Excess Mortality Among US Physicians During the COVID-19 Pandemic

This cross-sectional study examines the death rates among active and nonactive physicians aged 45 to 84 years.

Atrial Fibrillation Mechanisms Before and After Pulmonary Vein Isolation Characterized by Non-Contact Charge Density Mapping

BACKGROUND

The interaction of pulmonary vein and putative non-pulmonary triggers of atrial fibrillation (AF) remains unclear, and has yet to translate into patient tailored ablation strategies.

OBJECTIVE

To use non-contact mapping to detail the global conduction patterns in paroxysmal and persistent AF and how they are modified during pulmonary vein ablation.

METHODS

40 patients at atrial fibrillation ablation underwent mapping using a non-contact catheter (AcQMap, Acutus Medical Inc) before and after pulmonary vein isolation (PVI). Propagation history maps were analysed post-procedure for each patient to categorise conduction patterns into Focal, Organised reentrant and Disorganized patterns.

RESULTS

Activation patterns identified by using a non-contact mapping system can be sub-classified from three main patterns into subtypes (MacroReentrant and LocalisedReentrant subtypes, Disorganized 1 and Disorganized 2 subtypes). Persistent AF demonstrated more D-Patterns, and less O-Patterns and F-Patterns than paroxysmal AF. In addition, PAF patients inducible after PVI demonstrated a greater number and higher prevalence of MR subtypes than those non-inducible. PVs remained the critical region and included almost one third of all patterns across any AF-types. PVI was effective to eliminate PV-related functional phenotypes, and impacted on recurrence with other patterns.

CONCLUSION

Activation patterns identified using AcQMap can be classified into three main patterns (F-Patterns, O-Patterns and D-Patterns) as well as subtypes (MR and LR subtype, D1 and D2 subtype). PerAF was different from PAF in demonstrating a greater region number and prevalence of D-Patterns, but lower region number and prevalence of O-Patterns and F-Patterns.

Current perspectives on wearable rhythm recordings for clinical decision-making: the wEHRAbles 2 survey

Novel wearable devices for heart rhythm analysis using either photoplethysmography (PPG) or electrocardiogram (ECG) are in daily clinical practice. This survey aimed to assess impact of these technologies on physicians' clinical decision-making and to define, how data from these devices should be presented and integrated into clinical practice. The online survey included 22 questions, focusing on the diagnosis of atrial fibrillation (AF) based on wearable rhythm device recordings, suitable indications for wearable rhythm devices, data presentation and processing, reimbursement, and future perspectives. A total of 539 respondents {median age 38 [interquartile range (IQR) 34-46] years, 29% female} from 51 countries world-wide completed the survey. Whilst most respondents would diagnose AF (83%), fewer would initiate oral anticoagulation therapy based on a single-lead ECG tracing. Significantly fewer still (27%) would make the diagnosis based on PPG-based tracing. Wearable ECG technology is acceptable for the majority of respondents for screening, diagnostics, monitoring, and follow-up of arrhythmia patients, while respondents were more reluctant to use PPG technology for these indications. Most respondents (74%) would advocate systematic screening for AF using wearable rhythm devices, starting at patients' median age of 60 (IQR 50-65) years. Thirty-six percent of respondents stated that there is no reimbursement for diagnostics involving wearable rhythm devices in their countries. Most respondents (56.4%) believe that costs of wearable rhythm devices should be shared between patients and insurances. Wearable single- or multiple-lead ECG technology is accepted for multiple indications in current clinical practice and triggers AF diagnosis and treatment. The unmet needs that call for action are reimbursement plans and integration of wearable rhythm device data into patient's files and hospital information systems.

Individualized ablation strategy to treat persistent atrial fibrillation: Core-to-boundary approach guided by charge-density mapping

BACKGROUND

Noncontact charge-density mapping allows rapid real-time global mapping of atrial fibrillation (AF), offering the opportunity for a personalized ablation strategy.

OBJECTIVE

The purpose of this study was to compare the 2-year outcome of an individualized strategy consisting of pulmonary vein isolation (PVI) plus core-to-boundary ablation (targeting the conduction pattern core with an extension to the nearest nonconducting boundary) guided by charge-density mapping, with an empirical PVI plus posterior wall electrical isolation (PWI) strategy.

