Far-field Potentials Research Articles

Activation patterns and electrophysiologic characteristics of Marshall bundle–related left atrial tachycardias after atrial fibrillation ablation

BackgroundEpicardial Marshall bundles (MBs) are frequently used in left atrial tachycardias (LATs) after atrial fibrillation (AF) ablation with pulmonary vein isolation and substrate modification. ObjectiveThis study sought to classify different activation patterns of MB-mediated LATs and the corresponding electrophysiologic characteristics. MethodsFrom 2019 to 2021, 28 cases of atrial tachycardias after AF ablation were diagnosed as MB-mediated LATs by ultrahigh-density mapping and entrainment. Cannulation and mapping in the vein of Marshall (VOM) and epicardial mapping in the MB region were also performed in selected cases to further prove the mechanism. ResultsThree activation patterns were identified with a critical isthmus through the MB: perimitral macroreentry (perimitral LAT; n = 20 [71.4%]); left atrial appendage–related reentry (n = 5 [17.9%]); and left pulmonary vein–related reentry (n = 3 [10.7%]). In 18 patients, a characteristic triple potential observed along the previously endocardial left atrial ridge block line was composed of near-field double potentials and far-field MB potential. These findings were further delineated in 24 patients with either cannulation in the VOM (19 patients) or epicardial mapping (5 patients). Ethanol infusion of the VOM resulted in atrial tachycardia termination in 20 of 28 patients. ConclusionDifferent types of MB-mediated LATs after AF ablation could be identified by ultrahigh-density mapping. Ethanol infusion within the VOM was effective in eliminating these tachycardias.

Differentiation of high frequency near field versus far-field potentials in low voltage zones during sinus rhythm improves discrimination of local sites of termination during ventricular tachycardia

Abstract Background Ventricular tachycardia (VT) with structural heart disease (SHD) is often bad tolerated or presents with several inducible morphologies, this support mapping the arrhythmic substrate during sinus rhythm (SR). Poor discrimination between near-field (NF) and far-field (FF) electrogram (EGM) components in low voltage (LV) areas is the main limitation. The peak frequency (PF) associated with bipolar EGMs may distinguish NF from FF EGMs (Panel D). Objective To evaluate if PF combined with voltage mapping during SR enhances discrimination of the region of VT termination by radiofrequency application (RFa). Methods Bipolar activation and voltage maps were generated with a 16-pole grid catheter (HD Grid) during SR (Panel B). PF maps were retrospectively computed (Panel C). The maps were only analyzed if acute termination was achieved by focal RFa within a boundary diameter <1.5cm (Panel A). The mapped surface area (SA) was sub-regioned in termination (T-ZONE) and non-termination (NT-ZONE) zones. The T-ZONE surface was centered about the termination site and was allowed to extend to a rectangular kernel >0.5cm and <1.5cm across perpendicular axes, with the NT-ZONE encompassing the remainder mapped SA. Sensitivity (SE) and specificity (SP) of discrimination of the T-ZONE vs. NT-ZONE were measured according to the %SA covered at different LV thresholds (0.1-1.0mV in increments of 0.1mV - Panel F). LV high PF (LVHF) areas at different PF cutoffs from 150Hz (LVHF150) to 300Hz (LVHF300) were also assessed. Results 15 patients with SHD and sustained monomorphic VT were enrolled. 4 had 5 VT’s terminated by 1.4±0.9 focal RF lesions (60-74 y/o, 3 ischemic). All termination sites were located in a LVHF region mapped during SR (Panels B,C,E). The T-ZONE occupied 0.41±0.33cm /92.75±13.31cm global SA and consisted of 15±10 EGM points/1432±337 global points. T-ZONE voltage during SR (0.50±0.32mV) was significantly lower vs. global voltage (2.01±0.69mV, P<0.001), while T-ZONE PF was higher (324±51Hz) vs. global (270±37Hz, P<0.001). ROC discrimination of the T-ZONE yielded AUC’s of 0.79-LV alone, 0.87- LVHF150, 0.91-LVHF200 (Delta +12.2% vs LV alone, Panel F), 0.85-LVHF250 and 0.77-LVHF300. At a 0.7mV cutoff, LVHF200 yielded a balanced SE/SP of 0.89/0.87 vs. LV alone (0.90/0.63). Conclusion Assessment of regions with LVHF during SR improves SP for discrimination of sites of VT termination compared to LV alone.TV near field

