Unipolar voltage electroanatomical mapping detects structural atrial remodeling identified by LGE-MRI.

BACKGROUND: In atrial fibrillation (AF) management, understanding left atrial (LA) substrate is crucial. While both electroanatomical mapping (EAM) and late gadolinium enhancement MRI (LGE-MRI) are accepted methods for assessing the atrial substrate and are associated with ablation outcome, recent findings have highlighted discrepancies between low voltage areas (LVAs) in EAM and LGE-areas. OBJECTIVE: Explore the relationship between LGE regions and unipolar and bipolar-LVAs utilizing multipolar high-density (HD) mapping. METHODS: 20 patients scheduled for AF ablation underwent pre-ablation LGE-MRI. LA segmentation was conducted using a deep learning approach, which subsequently generated a 3D mesh integrating the LGE data. HD-EAM was performed in sinus rhythm for each patient. The EAM map and LGE-MRI mesh were co-registered. LVAs were defined using voltage cut-offs of 0.5mV for bipolar and 2.5mV for unipolar. Correspondence between LGE-areas and LVAs in the LA was analyzed using confusion matrices and performance metrics. RESULTS: A considerable 87.3% of LGE regions overlapped with unipolar-LVAs, compared to only 16.2% overlap observed with bipolar-LVAs. Across all performance metrics, unipolar-LVAs outperformed bipolar-LVAs in identifying LGE-areas [precision (78.6% vs. 61.1%); sensitivity (87.3% vs. 16.2%); F1 score (81.3% vs. 26.0%); accuracy (74.0% vs. 35.3%)]. CONCLUSION: Our findings demonstrate that unipolar-LVAs highly correlate with LGE regions. These findings support the integration of unipolar mapping alongside bipolar mapping into clinical practice. This would offer a nuanced approach to diagnose and manage atrial fibrillation by revealing critical insights into the complex architecture of the atrial substrate.

Correlation of extent of left ventricular endocardial unipolar low-voltage zones with ventricular tachycardia in nonischemic cardiomyopathy.

BACKGROUND: Endocardial electrogram (EGM) characteristics in nonischemic cardiomyopathy (NICM) have not been explored adequately for prognostication. OBJECTIVE: We aimed to study correlation of bipolar and unipolar EGM characteristics with left ventricular ejection fraction (LVEF) and ventricular tachycardia (VT) in NICM. METHODS: Electroanatomic mapping of the left ventricle was performed. EGM characteristics were correlated with LVEF. Differences between groups with and without VT and predictors of VT were studied. RESULTS: In 43 patients, unipolar EGM variables had better correlation with baseline LVEF than bipolar EGM variables: unipolar voltage (r = +0.36), peak negative unipolar voltage (r = -0.42), peak positive unipolar voltage (r = +0.38), and percentage area of unipolar low-voltage zone (LVZ; r = -0.41). Global mean unipolar voltage (hazard ratio [HR], 0.4; 95% confidence interval [CI], 0.2-0.8), extent of unipolar LVZ (HR, 1.6; 95% CI, 1.1-2.3), and percentage area of unipolar LVZ (HR, 1.6; 95% CI, 1.1-2.3) were significant predictors of VT. For classification of patients with VT, extent of unipolar LVZ had an area under the curve of 0.82 (95% CI, 0.69-0.95; P < .001), and percentage area of unipolar LVZ had an area under the curve of 0.83 (95% CI, 0.71-0.96; P = .01). Cutoff of >3 segments for extent of unipolar LVZ had the best diagnostic accuracy (sensitivity, 90%; specificity, 67%) and cutoff of 33% for percentage area of unipolar LVZ had the best diagnostic accuracy (sensitivity, 95%; specificity, 60%) for VT. CONCLUSION: In NICM, extent and percentage area of unipolar LVZs are significant predictors of VT. Cutoffs of >3 segments of unipolar LVZ and >33% area of unipolar LVZ have good diagnostic accuracies for association with VT.

Area-weighted unipolar voltage to predict heart failure outcomes in patients with ischaemic cardiomyopathy and ventricular tachycardia.

