Electrophysiological Cardiovascular Magnetic Resonance (EP-CMR)-Guided Interventional Procedures: Challenges and Opportunities.

PURPOSE OF REVIEW: Cardiovascular magnetic resonance (CMR) imaging excels in providing detailed three-dimensional anatomical information together with excellent soft tissue contrast and has already become a valuable tool for diagnostic evaluation, electrophysiological procedure (EP) planning, and therapeutical stratification of atrial or ventricular rhythm disorders. CMR-based identification of ablation targets may significantly impact existing concepts of interventional electrophysiology. In order to exploit the inherent advantages of CMR imaging to the fullest, CMR-guided ablation procedures (EP-CMR) are justly considered the ultimate goal. RECENT FINDINGS: Electrophysiological cardiovascular magnetic resonance (EP-CMR) interventional procedures have more recently been introduced to the CMR armamentarium: in a single-center series of 30 patients, an EP-CMR guided ablation success of 93% has been reported, which is comparable to conventional ablation outcomes for typical atrial flutter and procedure and ablation time were also reported to be comparable. However, moving on from already established workflows for the ablation of typical atrial flutter in the interventional CMR environment to treatment of more complex ventricular arrhythmias calls for technical advances regarding development of catheters, sheaths and CMR-compatible defibrillator equipment. CMR imaging has already become an important diagnostic tool in the standard clinical assessment of cardiac arrhythmias. Previous studies have demonstrated the feasibility and safety of performing electrophysiological interventional procedures within the CMR environment and fully CMR-guided ablation of typical atrial flutter can be implemented as a routine procedure in experienced centers. Building upon established workflows, the market release of new, CMR-compatible interventional devices may finally enable targeting ventricular arrhythmias.

Safety and durability of cavo-tricuspid isthmus linear ablation in the current era: Single-center 9-year experience from 1078 procedures.

BACKGROUND: Cavo-tricuspid isthmus (CTI) linear ablation is performed not only for atrial flutter (AFL) but empirically during atrial fibrillation (AF) ablation in real-world practice.  PURPOSE: We sought to evaluate the safety and durability of the CTI ablation.  METHODS: This retrospective study included 1078 consecutive patients who underwent a CTI ablation. AFL was documented before or during the procedure in 249 (23.1%) patients, and an empirical CTI and AF ablation were performed in 829 (76.9%) patients.  RESULTS: CTI block was successfully created in 1051 (97.5%) patients with a 10.3 ± 6.6 min total radiofrequency time. Repeat procedures were performed for recurrent arrhythmias in 187 (17.3%) patients at a median of 11.0 (5.0-30.0) months postprocedure, and conduction resumption was identified in 68/174 (39.1%). Among those undergoing a CTI ablation with an AF ablation, the durability was significantly higher in those with than without documented AFL (78.1% vs. 58.2%, p = .031).  The total radiofrequency time was significantly shorter (9.0 ± 5.3 vs. 10.0 ± 6.4 [mins], p = .024) and durability significantly higher (78.1 vs. 58.7[%], p = .043) in the large-tip than irrigated-tip catheter group. Iatrogenic AFL was observed after the empiric CTI ablation in 11 (1.3%) patients. Procedure-related complications occurred in 15 (1.4%) patients. Eight patients experienced coronary artery spasms, including one with ventricular fibrillation following ST elevation on the ward. The other six patients experienced transient atrioventricular block and one experienced cardiac tamponade requiring drainage.  CONCLUSIONS: Despite a high acute CTI ablation success, the conduction block durability was relatively low after the empiric ablation. An empiric CTI ablation at the time of the AF ablation is not recommended.

A multi-center experience of ablation index for evaluating lesion delivery in typical atrial flutter.

