was performed using multiple pairs of electrodes where PPs were recorded. The tachycardia cycle length (TCL), QRS pattern, electrogram sequences and post pacing intervals (PPI) were analyzed. PPIs were measured from both stimulus to return PP (PPI1) and ventricular electrogram (PPI2), respectively. P1 potentials was recorded in 3/4 patients. 18 bursts of entrainment were performed. QRS during overdrive was always slightly different from tachycardia QRS in morphology, but sequence of P2 suggested concealed fusion when entraining earliest P2, or P1-P2 fusion site(n=4). PPI1-TCL here was significantly shorter than PPI2-TCL (6±6.7ms vs. 33.8±6.7ms P<0.01) and PPI1-TCL at the next distal bipole (n=4, 6±6.7ms vs. 36.3±15.6ms, P<0.01), although their P2 timing difference were all less than 15ms. Ablation at sites with shortest PPI1 eliminated all ILVTs. Overdrive from earliest P2 site during ILVT demonstrated entrainment with concealed fusion in fascicles. PPI was significantly longer at the sites distal to earliest P2, indicating distal LPF was the "inner bystander" of the circuit, which may solely involve Purkinje network in the vicinity of LPF.

Successful termination of ventricular tachycardia with intrinsic anti-tachycardia pacing

Intrinsic anti-tachycardia pacing (iATP) is a novel automated ATP algorithm that employs post-pacing interval (PPI) to design the next ATP sequence based on an analysis of the prior failed ATP sequence. A patient with hypertrophic cardiomyopathy received an implantable cardioverter-defibrillator (ICD) (Cobalt™ XT DR, Medtronic, Minneapolis, MN, USA) following an episode of syncope due to macro-reentrant ventricular tachycardia (VT) (right bundle branch block configuration, cycle length [CL] 280 ms). The VF zone was set to VTCL <300 ms and iATP therapy was prescribed before and during capacitor charging. The iATP was initiated when VT recurred 3 months later. The first attempt with an assumption of 150 ms propagation time from the pacing site to the VT circuit (9 pulses) could not reset the VT, leaving a PPI of 650 ms. A subsequent attempt involving 20 pulses with an assumption of 250 ms propagation time terminated the VT. Failure to reach the circuit is a major cause of unsuccessful ATP. In this regard, iATP is expected to have theoretical advantages over empirical and traditional ATP therapies. To the best of our knowledge, this is the first intracardiac electrogram illustrating how automated precision ATP terminates VT in a clinical setting.