AIMS: Patients with ischaemic cardiomyopathy (ICM) referred for catheter ablation of ventricular tachycardia (VT) are at risk for end-stage heart failure (HF) due to adverse remodelling. Local unipolar voltages (UV) decrease with loss of viable myocardium. A UV parameter reflecting global viable myocardium may predict prognosis. We evaluate if a newly proposed parameter, area-weighted unipolar voltage (awUV), can predict HF-related outcomes [HFO; HF death/left ventricular (LV) assist device/heart transplant] in ICM. METHODS AND RESULTS: From endocardial voltage maps of consecutive patients with ICM referred for VT ablation, awUV was calculated by weighted interpolation of local UV. Associations between clinical and mapping parameters and HFO were evaluated and validated in a second cohort. The derivation cohort consisted of 90 patients [age 68 ±8 years; LV ejection fraction (LVEF) 35% interquartile range (IQR) (24-40)] and validation cohort of 60 patients [age 67 ± 9, LVEF 39% IQR (29-45)]. In the derivation cohort, during a median follow-up of 45 months [IQR (34-83)], 36 (43%) patients died and 23 (26%) had HFO. Patients with HFO had lower awUV [4.51 IQR (3.69-5.31) vs. 7.03 IQR (6.08-9.2), P < 0.001]. A reduction in awUV [optimal awUV (5.58) cut-off determined by receiver operating characteristics analysis] was a strong predictor of HFO (3-year HFO survival 97% vs. 57%). The cut-off value was confirmed in the validation cohort (2-year HFO-free survival 96% vs. 60%). CONCLUSION: The newly proposed parameter awUV, easily available from routine voltage mapping, may be useful at identifying ICM patients at high risk for HFO.

Unipolar-voltage-based evaluation of left atrial tissue properties and ablation outcome in patients with atrial fibrillation.

AIMS: The relationship between local unipolar voltage (UV) in the pulmonary vein (PV)-ostia and left atrial wall thickness (LAWT) and the utility of these parameters as indices of outcome after atrial fibrillation (AF) ablation remain unclear. METHODS AND RESULTS: Two-hundred seventy-two AF patients who underwent AF ablation were enrolled. Unipolar voltage of PV-ostia was measured using a CARTO system, and LAWT was measured using computed tomography. The primary endpoint was atrial tachyarrhythmia (ATA) recurrence including AF. The ATA recurrence was documented in 74 patients (ATA-Rec group). The UV and LAWT of the bilateral superior PV roof to posterior and around the right-inferior PV in the ATA-Rec group were significantly greater than in patients without ATA recurrence (ATA-Free group) (P < 0.001). The UV had a strong positive correlation with LAWT (R2 = 0.446, P < 0.001). The UV 2.7 mV and the corresponding LAWT 1.6 mm were determined as the cut-off values for ATA recurrence (P < 0.001, respectively). Multisite LA high UV (HUV, ≥4 areas of >2.7 mV) or multisite LA wall thickening (≥5 areas of >1.6 mm), defined as LA hypertrophy (LAH), was related to higher ATA recurrence. Among 92 LAH patients, 66 had HUV (LAH-HUV) and the remaining 26 had low UV (LAH-LUV), characterized by history of non-paroxysmal AF and heart failure, reduced LV ejection fraction, or enlarged LA. In addition, LAH-LUV showed the worst ablation outcome, followed by LAH-HUV and No LAH (log-rank P < 0.001). CONCLUSION: Combining UV and LAWT enables us to stratify recurrence risk and suggest a tailored ablation strategy according to LA tissue properties.

Atrial extrasystoles enhance low-voltage fractionation electrograms in patients with atrial fibrillation.