BACKGROUND: Anatomical studies demonstrate significant variation in cavotricuspid isthmus (CTI) architecture. METHODS: Thirty-eight patients underwent CTI ablation at two tertiary centers. Operators delivered 682 lesions with a target ablation index (AI) of 600 Wgs. Ablation parameters were recorded every 10-20 ms. Post hoc, Visitags were trisected according to CTI position: inferior vena cava (IVC), middle (Mid), or ventricular (V) lesions. RESULTS: There were no complications. 92.1% of patients (n = 35) remained in sinus rhythm after 14.6 ± 3.4 months. For the whole CTI, peak AI correlated with mean impedance drop (ID) (R2  = 0.89, p < .0001). However, analysis by anatomical site demonstrated a non-linear relationship Mid CTI (R2  = 0.15, p = .21). Accordingly, while mean AI was highest Mid CTI (IVC: 473.1 ± 122.1 Wgs, Mid: 539.6 ± 103.5 Wgs, V: 486.2 ± 111.8 Wgs, ANOVA p < .0001), mean ID was lower (IVC: 10.7 ± 7.5Ω, Mid: 9.0 ± 6.5Ω, V: 10.9 ± 7.3Ω, p = .011), and rate of ID was slower (IVC: 0.37 ± 0.05 Ω/s, Mid: 0.18 ± 0.08 Ω/s, V: 0.29 ± 0.06 Ω/s, p < .0001). Mean contact force was similar at all sites; however, temporal fluctuations in contact force (IVC: 19.3 ± 12.0 mg/s, Mid: 188.8 ± 92.1 mg/s, V: 102.8 ± 32.3 mg/s, p < .0001) and catheter angle (IVC: 0.42°/s, Mid: 3.4°/s, V: 0.28°/s, p < .0001) were greatest Mid CTI. Use of a long sheath attenuated these fluctuations and improved energy delivery. CONCLUSIONS: Ablation characteristics vary across the CTI. At the Mid CTI, higher AI values do not necessarily deliver more effective ablation; this may reflect localized fluctuations in catheter angle and contact force.

Electrophysiological significance of the interatrial conduction including cavo-tricuspid isthmus during atrial fibrillation.

KEY POINTS: The interatrial conduction, including Bachmann's bundle, the posterior septal conduction, the anterior septal conduction, and the cavo-tricuspid isthmus, contributes to the maintenance mechanisms of atrial fibrillation in a 3D biatrial model. The interatrial conduction ablation including a cavo-tricuspid isthmus ablation significantly affects the wave dynamics of atrial fibrillation (AF) and facilitates the AF termination or atrial tachycardia conversion of the AF after the circumferential pulmonary vein isolation. Additional cavo-tricuspid isthmus ablation after the circumferential pulmonary vein isolation improves long-term rhythm outcome after clinical AF catheter ablation. ABSTRACT: Although it is known that atrial fibrillation (AF) is mainly a left atrial (LA) disease, the role of the right atrium (RA) and interatrial conduction (IAC), including the cavo-tricuspid isthmus (CTI), has not been clearly defined. We tested AF wave dynamics with or without IAC in computational modelling and the rhythm outcome of AF catheter ablation (AFCA) including CTI ablation in clinical cohort data. We evaluated the dominant frequency (DF) in 3D biatrial AF simulations integrated with 3D-computed tomograms obtained from 10 patients. The IAC was implemented at Bachmann's bundle, posterior septum and the CTI. After virtual circumferential PV isolation (CPVI), we disconnected IACs one by one, and observed the wave dynamics. We compared the long-term rhythm outcome after CPVI alone and additional CTI ablation in 846 patients with AFCA. LA-DF was higher than RA-DF in AF (P < 0.001). After CPVI, the DF decreased significantly by additional IAC ablation (P = 0.003), especially in the LA (P = 0.016). The amount of DF reduction (P = 0.020) and rates of AF termination (P < 0.001) or AT conversion (P = 0.021) were significantly higher after IAC ablations including CTI than those without. In clinical AFCA, the AF recurrence rate was significantly lower in patients with additional CTI ablation than CPVI alone during 25 ± 20 months' follow-up (hazard ratio 0.60 [0.46-0.79], P < 0.001, Log rank P < 0.001). IAC contributes to the maintenance mechanism of AF, and IAC including CTI ablation affects AF wave dynamics, facilitating AF termination in 3D biatrial modelling. Additional CTI ablation after CPVI improves the long-term rhythm outcome in clinical AFCA, potentially in a paroxysmal type with accompanying atrial flutter, or atrial dimension close to normal.

Mapping potentials adjacent to the cavo-tricuspid isthmus ablation line during incremental pacing: A feasible and highly accurate maneuver to confirm complete CTI conduction block.

