Background: Early prognostication of the outcome in pediatric cardiac arrest (CA) patients is crucial for clinical decision-making. Heart rate variability (HRV) has shown potential in predicting outcomes after CA in adult patients. This study investigates whether HRV can be used to predict survival outcomes after pediatric CA using machine learning techniques. Methods: This retrospective study included children with CA, who achieved return of spontaneous circulation (ROSC), and were admitted to the pediatric intensive care unit (PICU) of a tertiary hospital between 2012 and 2021. A 5-min electrocardiogram (ECG) segment acquired at 24 h after CA was used to calculate HRV parameters (time-, frequency-, and non-linear domains). These parameters were used to train a random forest model. The primary outcome was 12-month survival or death. Model performance was evaluated using receiver-operating characteristics (ROC) analysis and predictive values. Feature importance was assessed using Shapley values. Results: A total of 76 patients (male: 63.2%, median age: 2.5 [IQR: 0.4–8.0] years) were divided into survival (34) or death (42) groups based on 12-month outcomes. The machine learning model achieved an accuracy of 77.6% and a positive predictive value of 0.879 for mortality prediction. The most influential features for model predictions were the frequency-domain parameters total power and very-low frequency (VLF) power, with lower values associated with an increased probability of death. Conclusions: Analysis of HRV at 24 h after ROSC may serve as a strong predictor of 12-month survival after pediatric CA.

Background Conduction blocks (CBs) play an important role in the initiation and perpetuation of atrial fibrillation and may be masked because of its direction- or rate dependency. Objective We aim to investigate how the highest amount and most severe CB at the right atrium (RA) can be unmasked by delivering programmed electrical stimulation (PES) from various directions and at different frequencies. Methods High-resolution epicardial mapping was performed at the middle of the RA on 40 patients during sinus rhythm (SR) and PES from the 4 sides of the mapping array at the average SR cycle length minus 50 ms (SR ₅₀) and 3 different S1S2 trains (S1 ₄₀₀, S2 ₃₀₀, S2 ₂₅₀ or S2 ₂₀₀). CB area percentage (CBA%) was defined as the proportion of electrodes with a local conduction time ≥12 ms. CB severity was defined as the 95th percentile of the conduction times over the lines of CB. Results CBA% increased from 0.6 [0-7.0]% during SR to 15.4 [12.3-19.2]% during S2 ₂₀₀ (P <.001). CB severity increased from 18 [14-29] ms during SR to 46 [29-53] ms during S2 ₂₀₀ (P <.001). PES increased CBA% over SR from 58% of patients during SR ₅₀ to 100% during S2 ₂₀₀. The largest increase in CBA% occurred during S2 ₂₅₀ during pacing from perpendicular (+7.3 [0.5-10.8]%) and opposite (+7.4 [3.5-15.5]%) to the direction of SR. Conclusion Perpendicular pacing opposite to the direction of SR using premature stimuli is optimal for unmasking CB. PES may also reduce CB in patients who already exhibit complex activation patterns during SR.

Background: Short atrial fibrillation cycle lengths (AFCLs) and regular activation patterns are associated with drivers of atrial fibrillation, although the relation with underlying patterns of activation is incompletely understood. Previous studies used automated assessment of electrograms to determine fast and regular fibrillatory rates. Objective: We investigated the relation among AFCL, temporal variation in AFCL, and the occurrence of driver-like patterns of activation using high-density local activation time mapping. Methods: High-density epicardial mapping of the right atrium and left atrial ventricular groove including Bachmann's bundle was performed in 71 patients admitted for elective cardiac surgery. Recording sites with the shortest median AFCL or the smallest standard deviation of AFCL were identified. Patterns of activation included focal or rotational activation, smooth propagation, propagation with conduction block (CB), collision, and remnant activity. Results: There was a higher number of fibrillation waves with CB (81% [interquartile range (IQR) 76%–85%] vs 74% [68%–76%]; P < .001) and fractionated potentials (22% [12%–37%] vs 12% [9%–15%]; P < .001) at shortest median AFCL than at other recording sites. Smallest standard deviation sites harbored more smoothly propagating waves (33% [24%–54%] vs 17% [11%–25%]; P < .001) and a higher proportion of single potentials (76% [60%–89%] vs 59% [54%–65%]; P < .001). Both highly regular and fastest reactivated sites did not correspond to the origin of (repetitive) focal fibrillation waves. Conclusion: During extensive mapping, the fastest or most regularly activated areas are characterized by CB and smoothly propagating fibrillation waves instead of repetitive occurrence of focal or rotational activation patterns. This study rejects the concept of detecting drivers by identifying the fastest or most regularly activated recording sites.