BACKGROUND AND AIMS: Atrial extrasystoles (AES) provoke conduction disorders and may trigger episodes of atrial fibrillation (AF). However, the direction- and rate-dependency of electrophysiological tissue properties on epicardial unipolar electrogram (EGM) morphology is unknown. Therefore, this study examined the impact of spontaneous AES on potential amplitude, -fractionation, -duration, and low-voltage areas (LVAs), and correlated these differences with various degrees of prematurity and aberrancy. METHODS AND RESULTS: Intra-operative high-resolution epicardial mapping of the right and left atrium, Bachmann's Bundle, and pulmonary vein area was performed during sinus rhythm (SR) in 287 patients (60 with AF). AES were categorized according to their prematurity index (>25% shortening) and degree of aberrancy (none, mild/opposite, moderate and severe). In total, 837 unique AES (457 premature; 58 mild/opposite, 355 moderate, and 154 severe aberrant) were included. The average prematurity index was 28% [12-45]. Comparing SR and AES, average voltage decreased (-1.1 [-1.2, -0.9] mV, P < 0.001) at all atrial regions, whereas the amount of LVAs and fractionation increased (respectively, +3.4 [2.7, 4.1] % and +3.2 [2.6, 3.7] %, P < 0.001). Only weak or moderate correlations were found between EGM morphology parameters and prematurity indices (R2 < 0.299, P < 0.001). All parameters were, however, most severely affected by either mild/opposite or severely aberrant AES, in which the effect was more pronounced in AF patients. Also, there were considerable regional differences in effects provoked by AES. CONCLUSION: Unipolar EGM characteristics during spontaneous AES are mainly directional-dependent and not rate-dependent. AF patients have more direction-dependent conduction disorders, indicating enhanced non-uniform anisotropy that is uncovered by spontaneous AES.

Volume-Weighted Unipolar Voltage Predicts Heart Failure Mortality in Patients With Dilated Cardiomyopathy and Ventricular Arrhythmias.

BACKGROUND: Patients with dilated cardiomyopathy (DCM) who are undergoing catheter ablation of ventricular arrhythmias (VAs) are at risk of rapidly progressive heart failure (HF). Endocardial voltages decrease with loss of viable myocardium. Global left ventricular (LV) voltage as a surrogate for the amount of remaining viable myocardium may predict prognosis. OBJECTIVES: This study evaluated whether the newly proposed parameter volume-weighted (vw) unipolar voltage (UV) can predict HF-related adverse outcomes (HFOs), including death, heart transplantation, or ventricular assist device implantation, in DCM. METHODS: In consecutive patients with DCM referred for VA ablation, vwUV was calculated by mathematically integrating UV over the left ventricle, divided by the endocardial LV surface area and wall thickness. Patients were followed for HFOs. RESULTS: A total of 103 patients (57 ± 14 years of age; left ventricular ejection fraction [LVEF], 39% ± 13%) were included. Median vwUV was 9.75 (IQR: 7.27-12.29). During a median follow-up of 24 months (IQR: 8-47 months), 25 patients (24%) died, and 16 had HFOs 7 months (IQR: 1-18 months) after ablation. Patients with HFOs had significantly lower LVEF (29% ± 10% vs 41% ± 12%), vw bipolar voltage (BV) (3.00 [IQR: 2.47-3.53] vs 5.00 [IQR: 4.12-5.73]), and vwUV (5.94 [IQR: 5.28-6.55] vs 10.37 [IQR: 8.82-12.81]; all P < 0.001), than patients without HFOs. In Cox regression analysis and goodness-of-fit tests, vwUV was the strongest and independent predictor for HFOs (HR: 3.68; CI: 2.09-6.45; likelihood ratio chi-square, 33.05; P < 0.001). CONCLUSIONS: The novel parameter vwUV, as a surrogate for the amount of viable myocardium, identifies patients with DCM with VA who are at high risk for HF progression and mortality.

Unipolar voltage mapping in right ventricular cardiomyopathy: pitfalls, solutions and advantages.

