Bipolar Electrogram Amplitude Research Articles

Verification of intra- and inter-atrial conduction during Bachmann's bundle pacing using longitudinal bi-atrial strain

Abstract Introduction Although atrial septal pacing has been reported to reduce atrial fibrillation (AF) burden, there is less evidence regarding its effect on the prevention of permanent AF and the improvement of long-term clinical outcomes. However, Bachmann's bundle pacing (BBp), which features P-wave morphology similar to sinus rhythm and shortened P-wave duration (PWD), was reported to significantly reduce permanent AF recurrences and occurrences compared with right atrial appendage pacing (RAAp) and non-specific right septal pacing. Purpose Possible mechanisms for AF suppression with BBp are that fast inter-atrial conduction through BB decreases global atrial activation time and the dispersion of the overall atrial refractoriness, and it prevents the decrease in left ventricular filling and increase in left atrial pressure associated with delayed left atrial contraction. Intra-and inter-atrial conduction during BBp was evaluated using longitudinal bi-atrial strain. Methods In patients with successful BBp implantation defined by electrocardiographic criteria using SelectSecure pacing lead and C315 delivery catheter (Medtronic, Inc), both left atrium (LA) and right atrium (RA) global longitudinal strain (GLS) in simultaneous phases were measured using Philips Ultrasound Workspace 2D Strain in apical 4-chamber view during atrial pacing to assess intra- and inter-atrial conduction delay. The atrial GLS were measured semi-automatically, and the strain rate was analyzed in the three segments of septal wall, lateral wall, and roof and their average. The negative peak of strain rate during atrial systole was the starting point of atrial contraction, and time to peak (TTP) was measured. The difference in TTP between septal and lateral walls in each atrium was measured as intra-atrial conduction delay and the difference in average TTP between LA and RA as inter-atrial conduction delay. Results Ten patients who underwent successful BBp were enrolled (Sick sinus syndrome: 3, advanced atrioventricular block: 2, complete atrioventricular block: 5). At implantation, bipolar atrial electrogram amplitude was 2.03±0.93 mV, atrial lead impedance was 632.7±157.6 Ω, and atrial pacing threshold was 0.7±0.2 V at 0.4 ms. The PWD during sinus rhythm on the 12-lead ECG was 132.8±10.6 ms, while during BBp it was 108.0±11.9 ms, which was significantly shorter in the BBp group (p<0.001). The intra-atrial conduction delay in RA and LA was 10.9 ± 12.1 ms and 12.1 ± 17.3 ms, respectively, and the inter-atrial conduction delay was 6.6 ± 8.6 ms. On the other hand, for the 10 RAAp and 10 sinus rhythm patients as control groups, the inter-atrial conduction delay was 29.7±13.8 ms and 8.5±9.5 ms, respectively. BBp had significantly less inter-atrial conduction delay than RAAp (p=0.005) and was comparable to sinus rhythm (p=0.719). Conclusion Longitudinal bi-atrial strain suggested that BBp significantly reduced inter-atrial delay and it might be effective in AF suppression.Longitudinal bi-atrial strain

Does a higher body mass index influence additional presence of low voltage areas in the left atrium in patients with persistent atrial fibrillation?

Abstract Introduction Pulmonary vein isolation (PVI) is recommended during all atrial fibrillation (AF) catheter ablation procedures. In nearly half of patients with persistent AF, low voltage areas (LVAs), commonly defined as areas in left atrium (LA) with a bipolar electrogram amplitude of < 0.5 mV, could be documented during electrophysiological study (EP). The remaining presence of these areas in LA after a PVI-only catheter ablation procedure is identified as a risk factor for recurrence of AF. Targeting and ablating (substrate modification) these areas reduces recurrency of AF. Pre-procedural identification of patients with additional LVAs is thus very important, until date very challenging and not established. Many markers are evaluated but it remains elusive. Extensive adipose tissue in obese patients leads to LA enlargement and remodeling via different mechanisms, leading to higher incidence of AF. The link between obesity and presence of LVAs in LA other than of pulmonary veins (PV) is to our knowledge not yet evaluated. Aim of the study Is to evaluate role of body mass index (BMI) in the presence of low voltage areas in left atrium besides pulmonary vein by comparing the BMI in patients with persistent AF with and without LVAs in LA, thus eventually identifying BMI as a possible pre-procedural marker of the presence of these areas. Methodology We analyzed data from 91 consecutive patients with persistent AF undergoing first time LA catheter ablation from 09/2021 until 10/2023 inside of the Jen-PACE study. In all patients a high-density 3D endocardial voltage mapping was carried out using EnSite Precision™/ Ensite X™ and the Advisor™ HD-Grid Mapping Catheter. Results The mean BMI was 29.6 ± 4.8, mean LV-EF was 53,4% ± 9.7, 24 patients (27%) were females, average age was 67 years. Depending on the presence of low voltage areas, the patients underwent either PVI only when no such areas were documented (61 patients, 67%) or PVI and substrate modification (30 patients, 33%) with documentation of LVAs. There was no statistical difference in the BMI between the two groups (29.9 ± 4.9 in patients with PVI only vs 29.0 ± 4.8 in patients with PVI + substrate modification; p=0.37). Furthermore, in a subgroup analysis of only adipose patients with a BMI higher than 30 (44 patients; 48%; mean BMI 33.8 ± 3.0), there was no significant difference in BMI between the two groups (34.2 ± 3.3 in PVI only vs 33.2 ± 2.4 in patients with PVI and substrate modification; p=0.2) Discussion and conclusion Even though a high BMI is generally related to a higher incidence of AF, a higher BMI was not observed in patients having additional low-voltage areas in LA compared to patients in whom such areas could not be identified. Electric remodeling caused by obesity could be rather diffuse than localized in specific areas in LA. BMI is not a pre-procedural marker for the presence of additional low voltage areas in LA.