METHODS

Forty patients (age 62 ± 12 years; 29 male) with persistent AF (10 ± 5 months) prospectively underwent charge-density mapping-guided PVI, followed by core-to-boundary stepwise ablation until termination of AF or depletion of identified cores. Freedom from AF/atrial tachycardia (AT) at 24 months was compared with a propensity score-matched control group of 80 patients with empirical PVI + PWI guided by conventional contact mapping.

RESULTS

Acute AF termination occurred in 8 of 40 patients after charge-density mapping-guided PVI alone and in 21 of the remaining 32 patients after core-to-boundary ablation in the study cohort, compared with 8 of 80 (10%) in the control cohort (P <.001). On average, 2.2 ± 0.6 cores were ablated post-PVI before acute AF termination. At 24 months, freedom from AF/AT after a single procedure was 68% in the study group vs 46% in the control group (P = .043).

CONCLUSION

An individualized ablation strategy consisting of PVI plus core-to-boundary ablation guided by noncontact charge-density mapping is a feasible and effective strategy for treating persistent AF, with a favorable 24-month outcome.

Spectral characterization and impact of stepwise ablation protocol including LAA electrical isolation on persistent AF

OBJECTIVES

To study how left atrial appendage electrical isolation (LAAEI) impacts atrial dominant frequency (DF) in patients with long-standing persistent atrial fibrillation (LSPAF).

BACKGROUND

LAAEI is associated with a high probability of freedom from atrial fibrillation (AF) and spectral analysis may identify high-frequency sources. How LAAEI impacts the AF dynamics and the subgroup of LSPAF patients in whom LAAEI would be most beneficial, is unclear.

METHODS

Twenty patients with LSPAF were included in the study. Fast Fourier transforms (FFT) were performed on atrial electrograms recorded from 13 sites in the LA and RA. The highest peak frequency was defined as DF.

RESULTS

There was no significant difference in DF between atrial sites except for at the superior vena cava which had the lowest DF at baseline. Stepwise ablation consisting of circumferential pulmonary vein isolation and a linear ablation set of mitral isthmus and roof significantly reduced the DF within the coronary sinus (CS) (5.93 ± 0.98 Hz vs. 5.09 ± 0.72 Hz, p < .05) and the LA posterior wall (LApos) (6.26 ± 0.92 Hz vs. 5.43 ± 0.98 Hz, p < .01). LAAEI preferentially further decreased the DF at the LApos (p < .01), but not at the CS. In cases where there was < 13.6% reduction in the DF of the LApos following the stepwise ablation, the addition of LAAEI was associated with an increased restoration of sinus rhythm (55%, p < .05).

CONCLUSION

LAAEI in addition to stepwise ablation results in further reduction of the DF in the LApos, which is associated with acute termination of AF and favorable ablation outcome.

Catheter Ablation of Atrial Fibrillation in Patients With Functional Mitral Regurgitation and Left Ventricular Systolic Dysfunction

Background: The efficacy of catheter ablation for atrial fibrillation (AF) in patients with functional mitral regurgitation (MR) and left ventricular (LV) systolic dysfunction (LVSD) is not known. The aim of the study is to determine the efficacy of catheter ablation for AF in patients with functional MR and LVSD, and to validate its effects on the severity of MR and cardiac reverse remodeling.

Methods: We performed a retrospective study of 54 patients with functional MR who underwent AF ablation, including 21 (38.9%) with LVSD and 33 (61.1%) with normal LV systolic function (LVF). The primary outcomes evaluated were freedom from recurrent atrial tachyarrhythmia (ATa), severity of MR, and left atrial (LA) and LV remodeling.

Results: During a mean follow-up of 20.7 ± 16.8 months, freedom from recurrent ATa was not significantly different between patients with LVSD and those with normal LVF after the first ablation (P = 0.301) and after multiple ablations (P = 0.728). Multivariable predictors of recurrent ATa were AF duration [hazard ratio (HR) 1.12, 95% confidence interval (CI) 1.01–1.25; P = 0.039), previous stroke (HR 5.28, 95% CI 1.46–19.14; P = 0.011), and estimated glomerular filtration rate (HR 0.97, 95% CI 0.95–0.99; P = 0.012). Compared with baseline, there was a significant reduction in severity of MR (P = 0.007), LA size (P < 0.001) and LV end-systolic dimension (P = 0.008), and improvement in the LV ejection fraction (P = 0.001) after restoring sinus rhythm in patients with LVSD.

Conclusion: Catheter ablation is a valid option for the treatment of AF in patients with functional MR and LVSD, even though multiple procedures may be required.

