Substrate Characterization and Outcome of Catheter Ablation of Ventricular Tachycardia in Patients With Nonischemic Cardiomyopathy and Isolated Epicardial Scar.

BACKGROUND: The substrate for ventricular tachycardia (VT) in left ventricular (LV) nonischemic cardiomyopathy may be epicardial. We assessed the prevalence, location, endocardial electrograms, and VT ablation outcomes in LV nonischemic cardiomyopathy with isolated epicardial substrate. METHODS: Forty-seven of 531 (9%) patients with LV nonischemic cardiomyopathy and VT demonstrated normal endocardial (>1.5 mV)/abnormal epicardial bipolar low-voltage area (LVA, <1.0 mV and signal abnormality). Abnormal endocardial unipolar LVA (≤8.3 mV) and endocardial bipolar split electrograms and predictors of ablation success were assessed. RESULTS: Epicardial bipolar LVA (27.3 cm2 [interquartile range, 15.8-50.0]) localized to basal (40), mid (8), and apical (3) LV with basal inferolateral LV most common (28/47, 60%). Of 44 endocardial maps available, 40 (91%) had endocardial unipolar LVA (24.5 cm2 [interquartile range, 9.4-68.5]) and 29 (67%) had characteristic normal amplitude endocardial split electrograms opposite the epicardial LVA. At mean of 34 months, the VT-free survival was 55% after one and 72% after multiple procedures. Greater endocardial unipolar LVA than epicardial bipolar LVA (hazard ratio, 10.66 [CI, 2.63-43.12], P=0.001) and number of inducible VTs (hazard ratio, 1.96 [CI, 1.27-3.00], P=0.002) were associated with VT recurrence. CONCLUSIONS: In patients with LV nonischemic cardiomyopathy and VT, the substrate may be confined to epicardial and commonly basal inferolateral. LV endocardial unipolar LVA and normal amplitude bipolar split electrograms identify epicardial LVA. Ablation targeting epicardial VT and substrate achieves good long-term VT-free survival. Greater endocardial unipolar than epicardial bipolar LVA and more inducible VTs predict VT recurrence.

PRECAF Randomized Controlled Trial.

BACKGROUND: We have previously shown that the presence of dual muscular coronary sinus (CS) to left atrial (LA) connections, coupled with rate-dependent unidirectional block in one limb, is associated with atrial fibrillation (AF) induction. This study sought to examine whether ablation of distal CS to LA connections at a first AF ablation reduces arrhythmia recurrence during follow-up. METHODS: In this single-center, randomized, controlled trial, 35 consecutive patients with drug-refractory AF undergoing first-time ablation between August 2018 and August 2019, were randomly assigned to (1) standard ablation (pulmonary vein isolation and nonpulmonary vein trigger ablation) versus (2) standard ablation plus elimination of distal CS to LA connections targeting the earliest LA activation during distal CS pacing with a deca-polar catheter placed with its proximal electrode at the ostium. Change of the local CS atrial electrogram and LA activation sequence to early activation of the LA septum or roof during distal CS pacing were the end point for CS-LA connection elimination. RESULTS: Thirty patients completed 6 months study follow-up (15 patients in each group). Demographic characteristics including age and AF persistence were similar in both groups. After a mean follow-up of 170±22 days, there were 7 atrial arrhythmia recurrences in the standard group and 1 recurrence in the CS-LA connection elimination group (46.7% versus 6.7%, hazard ratio, 0.12, P=0.047). CONCLUSIONS: Elimination of distal CS to LA connections reduced atrial arrhythmia recurrences compared with standard pulmonary vein isolation and nonpulmonary vein trigger ablation in patients undergoing a first AF ablation procedure in a small randomized study. This strategy warrants further evaluation in a multicenter randomized trial. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03646643.

Characterization of Structural Changes in Arrhythmogenic Right Ventricular Cardiomyopathy With Recurrent Ventricular Tachycardia After Ablation: Insights From Repeat Electroanatomic Voltage Mapping.