A novel method for septal reduction therapy by three-dimensional guided transvenous intraseptal pulsed-field ablation

BackgroundPulsed-field ablation (PFA) is a nonthermal method for achieving selective cell death with little inflammation response. However, there are no reports of PFA for septal reduction therapy (SRT). ObjectiveThe purpose of this study was to investigate the effectiveness and safety of PFA for SRT. MethodsA novel transvenous intraseptal PFA method with 3-dimensional (3D) guidance was introduced in Yorkshire pigs. Electrocardiographic parameters, transthoracic echocardiography, and histopathology were used to evaluated. ResultsThe maximum injury diameter of intramyocardial PFA increased with electric field intensity. After PFA, bipolar electrogram amplitude and pacing threshold measured by the PFA electrodes significantly decreased (F = 6.945, P = .007) or increased (F = 5.842, P = .024), respectively. In the ablated septal region, motion amplitude and systolic wall thickening rate significantly decreased and remained at low levels (motion amplitude: F = 20.793, P = .000; systolic wall thickening rate: F = 14.343, P = .000); however, septal thickness did not significantly change after PFA (F = 1.503, P = .248). Histologic examination showed specific cardiomyocyte death with gradually increased hyperchromatic cytoplasm and nuclear pyknosis, without obvious inflammatory cell infiltration in acute phase. TUNEL stain for fragmented DNA showed extensively positive in the ablation region 24 hours after PFA. During PFA, no sustained ventricular arrhythmia or atrioventricular conduction block occurred. ConclusionA novel intraseptal PFA method with 3D guidance was described. Intraseptal PFA resulted in effective myocardial injury and local hypokinesis without significant acute edema. Histologic examination showed widely programmed cardiomyocyte death with little inflammatory cell infiltration.

Characteristics and Clinical Value of Electroanatomic Voltage Mapping in Cardiac Amyloidosis

BackgroundCardiac amyloidoses (CAs) are an increasingly recognised group of infiltrative cardiomyopathies associated with high risk of adverse cardiac events. We sought to characterise the characteristics and clinical value of right ventricular (RV) electroanatomic voltage mapping (EVM) in CA. MethodsFifteen consecutive patients undergoing endomyocardial biopsy (EMB) for suspected CA (median age 75 years, 1st-3rd quartiles 64-78 years], 67% male) were enrolled in an observational prospective study. Each patient underwent RV high-density EVM using a multipolar catheter and EMB. The primary outcome was death or heart failure hospitalisation at 1-year follow-up. We recorded electrographic features at EMB sampling sites and electroanatomic data in the overall RV, and explored their correlations with histopathologic findings and primary outcomes events. ResultsA final EMB-proven diagnosis of immunoglobulin light chain or transthyretin CA was formulated in 6 and 9 patients, respectively. Electrogram amplitudes in the bipolar and unipolar configurations averaged 1.55 ± 0.44 mV and 5.14 ± 1.50 mV, respectively, in the overall RV, with lower values in AL CA patients. We found a significant inverse correlation between both bipolar and unipolar electrogram amplitude and amyloid burden according to EMB (P = 0.001 and P = 0.025, respectively). At 1-year follow-up, 7 patients (47%) experienced a primary outcome event; the extent of bipolar dense scar area at RV EVM was an independent predictor of primary outcome events at multivariable analysis (odds ratio 2.40; P = 0.037). ConclusionsIn CA, electrogram amplitudes are around the lower limit of normal yet disproportionately low compared with the increased wall thickness. Out data suggest that RV electrogram amplitude may be a quantitative marker of amyloid burden, and that RV EVM may have prognostic value.

P-wave duration-amplitude ratio quantifies atrial low-voltage area and predicts atrial arrhythmia recurrence following pulmonary vein isolation.