Machine Learning to Classify Intracardiac Electrical Patterns During Atrial Fibrillation: Machine Learning of Atrial Fibrillation

BACKGROUND

Advances in ablation for atrial fibrillation (AF) continue to be hindered by ambiguities in mapping, even between experts. We hypothesized that convolutional neural networks (CNN) may enable objective analysis of intracardiac activation in AF, which could be applied clinically if CNN classifications could also be explained.

METHODS

We performed panoramic recording of bi-atrial electrical signals in AF. We used the Hilbert-transform to produce 175 000 image grids in 35 patients, labeled for rotational activation by experts who showed consistency but with variability (kappa [κ]=0.79). In each patient, ablation terminated AF. A CNN was developed and trained on 100 000 AF image grids, validated on 25 000 grids, then tested on a separate 50 000 grids.

RESULTS

In the separate test cohort (50 000 grids), CNN reproducibly classified AF image grids into those with/without rotational sites with 95.0% accuracy (CI, 94.8%-95.2%). This accuracy exceeded that of support vector machines, traditional linear discriminant, and k-nearest neighbor statistical analyses. To probe the CNN, we applied gradient-weighted class activation mapping which revealed that the decision logic closely mimicked rules used by experts (C statistic 0.96).

CONCLUSIONS

CNNs improved the classification of intracardiac AF maps compared with other analyses and agreed with expert evaluation. Novel explainability analyses revealed that the CNN operated using a decision logic similar to rules used by experts, even though these rules were not provided in training. We thus describe a scaleable platform for robust comparisons of complex AF data from multiple systems, which may provide immediate clinical utility to guide ablation. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02997254. Graphic Abstract: A graphic abstract is available for this article.

Interaction of Localized Drivers and Disorganized Activation in Persistent Atrial Fibrillation: Reconciling Putative Mechanisms Using Multiple Mapping Techniques

BACKGROUND

Mechanisms for persistent atrial fibrillation (AF) are unclear. We hypothesized that putative AF drivers and disorganized zones may interact dynamically over short time scales. We studied this interaction over prolonged durations, focusing on regions where ablation terminates persistent AF using 2 mapping methods.

METHODS

We recruited 55 patients with persistent AF in whom ablation terminated AF prior to pulmonary vein isolation from a multicenter registry. AF was mapped globally using electrograms for 360±45 cycles using (1) a published phase method and (2) a commercial activation/phase method.

RESULTS

Patients were 62.2±9.7 years, 76% male. Sites of AF termination showed rotational/focal patterns by methods 1 and 2 (51/55 vs 55/55; P=0.13) in spatially conserved regions, yet fluctuated over time. Time points with no AF driver showed competing drivers elsewhere or disordered waves. Organized regions were detected for 61.6±23.9% and 70.6±20.6% of 1 minute per method (P=nonsignificant), confirmed by automatic phase tracking (P<0.05). To detect AF drivers with >90% sensitivity, 8 to 32 s of AF recordings were required depending on driver definition.

CONCLUSIONS

Sites at which persistent AF terminated by ablation show organized activation that fluctuate over time, because of collision from concurrent organized zones or fibrillatory waves, yet recur in conserved spatial regions. Results were similar by 2 mapping methods. This network of competing mechanisms should be reconciled with existing disorganized or driver mechanisms for AF, to improve clinical mapping and ablation of persistent AF.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02997254.

Recurrent Post-Ablation Paroxysmal Atrial Fibrillation Shares Substrates With Persistent Atrial Fibrillation : An 11-Center Study

INTRODUCTION

The role of atrial fibrillation (AF) substrates is unclear in patients with paroxysmal AF (PAF) that recurs after pulmonary vein isolation (PVI). We hypothesized that patients with recurrent post-ablation (redo) PAF despite PVI have electrical substrates marked by rotors and focal sources, and structural substrates that resemble persistent AF more than patients with (de novo) PAF at first ablation.

METHODS

In 175 patients at 11 centers, we compared AF substrates in both atria using 64 pole-basket catheters and phase mapping, and indices of anatomical remodeling between patients with de novo or redo PAF and first ablation for persistent AF.