Multipolar Electrograms: A New Configuration That Increases the Measurement Accuracy of Intracardiac Signals

BackgroundAccurate measurements of intracardiac electrograms (EGMs) remain a clinical challenge because of the suboptimal attenuation of far-field potentials. Multielectrode mapping catheters provide an opportunity to construct multipolar instead of bipolar EGMs for rejecting common far-field potentials recorded from a multivectorial space. ObjectivesThe purpose of this study was to develop a multipolar EGM and compare its characteristics to those of bipolar EGMs MethodsUsing a 36-electrode array catheter (Optrell-36, Biosense Webster), a far-field component was mathematically constructed from clusters of electrodes surrounding each inspected electrode. This component was subtracted from the unipolar waveform to produce a local unipolar, referred to as a “multipolar EGM.” The performance of multipolar EGMs was evaluated in 7 swine with healed anteroseptal infarction. ResultsMultipolar EGMs proved superior in attenuating far-field potentials in infarct border zones, increasing the near-field to far-field ratio from 0.92 ± 0.2 to 2.25 ± 0.3 (P < 0.001). Removal of far-field components reduced the voltage amplitude (P < 0.001) and enlarged the infarct surface area (P = 0.02), aligning more closely with histological findings. Of 379 EGMs with ≥20 ms activation time difference between bipolar and multipolar EGMs, 95.3% (361 of 379) were accurately annotated using multipolar EGMs, while annotation based on bipolar EGM was predominantly made on far-field components. ConclusionsMultielectrode array catheters provide a unique platform for constructing multipolar EGMs. This new EGM may be beneficial for "purifying" local potentials within a complex electrical field, resulting in more accurate voltage and activation maps.

Somatosensory evoked potentials recorded from DBS electrodes: the origin of subcortical N18.

The different peaks of somatosensory-evoked potentials (SEP) originate from a variety of anatomical sites in the central nervous system. The origin of the median nerve subcortical N18 SEP has been studied under various conditions, but the exact site of its generation is still unclear. While it has been claimed to be located in the thalamic region, other studies indicated its possible origin below the pontomedullary junction. Here, we scrutinized and compared SEP recordings from median nerve stimulation through deep brain stimulation (DBS) electrodes implanted in various subcortical targets. We studied 24 patients with dystonia, Parkinson's disease, and chronic pain who underwent quadripolar electrode implantation for chronic DBS and recorded median nerve SEPs from globus pallidus internus (GPi), subthalamic nucleus (STN), thalamic ventral intermediate nucleus (Vim), and ventral posterolateral nucleus (VPL) and the centromedian-parafascicular complex (CM-Pf). The largest amplitude of the triphasic potential of the N18 complex was recorded in Vim. Bipolar recordings confirmed the origin to be close to Vim electrodes (and VPL/CM-Pf) and less close to STN electrodes. GPi recorded only far-field potentials in unipolar derivation. Recordings from DBS electrodes located in different subcortical areas allow determining the origin of certain subcortical SEP waves more precisely. The subcortical N18 of the median nerve SEP-to its largest extent-is generated ventral to the Vim in the region of the prelemniscal radiation/ zona incerta.

PO-05-092 BIPOLAR ELECTROGRAM PEAK FREQUENCY VALUE DERIVED FROM HIGH-DENSITY ELECTROANATOMIC MAPPING EFFICIENTLY IDENTIFIES THE CRITICAL ISTHMUS IN SCAR-RELATED VENTRICULAR TACHYCARDIA