BACKGROUND: Data characterizing structural changes of arrhythmogenic right ventricular (RV) cardiomyopathy are limited. METHODS: Patients presenting with left bundle branch block ventricular tachycardia in the setting of arrhythmogenic RV cardiomyopathy with procedures separated by at least 9 months were included. RESULTS: Nineteen consecutive patients (84% males; mean age 39±15 years [range, 20-76 years]) were included. All 19 patients underwent 2 detailed sinus rhythm electroanatomic endocardial voltage maps (average 385±177 points per map; range, 93-847 points). Time interval between the initial and repeat ablation procedures was mean 50±37 months (range, 9-162). No significant progression of voltage was observed (bipolar: 38 cm2 [interquartile range (IQR), 25-54] versus 53 cm2 [IQR, 25-65], P=0.09; unipolar: 116 cm2 [IQR, 61-209] versus 159 cm2 [IQR, 73-204], P=0.36) for the entire study group. There was a significant increase in RV volumes (percentage increase, 28%; 206 mL [IQR, 170-253] versus 263 mL [IQR, 204-294], P<0.001) for the entire study population. Larger scars at baseline but not changes over time were associated with a significant increase in RV volume (bipolar: Spearman ρ, 0.6965, P=0.006; unipolar: Spearman ρ, 0.5743, P=0.03). Most patients with progressive RV dilatation (8/14, 57%) had moderate (2 patients) or severe (6 patients) tricuspid regurgitation recorded at either initial or repeat ablation procedure. CONCLUSIONS: In patients with arrhythmogenic RV cardiomyopathy presenting with recurrent ventricular tachycardia, >10% increase in RV endocardial surface area of bipolar voltage consistent with scar is uncommon during the intermediate term. Most recurrent ventricular tachycardias are localized to regions of prior defined scar. Voltage indexed scar area at baseline but not changes in scar over time is associated with progressive increase in RV size and is consistent with adverse remodeling but not scar progression. Marked tricuspid regurgitation is frequently present in patients with arrhythmogenic RV cardiomyopathy who have progressive RV dilation.

Analysis of local ventricular repolarization using unipolar recordings in patients with arrhythmogenic right ventricular cardiomyopathy.

PURPOSE: In arrhythmogenic right ventricular cardiomyopathy (ARVC), abnormal electroanatomic mapping (EAM) areas are proportional to extent of T-wave inversion on 12-lead ECG. We aimed to evaluate local repolarization changes and their relationship to EAM substrate in ARVC. METHODS: Using unipolar recordings, we analyzed the proportion of negative T waves ≥ 1 mV in depth (NegT), NegT area, Q-Tpeak (QTP), Tpeak-Tend (TPE) intervals and their relationship to bipolar (< 1.5 mV ENDO, < 1.0 mV EPI) and unipolar (< 5.5 mV) endocardial (ENDO) and epicardial (EPI) low-voltage area (LVA) in 21 pts. (15 men, mean age 39 ± 14) with ARVC. Control group included 5 pts. with normal hearts and idiopathic PVCs. RESULTS: On ENDO, the % of NegT (7 ± 5% vs 30 ± 20%, p = 0.004) and the NegT area (12.9 ± 9.7 c m2 vs 61.4 ± 30.0 cm2, p = 0.001) were smaller in ARVC compared to controls. On EPI, the % of NegT was similar (5 ± 7% vs 3 ± 4%, p = 0.323) and the NegT area, larger (11.0 ± 8.4 cm2 vs 2.7 ± 0.9 cm2, p = 0.027) in ARVC group. In ARVC group, the % of NegT area inside LVA was larger on EPI compared to ENDO for both bipolar (81 ± 27% vs 31 ± 33%, p < 0.001) and unipolar (90 ± 19% vs 73 ± 28%, p = 0.036) recordings. Compared to normal voltage regions, QTP inside ENDO abnormal LVA was on average 58 ± 26 ms shorter and TPE, 25 ± 56 ms longer (97 ± 26 ms and 56 ± 86 ms on EPI, respectively). CONCLUSIONS: In ARVC, NegT areas are more closely associated with abnormal depolarization LVA on the EPI and QTP is shorter and TPE longer inside ENDO and EPI abnormal LVA compared to normal voltage regions. The results add to our understanding of ARVC arrhythmia substrate.