RESULTS

Sources were seen in all patients. More patients with de novo PAF (78.0%) had sources near PVs than patients with redo PAF (47.4%, p=0.005) or persistent AF (46.9%, p=0.001). The total number of sources per patient (p=0.444), and number of non-PV sources (p=0.701) were similar between groups, indicating that redo PAF patients had residual non-PV sources after elimination of PV sources by prior PVI. Structurally, left atrial size did not separate de novo from redo PAF (49.5±9.5 vs. 49.0±7.1mm, p=0.956) but was larger in patients with persistent AF (55.2±8.4mm, p=0.001).

CONCLUSIONS

Patients with paroxysmal AF despite prior PVI show electrical substrates that resemble persistent AF more closely than patients with paroxysmal AF at first ablation. Notably, these subgroups of paroxysmal AF are indistinguishable by structural indices. These data motivate studies of trigger versus substrate mechanisms for patients with recurrent paroxysmal AF after PVI.

Oral Anticoagulants in Patients With Atrial Fibrillation and End-Stage Renal Disease

The role of oral anticoagulants (OAC) in atrial fibrillation (AF) is well established. However, none of the randomized controlled trials included patients with end-stage renal disease (ESRD) leaving a lack of evidence in this large, challenging and unique patient group. Patients on hemodialysis (HD) with AF have additional risk factors for stroke due to vascular comorbidities, HD treatment, age, and diabetes. Conversely, they are also at increased risk of major bleeding due to uremic platelet impairment. Anticoagulants increase bleeding risk in patients with ESRD and HD up to 10-fold compared with non chronic kidney disease (CKD) patients on warfarin. There are conflicting data and recommendations regarding use of OACs in ESRD which will be reviewed in this article. We conclude by proposing a modified strategy for OAC use in ESRD based on the latest evidence.

Early Diagnosis of Defibrillation Lead Dislodgement

OBJECTIVES

This study sought to develop and evaluate an algorithm for early diagnosis of dislodged implantable cardioverter-defibrillator (ICD) leads.

BACKGROUND

Dislodged defibrillation leads may sense atrial and ventricular electrograms (EGMs), triggering shocks in the vulnerable period that induce ventricular fibrillation (VF).

METHODS

We developed a 2-step algorithm by using experimental lead dislodgements (LDs) at ICD implantation and a control dataset of newly implanted, in situ leads. Step 1 consisted of an alert triggered by abrupt decrease in R-wave amplitude and increase in pacing threshold. Step 2 withheld therapy based on ventricular EGM evidence of LD identified from experimental LD behavior. We estimated the algorithm's performance using a registry dataset of 3,624 new implantations and an atrial dislodgement dataset of 14 LDs at the atrium.

RESULTS

In the registry dataset, the algorithm identified 20 of 21 radiographic LDs (95%) at a median of 11 days before clinical diagnosis. Step 1 had positive predictive values of 57% for radiographic LD and 77% for surgical revision. The false positive rate was 0.4% after step 1 and ≤0.2% after step 2. In the atrial dislodgement dataset, step 1 identified all 14 LDs; step 2 would have prevented inappropriate therapy in all 7 patients with stored EGMs at LD, including 2 patients with fatal, shock-induced VF.

CONCLUSIONS

An ICD algorithm can facilitate early diagnosis of defibrillation LD. Additional data are needed to determine the safety of withholding shocks based on EGM evidence of LD.

The Enduring Value of the Physical Examination

This article focuses exclusively on physical examination (PE) in the context of clinical medicine, that is, the interaction between a health care provider and patient. In essence, there is not only benefit (value) to PE but also that it will last (endure) for some time. Both "enduring" and "value" are explored in more depth with respect to the future integration of PE into the clinical assessment of a patient and how its value extends well beyond current diagnostic/cost-based metrics.

Independent mapping methods reveal rotational activation near pulmonary veins where atrial fibrillation terminates before pulmonary vein isolation

OBJECTIVE

To investigate mechanisms by which atrial fibrillation (AF) may terminate during ablation near the pulmonary veins before the veins are isolated (PVI).

INTRODUCTION

It remains unstudied how AF may terminate during ablation before PVs are isolated, or how patients with PV reconnection can be arrhythmia-free. We studied patients in whom PV antral ablation terminated AF before PVI, using two independent mapping methods.

METHODS

We studied patients with AF referred for ablation, in whom biatrial contact basket electrograms were studied by both an activation/phase mapping method and by a second validated mapping method reported not to create false rotational activity.