AIMS: Endocardial unipolar and bipolar voltage mapping (UVM/BVM) of the right ventricle (RV) are used for transmural substrate delineation. However, far-field electrograms (EGMs) and EGM changes due to injury current may influence automatically generated UVM. Epicardial BVM is considered less accurate due to the impact of fat thickness (FT). Data on epicardial UVM are sparse. The aim of the study is two-fold: to assess the influence of the manually corrected window-of-interest on UVM and the potential role of epicardial UVM in RV cardiomyopathies. METHODS AND RESULTS: Consecutive patients who underwent endo-epicardial RV mapping with computed-tomography (CT) integration were included. Mapping points were superimposed on short-axis CT slices and correlated with local FT. All points were manually re-analysed and the window-of-interest was adjusted to correct for false high unipolar voltage (UV). For opposite endo-epicardial point-pairs, endo-epicardial bipolar voltage (BV) and UV were correlated for different FT categories. A total of 3791 point-pairs of 33 patients were analysed. In 69% of endocardial points and 63% of epicardial points, the window-of-interest needed to be adjusted due to the inclusion of far-field EGMs, injury current components, or RV-pacing artifacts. The Pearson correlation between corrected endo-epicardial BV and UV was lower for point-pairs with greater FT; however, this correlation was much stronger and less influenced by fat for UV. CONCLUSION: At the majority of mapping sites, the window-of-interest needs to be manually adjusted for correct UVM. Unadjusted UVM underestimates low UV regions. Unipolar voltage seems to be less influenced by epicardial fat, suggesting a promising role for UVM in epicardial substrate delineation.

Detection of endo-epicardial atrial low-voltage areas using unipolar and omnipolar voltage mapping.

Background: Low-voltage areas (LVA) can be located exclusively at either the endocardium or epicardium. This has only been demonstrated for bipolar voltages, but the value of unipolar and omnipolar voltages recorded from either the endocardium and epicardium in predicting LVAs at the opposite layer remains unknown. The goal of this study was therefore to compare simultaneously recorded endo-epicardial unipolar and omnipolar potentials and to determine whether their voltage characteristics are predictive for opposite LVAs. Methods: Intra-operative simultaneous endo-epicardial mapping (256 electrodes, interelectrode distances 2 mm) was performed during sinus rhythm at the right atrium in 93 patients (67 ± 9 years, 73 male). Cliques of four electrodes (2 × 2 mm) were used to define maximal omnipolar (Vomni,max) and unipolar (Vuni,max) voltages. LVAs were defined as Vomni,max ≤0.5 mV or Vuni,max ≤1.0 mV. Results: The majority of both unipolar and omnipolar LVAs were located at only the endocardium (74.2% and 82.0% respectively) or epicardium (52.7% and 47.6% respectively). Of the endocardial unipolar LVAs, 25.8% were also located at the opposite layer and 47.3% vice-versa. In omnipolar LVAs, 18.0% of the endocardial LVAs were also located at the epicardium and 52.4% vice-versa. The combination of epicardial Vuni,max and Vomni,max was most accurate in identifying dual-layer LVAs (50.4%). Conclusion: Unipolar and omnipolar LVAs are frequently located exclusively at either the endocardium or epicardium. Endo-epicardial LVAs are most accurately identified using combined epicardial unipolar and omnipolar voltages. Therefore, a combined endo-epicardial unipolar and omnipolar mapping approach is favoured as it may be more indicative of possible arrhythmogenic substrates.

Myocardial Substrate Characterization by CMR T1 Mapping in Patients With NICM and No LGE Undergoing Catheter Ablation of VT.

OBJECTIVES: The goal of this study was to characterize the relationship between DF, the electroanatomic mapping (EAM) substrate, and outcomes of catheter ablation of VT in NICM. BACKGROUND: A substantial proportion of patients with nonischemic dilated cardiomyopathy (NICM) and ventricular tachycardia (VT) do not have scar detectable by cardiac magnetic resonance late gadolinium enhancement (LGE) imaging. In these patients, the significance of diffuse fibrosis (DF) detected with T1 mapping has not been previously investigated. METHODS: This study included 51 patients with NICM and VT undergoing catheter ablation (median age 55 years; 77% male subjects) who had no evidence of LGE on pre-procedural cardiac magnetic resonance. Post-contrast T1 relaxation time determined on the septum was assessed as a surrogate of DF burden. The extent of endocardial low-voltage areas (LVAs) at EAM was correlated with T1 mapping data. RESULTS: Bipolar LVAs were present in 22 (43%) patients (median extent 15 cm2 [8 to 29 cm2]) and unipolar LVA in all patients (median extent 48 cm2 [26 to 120 cm2]). A significant inverse correlation was found between T1 values and both unipolar-LVA (R2 = 0.64; ß = -0.85; p < 0.01) and bipolar-LVA (R2 = 0.16; ß = -1.63; p < 0.01). After a median follow-up of 45 months (22 to 57 months), 2 (4%) patients died, 3 (6%) underwent heart transplantation, and 8 (16%) experienced VT recurrence. Shorter post-contrast T1 time was associated with an increased risk of VT recurrence (hazard ratio: 1.16; 95% confidence interval: 1.03 to 1.33 per 10 ms decrease; p = 0.02). CONCLUSIONS: In patients with NICM and no evidence of LGE undergoing catheter ablation of VT, DF estimated by using post-contrast T1 mapping correlates with the voltage abnormality at EAM and seems to affect post-ablation outcomes.