Epicardial Conduction Speed, Electrogram Abnormality, and Computed Tomography Attenuation Associations in Arrhythmogenic Right Ventricular Cardiomyopathy.

OBJECTIVES: This study sought to evaluate the association between contrast-enhanced multidetector computed tomography (CE-MDCT) attenuation and local epicardial conduction speed (ECS) and electrographic abnormalities in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) and ventricular tachycardia (VT). BACKGROUND: CE-MDCT is a widely available and fast imaging technology with high spatial resolution that is less prone to defibrillator generator-related safety issues and image artifacts. However, the association between hypoattenuation on MDCT and VT substrates in ARVC remains unknown. METHODS: Patients with ARVC who underwent CE-MDCT followed by endocardial (n = 30) and epicardial (n = 21) electroanatomical mapping (EAM) and VT ablation were prospectively enrolled. Right ventricular (RV) mid-myocardial attenuation was calculated from 3-dimensional MDCT images and registered to EAM. Local ECS was calculated by averaging the ECS between each point and 5 adjacent points with concordant wave front direction. RESULTS: A total of 17,311 epicardial and 5,204 endocardial points were included. In multivariable regression analysis clustered by patient, RV myocardial attenuation was associated with epicardial bipolar voltage amplitude (2.5% decrease in amplitude per 10 HU decrease in attenuation; p < 0.001), with endocardial unipolar voltage amplitude (0.9% decrease in amplitude per 10 HU decrease in attenuation; p < 0.001), and with ECS (0.4% decrease in ECS per 10 HU decrease in attenuation; p = 0.001). CONCLUSIONS: CE-MDCT attenuation distribution is associated with regional ECS and electrographic amplitude in ARVC. Regions with low attenuation likely reflect fibro-fatty involvement in the RV and may serve as important VT substrates in patients with ARVC who are undergoing VT ablation.

Catheter ablation of premature ventricular complexes with low intraprocedural burden guided exclusively by pace-mapping.

BACKGROUND: Catheter ablation (CA) of idiopathic premature ventricular complexes (PVCs) is typically guided by both activation and pace-mapping, with ablation ideally delivered at the site of the earliest local activation. However, activation mapping requires sufficient intraprocedural quantity of PVCs. This study aimed to investigate the outcome of CA of infrequent PVCs guided exclusively by pace-mapping. METHODS: We retrospectively analyzed all patients undergoing CA of idiopathic PVCs between 2014 and 2017. RESULTS: Among 327 patients, 24 (7.3%) had low intraprocedural PVC burden despite isoproterenol, including two patients with zero PVCs, rendering activation mapping impractical/impossible. All 24 had a history of symptomatic PVCs. During ablation, a median of 27 (17-55) pace-maps were performed, with best median PASO score of 97 (96-98)%. A median of 12 (8.75-18.75) radiofrequency (RF) lesions were delivered with 11.4 (8.5-17.6) minutes of total RF time. Clinical success, defined as more than 80% reduction in the burden of previously frequent PVCs and/or absence of symptoms as well as any documented clinical PVCs among those with infrequent or exercise-induced PVCs, was achieved in 19 (79%) patients over 9.2 (2.0-15.0) months of follow-up. CONCLUSIONS: When activation mapping cannot be performed due to inadequate intraprocedural PVC burden, detailed pace-mapping can frequently identify the precise arrhythmia site of origin, thereby guiding successful CA.

Ventricular tachycardia in nonischemic cardiomyopathy: Anteroseptal vs inferolateral origin based on ICD ventricular electrogram timing.