RESULTS

In 22 patients (age 60.1 ± 10.4, 36% persistent AF), ablation at sites near the PVs terminated AF (77% to sinus rhythm) prior to PVI. AF propagation revealed rotational (n  =  20) and focal (n  =  2) patterns at sites of termination by mapping method 1 and method 2. Both methods showed organized sites that were spatially concordant (P < 0.001) with similar stability (P < 0.001). Vagal slowing was not observed at sites of AF termination.

DISCUSSION

PV antral regions where ablation terminated AF before PVI exhibited rotational and focal activation by two independent mapping methods. These data provide an alternative mechanism for the success of PVI, and may explain AF termination before PVI or lack of arrhythmias despite PV reconnection. Mapping such sites may enable targeted PV lesion sets and improved freedom from AF.

Interpreting Activation Mapping of Atrial Fibrillation: A Hybrid Computational/Physiological Study

Atrial fibrillation is the most common rhythm disorder of the heart associated with a rapid and irregular beating of the upper chambers. Activation mapping remains the gold standard to diagnose and interpret atrial fibrillation. However, fibrillatory activation maps are highly sensitive to far-field effects, and often disagree with other optical mapping modalities. Here we show that computational modeling can identify spurious non-local components of atrial fibrillation electrograms and improve activation mapping. We motivate our approach with a cohort of patients with potential drivers of persistent atrial fibrillation. In a computational study using a monodomain Maleckar model, we demonstrate that in organized rhythms, electrograms successfully track local activation, whereas in atrial fibrillation, electrograms are sensitive to spiral wave distance and number, spiral tip trajectories, and effects of fibrosis. In a clinical study, we analyzed n = 15 patients with persistent atrial fibrillation that was terminated by limited ablation. In five cases, traditional activation maps revealed a spiral wave at sites of termination; in ten cases, electrogram timings were ambiguous and activation maps showed incomplete reentry. By adjusting electrogram timing through computational modeling, we found rotational activation, which was undetectable with conventional methods. Our results demonstrate that computational modeling can identify non-local deflections to improve activation mapping and explain how and where ablation can terminate persistent atrial fibrillation. Our hybrid computational/physiological approach has the potential to optimize map-guided ablation and improve ablation therapy in atrial fibrillation.

Identification and Characterization of Sites Where Persistent Atrial Fibrillation Is Terminated by Localized Ablation

BACKGROUND

The mechanisms by which persistent atrial fibrillation (AF) terminates via localized ablation are not well understood. To address the hypothesis that sites where localized ablation terminates persistent AF have characteristics identifiable with activation mapping during AF, we systematically examined activation patterns acquired only in cases of unequivocal termination by ablation.

METHODS AND RESULTS

We recruited 57 patients with persistent AF undergoing ablation, in whom localized ablation terminated AF to sinus rhythm or organized tachycardia. For each site, we performed an offline analysis of unprocessed unipolar electrograms collected during AF from multipolar basket catheters using the maximum -dV/dt assignment to construct isochronal activation maps for multiple cycles. Additional computational modeling and phase analysis were used to study mechanisms of map variability. At all sites of AF termination, localized repetitive activation patterns were observed. Partial rotational circuits were observed in 26 of 57 (46%) cases, focal patterns in 19 of 57 (33%), and complete rotational activity in 12 of 57 (21%) cases. In computer simulations, incomplete segments of partial rotations coincided with areas of slow conduction characterized by complex, multicomponent electrograms, and variations in assigning activation times at such sites substantially altered mapped mechanisms.

CONCLUSIONS

Local activation mapping at sites of termination of persistent AF showed repetitive patterns of rotational or focal activity. In computer simulations, complete rotational activation sequence was observed but was sensitive to assignment of activation timing particularly in segments of slow conduction. The observed phenomena of repetitive localized activation and the mechanism by which local ablation terminates putative AF drivers require further investigation.

Spatial relationship of sites for atrial fibrillation drivers and atrial tachycardia in patients with both arrhythmias

INTRODUCTION

Atrial fibrillation (AF) often converts to and from atrial tachycardia (AT), but it is undefined if these rhythms are mechanistically related in such patients. We tested the hypothesis that critical sites for AT may be related to regional AF sources in patients with both rhythms, by mapping their locations and response to ablation on transitions to and from AF.

METHODS

From 219 patients undergoing spatial mapping of AF prior to ablation at 3 centers, we enrolled 26 patients in whom AF converted to AT by ablation (n=19) or spontaneously (n=7; left atrial size 42±6cm, 38% persistent AF). Both atria were mapped in both rhythms by 64-electrode baskets, traditional activation maps and entrainment.