It is of challenges to differentiate local activities from far-field potentials, especially the multicomponent electrograms of diastolic potentials in scar-related reentrant ventricular tachycardia (VT). The peak frequency (PF) of each electrogram has the potential to discriminate near-field from far-field potentials. The study aimed to identify the VT isthmus by applying PF criteria on VT activation maps. The study consisted of 10 patients with scar-related VT (ischemic/nonischemic cardiomyopathy 6/4). The characteristics of the VT circuits were assessed using high-density multielectrode catheters. VT isthmuses were identified based on activation maps, entrainment, and ablation results. The accuracy of applying PF value over the activation map in detecting VT isthmus was assessed. 12 VT isthmuses were identified. The mean bipolar voltage and PF of the VT isthmuses were 0.26 ± 0.13 mV and 319.3 ± 58.6 Hz respectively. All isthmuses were within areas of bipolar voltage less than 0.5 mV and PF of more than 250 Hz. With the automated -dv/dtmax annotation during VT, the isthmus could be identified in 5 of 12 (41.7%) VT circuits without manual annotation. By automated PF annotation, the VT isthmus could be identified in 9 of 12 (75.0%) VT circuits without the need for manual adjustment. VT isthmus was always located in the electrogram with bipolar LVZ (<0.5 mV) with a PF value over 250Hz during VT. Moreover, the VT isthmus could be more intuitively identified by the automated peak frequency annotation than -dv/dtmax annotation in the current daily practice using high-density 3D electroanatomic mapping system.

PO-05-040 APPLICATION OF ELECTROGRAM PEAK FREQUENCY VALUE FOR IDENTIFICATION OF SCAR-RELATED VENTRICULAR TACHYCARDIA ISTHMUS DURING SINUS RHYTHM

Isolated late activation mappings (ILAMs) can identify possible ventricular tachycardia (VT) isthmus during sinus rhythm (SR). The interference of far-field potentials at the deceleration zone (DZ) may cause misleading results. Electrogram peak frequency (PF) has the potential to discriminate between far-field and near-field signals. We aimed to identify the VT isthmus by applying PF over SR substrate maps. Ten patients with scar-related VT (ischemic/nonischemic cardiomyopathy 6/4) were studied. VT isthmuses were identified based on the activation maps, entrainment, and ablation results during tachycardia. The accuracy of PF maps in detecting potential VT isthmuses during SR before ablation was assessed. Twelve VT isthmuses were identified. The bipolar mean voltage and PF of isthmus areas over the pre-ablation SR map were 0.25 ± 0.12 mV and 307.5 ± 54.3 Hz, respectively. All isthmuses were within low voltage zones (LVZ) with PF of more than 250Hz. Before ablation, 11 of 25 (44.0%) DZs identified from ILAM by annotating the last deflection EGMs in LVZ were compatible with VT isthmuses (mean PF 311.0 ± 66.0Hz); mean PF of DZs which were not isthmus locations was 177.6 ± 51.5 Hz. There were 12 of 15 (80.0%) DZs on ILAMs constructed by annotating PF EGMs compatible with VT isthmuses. VT isthmus is mostly located in LVZ (<0.5 mV) with PF value over 250Hz from pre-ablation SR maps. The DZs during SR with a low PF could be bystanders. Identifying DZs by annotating EGMs with PF, rather than last deflections, is better to discriminate critical VT substrates.

Far-field potential of the compound muscle action potential as a reliable marker in amyotrophic lateral sclerosis.

Reliable neurophysiological markers in amyotrophic lateral sclerosis (ALS) are of great interest. The compound muscle action potential (CMAP) amplitude has been a conventional marker, although it is greatly influenced by the electrode position. We propose the far-field potential of the CMAP (FFP-CMAP) as a new neurophysiological marker in ALS. Patients with ALS and age-matched healthy controls were enrolled. We used a proximal reference (pref) in addition to the conventional distal reference (dref). Routine CMAP was recorded from the belly-dref lead and FFP-CMAP from the dref-pref lead for the ulnar and tibial nerves. Multiple point stimulation motor unit number estimation (MUNE) was also examined in the ulnar nerve. Inter-rater reproducibility was evaluated by two examiners, and some patients were followed up every 3 mo for 1 y. We tested 17 patients with ALS and 10 controls. The amplitudes of routine CMAP and FFP-CMAP in the ulnar and tibial nerves, and hypothenar MUNE value in the ulnar nerve were significantly decreased in ALS compared to controls. Ulnar FFP-CMAP achieved the highest inter-rater intraclass correlation coefficient (ICC) value (0.942) when compared with routine CMAP (0.880) and MUNE (0.839). The tibial FFP-CMAP had a higher ICC value (0.986) than the routine CMAP (0.697). In this way, the FFP-CMAP showed high inter-rater reproducibility because its shape was not much influenced by the electrode position. During 1-y follow-up, decline of CMAP, FFP, and MUNE showed significant correlations with the Amyotrophic Lateral Sclerosis Functional Rating Scale - Revised (ALSFRS-R). The FFP-CMAP shows promise as a reliable marker for ALS.