INTRODUCTION: The majority of patients with nonischemic cardiomyopathy (NICM) present a perivalvular substrate that is either predominantly antero-septal (AS) or infero-lateral (IL), corresponding to specific ventricular tachycardia (VT) morphologies. The relative timing of far-field and near-field ventricular electrograms (EGMs) from stored implantable cardioverter-defibrillator (ICD) events of VT may be used to distinguish AS from IL VT in NICM. METHODS AND RESULTS: We analyzed 48 patients with NICM with either a primarily AS (54%) or IL (56%) VT source undergoing catheter ablation between 2003 and 2018. Only patients with retrievable ICD-EGMs of spontaneous VT events which could be matched with VTs induced during the ablation procedure were included. A total of 56 VT events (52% AS origin and 48% IL origin) were analyzed, yielding a mean far-field to near-field interval of 31 ± 13 milliseconds for AS VTs and 47 ± 19 milliseconds for IL VTs (P = .001). At receiver operating characteristic analysis (AUC = 0.734), a far-field to near-field interval of ≥ 60 milliseconds ruled out AS VTs in 29 (100%) cases and diagnosed IL VTs with a positive predictive value (PPV) of 100% and a negative predictive value (NPV) of 63%. An interval of ≤ 20 milliseconds ruled out IL VTs in 25 (93%) cases and diagnosed AS VTs with a PPV of 83% and NPV of 57%. Significant overlap between the two groups was observed among far-field to near-field intervals in between 20 milliseconds and 60 milliseconds. CONCLUSIONS: The relative timing of far-field and near-field EGMs from stored clinical ICD events of VT can be helpful to differentiate AS vs IL origin of VT in NICM.

Comparison of the Ventricular Tachycardia Circuit Between Patients With Ischemic and Nonischemic Cardiomyopathies: Detailed Characterization by Entrainment.

BACKGROUND: There has been increasing awareness of the 3-dimensional nature of ventricular tachycardia (VT) circuits. VT circuits in patients with ischemic cardiomyopathies (ICM) and non-ICM (NICM) may differ in this regard. METHODS: Among patients with structural heart disease and at least 1 hemodynamically tolerated VT undergoing ablation, we retrospectively analyzed responses to all entrainment maneuvers. RESULTS: Of 445 patients (ICM 228, NICM 217) undergoing VT ablation, detailed entrainment mapping of at least 1 tolerated VT was performed in 111 patients (ICM 71, NICM 40). Of 89 ICM VTs, the isthmus could be identified by endocardial entrainment in 55 (62%), compared with only 8 of 47 (17%) NICM VTs ( P<0.01). With combined endocardial and epicardial mapping, the isthmus could be identified in 56 (63%) ICM VTs and 12 (26%) NICM VTs ( P<0.01), whereas any critical component (defined as entrance, isthmus or exit) could be identified in 76 (85%) ICM VTs and 37 (79%) NICM VTs ( P=0.3). Complete success (no inducible VT at the end of ablation, 82% versus 65%, P=0.04) and 1-year, single-procedure VT-free survival (82% versus 55%, P<0.01) were both higher among patients with ICM. CONCLUSIONS: Among mappable ICM VTs, critical circuit components can usually be identified on the endocardium. In contrast, among mappable NICM VTs, although some critical component can typically be identified with the addition of epicardial mapping, the isthmus is less commonly identified, possibly due to midmyocardial location.

Electrocardiographic and Electrophysiologic Characteristics of Idiopathic Ventricular Arrhythmias Originating From the Basal Inferoseptal Left Ventricle.

OBJECTIVES: This study sought to characterize ventricular arrhythmia (VA) ablated from the basal inferoseptal left ventricular endocardium (BIS-LVe) and identify electrocardiographic characteristics to differentiate from inferobasal crux (IBC) VA. BACKGROUND: The inferior basal septum is an uncommon source of idiopathic VAs, which can arise from its endocardial or epicardial (crux) aspect. Because the latter are often targeted from the coronary venous system or epicardium, distinguishing between the 2 is important for successful ablation. METHODS: Consecutive patients undergoing ablation of idiopathic VA from the BIS-LVe or IBC from 2009 to 2018 were identified and clinical characteristics and electrocardiographs of VA were compared. RESULTS: Of 931 patients undergoing idiopathic VA ablation, Virginia was eliminated from the BIS-LVe in 19 patients (2%) (17 male, age 63.7 ± 9.2 years, LV ejection fraction: 45.0 ± 9.3%). QRS complexes typically manifested right bundle branch block morphology with "reverse V2 pattern break" and left superior axis (more negative in lead III than II). VA elimination was achieved after median of 2 lesions (interquartile range [IQR]: 1-6; range 1 to 20) (radiofrequency ablation time: 123 s [IQR: 75-311]). Compared with 7 patients with IBC VA (3 male, age 51.9 ± 20.1 years, LV ejection fraction: 51.4 ± 17.7%), BIS-LVe VA less frequently had initial negative forces (QS pattern) in leads II, III, and/or aVF (p < 0.001), R-S ratio <1 in lead V1 (p = 0.005), and notching in lead II (p = 0.006) were narrower (QRS duration: 178.2 ± 22.4 vs. 221.1 ± 41.9 ms; p = 0.04) and more frequently had maximum deflection index of <0.55 (p < 0.001). CONCLUSIONS: The BIS-LVe region is an uncommon source of idiopathic VA. Distinguishing these from IBC VA is important for procedural planning and ablation success.