RESULTS

Each patient had a single mapped AT (17 reentrant, 9 focal) and 3.7±1.7 AF sources. The mapped AT spatially overlapped one AF source in 88% (23/26) of patients, in left (15/23) or right (8/23) atria. AF transitioned to AT by 3 mechanisms: (a) ablation anchoring AF rotor to AT (n=13); (b) residual, unablated AF source producing AT (n=6); (c) spontaneous slowing of AF rotor leaving reentrant AT at this site without any ablation (n=7). Electrogram analysis revealed a lower peak-to-peak voltage at overlapping sites (0.36±0.2mV vs 0.49±0.2mV p=0.03).

CONCLUSIONS

Mechanisms responsible for AT and AF may arise in overlapping atrial regions. This mechanistic inter-relationship may reflect structural and/or functional properties in either atrium. Future work should delineate how acceleration of an organized AT may produce AF, and whether such regions can be targeted a priori to prevent AT recurrence post AF ablation.

The continuous challenge of AF ablation: From foci to rotational activity

Pulmonary vein isolation (PVI) is central to ablation approaches for atrial fibrillation (AF), yet many patients still have arrhythmia recurrence after one or more procedures despite the latest technology for PVI. Ablation of rotational or focal sources for AF, which lie outside the pulmonary veins in many patients, is a practical approach that has been shown to improve success by many groups. Localized sources lie in atrial regions shown mechanistically to sustain AF in optical mapping and clinical studies of human AF, as well as computational and animal studies. Because they arise in localized atrial regions, AF sources may explain central paradoxes in clinical practice - such as how limited ablation in patient specific sites can terminate persistent AF yet extensive anatomical ablation at stereotypical locations, which should extinguish disordered waves, does not improve success in clinical trials. Ongoing studies may help to resolve many controversies in the field of rotational sources for AF. Studies now verify rotational activation by multiple mapping approaches in the same patients, at sites where ablation terminates persistent AF. However, these studies also show that certain mapping methods are less effective for detecting AF sources than others. It is also recognized that the success of AF source ablation is technique dependent. This review article provides a mechanistic and clinical rationale to ablate localized sources (rotational and focal), and describes successful techniques for their ablation as well as pitfalls to avoid. We hope that this review will serve as a platform for future improvements in the patient-tailored ablation for complex arrhythmias.

Spatial relationship of organized rotational and focal sources in human atrial fibrillation to autonomic ganglionated plexi

BACKGROUND

One approach to improve ablation for atrial fibrillation (AF) is to focus on physiological targets including focal or rotational sources or ganglionic plexi (GP). However, the spatial relationship between these potential mechanisms has never been studied. We tested the hypothesis that rotors and focal sources for AF may co-localize with ganglionated plexi (GP).

METHODS

We prospectively identified locations of AF rotors and focal sources, and correlated these to GP sites in 97 consecutive patients (age 59.9±11.4, 73% persistent AF). AF was recorded with 64-pole catheters with activation/phase mapping, and related to anatomic GP sites on electroanatomic maps.

RESULTS

AF sources arose in 96/97 (99%) patients for 2.6±1.4 sources per patient (left atrium: 1.7±0.9 right atrium: 1.1±0.8), each with an area of 2-3cm². On area analyses, the probability of an AF source randomly overlapping a GP area was 26%. Left atrial sources were seen in 94 (97%) patients, in whom ≥1 source co-localized with GP in 75 patients (80%; p<0.05). AF sources were more likely to colocalize with left vs right GPs (p<0.05), and colocalization was more likely in patients with higher CHADS2VASc scores (age>65, diabetes; p<0.05).

CONCLUSIONS

This is the first study to demonstrate that clinically detected AF focal and rotational sources in the left atrium often colocalize with regions of autonomic innervation. Studies should define if the role of AF sources differs by their anatomical location.

Mechanistic targets for the ablation of atrial fibrillation

The mechanisms responsible for sustaining atrial fibrillation are a key debate in cardiovascular pathophysiology, and directly influence the approach to therapy including ablation Clinical and basic studies have split AF mechanisms into two basic camps: ‘spatially distributed disorganization’ and ‘localized sources’. Recent data suggest that these mechanisms can also be separated by the method for mapping – with nearly all traditional electrogram analyses showing spatially distributed disorganization and nearly all optical mapping studies showing localized sources We will review this dichotomy in light of these recently identified differences in mapping, and in the context of recent clinical studies in which localized ablation has been shown to impact AF, also lending support to the localized source hypothesis. We will conclude with other concepts on mechanism-based ablation and areas of ongoing research that must be addressed to continue improving our knowledge and treatment of AF.