Magnetoneurography to investigate the mechanisms underlying the P9 far-field potential

ObjectiveThe mechanism underlying the generation of P9 far-field somatosensory evoked potentials (SEPs) is unresolved. Accordingly, we used magnetoneurography to visualize the current distribution in the body at the P9 peak latency and elucidate the origin of P9 generation. MethodsWe studied five healthy male volunteers without neurological abnormalities. We recorded far-field SEPs after median nerve stimulation at the wrist to identify the P9 peak latency. Using magnetoneurography, we recorded the evoked magnetic fields in the whole body under the same stimulus conditions as the SEP recording. We analyzed the reconstructed current distribution at the P9 peak latency. ResultsAt the P9 peak latency, we observed the reconstructed current distribution dividing the thorax into two parts, upper and lower. Anatomically, the depolarization site at the P9 peak latency was distal to the interclavicular space and at the level of the second intercostal space. ConclusionsBy visualizing the current distribution, we proved that P9 peak latency originates in the change in volume conductor size between the upper and lower thorax. SignificanceWe clarified that magnetoneurography analysis is affected by the current distribution due to the junction potential.

Promising application of a new ulnar nerve compound muscle action potential measurement montage in amyotrophic lateral sclerosis: a prospective cross-sectional study.

Previous studies have shown that ulnar nerve compound muscle action potential recorded by the conventional "belly-tendon" montage does not accurately and completely reflect the action potential of the ulnar nerve dominating the abductor digiti minimi muscle due to the effects of far-field potentials of intrinsic hand muscles. A new method of ulnar nerve compound muscle action potential measurement was developed in 2020, which adjusts the E2 electrode from the distal tendon of the abductor digitorum to the middle of the back of the proximal wrist. This new method may reduce the influence of the reference electrode and better reflect the actual ulnar nerve compound muscle action potential. In this prospective cross-sectional study, we included 64 patients with amyotrophic lateral sclerosis and 64 age- and sex-matched controls who underwent conventional and novel ulnar nerve compound muscle action potential measurement between April 2020 and May 2021 in Peking University Third Hospital. The compound muscle action potential waveforms recorded by the new montage were unimodal and more uniform than those recorded by traditional montage. In the controls, no significant difference in the compound muscle action potential waveforms was found between the traditional montage and new montage recordings. In amyotrophic lateral sclerosis patients presenting with abductor digiti minimi spontaneous activity and muscular atrophy, the amplitude of compound muscle action potential-pE2 was significantly lower than that of compound muscle action potential-dE2 (P < 0.01). Using the new method, damaged axons were more likely to exhibit more severe amplitude decreases than those measured with the traditional method, in particular for patients in early stage amyotrophic lateral sclerosis. In addition, the decline in compound muscle action potential amplitude measured by the new method was correlated with a decrease in Revised Amyotrophic Lateral Sclerosis Functional Rating Scale scores. These findings suggest that the new ulnar nerve compound muscle action potential measurement montage reduces the effects of the reference electrode through altering the E2 electrode position, and that this method is more suitable for monitoring disease progression than the traditional montage. This method may be useful as a biomarker for longitudinal follow-up and clinical trials in amyotrophic lateral sclerosis.