Atrial low-voltage area (LVA) in AF patients increase the risk of atrial arrhythmia (AA) recurrence following pulmonary vein isolation (PVI). Contemporary LVA prediction scores (DR-FLASH, APPLE) do not include P-wave metrics. We aimed to evaluate the utility of P-wave duration-amplitude ratio (PWR) in quantifying LVA and predicting AA recurrence post-PVI. In 65 patients undergoing first-time PVI, 12-lead ECGs were recorded during sinus rhythm. PWR was calculated as the ratio between the longest P-wave duration and P-wave amplitude in lead I. High-resolution bi-atrial voltage maps were collected and LVAs included bipolar electrogram amplitudes <0.5mV or <1.0mV. A LVA quantification model was created using clinical variables and PWR, then validated in a separate cohort of 24 patients. Seventy-eight patients were followed for 12-months to evaluate AA recurrence. PWR strongly correlated with left atrial (LA) (<0.5mV: r=0.60; <1.0mV: r=0.68; p<0.001) and bi-atrial LVA (<0.5mV: r=0.63; <1.0mV: r=0.70; p<0.001). Addition of PWR to clinical variables improved model quantification of LA LVA at the <0.5mV (adjusted R2: 0.59 to 0.68) and <1.0mV cutpoints (adjusted R2: 0.59 to 0.74). In the validation cohort, PWR model-predicted LVA correlated strongly with measured LVA (<0.5mV: r=0.78; <1.0mV: r=0.81; p<0.001). PWR model was superior to DR-FLASH (AUC 0.90 vs. 0.78; p=0.030) and APPLE (AUC 0.90 vs. 0.67; p=0.003) at detecting LA LVA and comparable at predicting AA recurrence post-PVI (AUC=0.67 vs. 0.65 and 0.60). Our novel PWR model accurately quantifies LVA and predicts AA recurrence post-PVI. PWR model-predicted LVA may help guide patient selection for PVI.

Electroanatomical features of biopsy-proven cardiac amyloidosis

Abstract Funding Acknowledgements Type of funding sources: None. Background Cardiac amyloidoses (CA) are an increasingly recognized group of infiltrative cardiomyopathies associated with high risk of heart failure, thromboembolic events, arrhythmias, and sudden death. Endomyocardial biopsy may be required to differentiate the amyloid type (mainly, Immunoglobulin light chain [AL] versus transthyretin-related [ATTR]) in some cases. Purpose to provide a first description of electroanatomical characteristics of amyloid cardiomyopathy, and relate them to endomyocardial biopsy findings. Methods we enrolled ten consecutive patients (median age, 68 [63-77]; male, 50%) in an observational, retrospective study. All of them had a clinical diagnosis of CA, but a diagnosis of CA type was hampered by the presence of inconclusive or discordant laboratory-imaging findings (abnormal serum free light chain assay and positive bone scintigraphy, n=5; ambiguous imaging results, n=4; abnormal serum free light chain assay and TTR gene mutation, n=1). Therefore, all patients underwent right ventricular high-density electroanatomical mapping (EAM) using a multipolar catheter (Advisor HD Grid, Abbott), and EAM-guided endomyocardial biopsy (EMB). We recorded electrogram features at EMB sampling site, and explored their correlation with histological findings with mixed effect models. Results The clinical, electroanatomical, and histological features of enrolled patients according to the EMB-proven type of CA (AL, n=6; ATTR, n=4) are resumed in Table. Electrogram amplitudes in both the bipolar and the unipolar configuration were generally normal both in the overall right ventricle, and at EMB sites. We found a significant correlation between both unipolar and bipolar electrogram amplitude and the percentage of both amyloid tissue (p&amp;lt;0.01 and p=0.016, respectively) and fibrous tissue (both p&amp;lt;0.01) at EMB (Figure). We observed the strongest linear association (i.e., highest R2) between unipolar electrogram amplitude and amyloid tissue, as well as between bipolar electrogram amplitude and fibrous tissue. On the other hand, electrogram duration and the number of electrogram peaks were unrelated to histological findings. The unipolar voltage cutoff that best identified regions with &amp;gt;15% amyloid tissue infiltration according to Youden index was 9.1 mV (sensitivity, 43%; specificity, 100%; accuracy, 77%). Conclusion CA is associated with normal electrogram amplitudes using ahigh density mapping catheter and conventional voltage cutoffs. Nevertheless, unipolar electrogram amplitude is strongly related to the extent of amyloid infiltration, and unipolar voltage&amp;lt;9.1 mV is 100% specific for &amp;gt;15% amyloid tissue deposition.