Electrocardiographic spatial loops indicate organization of atrial fibrillation minutes before ablation-related transitions to atrial tachycardia

BACKGROUND

During ablation for atrial fibrillation (AF), it is challenging to anticipate transitions to organized tachycardia (AT). Defining indices of this transition may help to understand fibrillatory conduction and help track therapy.

OBJECTIVE

To determine the timescale over which atrial fibrillation (AF) organizes en route to atrial tachycardia (AT) using the ECG referenced to intracardiac electrograms.

METHODS

In 17 AF patients at ablation (58.7±9.6years; 53% persistent AF) we analyzed spatial loops of atrial activity on the ECG and intracardiac electrograms over successive timepoints. Loops were tracked at precisely 15, 10, 5, 3 and 1min prior to defined transitions of AF to AT.

RESULTS

Organizational indices reliably quantified changes from AF to AT. Spatiotemporal AF organization on the ECG was identifiable at least 15min before AT was established (p=0.02).

CONCLUSIONS

AF shows anticipatory global organization on the ECG minutes before AT is clinically evident. These results offer a foundation to establish when AF therapy is on an effective path, and for a quantitative classification separating AT from AF.

Ablation of Atrial Fibrillation Drivers

Pulmonary vein isolation (PVI) is central to ablation approaches for atrial fibrillation (AF), yet many patients still have arrhythmia recurrence after one or more procedures, despite evolving technologies for PVI. Ablation of localised AF drivers, which lie outside the pulmonary veins in many patients, is a practical approach that has been shown to improve success by many groups. Such localised drivers lie in atrial regions shown mechanistically to sustain AF in optical mapping and clinical studies of human AF, as well as computational and animal studies. Clinical studies now verify rotational activation by multiple mapping approaches in the same patients, at sites where ablation terminates persistent AF. This review article provides a mechanistic and clinical rationale to ablate localised drivers, and describes successful techniques for their ablation as well as pitfalls to avoid, which may explain discrepancies between results from some centres. We hope that this review will serve as a platform for future improvements in the patient-tailored ablation for complex arrhythmias.

Post-operative atrial fibrillation is associated with a pre-existing structural and electrical substrate in human right atrial myocardium

Background

Post-operative atrial fibrillation (POAF) is a major health economic burden. However, the precise mechanisms in POAF remain unclear. In other forms of AF, sites of high dominant frequency (DF) in sinus rhythm (SR) may harbour ‘AF nests’. We studied AF inducibility in relation to substrate changes using epicardial electrograms and cardiomyocyte calcium handling in the atria of AF naïve patients.

Method

Bipolar electrograms were recorded from the lateral right atrial (RA) wall in 34 patients undergoing coronary surgery using a high-density array in sinus rhythm (NSR). RA burst pacing at 200/500/1000 ms cycle lengths (CL) was performed, recording episodes of AF > 30 s. Co-localised RA tissue was snap frozen for RNA and protein extraction.

Results

Electrograms prolonged during AF (76.64 ± 29.35 ms) vs. NSR/pacing (p < 0.001). Compared to NSR, electrogram amplitude was reduced during AF and during pacing at 200 ms CL (p < 0.001). Electrogram DF was significantly lower in AF (75.87 ± 23.63 Hz) vs. NSR (89.33 ± 25.99 Hz) (p < 0.05), and NSR DF higher in AF inducible patients at the site of AF initiation (p < 0.05). Structurally, POAF atrial myocardium demonstrated reduced sarcolipin gene (p = 0.0080) and protein (p = 0.0242) expression vs. NSR. Phospholamban gene and protein expression was unchanged. SERCA2a protein expression remained unchanged, but MYH6 (p = 0.0297) and SERCA2A (p = 0.0343) gene expression was reduced in POAF.

Conclusions

Human atrial electrograms prolong and reduce in amplitude in induced peri-operative AF vs. NSR or pacing. In those sustaining AF, high DF sites in NSR may indicate ‘AF nests’. This electrical remodelling is accompanied by structural remodelling with altered expression of cardiomyocyte calcium handling detectable before POAF. These novel upstream substrate changes offer a novel mechanism and manifestation of human POAF.