Test charge driven response of a dusty plasma with polarization force

By using the framework of kinetic model, the test charge driven response of a dusty plasma is evaluated in the presence of polarization force. The plasma containing electrons, singly ionized positive ions, and highly charged negative dust particulates is known as a dusty plasma, which can be perturbed by a test particle of charge qT moving with velocity vT along the z-axis. The polarization force purely comes from the high charging state of micron-sized dust particles, causing a deformation of shielding length due to density gradient and modifying the collective motion and particulates’ acceleration. The application of Fourier transformation technique to the set of dynamical equations may result in the shielded potential for a test charge with a modified dielectric constant. Several possibilities have been explored to evaluate the shielded potentials by imposing different conditions on the test charge speed in comparison with the thermal speeds of plasma species. It is found that the profiles of wakefield, Debye-Hückel and farfield (FF) potentials are strongly modified by the polarization force coefficient via the dust charging state and dust concentration. The present findings are useful in the study of strongly coupled dusty plasma, where micron-sized negatively charged dust grains are characterized by a high charging state.

WE-147. Clinical utility of far-field potential of CMAP (FFP-CMAP) as a neurophysiological marker in ALS

WE-147. Clinical utility of far-field potential of CMAP (FFP-CMAP) as a neurophysiological marker in ALS

TU-239. Investigation into the generating mechanism of P9 far-field potentials after the median nerve stimulation with Magnetoneurography

TU-239. Investigation into the generating mechanism of P9 far-field potentials after the median nerve stimulation with Magnetoneurography

Effect of radiofrequency and ethanol ablation on epicardial conduction through the vein of Marshall: How to detect and manage epicardial connection across the mitral isthmus.

The vein of Marshall (VOM), which is surrounded by the Marshall bundle (MB), behaves as an epicardial connection bypassing the mitral isthmus. The influence of radiofrequency ablation and VOM ethanol infusion (VOM-EI) on epicardial MB conduction remains unclear. The purpose of this study was to evaluate MB conduction status during mitral isthmus ablation. Of 57 consecutive patients undergoing mitral isthmus ablation, 50 with electrode catheter cannulation into the VOM were analyzed. MB conduction was investigated by evaluating electrograms inside the VOM. Endocardial ablation was initially performed, followed by ablation inside the coronary sinus (CS), if required. Selective VOM-EI was performed if the MB potentials still exhibited early activation after radiofrequency ablation, suggesting the presence of MB connection bridging the mitral isthmus. VOM electrograms composed of near-field MB and far-field left atrial potentials were recorded in all patients. Solely with endocardial ablation, 33 patients (66%) achieved entire mitral isthmus block, and 43 patients (86%) achieved an epicardial MB conduction block. MB potentials exhibited early activation in the remaining 7 (14%), even after requiring CS ablation. VOM-EI then was performed. Elimination of MB potentials was verified by electrode catheter reinsertion after VOM-EI. Mitral isthmus conduction was successfully blocked during VOM-EI in 4 patients and during additional radiofrequency ablation in the remaining 3. All patients finally achieved entire mitral isthmus block. MB is effectively ablated by radiofrequency ablation. Continuous evaluation of MB conduction can reveal epicardial conduction and ablation effect. A residual MB epicardial connection is relatively rare but can be ablated by VOM-EI.

Anatomy-based characteristics of far-field SVC electrograms in right superior pulmonary veins after isolation

Background. Far-field electrograms from superior vena cava (SVC) can be present in right superior pulmonary vein (RSPV) after pulmonary vein (PV) isolation. Objectives. To analyze the characteristics of far-field SVC potentials in RSPV after PV isolation and the local anatomy difference between patients with and without the potentials. Methods. Patients undergoing PV isolation were retrospectively reviewed, contrast-enhanced computed tomography (CT) was performed before procedure for observing the anatomical relationship between RSPV and SVC. The prevalence and characteristics of far-field SVC electrograms were described and compared to far-field left atrial potentials at the nearest point along the linear ablation lesion. The anatomical proximity of RSPV and SVC on a 2-dimensional horizontal CT view was compared between patients with and without far-field SVC potentials. Results. Far-field SVC electrograms were observed in 35/92(38%) patients with an amplitude of 0.24 ± 0.11 mV and a major deflection slope of 0.051 ± 0.036 mV, both significantly higher than far-field left atrial electrograms (p < .001). In patients with far-field SVC electrograms, 83% had connected RSPV-SVC, defined as distance between RSPV and SVC endocardium less than 3 mm at the layer of RSPV ostium roof, while in patients without far-field SVC electrograms, 70% had disconnected RSPV-SVC. Conclusions. Far-field SVC electrograms appeared in RSPV had a prevalence higher than previously reported and a sharper major deflection compared to far-field left atrial electrograms. Connected RSPV-SVC on CT was associated with the presence of far-field SVC electrograms.