PO-02-213 ELECTROANATOMICAL ASPECTS OF BIOPSY-PROVEN CARDIAC AMYLOIDOSIS

Cardiac amyloidoses (CA) are a common and increasingly recognized group of infiltrative cardiomyopathies associated with high risk of heart failure, thromboembolic events, arrhythmias, and sudden death. Endomyocardial biopsy may be required to differentiate the amyloid type (mainly, Immunoglobulin light chain [AL] versus transthyretin-related [ATTR]) in selected cases. To describe electroanatomical characteristics of amyloid cardiomyopathy, and relate them to endomyocardial biopsy findings. We included ten consecutive patients (median age, 68 [63-77]; male, 50%) in an observational, retrospective study. All of them had a clinical diagnosis of CA, but a diagnosis of CA type was uncertain based on non-invasive findings. Therefore, all patients underwent right ventricular high-density electroanatomical mapping (EAM) using a multipolar catheter (Advisor HD Grid, Abbott), and EAM-guided endomyocardial biopsy (EMB). We recorded electrogram features at EMB sampling site, and assessed their correlation with histological findings with mixed effect models. The clinical, electroanatomical, and histological features of enrolled patients according to the EMB-proven type of CA (AL, n=6; ATTR, n=4) are resumed in Table. Electrogram amplitudes in both the bipolar and the unipolar configurations were largely preserved in the overall right ventricle, and at EMB sites. There were highly significant correlations among electrogram amplitudes in both the unipolar and bipolar configurations, and the extent of amyloid and fibrous tissue substitution at EMB (all p<0.01, Figure). We observed the strongest linear associations (i.e., highest R2) between unipolar electrogram amplitude and the percentage of amyloid tissue, as well as between bipolar electrogram amplitude and the percentage of fibrous tissue. On the other hand, electrogram duration and the number of electrogram peaks were unrelated to histological findings. The unipolar voltage cutoff that best identified regions with >15% amyloid tissue infiltration according to Youden index was 9.1 mV (sensitivity, 43%; specificity, 100%; accuracy, 77%). CA is associated with preserved electrogram amplitudes at high-density electroanatomical mapping with conventional voltage cutoffs. Nevertheless, unipolar electrogram amplitude is strongly related to the extent of amyloid infiltration, and unipolar voltage<9.1 mV is 100% specific for >15% amyloid tissue deposition.

Atrial electrogram amplitude variability during atrial fibrillation ablation.

Variability of the bipolar atrial electrogram amplitude may affect voltage maps created during ablation procedures, and thus also the extent of ablations. Therefore, the aim of the study was to assess the beat-to-beat electrogram amplitude variability in the left atrium in patients undergoing atrial fibrillation ablation. In 11 patients undergoing ablation for atrial fibrillation, 362 mapping points were collected in two series. At each point, three consecutive beats were recorded and verified including the bipolar electrogram amplitude, contact force (CF), and orientation of the catheter tip. The repeatability and reproducibility of obtained measurements between consecutive beats and series were assessed by the Pearson correlation coefficient (r), the Bland-Altman test, repeatability coefficient (RC), relative standard deviation (RSD), and concordance correlation coefficient (CCC). A total of 1086 beats were analyzed. The correlation coefficient for bipolar atrial electrogram amplitude for the first two beats, and for the first and the third beats were 0.94 and 0.86, respectively. The average of differences between the first two beats and between the first and the third beats were 0.06and 0.13 mV with 95% limits of agreement (LoA)within ±0.98and ±1.74 mV, respectively. For CF values ≤5and ≥20 g, the 95% LoA were narrower compared to other CF rangesand were ±0.49and ±0.71 mV from the average value, respectively. When the analyzes were performed within the predefined ranges of bipolar electrogram amplitude: 0.05-1; 1-2; 2-3 mV, the 95% LoA were within ±0.33, ±0.98, and ±0.84 mV from the average value, respectively. RC and RSD were 1.41 mV and 20.8%, respectively. For repeated measurement between series,CCC ranged from 0.67 to 0.71 and the 95% LoA were within ±2.7 to 2.9 mV from the average value. Bipolar atrial electrogram amplitude recorded at a given site during ablation procedures is variable to an extent that may be clinically relevant. The magnitude of the observed variability is greater during remapping.

Atrial fibrosis identification with unipolar electrogram eigenvalue distribution analysis in multi-electrode arrays

Atrial fibrosis plays a key role in the initiation and progression of atrial fibrillation (AF). Atrial fibrosis is typically identified by a peak-to-peak amplitude of bipolar electrograms (b-EGMs) lower than 0.5 mV, which may be considered as ablation targets. Nevertheless, this approach disregards signal spatiotemporal information and b-EGM sensitivity to catheter orientation. To overcome these limitations, we propose the dominant-to-remaining eigenvalue dominance ratio (EIGDR) of unipolar electrograms (u-EGMs) within neighbor electrode cliques as a waveform dispersion measure, hypothesizing that it is correlated with the presence of fibrosis. A simulated 2D tissue with a fibrosis patch was used for validation. We computed EIGDR maps from both original and time-aligned u-EGMs, denoted as mathcal {R} and mathcal{R}^{mathcal{A}}, respectively, also mapping the gain in eigenvalue concentration obtained by the alignment, Delta mathcal{R}^{mathcal{A}}. The performance of each map in detecting fibrosis was evaluated in scenarios including noise and variable electrode-tissue distance. Best results were achieved by mathcal{R}^{mathcal{A}}, reaching 94% detection accuracy, versus the 86% of b-EGMs voltage maps. The proposed strategy was also tested in real u-EGMs from fibrotic and non-fibrotic areas over 3D electroanatomical maps, supporting the ability of the EIGDRs as fibrosis markers, encouraging further studies to confirm their translation to clinical settings.Graphical Upper panels: map of mathcal {R}^{mathcal {A}} from 3×3 cliques for Ψ= 0∘ and bipolar voltage map Vb-m, performed assuming a variable electrode-to-tissue distance and noisy u-EGMs (noise level σv = 46.4 μV ). Lower panels: detected fibrotic areas (brown), using the thresholds that maximize detection accuracy of each map

Circle Method for Robust Estimation of Local Conduction Velocity High-Density Maps From Optical Mapping Data: Characterization of Radiofrequency Ablation Sites.