Background: Aging induces structural remodeling, altering atrial electrogram morphology. Over time, structural and consequently electrical remodeling creates a substrate for atrial fibrillation. In structural heart disease, age-induced remodeling comes on top of a pre-existing degree of structural remodeling due to pressure or volume overload. Objective: Investigate the severity of age-related electrical remodeling in patients undergoing surgery for structural heart disease by utilizing a high resolution epicardial mapping approach. Methods: Five seconds of sinus rhythm were recorded intraoperatively at the right atrium (RA), Bachmann's bundle (BB), the left atrium, and the pulmonary vein area. Potential voltage, low-voltage area (LVA) and conduction velocity (CV) were assessed in all regions. Results: 104 patients were included (62,5 % male, age: 26–84 years) and categorized in three age groups: young-age (age <60 years, n = 40), middle-age (age 60–71 years, n = 33), or old-age (age ≥72 years, n = 31) group. Compared to the young-age group, the old-age group had 1) lower median potential voltages at RA (4.65 [3.53–5.62]mV versus 5.94 [4.86–6.79]mV, p = 0.001) and 2) lower CV at RA (87.86 [82.53–96.67]cm/s versus 94.81 [90.14–98.59]cm/s, p = 0.016) and BB (83.38 [67.72–94.96]cm/s versus 98.84 [86.58–102.90]cm/s, p = 0.005). Conclusions: Age-related electrophysiological changes in patients with structural heart disease include reduction in atrial potential voltages and slowing of CV. These changes were less pronounced in the middle-age group. This indicates that electrical remodeling is a combination of both the underlying heart disease and the aging process. However, the less pronounced changes in the middle-age group may reflect a more gradual progression of age-related remodeling.

Arrhythmias significantly contribute to morbidity and mortality in patients with congenital heart disease (CHD). While postoperative factors predisposing to arrhythmias are well-established, early electrophysiological alterations in pediatric CHD remain poorly understood. This review summarizes current knowledge on postnatal cardiac maturation, conduction-system development, and electrophysiological abnormalities in pediatric patients with and without CHD. Importantly, arrhythmia prevalence, mechanisms, and clinical relevance are systematically discussed across three pediatric groups, including healthy children and patients with unrepaired and repaired CHD. Understanding developmental arrhythmogenic mechanisms may facilitate early risk stratification, guide clinical management decisions, and improve long-term outcomes for pediatric patients with CHD. This review discusses the complex interplay between cardiac maturation, congenital defects, and arrhythmogenesis. It also outlines future directions that include noninvasive monitoring, selective intraoperative mapping, animal model studies, and standardized data collection to improve early risk stratification and long-term outcomes in children with CHD.

Background: Electrical activity from the sino-atrial node (SAN) spreads via specific pathways into surrounding atrial tissue. Inferior sino-atrial node exit sites (SAN_i) have been observed in patients with structural heart disease and atrial fibrillation. However, determinants of preferential sino-atrial conduction pathways and the associated electrical properties of the SAN_i region remain poorly understood. Objectives: This study sought to examine differences in unipolar potential morphology and the degree of remodeling at the right atrium (RA) between patients with superior sino-atrial node exit sites (SAN_s) and SAN_i. Methods: High-resolution epicardial mapping was performed in 27 patients with structural heart disease undergoing elective open-heart surgery. Electrodes within an 8-mm radius of the SAN exit site were classified as the SAN area. Electrophysiological properties, including potential voltage, conduction block, and R/S ratios, were computed. Results: SAN_i, identified in 7 patients, exhibited lower potential voltages (median: 1.3 [Q1-Q3: 1.2-1.7] vs 2.6 [Q1-Q3: 2.2-3.6] mV; P = 0.014) and unipolar rS-wave morphologies, whereas SAN_s had full S-wave morphologies. The total activation times of RA were prolonged in SAN_i patients (median: 89 [Q1-Q3: 79-98] vs 78 [Q1-Q3: 66-85] milliseconds; P = 0.046). Heart rates were comparable between groups and remained consistent during both the preoperative and intraoperative periods. Conclusions: SAN_i identified by high-resolution epicardial mapping were associated with extensive RA remodeling and are most likely due to altered sino-atrial conduction pathways.