Principal component decomposition of acoustic and neural representations of time-varying pitch reveals adaptive efficient coding of speech covariation patterns

Understanding the effects of statistical regularities on speech processing is a central issue in auditory neuroscience. To investigate the effects of distributional covariance on the neural processing of speech features, we introduce and validate a novel approach: decomposition of time-varying signals into patterns of covariation extracted with Principal Component Analysis. We used this decomposition to assay the sensory representation of pitch covariation patterns in native Chinese listeners and non-native learners of Mandarin Chinese tones. Sensory representations were examined using the frequency-following response, a far-field potential that reflects phase-locked activity from neural ensembles along the auditory pathway. We found a more efficient representation of the covariation patterns that accounted for more redundancy in the form of distributional covariance. Notably, long-term language and short-term training experiences enhanced the sensory representation of these covariation patterns.

Far-field electric potentials provide access to the output from the spinal cord from wrist-mounted sensors

Objective. Neural interfaces need to become more unobtrusive and socially acceptable to appeal to general consumers outside rehabilitation settings. Approach. We developed a non-invasive neural interface that provides access to spinal motor neuron activities from the wrist, which is the preferred location for a wearable. The interface decodes far-field potentials present at the tendon endings of the forearm muscles using blind source separation. First, we evaluated the reliability of the interface to detect motor neuron firings based on far-field potentials, and thereafter we used the decoded motor neuron activity for the prediction of finger contractions in offline and real-time conditions. Main results. The results showed that motor neuron activity decoded from the far-field potentials at the wrist accurately predicted individual and combined finger commands and therefore allowed for highly accurate real-time task classification. Significance. These findings demonstrate the feasibility of a non-invasive, neural interface at the wrist for precise real-time control based on the output of the spinal cord.

Linear increase in the number of non-pulmonary vein triggers from paroxysmal to persistent and long-standing persistent AF in patients undergoing repeat procedure after successful isolation of pulmona

Abstract Introduction This study evaluated the prevalent triggers responsible for recurrence following successful PVI in different types of atrial fibrillation (AF). Methods Consecutive AF patients undergoing repeat catheter ablation with permanently isolated PV were included in the analysis. High-dose isoproterenol challenge (20- 30μg/min for 15–20min) was used to confirm PV reconnection and identify non-PV triggers. Circular mapping catheter (CMC) was used to map the site of origin of significant ectopic activity by comparing the activation sequence of the sinus beat with that of the ectopic beat. For the coronary sinus (CS), ablation catheter was positioned at the level of the mitral valve annulus, parallel to the one positioned in the CS. Left atrial appendage (LAA) firing was detected by placing the CMC in the left superior PV and thus recording far-field potentials from the LAA. Results This prospective study included 1850 AF patients undergoing repeat AF ablation (Table 1), of which 573 (31%) had received one and the remaining 1277 patients had received 2 earlier ablations. Permanent PVI was confirmed with isoproterenol challenge. Table 1 shows the distribution of non-PV triggers. A linear increase in the number of non-PV triggers was observed from PAF to PerAF to LSPAF. Significantly higher number of LSPAF patients had detectable non-PV triggers compared to PerAF and PAF cases. Conclusion We observed a linear increase in the number of non-PV triggers in PAF to PerAF and LSPAF patients experiencing recurrence with successful isolation of PVs. As non-PV triggers are often not targeted by operators, this could be the underlying mechanism for more frequent recurrences in non-paroxysmal AF. Funding Acknowledgement Type of funding sources: None. Table 1

Electrophysiological Responses in the Human S3 Nerve During Sacral Neuromodulation for Fecal Incontinence.