BACKGROUND: The diagnostic accuracy of incremental atrial pacing (IP) to determine complete cavo-tricuspid isthmus (CTI) block during typical atrial flutter (AFL) ablation is limited by both an extensive/nonlinear ablation and/or the presence of intra-atrial conduction delay elsewhere in the right atrium. We examined the diagnostic performance of an IP variant based on the assessment of the atrial potentials adjacent to the ablation line which aims at overcoming both limitations. METHODS: From a prospective population of 108 consecutive patients, 15 were excluded due to observation of inconclusive CTI ablation potentials precluding for a straight comparison between the IP maneuver and its variant. In the remaining 93, IP was performed from the low lateral right atrium and the coronary sinus ostium, with the ablation catheter positioned both at the CTI line and adjacent (<5 mm) to its septal and lateral aspect. The IP variant consisted of measuring the interval between the two atrial electrograms situated on the same side of the ablation line, opposite to the pacing site, a ≤10 ms increase indicating complete CTI block. RESULTS: The IP maneuver and its variant were consistent with complete CTI block in 82/93 (88%) and 87/93 (93%) patients, respectively. Four patients had AFL recurrence during follow-up: 2/4 and 4/4 had been adequately classified as incomplete block by the IP maneuver and its variant, respectively. Twenty-three patients (24%) had significant intra-atrial conduction delay elsewhere in the right atrium. The IP maneuver and its variant were suggestive of an incomplete CTI block in 11/23 and 4/23 in this setting (P = .028), with the later best predicting subsequent AFL relapses (2/12 vs 2/4, P = .01). CONCLUSIONS: The IP variant, which was designed to overcome the limitations of the conventional IP maneuver, accurately distinguishes complete from incomplete CTI block and helps to predict AFL recurrences after ablation.

Intra-procedural evaluation of the cavo-tricuspid isthmus anatomy with different techniques: comparison of angiography and intracardiac echocardiography.

Cavo-tricuspid isthmus (CTI) anatomies are highly variable, and specific anatomies lead to a difficult CTI ablation. This study aimed to compare the clinical utility of angiography and intracardiac echocardiography (ICE) in evaluating CTI anatomies, and to investigate the impact of the CTI anatomy on the procedure when the ablation tactic was adjusted to the anatomy. This study included 92 consecutive patients who underwent a CTI ablation. The CTI morphology was assessed with both right atrial angiography and ICE before the ablation, and the ablation tactic was adjusted to the anatomy. The mean CTI length was 34 ± 9 mm. On ICE imaging, 21 (23%) patients had a flat CTI, while 41 (45%) had a concave CTI with a mean depth of 5.6 ± 2.7 mm. The remaining 30 (32%) had a distinct pouch with a mean depth of 6.4 ± 2.3 mm, located at the posterior, middle, and anterior isthmus in 15, 14, and 1 patients, respectively. The Eustachian ridge (ER) was visualized in 46 (50%) patients. On angiography, a pouch and ER were detected in 22 and 15 patients, but not in the remaining 8 and 31, respectively. A complete CTI block line was created in all patients without any complications. The CTI anatomy did not significantly impact any procedural parameters. ICE was superior to angiography in evaluating the detailed CTI anatomy, especially pouches and the ER. An adjustment of the ablation tactic to the anatomy could overcome the procedural difficulties of the CTI ablation in cases with specific anatomies.

Complication detection in MRI guided cardiac ablation: Atrial wall damage and hepatic oedema.

Magnetic resonance imaging is a novel imaging technique for guiding electrophysiology based ablation operations for atrial flutter and typical atrial fibrillation. When compared to standard electrophysiology ablation, this innovative method allows for better outcomes. Intra-procedural imaging is important for following the catheter in real time throughout the ablation operation while also seeing cardiac architecture and determining whether the ablation is being completed appropriately utilizing oedema sequences. At the same time, intra-procedural imaging allows immediate visualization of any complications of the procedure. We describe a case of a 67 year old male underwent an isthmus-cavo-tricuspid magnetic resonance-guided thermoablation procedure for atrial flutter episodes. During the procedure we noted an atypical focal thinning of the right atrial wall at the isthmus cava-tricuspidal zone. The post-procedural Black Blood T2 STIR showed an area of hyperintensity at the hepatic dome and glissonian capsule, which was consistent with intraparenchymal hepatic oedema, in close proximity to the atrial finding. Given the opportunity to direct monitoring of adjacent tissues, we aim to highlight with our case the ability of magnetic resonance-guided cardiac ablation to immediately detect peri-procedural complications in the ablative treatment of atrial fibrillation.