Background: There is increasing evidence that presentation, progression, and management of atrial arrhythmias, such as atrial fibrillation (AF), differ between women and men. Bachmann’s bundle (BB) is the main route for interatrial conduction, and sex-related differences in structural and electrical remodeling of BB may contribute to differences in AF development between women and men. Objective: Investigate whether sex differences in the electrophysiological properties of BB assessed by high-resolution and density maps exist in patients with AF. Methods: Sinus rhythm at BB was recorded for 5 s during cardiac surgery. Potential voltage, low-voltage area (LVA), conduction heterogeneity, unipolar potential morphology, and conduction velocity were assessed for both men and women. Results: The study population consisted of 108 patients (73 men, 35 women). Women had significantly lower potential voltages (5th percentile: 0.7 mV [0.6–1.0] vs 1.1 mV [0.6–1.4], p = 0.028), more LVAs (10.8% [4.6–19.7] vs 4.3% [2.2–11.7], p = 0.012) and more long double potentials (11.1% [3.6–13.5] vs 5.0% [1.0–10.3], p = 0.015) compared to men. Conclusions: We observed sex-related differences in the electrical remodeling of BB in AF patients. Women have a higher proportion of low voltage potentials, and more abnormal potential morphologies compared to men. These findings may reflect sex-specific differences in the underlying substrate of AF at BB.

Background: Areas of conduction disorders play an important role in both initiation and perpetuation of AF and can be recognized by specific changes in unipolar potential morphology. For example, EGM fractionation may be caused by asynchronous activation of adjacent cardiomyocytes because of structural barriers such as fibrotic strands. However, it is unknown whether there are sex differences in unipolar potential morphology. Therefore, atrial potential morphologies during sinus rhythm (SR) were compared between male and female patients. Methods: Based on propensity score matching, 62 male and female patients in whom high-resolution mapping of the right atrium (RA), left atrium (LA), and pulmonary vein area (PVA) including Bachmann's bundle (BB) was performed during coronary bypass grafting surgery and/or valvular heart surgery. Unipolar potentials were classified as single potentials (SPs), short double potentials (SDPs), long double potentials (LDP), fractionated potentials (FPs) and fraction duration (FD). The proportion of conduction block lines was also determined. Results: Female patients had a higher proportion of SDPs, LDPs and FPs at the RA, and SDPs at BB. At the PVA, there were less SPs and more SDPs and FPs. In females, FDs were longer at the RA and PVA, and potential voltages of only SPs were lower at the RA (all P < 0.05). Females also had more CB at the RA and at PVA (P < 0.05). Conclusion: In females, the proportion of single unipolar potentials indicative of smooth conduction, was lower compared to males, at the RA and PVA and to a lesser degree at BB. Females also had more CB at RA and PVA. Hence, these results may reflect sex-differences in the degree of electrical remodeling.

Living myocardial slices (LMSs) have shown great promise in cardiac research, allowing multicellular and complex interplay analyses with disease and patient specificity, yet their wider clinical use is limited by the large tissue sizes usually required. We therefore produced mini-LMSs (<10 mm²) from routine human cardiac surgery specimens and compared them with medium (10–30 mm²) and large (>30 mm²) slices. Size effects on biomechanical properties were examined with mathematical modeling, and viability, contraction profiles, and histological integrity were followed for 14 days. In total, 34 mini-, 25 medium, and 30 large LMS were maintained viable, the smallest measuring only 2 mm². Peak twitch force proved to be size-independent, whereas time-to-peak shortened as slice area decreased. Downsized LMSs displayed excellent contractile behavior for five to six days, after which a gradual functional decline and micro-architectural changes emerged. These findings confirm, for the first time, that mini-LMSs are feasible and viable, enabling short-term, patient-specific functional studies and pharmacological testing when tissue is scarce.

Background: Atrial fibrillation (AF) persistence is associated with molecular remodeling that fuels electrical conduction abnormalities in atrial tissue. Previous research revealed DNA damage as a molecular driver of AF. Objectives: This study sought to explore the diagnostic value of DNA damage in atrial tissue and blood samples as an indicator of the prevalence of electrical conduction abnormalities and stage of AF. Methods: High-sensitivity long-run real-time PCR was performed on mitochondrial (ND1) and nuclear (P53) DNA from atrial tissue samples from paroxysmal (PAF), persistent (PeAF), and longstanding persistent (LS-PeAF) AF, and sinus rhythm (SR) patients (n = 83). PicoGreen assay and quantitative polymerase chain reaction were used on circulating free DNA (cfDNA) markers (total cfDNA, β-globin, ND1, and P53) in blood samples of 70 patients with AF or SR. High-resolution epicardial mapping of the atria (n = 48) was conducted to quantify electrical conduction abnormalities. Results: The number of DNA lesions gradually and significantly increased in PAF and PeAF and in patients with <3 years of AF compared with SR. In SR, the quantity of nuclear DNA damage significantly correlated with the proportion of fractionated potentials. Mitochondrial DNA lesions correlated with slower conduction velocity and lower potential amplitudes in AF samples. Also, mitochondrial cfDNA levels decreased in patients with >3 years of AF compared with <3 years of AF (P = 0.004). Conclusions: The quantity of DNA lesions in atrial tissue samples is associated with atrial conduction abnormalities and stage of AF. Serum DNA damage markers discriminate short- from long-term AF. Therefore, the quantity of DNA damage may have diagnostic value in clinical AF management.