Intra-operative electrode placement for sacral neuromodulation (SNM) relies on visual observation of motor contractions alone, lacking complete information on neural activation from stimulation. This study aimed to determine whether electrophysiological responses can be recorded directly from the S3 sacral nerve during therapeutic SNM in patients with fecal incontinence, and to characterize such responses in order to better understand the mechanism of action (MOA) and whether stimulation is subject to changes in posture. Eleven patients undergoing SNM were prospectively recruited. A bespoke stimulating and recording system was connected (both intraoperatively and postoperatively) to externalized SNM leads, and electrophysiological responses to monopolar current sweeps on each electrode were recorded and analyzed. The nature and thresholds of muscle contractions (intraoperatively) and patient-reported stimulation perception were recorded. We identified both neural responses (evoked compound action potentials) as well as myoelectric responses (far-field potentials from muscle activation). We identified large myelinated fibers (conduction velocity: 36–60 m/s) in 5/11 patients, correlating with patient-reported stimulation perception, and smaller myelinated fibers (conduction velocity <15 m/s) in 4/11 patients (not associated with any sensation). Myoelectric responses (observed in 7/11 patients) were attributed to pelvic floor and/or anal sphincter contraction. Responses varied with changes in posture. We present the first direct electrophysiological responses recorded from the S3 nerve during ongoing SNM in humans, showing both neural and myoelectric responses. These recordings highlight heterogeneity of neural and myoelectric responses (relevant to understanding MOA of SNM) and confirm that electrode lead position can change with posture.

Significance of electrical activity in the right superior pulmonary vein post-isolation and relationship to superior vena cava potentials.

After antral pulmonary vein isolation (PVI), electrical potentials may persist deep in the right superior pulmonary vein (RSPV). Whether these potentials signify true pulmonary vein potential (PVP) (implying inadequate RSPV isolation) or are far-field potentials (FFP) from the superior vena cava (SVC) is unclear. Here, we attempt to assess the incidence of persistent potentials in RSPV post-isolation and methods to differentiate PVP from FFP. Following PVI, we mapped the RSPV and the SVC with simultaneously placed catheters. We recorded the incidence of SVC potentials, RSPV potentials, and distance between the 2 structures. When RSPV potentials were present, we assessed (1) relationship to SVC potentials, (2) RSPV-SVC distance, and (3) responses on pacing from either site. Among 43 consecutive post-PVI patients, 39 (91%) patients had SVC electrical activity but only 10 had persistent RSPV potentials. Of these, 2/10 had true PVP, and 8 were FFP from SVC. Bipolar electrogram morphology did not differentiate PVP from FFP, but low-amplitude (5mA) SVC pacing was an effective maneuver. However, high-amplitude (≥ 10mA) pacing from SVC and/or RSPV could result in far-field capture of the other site even when RSPV was devoid of electrical activity. Average RSPV-SVC distance was 15.9mm. Persistent RSPV potentials occur rarely post-PVI despite the close proximity to electrically active SVC. When present, true PVP can be differentiated from FFP by low-amplitude pacing from SVC. Bipolar EGM morphology and high-amplitude pacing are unreliable at differentiating these potentials.

Novel Clue to Locate Conduction Gaps in the Pulmonary Vein Isolation Ablation Line.

Background: Several methods have been reported for locating the conduction gap (CG) in the pulmonary vein isolation (PVI) ablation line. However, the value of the interval between far-field atrial potential (FFP) and pulmonary vein potential (PVP) remains unknown.Methods: Consecutive patients with a CG during observation on the table after PVI were included. The PVP, FFP, and the CG location were evaluated to develop a novel algorithm to identify the CG location in the left superior pulmonary vein. The performance of this novel algorithm was prospectively tested in a validation cohort of consecutive patients undergoing repeat PVI ablation.Results: A total of 116 patients with atrial fibrillation (AF) were recruited, 56 of whom formed the validation cohort. The interval between FFP and PVP of the left superior pulmonary vein was associated with the CG location, and an interval <5 ms predicted the presence of CG in the upper portion of the ostium with a sensitivity of 92.9% and a specificity of 96.9%. In the prospective evaluation, the interval was able to correctly predict the site of CG in 89.6% of cases.Conclusions: The interval between FFP and PVP is a novel and accurate index that can be used to predict the CG location in the left superior pulmonary vein. An far-field atrial potential and pulmonary vein potential (FFP–PVP) interval value of ≥5 ms could be used to exclude a CG in the upper portion of the ostium in the majority of patients undergoing AF ablation.