Conduction velocity (CV) slowing is associated with atrial fibrillation (AF) and reentrant ventricular tachycardia (VT). Clinical electroanatomical mapping systems used to localize AF or VT sources as ablation targets remain limited by the number of measuring electrodes and signal processing methods to generate high-density local activation time (LAT) and CV maps of heterogeneous atrial or trabeculated ventricular endocardium. The morphology and amplitude of bipolar electrograms depend on the direction of propagating electrical wavefront, making identification of low-amplitude signal sources commonly associated with fibrotic area difficulty. In comparison, unipolar electrograms are not sensitive to wavefront direction, but measurements are susceptible to distal activity. This study proposes a method for local CV calculation from optical mapping measurements, termed the circle method (CM). The local CV is obtained as a weighted sum of CV values calculated along different chords spanning a circle of predefined radius centered at a CV measurement location. As a distinct maximum in LAT differences is along the chord normal to the propagating wavefront, the method is adaptive to the propagating wavefront direction changes, suitable for electrical conductivity characterization of heterogeneous myocardium. In numerical simulations, CM was validated characterizing modeled ablated areas as zones of distinct CV slowing. Experimentally, CM was used to characterize lesions created by radiofrequency ablation (RFA) on isolated hearts of rats, guinea pig, and explanted human hearts. To infer the depth of RFA-created lesions, excitation light bands of different penetration depths were used, and a beat-to-beat CV difference analysis was performed to identify CV alternans. Despite being limited to laboratory research, studies based on CM with optical mapping may lead to new translational insights into better-guided ablation therapies.

PO-634-03 RIPPLE MAPPING: A PRACTICAL APPROACH TO DIFFERENTIATE VENTRICULAR SCAR FROM BORDER-ZONE SLOW CONDUCTION USING CARTO RIPPLE MAPPING DURING VENTRICULAR TACHYCARDIA ABLATION

Areas of ventricular scar and border-zone slow conduction are often highlighted on a bipolar voltage map with generalized values 0.5mV-1.5mV. The true voltage that differentiates regions of conducting tissue from non-conducting scar is unknown. Ripple mapping (RM) is a core feature within CARTO3 that displays the bipolar electrogram amplitude from each point as a white moving bar. Conducting tissue is seen as areas supporting Ripple activation, and electrical scar as areas devoid of Ripple activation.

Pre-procedural predictors of left atrial low-voltage zones in patients undergoing catheter ablation of atrial fibrillation.

Pulmonary vein isolation has become a cornerstone treatment for catheter ablation of atrial fibrillation (AF). Recent reports show that additional ablation targeting low-voltage zones reduces AF recurrence. However, the pre-procedural predictors of low-voltage zones remain elusive. We retrospectively enrolled 359 patients (mean age 63.7 ± 10.8 years; 73 females; and 149 had persistent atrial fibrillation) who underwent catheter ablation for AF and left atrial (LA) voltage mapping during sinus rhythm or atrial pacing. Low-voltage zones were defined as area of > 5 cm2 with a bipolar electrogram amplitude of < 0.50 mV. Overall, 51 (14.2%) patients had low-voltage zones. Patients with low-voltage zones were older (67.9 ± 9.9 vs. 63.0 ± 10.8 years; P = 0.003), predominantly female (33.3% vs. 18.2%; P = 0.013), had higher prevalence of dilated cardiomyopathy (DCM) (11.8% vs. 1.6%; P = 0.002) and hypertrophic cardiomyopathy (HCM) (9.8% vs. 2.6%; P = 0.025), and had larger LA volumes (153.6 ± 46.4 vs. 117.7 ± 67.8 mL; P < 0.001) than those without low-voltage zones. Multivariate logistic regression analysis revealed that age (OR 1.060; 95% CI 1.022–1.101, P = 0.002), female sex (OR 2.978; 95% CI 1.340–6.615, P = 0.007), DCM (OR 8.341; 95% CI 1.381–50.372, P = 0.021), HCM (OR 5.044; 95% CI 1.314–19.363, P = 0.018), persistent AF (OR 4.188; 95% CI 1.928–9.100, P < 0.001), and larger LA volume (OR 3.215; 95% CI 1.378–7.502, P = 0.007) were independently associated with the presence of low-voltage zones. Patient age, female sex, DCM, HCM, persistent AF and larger LA volume may predict the presence of low-voltage zones and could be useful in selecting the appropriate ablation strategy for AF.