Background: Bachmann's bundle (BB) may potentially play a role in the earlier onset and faster progression of atrial fibrillation in adult patients with congenital heart disease (CHD). It is unknown whether electrophysiological alterations already exist at BB in pediatric patients with CHD and whether they are related to aging. Objective: This study aimed to investigate BB electrophysiology in pediatric patients with CHD and assess the impact of age on BB electrophysiology. Methods: BB mapping was conducted in 55 patients (0.2–17.5 years). Activation patterns, potential voltages, low-voltage areas (LVAs), potential morphology, and conduction disorders of BB were analyzed and correlated with age. Results: Right-to-left activation across BB occurred in 96.4% of patients. Potential voltage was on average 7.2 ± 3.0 mV, and LVAs occurred in 85.4% of patients. Median local conduction velocity was 96.6 (72.9–121.0) cm/s, and conduction block occurred in 56.4% of patients. Most potentials were single and short-double potentials; long-double and fractionated potentials were recorded in 49.1% and 72.7% of patients, respectively. Age was weakly correlated with potential voltages (r = 0.312, P = .020) and moderately with local conduction velocity (r = 0.439, P < .001), but not with potential morphology or conduction block. Conclusion: In pediatric patients with CHD, BB already contains a considerable amount of conduction disorders, LVAs, and potentials with complex morphology. The prevalence of these early electrophysiological alterations is not age related and does not differ among the right, left, and middle parts of BB.

Background: Quantified features of local conduction heterogeneity due to pathological alterations of myocardial tissue could serve as a marker for the degree of electrical remodeling and hence be used to determine the stage of atrial fibrillation (AF). Objectives: In this study, the authors investigated whether local directional heterogeneity (LDH) and anisotropy ratio, derived from estimated local conduction velocities (CVs) during AF, are suitable electrical parameters to stage AF. Methods: Epicardial mapping (244-electrode array, interelectrode distance 2.25 mm) of the right atrium was performed during acute atrial fibrillation (AAF) (n = 25, 32 ± 11 years of age) and during long-standing persistent atrial fibrillation (LSPAF) (n = 23, 64 ± 9 years of age). Episodes of 9 ± 4 seconds of AF were analyzed. Local CV vectors were constructed to assess the degree of anisotropy. Directions and magnitudes of individual vectors were compared with surrounding vectors to identify LDH. Results: Compared with the entire AAF group, LSPAF was characterized by slower conduction (71.5 ± 6.8 cm/s vs 67.6 ± 5.6 cm/s; P = 0.037) with a larger dispersion (1.59 ± 0.21 vs 1.95 ± 0.17; P < 0.001) and temporal variability (32.0 ± 4.7 cm/s vs 38.5 ± 3.3 cm/s; P < 0.001). Also, LSPAF was characterized by more LDH (19.6% ± 4.4% vs 26.0% ± 3.4%; P < 0.001) and a higher degree of anisotropy (1.38 ± 0.07 vs 1.51 ± 0.14; P < 0.001). Compared with the most complex type of AAF (type III), LSPAF was still associated with a larger CV dispersion, higher temporal variability of CV, and larger amount of LDH. Conclusions: Increasing AF complexity was associated with increased spatiotemporal variability of local CV vectors, local conduction heterogeneity, and anisotropy ratio. By using these novel parameters, LSPAF could potentially be discriminated from the most complex type of AAF. These observations may indicate pathological alterations of myocardial tissue underlying progression of AF.