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.

The pitfalls of automatic point acquisition with high-resolution mapping.

An 81-year-old man with a typical atrial flutter underwent cavo-tricuspid isthmus (CTI) ablation. After the creation of wide planar lesion at the CTI, a high-resolution activation map with Rhythmia™ (Boston Scientific, Cambridge, MA, USA) was acquired during lateral right atrium pacing, which demonstrated a centrifugal activation at the septal side of ablation line. A review of points acquired at the earliest activation site demonstrated that perivalvular premature ventricular contractions (PVCs) at tricuspid annulus had been inappropriately acquired as atrial electrograms. This mis-acquisition was explained by the following: (i) no change in the beat acceptance criteria of the propagation reference in the coronary sinus due to the absence of ventriculoatrial conduction of mechanical PVCs, and (ii) failure to reject beats overlapping the PVCs because those voltages did not reach the threshold of 0.64 mV. When the mapping system shows centrifugal activation over the linear lesion, passive activation from the epicardial structures or the other chamber is an important differential diagnosis; however, mis-annotation due to automated acquisition must be also ruled out. It is important to understand the automated point-acquisition criteria in each mapping system and to be familiar with the pitfalls of the criteria. Learning objective: The evolution of ultra-high-resolution mapping technology enables us to understand the details of tachycardia circuit with much fewer manual reannotations. The criteria for automatic point acquisition installed in the mapping system usually works effectively, resulting in a demonstration of a precise tachycardia circuit. However, the present case logically showed how we noticed the mis-annotation of the high-resolution activation map and explained the pitfall of the function of automatic beat acquisition.

Three-Dimensional (3D) Mapping and Catheter Ablation for Simultaneous Reverse Typical and Atypical Atrial Flutter: A Case Report.

Atrial flutter, a common cardiac arrhythmia, is characterized by rapid and regular atrial contractions that result in a characteristic sawtooth pattern on the electrocardiogram. It emerges due to the formation of reentrant electrical circuits within the atria, giving rise to structured, sawtooth-patterned atrial waves as observed on electrocardiography. We present the case of a 52-year-old female with a medical history of ankylosing spondylitis, dyslipidemia, and a previous surgical closure of an atrial septal defect. The patient developed a rare form of atrial flutter, characterized by two distinct mechanisms: a clockwise isthmus-dependent flutter and an atypical scar-related flutter around the atriotomy scar. In order to effectively address this complex condition, a successful ablation procedure was performed to target both mechanisms. This case report offers valuable insights into the complexities surrounding the diagnosis and treatment of a complex case characterized by the coexistence of multiple mechanisms of atrial flutter within a single patient. While catheter ablation has demonstrated improved success rates for typical and atypical atrial flutters when occurring in isolation, predicting the prognosis of complex cases continues to pose challenges.

A simplified differential pacing technique for the evaluation of bidirectional cavo-tricuspid isthmus block during ablation of typical atrial flutter.

PURPOSE: Bidirectional block of the cavo-tricuspid isthmus (CTI) is an established endpoint of CTI-dependent atrial flutter (AFl) ablation. Differential pacing has been used to evaluate the CTI block. The purpose of this study is to describe a modified differential pacing technique to evaluate the CTI block. METHODS: Sixty-two patients underwent radiofrequency (RF) ablation of CTI-dependent AFl. The acute endpoints were non-inducibility of the AFl, and verification of the bidirectional CTI block by our methodology. Pacing was performed in the CS with an ablation catheter positioned immediately lateral to the CTI ablation line, and then 1-2 cm more laterally. The stimulus-to-ablation catheter atrial electrogram intervals were measured at these sites (StimCS-Abl1 and StimCS-Abl2, respectively). Pacing with the ablation catheter also was performed at these 2 sites, and the stimulus-to-CS electrogram intervals (StimABL1-CS and StimABL2-CS) were measured. The criteria for the bidirectional block were StimCS-Abl1 > StimCS-Abl2, and StimABL1-CS > StimABL2-CS. Clinical efficacy was defined as freedom from recurrent AFl during follow-up. RESULTS: Following 12.2 ± 3.7 min of RF delivery across the CTI, intervals were StimCS-Abl1 = 181.2 ± 22.7 ms and StimABL1-CS = 181.0 ± 23.6 ms, and StimCS-Abl2 = 152.2 ± 26.5 ms and StimABL2-CS = 151.2 ± 22.7 (P < 0.001). Atrial flutter was rendered not inducible in all patients, and no procedural complications were encountered. During the next 15.9 ± 0.7 months, two patients were lost to follow-up, and among the 62 other patients, one (1.7%) had flutter recurrence. CONCLUSIONS: The bidirectional CTI block can be assessed quickly and easily using only the ablation and CS catheters for differential pacing.