Usefulness of ICD electrograms analysis to distinguish endocardial vs epicardial ventricular tachycardia in arrhythmogenic right ventricular cardiomyopathy.

INTRODUCTION: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by an epicardial (EPI) to endocardial (ENDO) fibrofatty infiltration of the RV predisposing to both EPI and ENDO ventricular tachycardia (VT). The relative timing between the VT QRS onset on the far-field ventricular electrogram (VEGM) to the local activation time recorded at the RV apex on the near-field VEGM from stored implantable cardioverter-defibrillator (ICD) events of VT can be helpful to discriminate ENDO from EPI VT in ARVC. METHODS AND RESULTS: We analyzed consecutive ARVC patients undergoing catheter ablation between 2006 and 2018. Only patients with retrievable ICD VEGMs of clinical VTs which could be matched with VTs induced at the time of ablation were included. A total of 26 VT events (16 ENDO, 10 EPI) from 19 ARVC patients were examined, yielding a mean far-field to near-field interval of 33 ± 15 ms for ENDO VTs and 52 ± 20 ms for EPI VTs (P = .020). At receiver-operating characteristic analysis, a far-field to a near-field interval of 60 ms or more ruled out ENDO VTs in 16 (100%) cases and identified EPI VTs with a positive predictive value (PPV) of 100% and a negative predictive value (NPV) of 73%. An interval of less than or equal to 30 ms ruled out EPI VTs in eight (80%) cases and diagnosed ENDO VTs with a PPV of 80% and an NPV of 50%. CONCLUSION: Far-field to near-field ICD VEGM timing may be used to predict ENDO vs EPI VT in ARVC before ablation, indicating an ENDO origin if the timing is less than or equal to 30 ms and an EPI origin if greater than or equal to 60 ms.

Long term follow-up after ventricular tachycardia ablation in patients with congenital heart disease.

BACKGROUND: Ventricular tachycardia (VT) is frequently encountered in patients with repaired and unrepaired congenital heart disease (CHD), causing significant morbidity and sudden cardiac death. Data regarding underlying VT mechanisms and optimal ablation strategies in these patients remain limited. OBJECTIVE: To describe the electrophysiologic mechanisms, ablation strategies, and long-term outcomes in patients with CHD undergoing VT ablation. METHODS: Forty-eight patients (mean age 41.3 ± 13.3 years, 77.1% male) with CHD underwent a total of 57 VT ablation procedures at two centers from 2000 to 2017. Electrophysiologic and follow-up data were analyzed. RESULTS: Of the 77 different VTs induced at initial or repeat ablation, the underlying mechanism in 62 (81.0%) was due to scar-related re-entry; the remaining included four His-Purkinje system-related macrore-entry VTs and focal VTs mainly originating from the outflow tract region (8 of 11, 72.7%). VT-free survival after a single procedure was 72.9% (35 of 48) at a median follow-up of 53 months. VT-free survival after multiple procedures was 85.4% (41 of 48) at a median follow-up of 52 months. There were no major complications. Three patients died during the follow-up period from nonarrhythmic causes, including heart failure and cardiac surgery complication. CONCLUSION: While scar-related re-entry is the most common VT mechanism in patients with CHD, importantly, nonscar-related VT may also be present. In experienced tertiary care centers, ablation of both scar-related and nonscar-related VT in patients with CHD is safe, feasible, and effective over long-term follow-up.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias.

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Septal Coronary Venous Mapping to Guide Substrate Characterization and Ablation of Intramural Septal Ventricular Arrhythmia.