Normothermic ex-situ heart perfusion (ESHP) enables assessment of hearts donated after circulatory death (DCD) prior to transplantation. However, sensitive parameters of cardiac function of DCD hearts on ESHP are needed. This study proposes a novel approach using electrophysiological (EP) parameters derived from electrical mapping as biomarkers of post-ischemic cardiac performance. Porcine slaughterhouse hearts (PSH) were divided in two groups based on the type of warm ischemia (Group 1: 10 ± 1 min with animal depilation vs. Group 2: ≤5 min without depilation). Electrical mapping of the right (RV) and left ventricle (LV) was performed on ESHP. Potential voltages, slopes and conduction velocities were computed from unipolar electrograms and compared between groups. Voltages were lower in Group 1 compared to Group 2 (RV: 3.6 vs. 15.3 mV, p = 0.057; LV: 10.8 vs. 23.6 mV, p = 0.029). In addition, the percentage of low-voltage potentials was higher and potential slopes were flatter in Group 1. Voltages and slopes strongly correlated with the visual contractile performance of PSH, but showed weaker correlation with lactate profiles. In conclusion, unipolar potential voltages and potential slopes were decreased in hearts with severe warm ischemia. As such, EP parameters could aid transplantation teams in decision-making on transplantability of DCD hearts.

Objective: The severity of atrial fibrillation (AF) can be assessed from intra-operative epicardial measurements (high-resolution electrograms), using metrics such as conduction block (CB) and continuous conduction delay and block (cCDCB). These features capture differences in conduction velocity and wavefront propagation, but ignore complementary properties such as the morphology of the action potentials. In this work, we focus on such complementary properties, and derive features to detect variations in the atrial potential waveforms. Methods: We show that the spatial variation of atrial potential morphology during a single beat may be described by changes in the singular values of the epicardial measurement matrix. The method is non-parametric and requires little preprocessing. A corresponding singular value map points at areas subject to fractionation and block. Further, we developed an experiment where we simultaneously measure electrograms (EGMs) and a multi-lead ECG. Results: The captured data showed that the normalized singular values of the heartbeats during AF are higher than during SR, and that this difference is more pronounced for the (non-invasive) ECG data than for the EGM data, if the electrodes are positioned at favorable locations. Conclusion: Overall, the singular value-based features are a useful indicator to detect and evaluate AF. Significance: The proposed method might be beneficial for identifying electropathological regions in the tissue without estimating the local activation time.

(1) Background: Structural remodeling plays an important role in the pathophysiology of atrial fibrillation (AF). It is likely that structural remodeling occurs transmurally, giving rise to electrical endo-epicardial asynchrony (EEA). Recent studies have suggested that areas of EEA may be suitable targets for ablation therapy of AF. We hypothesized that the degree of EEA is more pronounced in areas of transmural conduction block (T-CB) than single-sided CB (SS-CB). This study examined the degree to which SS-CB and T-CB enhance EEA and which specific unipolar potential morphology parameters are predictive for SS-CB or T-CB. (2) Methods: Simultaneous endo-epicardial mapping in the human right atrium was performed in 86 patients. Potential morphology parameters included unipolar potential voltages, low-voltage areas, potential complexity (long double and fractionated potentials: LDPs and FPs), and the duration of fractionation. (3) Results: EEA was mostly affected by the presence of T-CB areas. Lower potential voltages and more LDPs and FPs were observed in T-CB areas compared to SS-CB areas. (4) Conclusion: Areas of T-CB could be most accurately predicted by combining epicardial unipolar potential morphology parameters, including voltages, fractionation, and fractionation duration (AUC = 0.91). If transmural areas of CB indeed play a pivotal role in the pathophysiology of AF, they could theoretically be used as target sites for ablation.

In this paper, we present an equivalent circuit model that integrates a living myocardial slice (LMS) cultured on a microelectrode array (MEA) to effectively simulates a heart-on-a-chip (HoC) within Electronic Design Automation (EDA) software. The cardiac fiber model consists of cardiomyocytes interconnected by gap junctions to simulate the action potential (AP) conduction in the longitudinal direction. We systematically explored several parameters, including gap junction resistors, seal resistors, and electrode diameters, to assess their effects on local field potential (LFP). The model accuracy was validated through in vitro experiments using mouse LMS, confirming its potential for guiding HoC design in cardiac research.

The electrical arrhythmogenic substrate underlying the most common cardiac arrhythmia atrial fibrillation (AF) may consist of conduction disorders, low-voltage areas, or fractionated potentials. High-density and resolution epicardial mapping (HDREM) approaches have been introduced to quantify and visualize electrophysiological properties of the atria. These approaches are essential for obtaining innovative insights into arrhythmogenic substrates and identifying novel targets for therapy. The aim of this review is to summarize and discuss the (1) contribution of HDREM studies to the knowledge on atrial arrhythmogenesis and (2) future applications of HDREM of atria in daily clinical practice.