Spontaneous demonstration of counterclockwise right atrial activation following successful isthmus ablation.

We describe an uncommon case of typical flutter with symptomatic sinus node dysfunction, in which a permanent junctional rhythm developed following ablation of the cavo-tricuspid isthmus. This rhythm activated the right atrium in counter clockwise manner thus providing spontaneous proof of unidirectional isthmus block, a phenomenon that is usually demonstrated by proximal coronary sinus pacing.

Cryoballoon pulmonary vein isolation as first line treatment for typical atrial flutter (CRAFT): study protocol for a randomised controlled trial.

PURPOSE: Treatment of typical atrial flutter (AFL) with cavo-tricuspid isthmus (CTI) ablation is associated with a high occurrence rate of new onset atrial fibrillation (AF) during follow-up. There are data to support the addition of pulmonary vein isolation (PVI) to CTI ablation in patients with both AF and AFL, but the role of cryoballoon PVI only, with no CTI ablation, in AFL patients with no prior documentation of AF has not been studied. METHODS: CRAFT is an international, prospective, randomised, open with blinded assessment, multicentre superiority study comparing radiofrequency CTI ablation and cryoballoon PVI in patients with typical AFL. Participants with typical AFL are randomised in a 1:1 ratio to either treatment arm, with patients randomised to PVI not receiving CTI ablation. Post-procedural cardiac monitoring is performed using an implantable loop recorder. The primary endpoint is time to first recurrence of sustained symptomatic atrial arrhythmia. Key secondary endpoints include (1) total arrhythmia burden at 12 months, (2) time to first episode of AF lasting ≥ 2 min, (3) time to recurrence of AFL or AT and (4) procedural and fluoroscopy times. The primary safety endpoint is the composite of death, stroke/transient ischaemic attack, cardiac tamponade requiring drainage, atrio-oesophageal fistula, requirement for a permanent pacemaker, serious vascular complications requiring intervention or delaying discharge and persistent phrenic nerve palsy lasting > 24 h. CONCLUSION: This study compares the outcomes of 2 different approaches to typical AFL-the conventional 'substrate'-based strategy of radiofrequency CTI ablation versus a novel 'trigger'-based strategy of cryoballoon PVI. TRIAL REGISTRATION: ( ClinicalTrials.gov ID: NCT03401099 ).

How to avoid unnecessary RF applications in cavo-tricuspid isthmus: common atrial flutter ablation using 8-mm-tip mini-electrode-equipped catheter.

PURPOSE: Eight-millimeter-tip ablation catheters are characterized by poor mapping resolution as they depend on electrode size and spacing. IntellaTip MiFi XP 8-mm (Boston Scientific) catheters offer high mapping resolution due to 3 mini-electrodes (ME) located at the distal tip of the catheter and are dedicated for cavo-tricuspid isthmus (CTI) radiofrequency ablation (RFA). The aim of the study was to evaluate the usefulness, effectiveness and safety of novel IntellaTip MiFi XP catheter for CTI RFA and its ability to localize anatomical structures of the heart. METHODS: The study included 10 patients referred for atrial flutter ablation. The 3D mapping system EnSite Velocity was utilized for catheter visualization. The ME signals were used for tricuspid annulus visualization, RF delivery effectiveness assessment defined as ME signal attenuation, and localization of the gaps in the ablation line. The use of ME signals for TV annulus localization resulted in a 13.9 mm (35.5 ± 4.8 mm vs 49.4 ± 7.8 mm; p < 0.01) shorter ablation line in comparison with the potential ablation line designed using standard bipol. The ablation endpoint, bidirectional block, was achieved in all 10 cases (100%) and lasted for at least 15 min after the last RF delivery. The ablation endpoint was reached after 5.1 ± 1.67 RF applications. The total RF time was 220 ± 61 s. Total procedure time was 66 ± 13.5 min, fluoroscopy time 3.92 ± 4.21 min, and total fluoroscopy dose 40.3 ± 56.5 mGy. RESULTS: In 3 out of 10 cases, there was a need of filling the gap with 1-2 additional applications after the first linear lesion set. No additional RF applications were required at the annular end of the ablation line. The indirect comparison with previously conducted studies using a standard 8-mm ablation catheter shows that the studied catheter has at least the same or even better performance. CONCLUSIONS: The use of the novel IntellaTip MiFi XP may help to avoid unnecessary RF application especially at the annular part of cavo-tricuspid isthmus and enables a purely electrophysiological approach to atrial flutter ablation, as high-resolution ME signals help to understand local electrophysiological phenomena.