Comparison of Unipolar and Bipolar Voltage Mapping for Localization of Left Atrial Arrhythmogenic Substrate in Patients With Atrial Fibrillation.

Background: Presence of left atrial low voltage substrate in bipolar voltage mapping is associated with increased arrhythmia recurrences following pulmonary vein isolation for atrial fibrillation (AF). Besides local myocardial fibrosis, bipolar voltage amplitudes may be influenced by inter-electrode spacing and bipole-to-wavefront-angle. It is unclear to what extent these impact low voltage areas (LVA) in the clinical setting. Alternatively, unipolar electrogram voltage is not affected by these factors but requires advanced filtering. Objectives: To assess the relationship between bipolar and unipolar voltage mapping in sinus rhythm (SR) and AF and identify if the electrogram recording mode affects the quantification and localization of LVA. Methods: Patients (n = 28, 66±7 years, 46% male, 82% persistent AF, 32% redo-procedures) underwent high-density (>1,200 sites, 20 ± 10 sites/cm2, using a 20-pole 2-6-2 mm-spaced Lasso) voltage mapping in SR and AF. Bipolar LVA were defined using four different thresholds described in literature: <0.5 and <1 mV in SR, <0.35 and <0.5 mV in AF. The optimal unipolar voltage threshold resulting in the highest agreement in both unipolar and bipolar mapping modes was determined. The impact of the inter-electrode distance (2 vs. 6 mm) on the correlation was assessed. Regional analysis was performed using an 11-segment left atrial model. Results: Patients had relevant bipolar LVA (23 ± 23 cm2 at <0.5 mV in SR and 42 ± 26 cm2 at <0.5 mV in AF). 90 ± 5% (in SR) and 85 ± 5% (AF) of mapped sites were concordantly classified as high or low voltage in both mapping modes. Discordant mapping sites located to the border zone of LVA. Bipolar voltage mapping using 2 vs. 6 mm inter-electrode distances increased the portion of matched mapping points by 4%. The unipolar thresholds (y) which resulted in a high spatial concordance can be calculated from the bipolar threshold (x) using following linear equations: y = 1.06x + 0.26mV (r = 0.994) for SR and y = 1.22x + 0.12mV (r = 0.998) for AF. Conclusion: Bipolar and unipolar voltage maps are highly correlated, in SR and AF. While bipole orientation and inter-electrode spacing are theoretical confounders, their impact is unlikely to be of clinical importance for localization of LVA, when mapping is performed at high density with a 20-polar Lasso catheter.

Dynamic unipolar voltage criteria of right ventricular septum for identifying left ventricular septal scar.

PURPOSE: The right ventricular (RV) septal unipolar voltage (UV) for predicting left ventricular (LV) septal scar wall thickness (WT) remains to be elucidated. METHODS: From 2013 to 2015, data obtained from RV and LV electroanatomic maps of 28 patients (mean age, 53 ± 16 years; 19 men [67.9%]) with/without identified LV septal scars were reviewed. Patients with an RV septal scar were excluded (n = 90). Direct measurement of septal WT was conducted (mean distance, 10.4 ± 3.3 mm). Patients in group 1 had a normal LV substrate, while those in group 2 had an LV septal scar. Fisher's linear discriminant formula was used to determine the dynamic UV criteria. RESULTS: A total of 552 points were collected: 323 in 12 patients from group 1 and 229 in 16 patients from group 2. The UV of the RV septum is capable of identifying the opposite LV endocardial bipolar scar and is proportional to the WT of the interventricular septum. In the absence of an RV endocardial scar, the formula of "RV septal cut-off value = 0.736 × WT - 0.117 mV" has better sensitivity and specificity for predicting the LV septal scar (0.96 vs. 0.68 and 0.91 vs. 0.80, respectively) than the predefined fixed criteria of 8.3 mV with a net reclassification improvement of 25.7% (P < 0.001). CONCLUSIONS: The combined measurement of UV and WT is more sensitive than the predefined fixed UV criteria for defining deep scars.