Ablating Atrial Fibrillation: Customizing Lesion Sets Guided by Rotor Mapping

Ablation occupies an increasing role in the contemporary management of atrial fibrillation (AF), but results are suboptimal, particularly for persistent AF. While an anatomic approach to ablation is a highly efficacious and safe method to isolate pulmonary vein (PV) triggers, recurrence of AF is not always associated with PV reconnection, and there is compelling evidence that non-PV sites sustain AF after it is triggered. Recent developments in wide-area mapping and signal processing now identify rotors in the vast majority of AF patients that sustain AF and whose elimination improves long-term freedom from AF in multicenter studies. Investigators have now demonstrated rotor and focal sources for AF that show many analogous properties between approaches: they lie in spatially reproducible regions temporally over hours to days, and they are amenable to targeted ablation. This review outlines the rationale and technical developments supporting this mechanistic paradigm for human AF, and discusses how rotor mapping may be implemented for individual patient customization of lesion sets. Mechanistic studies are required to explain why rotor elimination (or other ablation approaches) producing long-term elimination of AF may not always terminate AF acutely, how AF correlates with structural changes on magnetic resonance imaging, and how these findings can be integrated clinically with current ablation strategies to improve patient outcomes.

Mechanistically based mapping of human cardiac fibrillation

The mechanisms underpinning human cardiac fibrillation remain elusive. In his 1913 paper ‘On dynamic equilibrium in the heart’, Mines proposed that an activation wave front could propagate repeatedly in a circle, initiated by a stimulus in the vulnerable period. While the dynamics of activation and recovery are central to cardiac fibrillation, these physiological data are rarely used in clinical mapping. Fibrillation is a rapid irregular rhythm with spatiotemporal disorder resulting from two fundamental mechanisms – sources in preferred cardiac regions or spatially diffuse self‐sustaining activity, i.e. with no preferred source. On close inspection, however, this debate may also reflect mapping technique. Fibrillation is initiated from triggers by regional dispersion in repolarization, slow conduction and wavebreak, then sustained by non‐uniform interactions of these mechanisms. Notably, optical mapping of action potentials in atrial fibrillation (AF) show spiral wave sources (rotors) in nearly all studies including humans, while most traditional electrogram analyses of AF do not. Techniques may diverge in fibrillation because electrograms summate non‐coherent waves within an undefined field whereas optical maps define waves with a visually defined field. Also fibrillation operates at the limits of activation and recovery, which are well represented by action potentials while fibrillatory electrograms poorly represent repolarization. We conclude by suggesting areas for study that may be used, until such time as optical mapping is clinically feasible, to improve mechanistic understanding and therapy of human cardiac fibrillation.

Mechanisms for the Termination of Atrial Fibrillation by Localized Ablation: Computational and Clinical Studies

BACKGROUND

Human atrial fibrillation (AF) can terminate after ablating localized regions, which supports the existence of localized rotors (spiral waves) or focal drivers. However, it is unclear why ablation near a spiral wave tip would terminate AF and not anchor reentry. We addressed this question by analyzing competing mechanisms for AF termination in numeric simulations, referenced to clinical observations.

METHODS AND RESULTS

Spiral wave reentry was simulated in monodomain 2-dimensional myocyte sheets using clinically realistic rate-dependent values for repolarization and conduction. Heterogeneous models were created by introduction of parameterized variations in tissue excitability. Ablation lesions were applied as nonconducting circular regions. Models confirmed that localized ablation may anchor spiral wave reentry, producing organized tachycardias. Several mechanisms referenced to clinical observations explained termination of AF to sinus rhythm. First, lesions may create an excitable gap vulnerable to invasion by fibrillatory waves. Second, ablation of rotors in regions of low-excitability (from remodeling) produced re-entry in more excitable tissue allowing collision of wavefront and back. Conversely, ablation of rotors in high-excitability regions migrated spiral waves to less excitable tissue, where they detached to collide with nonconducting boundaries. Third, ablation may connect rotors to nonconducting anatomic orifices. Fourth, reentry through slow-conducting channels may terminate if ablation closes these channels.

CONCLUSIONS

Limited ablation can terminate AF by several mechanisms. These data shed light on how clinical AF may be sustained in patients' atria, emphasizing heterogeneities in tissue excitability, slow-conducting channels, and obstacles that are increasingly detectable in patients and should be the focus of future translational studies.