Safety, efficacy, and monitoring of bipolar radiofrequency ablation in beating myopathic human and healthy swine hearts.

The safety and efficacy parameters for bipolar radiofrequency (RF) ablation are not well defined. The purpose of this study was to investigate the safe range of power, utility of transmyocardial bipolar electrogram (EGM) amplitude, and circuit impedance in ablation monitoring. Sixteen beating exvivo human and swine hearts were studied in a Langendorff setup. Ninety-two bipolar ablations using two 4-mm irrigated catheters were performed at settings of 20-50 W, 60 seconds, and 30 mL/min irrigation in the left ventricle. For low-power ablations (20 and 30 W), transmurality was observed in 29 of 38 (76%) and 10 of 28 (36%) ablations for tissue thickness ≤17 mm and >17 mm, respectively. For high-power ablations (40 and 50 W), transmurality was observed in 5 of 7 (71%) and 7 of 19 (37%) ablations for tissue thickness ≤17 mm and >17 mm, respectively. Steam pop occurrence for low- and high-power ablations was 11 of 66 (16%) and 16 of 26 (62%), respectively (P = .0001), respectively. Lesion depth (limited by transmurality) was 12.0 ± 5.7 mm and 12.3 ± 5.8 mm, respectively (P = 1). Transmyocardial EGM amplitude decrement >60% strongly predicted transmurality (area under the curve [AUC] 0.8), and circuit impedance decrement >26% predicted steam pops (AUC 0.75). Half-normal saline did not affect transmurality or incidence of steam pops compared to normal saline irrigation. Bipolar RF ablation at power of 20-30 W provided an ideal balance of safety and efficacy, whereas power ≥40 W should be used with caution due to the high incidence of steam pops. Lesion transmurality monitoring and steam pop avoidance were best achieved using transmyocardial bipolar EGM voltage and circuit impedance, respectively.

B-PO02-098 PRE-PROCEDURAL PREDICTORS OF LEFT ATRIAL LOW VOLTAGE ZONES IN PATIENTS UNDERGOING CATHETER ABLATION OF ATRIAL FIBRILLATION

Pulmonary vein isolation (PVI) has become a cornerstone treatment for catheter ablation of AF. Recent reports have shown that additional ablation targeting low voltage zones (LVZs) reduces AF recurrence. Although balloon-based ablation is normally available for only PVI, radiofrequency open-irrigated catheters can perform substrate modification targeting LVZs beyond PVI. Therefore, to assume the presence of LVZs is important to select the ablation devices before the ablation. However, the preprocedural predictors of LVZs are still elusive. To investigate the preprocedural predictors of LVZs in patients with AF. We retrospectively enrolled 395 patients (mean age of 63.8 ± 10.8 years, 82 females, 172 with persistent AF) who underwent catheter ablation for AF and left atrium (LA) voltage mapping during sinus rhythm or under atrial pacing. The LVZs were defined as sites with a peak-to-peak bipolar electrogram amplitude < 0.50 mV. Within the entire cohort, 77 (19.5%) had LVZs. Patients with LVZs were older (P < 0.001) and had higher prevalence of female gender (P = 0.010) and persistent AF (P = 0.003). Concomitant hypertension (P = 0.007), heart failure (P = 0.001), non-ischemic cardiomyopathy (NICM) (P < 0.001), and history of sleep apnea syndrome (SAS) (P = 0.001) were higher in patients with LVZs. Laboratory testing showed that estimated glomerular filtration rate (P = 0.010) was lower and NT-proBNP (P < 0.001) was higher in patients with LVZs. Patients with LVZs had larger LA volume measured by CT (P < 0.001) and longer LA diameter measured by echocardiography (P = 0.003). Multivariate logistic regression analysis revealed that age (Odds ratio [OR] 1.050; 95% confidence interval [CI] 1.015-1.086, P = 0.005), female gender (OR 2.440; 95% CI 1.238-4.808, P = 0.010), NICM (OR 2.969; 95% CI 1.080-8.163, P = 0.035), history of SAS (OR 2.763; 95% CI 1.120-6.813, P = 0.027), and LA volume (per 10 ml) (OR 1.088; 95% CI 1.007-1.176, P = 0.034) were independently associated with the presence of LVZs. Patient’s age, female gender, NICM, history of SAS, and LA volume would predict the presence of LVZs and could be useful to select an ablation strategy for AF before the procedure.