Background: Ablation strategies targeting fractionated or low-voltage potentials have been widely used in patients with persistent types of atrial fibrillation (AF). However, recent studies have questioned their role in effectively representing sites of conduction slowing, and thus arrhythmogenic substrates. Objectives: The authors studied the relationship between local conduction velocity (CV) and the occurrence of fractionated and/or low-voltage potentials in order to identify areas with critically slowing of conduction. Methods: Intraoperative epicardial mapping was performed during sinus rhythm. Unipolar potentials with an amplitude <1.0 mV were initially classified as low-voltage and potentials with ≥3 deflections as fractionation. A range of thresholds were also explored. Local CV was computed using discrete velocity vectors. Results: A total of 319 patients were included. Fractionated, low-voltage potentials were rare, accounting for only 0.36% (Q1-Q3: 0.15%-0.78%) of all atrial sites. Local CV at sites with fractionated, low-voltage potentials (46.0 cm/s [Q1-Q3: 22.6-72.7 cm/s]) was lowest compared with sites with either low-voltage, nonfractionated potentials (64.5 cm/s [Q1-Q3: 34.8-99.4 cm/s]) or fractionated, high-voltage potentials (65.9 cm/s [Q1-Q3: 41.7-92.8 cm/s]; P < 0.001). Slow conduction areas (CV <50 cm/s) could be most accurately identified by using a low voltage threshold (<1 mV) and a minimum of 3 deflections (positive predictive value: 54.2%-70.7%), although the overall sensitivity remained low (0.1%-1.9%). Conclusions: Sites with fractionated, low-voltage potentials have substantially slower local CV compared with sites with either low-voltage, nonfractionated potentials or fractionated, high-voltage potentials. However, the strong inverse relationship between the positive predictive value and sensitivity of a combined voltage and fractionation threshold for slowed conduction is likely to complicate the use of these signal-based ablation approaches in AF patients.

Background: Dominant frequencies (DFs) or complex fractionated atrial electrograms (CFAEs), indicative of focal sources or rotational activation, are used to identify target sites for atrial fibrillation (AF) ablation in clinical studies, although the relationship among DF, CFAE, and activation patterns remains unclear. Objectives: This study sought to investigate the relationship between patterns of activation underlying DF and CFAE sites during AF. Methods: Epicardial high-resolution mapping of the right and left atrium including Bachmann's bundle was performed in 71 participants. We identified the highest dominant frequency (DF _max) and highest degree of CFAE (CFAE _max) with the use of existing clinical criteria and classified patterns of activation as focal or rotational activation and smooth propagation, conduction block (CB), collision and remnant activity, and fibrillation potentials as single, double, or fractionated potentials containing, respectively, 1, 2, or 3 or more negative deflections. Relationships among activation patterns, DF _max, and potential types were investigated. Results: DF _max were primarily located at the left atrioventricular groove and did not harbor focal activation (proportion focal waves: 0% [IQR: 0%-2%]). Compared with non-DF _max sites, DF _max were characterized by more frequent smooth propagation (22% [IQR: 7%-48%] vs 17% [IQR: 11%-24%]; P = 0.001), less frequent conduction block (69% [IQR: 51%-81%] vs 74% [IQR: 69%-78%]; P = 0.006), a higher proportion of single potentials (72% [IQR: 55%-84%] vs 6%1 [IQR: 55%-65%]; P = 0.003), and a lower proportion of fractionated potentials (4% [IQR: 1%-11%] vs 12% [IQR: 9%-15%]; P = 0.004). CFAE _max were mainly found at the pulmonary veins area, and only 1% [IQR: 0%-2%] of all CFAE _max contained focal activation. Compared with non-CFAE _max sites, CFAE _max sites were characterized by less frequent smooth propagation (1% [IQR: 0%-1%] vs 17% [IQR: 12%-24%]; P < 0.001) and more frequent remnant activity (20% [IQR: 12%-29%] vs 8% [IQR: 5%-10%]; P < 0.001), and harbored predominantly fractionated potentials (52% [IQR: 43%-66%] vs 12% [IQR: 9%-14%]; P < 0.001). Conclusions: Focal or rotational patterns of activation were not consistently detected at DF _max domains and CFAE _max sites. These findings do not support the concept of targeting DF _max or CFAE _max according to existing criteria for AF ablation.