Outcome of ACHD patients with non-inducible versus inducible IART undergoing cavo-tricuspid isthmus ablation: the role of empiric ablation.

PURPOSE: Catheter ablation for supraventricular tachycardia (SVT) in adults with congenital heart disease (ACHD) is an important therapeutic option. Cavo-tricuspid isthmus (CTI)-dependent intraatrial re-entrant tachycardia (IART) is common. However, induction of sustained tachycardia at the time of ablation is not always possible. We hypothesised that performing an empiric CTI line in case of non-inducibility leads to good outcomes. Long-term outcomes of empiric versus entrained CTI ablation in ACHD patients were examined. METHODS: Retrospective, single-centre, case-control study over 7 years. Arrhythmia-free survival after empiric versus entrained CTI ablation was compared. RESULTS: Eighty-seven CTI ablations were performed in 85 ACHD patients between 2010 and 2017. The mean age of the cohort was 43 years and 48% were male. Underlying aetiology included ASD (31%), VSD (11.4%), AVSD (9.1%), AVR (4.8%), Fallot's (18.4%), Ebstein's (2.3%), Fontan's palliation (9.2%) and atrial switch (13.8%). CTI-dependent IART was entrained in 59 patients whereas it was non-inducible in 28. The latter had an empiric CTI ablation. Forty-three percent of procedures were performed under general anaesthesia. There were no reported procedural complications. There was no significant difference in the mean procedure or fluoroscopy times between the groups (empiric vs entrained CTI; 169.1 vs 183.3 and 28.1 vs 19.9 min). Arrhythmia-free survival was 64.3% versus 72.8% (p value 0.44) in the empiric and entrained groups at 21 months follow-up. CONCLUSIONS: Long-term outcomes after empiric and entrained CTI ablation for IART in ACHD patients are comparable. This is a safe and effective therapeutic option. In the case of non-inducibility of IART, an empiric CTI line should be considered in this cohort.

3D navigation system allows remarkable reduction in fluoroscopy use during cavo-tricuspid isthmus ablation.

PURPOSE: Typical atrial flutter (AFL) is one of the most common supraventricular arrhythmias. Its treatment mainly relies on cavo-tricuspid isthmus (CTI) ablation, which can be performed either using conventional fluoroscopy, still mainly used, or 3D navigation system to track the position of the catheter. The aim of this study is to show that the use of a 3D navigation system allows a dramatic reduction of fluoroscopy use during CTI ablation, without any loss of efficacy, time, or safety. METHODS: In this single-center study, we retrospectively compared 134 cases of CTI ablation performed for typical AFL without a 3D navigation system with 95 cases of CTI ablation performed with such a 3D system. We compared the rates of procedural success (defined as obtaining a bidirectional electrical conduction block), freedom from AFL recurrence at 1-year follow-up, procedural time and safety, and fluoroscopy use. RESULTS: Compared to conventional fluoroscopy, the use of a 3D navigation system significantly decreased the duration of fluoroscopy use (2 min 13 s ± 2 min 16 s versus 14 min 41 s ± 10 min 39 s, p < 0.0001) and dose-area products (1567.9 ± 1329.5 mGy cm2 versus 8263.3 ± 8636.6 mGy cm2, p < 0.0001). Procedure success rates, duration, and safety were not different between groups. CONCLUSIONS: The use of 3D navigation during CTI ablation substantially reduces fluoroscopy use duration, without reducing the success rates and safety or prolonging the procedure duration, as compared to conventional fluoroscopy. We therefore suggest the generalization of this navigation system.