High-Resolution Measurement of Local Activation Time Differences From Bipolar Electrogram Amplitude

Localized changes in myocardial conduction velocity (CV) are pro-arrhythmic, but high-resolution mapping of local CV is not yet possible during clinical electrophysiology procedures. This is in part because measurement of local CV at small spatial scales (1 mm) requires accurate annotation of local activation time (LAT) differences with very high temporal resolution (≤1 ms), beyond that of standard clinical methods. We sought to develop a method for high-resolution measurement of LAT differences and validate against existing techniques. First, we use a simplified theoretical model to identify a quantitative relationship between the LAT difference of a pair of electrodes and the peak amplitude of the bipolar EGM measured between them. This allows LAT differences to be calculated from bipolar EGM peak amplitude, by a novel “Determination of EGM Latencies by Transformation of Amplitude” (DELTA) method. Next, we use simulated EGMs from a computational model to validate this method. With 1 kHz sampling, LAT differences less than 4 ms were more accurately measured with DELTA than by standard LAT annotation (mean error 3.8% vs. 22.9%). In a 1-dimensional and a 2-dimension model, CV calculations were more accurate using LAT differences found by the DELTA method than by standard LAT annotation (by unipolar dV/dt timing). DELTA-derived LAT differences were more accurate than standard LAT annotation in simulated complex fractionated EGMs from a model incorporating fibrosis. Finally, we validated the DELTA method in vivo using 18,740 bipolar EGMs recorded from the left atrium of 10 atrial fibrillation patients undergoing catheter ablation. Using clinical EGMs, there was agreement in LAT differences found by DELTA, standard LAT annotation, and unipolar waveform cross-correlation. These results demonstrate an underlying relationship between a bipolar EGM’s peak amplitude and the activation time difference between its two electrodes. Our computational modeling and clinical results suggest this relationship can be leveraged clinically to improve measurement accuracy for small LAT differences, which may improve CV measurement at small spatial scales.

Lesion Sequence and Catheter Spatial Stability Affect Lesion Quality Markers in Atrial Fibrillation Ablation.

This study sought to analyze high-frequency catheter excursion in relation to lesion quality markers in 20 consecutive patients undergoing first-time radiofrequency (RF) ablation for paroxysmal atrial fibrillation (AF). Ablation therapy for AF requires the delivery of durable lesions. The extent to which lesion sequence, catheter spatial stability, and anatomic location influence lesion formation during RF ablation of AF is not well understood. Three-dimensional spatial excursion of the ablation catheter sampled at 60Hz during pre-specified pairs of RF lesions was extracted from the CARTO3 System (Biosense Webster Inc., Irvine, California) and analyzed by using custom-developed MATLAB software (MathWorks, Natick, Massachusetts) to define precise catheter spatial stability during RF ablation. Ablation parameters including bipolar electrogram amplitude reduction, impedance decline and transmurality-associated unipolar electrogram (TUE) as evidence of lesion transmurality during lesion placement were recorded and analyzed. We collected 437,760 position data points during lesion placement. Ablation catheter spatial stability and lesion formation parameters varied considerably by anatomic location. Lesions placed immediately had similar bipolar electrogram amplitude reduction, smaller impedance decline, but higher likelihood of achieving TUE compared to delayed lesions. Greater catheter spatial stability correlated with lesser impedance decline. Lesion sequence, ablation catheter spatial stability, and anatomic location are important modifiers of RF lesion formation. Lesions placed immediately are more likely to exhibit TUE. Greater ablation catheter stability is associated with lesser impedance decline but greater likelihood of TUE.

Circulating intermediate monocytes and toll-like receptor 4 correlate with low-voltage zones in atrial fibrillation.

Inflammation has been suggested to play a key role in the pathogenesis of atrial fibrillation (AF). Our hypothesis was that this inflammation, mediated by intermediate monocytes and toll-like receptor 4 (TLR4), causes the formation and expansion of low-voltage zones (LVZs). Prior to ablation, the monocyte subsets of 78 AF patients and TLR4 expression of 66 AF patients were analyzed via a flow cytometric analysis. Based on the CD14/CD16 expression, the monocytes were divided into three subsets: classical, intermediate, and non-classical. At the beginning of the ablation session, voltage mapping was performed. LVZs were defined as all bipolar electrogram amplitudes of < 0.5mV. Correlations between the flow cytometric analysis results and presence of LVZs, as well as the total area of the LVZ, were examined. Patients with LVZs clearly had a higher proportion of intermediate monocytes (10.0 ± 3.6% vs. 7.2 ± 2.7%, p < 0.001) than those without LVZs. TLR4 was much more frequently expressed in the intermediate monocytes than other two monocyte subsets (p < 0.001). Moreover, the TLR4 expression level in intermediate monocytes correlated positively with the total area of the LVZs (r = 0.267, p = 0.030), especially in patients with paroxysmal AF (r = 0.365, p = 0.015). The intermediate monocytes and TLR4 expression positively correlated with LVZs in AF patients.