OBJECTIVES: This study describes the use of septal coronary venous mapping to facilitate substrate characterization and ablation of intramural septal ventricular arrhythmia (VA). BACKGROUND: Intramural septal VA represents a challenge for substrate definition and catheter ablation. METHODS: Between 2015 and 2018, 12 patients with structural heart disease, recurrent VA, and suspected intramural septal substrate underwent a septal coronary venous procedure in which mapping was performed by advancement of a wire into the septal perforator branches of the anterior interventricular vein. A total of 5 patients with idiopathic VA were also included as control subjects to compare substrate characteristics. RESULTS: Patients were 63 ± 14 years of age, and 11 (92%) were men. Most patients with structural heart disease had nonischemic cardiomyopathy (83%). Six patients underwent ablation for premature ventricular contractions (PVC) and 6 for ventricular tachycardia. All patients had larger septal unipolar voltage abnormalities than bipolar voltage abnormalities (mean area 35.3 ± 16.8 cm2 vs. 10.7 ± 8.4 cm2, respectively; p = 0.01), Patients with idiopathic VA had normal voltage. Septal coronary venous mapping revealed low-voltage, fractionated, and multicomponent electrograms in sinus rhythm in all patients with substrate compared to that in patients with idiopathic VA (amplitude 0.9 ± 0.9 mV vs. 4.4 ± 3.7 mV, respectively; p = 0.007; and duration 147 ± 48 ms vs. 92 ± 10 ms, respectively; p = 0.03). Ablation targeted early activation, pace map match, and/or good entrainment sites from intraseptal recording. Over a mean follow-up of 339 ± 240 days, the PVC and insertable cardioverter-defibrillator therapies burden were significantly reduced (from a mean of 22 ± 11% to 4 ± 8%; p = 0.005; and a mean 5 ± 2 to 1 ± 1; p = 0.001, respectively). Most patients (80%) with idiopathic VA remained arrhythmia free. CONCLUSIONS: In patients with suspected intramural septal VA, mapping of the septal coronary veins may be helpful to characterize the arrhythmia substrate, identify ablation targets, and guide endocardial ablation.

P-wave morphology and multipolar intracardiac atrial activation to facilitate nonpulmonary vein trigger localization.

INTRODUCTION: Nonpulmonary vein (non-PV) triggers of atrial fibrillation (AF) are targets for ablation but their localization remains challenging. The aim of this study was to describe P-wave (PW) morphologic characteristics and intra-atrial activation patterns and timing from multipolar coronary sinus (CS) and crista terminalis (CT) catheters that localize non-PV triggers. METHODS AND RESULTS: Selective pacing from six right and nine left atrial common non-PV trigger sites was performed in 30 consecutive patients. We analyzed 12 lead ECG features based on PW duration, amplitude and morphology, and patterns and timing of multipolar activation for all 15 sites. Regionalization and then precise localization required criteria present in at least 70% of assessments at each pacing site. The algorithm was then prospectively evaluated by four blinded observers in a validation cohort of 18 consecutive patients undergoing the same pacing protocol and 60 consecutive patients who underwent successful non-PV trigger ablation. The algorithm for site regionalization included 1) negative PW in V1, ≥30 µV change in PW amplitude across the leads V1-V3, and PW duration ≤100 milliseconds in lead 2 and 2) unique intra-atrial activation patterns and timing noted in the multipolar catheters. Specific ECG and intra-atrial activation timing characteristics included in the algorithm allowed for more precise site localization after regionalization. In the prospective evaluation, the algorithm identified the site of origin for 72% of paced and 70% of spontaneous non-PV trigger sites. CONCLUSION: An algorithm based on PW morphology and intra-atrial multipolar activation pattern and timing can help identify non-PV trigger sites of origin.

Roof-dependent atrial flutter with an epicardial component: Role of the septopulmonary bundle.

Catheter ablation of atrial fibrillation may predispose patients to the development of atypical atrial flutters (AFL). We describe two cases of roof dependent AFLs that failed to terminate despite posterior wall isolation. An epicardial breakthrough involving the septopulmonary bundle is proposed. The correlation between the electrophysiological findings and the anatomical substrate is described.