Atrial Flutter in Patient With Critical COVID-19: Beneficial Effects of Rhythm Control on Respiratory Distress.

We report the case of a patient critically ill with coronavirus disease-2019 (COVID-19) in which atrial flutter with high ventricular response rate occurred, contributing to worsening of the respiratory distress. After failure of noninvasive rate and rhythm control strategies, successful transcatheter ablation was performed and the respiratory distress of the patient improved. (Level of Difficulty: Beginner.).

Atrial tachycardia originating from the cavo-tricuspid isthmus may exhibit narrow P waves.

An 83-year-old man underwent electrophysiological testing for focal atrial tachycardia (AT) exhibiting narrow P waves with negative deflections in the inferior leads. Catheter ablation at the cavo-tricuspid isthmus (CTI) successfully eliminated the AT. The propagation map during AT and pacing study from the successful ablation site demonstrated that the atrial activation throughout the CTI did not produce significant P wave deflections. Consequently, during AT, the left atrial activation time determined the P wave duration. This case demonstrates that AT originating from the CTI may exhibit narrow P waves which can be misinterpreted as AT originating from the inter-atrial septum.

Optimal local impedance drops for an effective radiofrequency ablation during cavo-tricuspid isthmus ablation.

PURPOSE: A novel ablation catheter capable of local impedance (LI) monitoring (IntellaNav MiFi OI, Boston Scientific) has been recently introduced to clinical practice. We aimed to determine the optimal LI drops for an effective radiofrequency ablation during cavo-tricuspid isthmus (CTI) ablation. METHODS: This retrospective observational study enrolled 50 consecutive patients (68 ± 9 years; 34 males) who underwent a CTI ablation using the IntellaNav MiFi OI catheter, guided by Rhythmia. The LI at the start of radiofrequency applications (initial LI) and minimum LI during radiofrequency applications were evaluated. The absolute and percentage LI drops were defined as the difference between the initial and minimum LIs and 100× absolute LI drop/initial LI, respectively. RESULTS: A total of 518 radiofrequency applications were analyzed. The absolute and percentage LI drops were significantly greater at effective ablation sites than ineffective sites (median, 15 ohms vs 8 ohms, P < .0001; median, 14.7% vs 8.3%, P < .0001). A receiver-operating characteristic analysis demonstrated that at optimal cutoffs of 12 ohms and 11.6% for the absolute and percentage LI drops, the sensitivity and specificity for predicting the effectiveness of the ablation were 66.5% and 88.2%, and 65.1% and 88.2%, respectively. Finally, bidirectional conduction block along the CTI was achieved in all patients. CONCLUSIONS: During the LI-guided CTI ablation, the effective RF ablation sites exhibited significantly greater absolute and percentage LI drops than the ineffective RF ablation sites. Absolute and percentage LI drops of 12 ohms and 11.6% may be suitable targets for effective ablation.

An unusual propagation pattern along the tricuspid annulus after cavo-tricuspid isthmus ablation: Insights into posterior transverse conduction revealed by an ultra-high-resolution 3-dimensional mapping system.

Cavo-tricuspid isthmus (CTI) ablation is a cornerstone of atrial flutter ablation. The goal of CTI-dependent flutter ablation is achievement of bidirectional CTI block. Usually bidirectional CTI block is confirmed by atrial activation during septal and lateral atrial pacing or the use of differential pacing maneuvers. According to the pathological findings, the transmural muscle fibers connect the endo- and epicardium. An epicardial-endocardial breakthrough (EEB) sometimes interferes with the confirmation of bidirectional block. Recently, a new ultra-high-resolution 3-dimentional mapping systems (Rhythmia®, Boston Scientific, Marlborough [Cambridge] MA, USA) that allows rapid ultra-high-resolution electroanatomical mapping was introduced. A 64-year-old man with a sustained atrial flutter (AFL) was referred to us. Catheter ablation was performed using an ultra-high-resolution 3-dimensional mapping system. Here, we report the case of a patient with an EEB visualized by ultra-high-resolution 3-dimensional mapping. .