221Evaluating the ability of different substrate mapping techniques to identify scar-related ventricular tachycardia circuits using computational modelling

Abstract Funding Acknowledgements National Institute for Health Research; British Heart Foundation; and The Wellcome Trust and Engineering and Physical Sciences Research Council. Background Accurate identification of targets for catheter ablation therapy of ventricular tachycardias (VTs) in the postinfarction heart remains a significant challenge. Identification of such targets often requires VT-induction to delineate the entry/exit points of the reentrant circuit sustaining the VT. However, inducibility may not be possible due to hemodynamic instability. In this scenario, substrate ablation strategies can still be performed to uncover the arrhythmogenic substrate during sinus or paced rhythm. However, substrate mapping may fail to accurately delineate the reentrant circuit resulting in VT recurrence after the procedure. Purpose To use computer simulations to compare the ability of different electroanatomical maps constructed following typical substrate ablation strategies to identify the VT exit site. Methods An image-based computational model of the porcine post-infarction left ventricle was constructed to simulate VT and paced rhythm. Electroanatomical maps were constructed based on the following features extracted from electrograms computed on the endocardial surface: activation time (AT), bipolar electrogram amplitude, signal fractionation and the reentry vulnerability index (RVI - a metric combining activation and repolarization timings to identify tissue susceptibility to reentry). Potential ablation targets during substrate mapping were compared for: highest 5% AT gradient; lowest 5% bipolar signal amplitudes; areas with fragmented signals (more than one peak); and lowest 5% RVI. The minimum distance, d, between the manually identified VT exit site and the targets was measured. Results The RVI performed better than the other metrics at detecting the VT exit site (see Figure). The minimum distance between sites of lowest RVI and the exit site was 3.2mm compared to 13.1mm and 15.9mm in traditional AT and voltage maps, respectively. As the scar was not transmural, parameters derived from all electrograms (including those located on dense scar regions) were used to construct the electroanatomical maps. This improved the performance of the RVI significantly, making it more specific than the other metrics as can be seen in the Figure. Conclusions Among all metrics investigated here, the RVI identified the vulnerable region closest to VT exit site. This finding suggests that activation-repolarization metrics may improve the detection of pro-arrhythmic regions without having to induce VT. Moreover, the RVI may be particularly well suited for detecting vulnerable regions within non-transmural scars. Abstract Figure. VT and Substrate Mapping

Mechanism and magnitude of bipolar electrogram directional sensitivity: Characterizing underlying determinants of bipolar amplitude

The amplitude of bipolar electrograms (EGMs) is directionally sensitive, decreasing when measured from electrode pairs oriented oblique to a propagating wavefront. The purpose of this study was to use a computational model and clinical data to establish the mechanism and magnitude of directional sensitivity. Simulated EGMs were created using a computational model with electrode pairs rotated relative to a passing wavefront. A clinical database of 18,740 EGMs with varying electrode separation and orientations was recorded from the left atrium of 10 patients with atrial fibrillation during pacing. For each EGM, the angle of incidence between the electrodes and the wavefront was measured using local conduction velocity (CV) mapping. A theoretical model was derived describing the effect of the changing angle of incidence, electrode spacing, and CV on the local activation time difference between a pair of electrodes. Model predictions were validated using simulated and clinical EGMs. Bipolar amplitude measured by an electrode pair is decreased (directionally sensitive) at angles of incidence resulting in local activation time differences shorter than unipolar downstroke duration. Directional sensitivity increases with closer electrode spacing, faster CV, and longer unipolar EGM duration. For narrowly spaced electrode pairs (<5 mm), it is predicted at all orientations. Directional sensitivity occurs because bipolar amplitude is reduced when the component unipolar EGMs overlap, such that neither electrode is "indifferent." At the electrode spacing of clinical catheters, this is predicted to occur regardless of catheter orientation. This suggests that bipolar directional sensitivity can be lessened but not overcome by recently introduced catheters with additional rotated electrode pairs.

Impact of recanalization of chronic total occlusion on left ventricular electrical remodeling

BackgroundSuccessful percutaneous coronary intervention (PCI) for chronic total occlusion (CTO) is associated with reduction of cardiac mortality, as well as reducing fatal ventricular arrhythmias. The aim of this study was to evaluate the effect of recanalization of CTO on endocardial left ventricular voltages by paired electrophysiological studies.MethodsSixteen consecutive patients who underwent PCI for de novo CTO lesions were included. High‐density mapping was performed during sinus rhythm before and 8 months after PCI. According to the amplitude of bipolar electrograms, the left ventricular endocardium was classified into a preserved normal voltage (>1.5 mV), border zone (0.5–1.5 mV), and dense scar areas (<0.5 mV).ResultsThe border zone area had a significant positive correlation with CTO length, as well as a significant negative correlation observed in the preserved voltage region. In the successful PCI patient, the median dense scar area did not change significantly (reported as [median difference: 95% confidence interval]) between baseline and after PCI (0.1 cm2: –2.8 to 2.9). However, the area of the border zone decreased (–10.5 cm2: –16.8 to –4.1) and the preserved voltage area increased significantly (19.2 cm2: 7.7–30.6). In addition, successful PCI was related to slight, but significant, increase in the amplitude of unipolar and bipolar voltage (1.55 mV: 0.88–3.33, 0.23 mV: 0.08–0.36).ConclusionsRecanalization of CTO may promote reverse electrical remodeling in the border zone of the left ventricle, without affecting the dense scar tissue.