Correlation of right ventricular multielectrode endocardial unipolar mapping and epicardial scar.

AIMS: Prior studies identified a relationship between epicardial bipolar and endocardial unipolar voltage. Whether the relationship is valid with smaller multielectrode mapping catheters has not been reported. We explored the association of right ventricular (RV) endocardial unipolar voltage mapping with epicardial bipolar voltage mapping using a multielectrode mapping catheter. METHODS: Electrograms from patients who underwent multielectrode endocardial and epicardial RV electroanatomical mapping during ablation procedures were analyzed. Each endocardial mapping point was matched to the corresponding nearest epicardial point. The correlation between unipolar endocardial voltage and epicardial bipolar voltage was determined. The optimal unipolar threshold to detect epicardial low voltage (< 1.0 mV) and dense scar (0.5 mV) was calculated. RESULTS: A total of 4,895 points were analyzed. There was a significant correlation between endocardial unipolar and epicardial bipolar voltage (Spearman rho  =  0.499, P  =  < 0.001). The extent of the correlation was inversely associated with wall thickness. The receiver operator characteristic analysis of endocardial unipolar voltage predicting epicardial bipolar voltage of < 1.0 mV and < 0.5 showed an area under the curve of 0.769 and 0.812, respectively. The endocardial unipolar voltage that had the highest sensitivity and specificity in detecting epicardial bipolar voltage of < 1.0 mV and < 0.5 mV was 3.3 mV (70.3% sensitivity, 70.3% specificity), and 2.8 mV (sensitivity 73.8%, specificity 73.3%), respectively. CONCLUSION: Epicardial low voltage of the RV can be assessed by unipolar endocardial voltage using small multielectrode catheters. The strength of the association was inversely correlated with the wall thickness.

Unipolar voltage abnormality is associated with greater left ventricular dysfunction in ischemic cardiomyopathy.

INTRODUCTION: Following myocardial infarction (MI), left ventricular function is determined by cardiac remodeling occurring in both infarcted and noninfarcted myocardium (NIM). Unipolar voltage mapping may detect remodeling changes in NIM that are associated with the left ventricular ejection fraction (LVEF). We aimed to identify (1) unipolar voltage characteristics in patients with chronic MI, and (2) association of voltage abnormalities with degree of left ventricular dysfunction (LVD). METHODS AND RESULTS: Two groups of patients with ischemic cardiomyopathy (ICM) who underwent LV endocardial mapping during catheter ablation for ventricular tachycardia (VT) between January 2010 and December 2012 were studied. The first group (19 males) had mild to moderate LVD (M-LVD, LVEF >35%) and was matched for age, sex, infarction size, and infarction location with 10 males who had severe LVD (S-LVD, LVEF <35%). Both bipolar and unipolar endocardial abnormal voltage areas were measured and compared between groups. Abnormal bipolar area was comparable in both groups (30 ± 8% in the S-LVD group vs 28 ± 8% in the M-LVD group; P = 0.5). Total abnormal unipolar voltage area was significantly larger in the S-LVD group (57 ± 14% vs 43 ± 13%; P = 0.02). The abnormal unipolar voltage area within the normal bipolar voltage area was greater in the S-LVD group (26 ± 11% vs 15 ± 16%; P = 0.03). In receiver operating characteristic curve analysis, an 18.0% cut-off value for abnormal unipolar area within NIM identified severe LVD, with 90% sensitivity and 79% specificity (area under the curve 0.821). CONCLUSIONS: Patients with ICM and severe LVD have larger areas of unipolar voltage abnormality in the noninfarcted tissue than patients with M-LVD.