106 results found
Chowdhury RA, Tzortzis KN, Dupont E, et al., 2018, Concurrent micro- to macro-cardiac electrophysiology in myocyte cultures and human heart slices, Scientific Reports, Vol: 8, ISSN: 2045-2322
The contact cardiac electrogram is derived from the extracellular manifestation of cellular action potentials and cell-to-cell communication. It is used to guide catheter based clinical procedures. Theoretically, the contact electrogram and the cellular action potential are directly related, and should change in conjunction with each other during arrhythmogenesis, however there is currently no methodology by which to concurrently record both electrograms and action potentials in the same preparation for direct validation of their relationships and their direct mechanistic links. We report a novel dual modality apparatus for concurrent electrogram and cellular action potential recording at a single cell level within multicellular preparations. We further demonstrate the capabilities of this system to validate the direct link between these two modalities of voltage recordings.
Houston C, Ng FS, Dupont E, 2018, Letter by Houston et al regarding article, "Localized Optogenetic Targeting of Rotors in Atrial Cardiomyocyte Monolayers", Circulation: Arrhythmia and Electrophysiology, Vol: 11, Pages: e006118-e006118, ISSN: 1941-3084
Luther V, Qureshi N, Lim PB, et al., 2018, Isthmus sites identified by Ripple Mapping are usually anatomically stable: A novel method to guide atrial substrate ablation?, Journal of Cardiovascular Electrophysiology, Vol: 29, Pages: 404-411, ISSN: 1045-3873
BACKGROUND: Postablation reentrant ATs depend upon conducting isthmuses bordered by scar. Bipolar voltage maps highlight scar as sites of low voltage, but the voltage amplitude of an electrogram depends upon the myocardial activation sequence. Furthermore, a voltage threshold that defines atrial scar is unknown. We used Ripple Mapping (RM) to test whether these isthmuses were anatomically fixed between different activation vectors and atrial rates. METHODS: We studied post-AF ablation ATs where >1 rhythm was mapped. Multipolar catheters were used with CARTO Confidense for high-density mapping. RM visualized the pattern of activation, and the voltage threshold below which no activation was seen. Isthmuses were characterized at this threshold between maps for each patient. RESULTS: Ten patients were studied (Map 1 was AT1; Map 2: sinus 1/10, LA paced 2/10, AT2 with reverse CS activation 3/10; AT2 CL difference 50 ± 30 ms). Point density was similar between maps (Map 1: 2,589 ± 1,330; Map 2: 2,214 ± 1,384; P = 0.31). RM activation threshold was 0.16 ± 0.08 mV. Thirty-one isthmuses were identified in Map 1 (median 3 per map; width 27 ± 15 mm; 7 anterior; 6 roof; 8 mitral; 9 septal; 1 posterior). Importantly, 7 of 31 (23%) isthmuses were unexpectedly identified within regions without prior ablation. AT1 was treated following ablation of 11/31 (35%) isthmuses. Of the remaining 20 isthmuses, 14 of 16 isthmuses (88%) were consistent between the two maps (four were inadequately mapped). Wavefront collision caused variation in low voltage distribution in 2 of 16 (12%). CONCLUSIONS: The distribution of isthmuses and nonconducting tissue within the ablated left atrium, as defined by RM, appear concordant between rhythms. This could guide a substrate ablative approach.
Leong KMW, chow J-J, Ng FS, et al., 2017, Comparison of the Prognostic Usefulness of the European Society of Cardiology and American Heart Association/American College of Cardiology Foundation Risk Stratification Systems for Patients With Hypertrophic Cardiomyopathy, American Journal of Cardiology, Vol: 121, Pages: 349-355, ISSN: 0002-9149
Implantable cardio-defibrillators (ICDs) have proven benefit in preventing sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HC), making risk stratification essential. Data on the predictive accuracy on the European Society of Cardiology (ESC) risk scoring system has been conflicting. We independently evaluated the ESC risk scoring system in our cohort of HC patients from a large tertiary centre and compared this to previous guidance by the American College of Cardiology Foundation and Heart Association (ACCF/AHA). Risk factor profiles, 5-year SCD risk estimates and ICD recommendations as defined by the ACCF/AHA and ESC guidelines, were retrospectively ascertained for 288 HC patients with and without SCD or equivalent events at our centre. In the SCD group (n=14), a significantly higher proportion of patients would not have met the criteria for an ICD implant using the ESC scoring algorithm than ACCF/AHA guidance (43%vs7%, p=0.029). In those without SCD events (n=274), a larger proportion of individuals not requiring an ICD was identified using the ESC risk score model compared to the ACCF/AHA model (82%vs57%; p<0.0001). Based on risk stratification criteria alone, 5 more individuals with a previously aborted SCD event would not have received an ICD with the ESC risk model than the ACCF/AHA risk model. In conclusion, we found that the current ESC scoring system potentially leaves more high-risk patients unprotected from sudden death in our cohort of patients.
Leong KMW, Ng FS, Roney C, et al., 2017, Repolarization abnormalities unmasked with exercise in sudden cardiac death survivors with structurally normal hearts, Journal of Cardiovascular Electrophysiology, Vol: 29, Pages: 115-126, ISSN: 1045-3873
BACKGROUND: Models of cardiac arrhythmogenesis predict that non-uniformity in repolarization and/or depolarization promotes ventricular fibrillation and is modulated by autonomic tone, but this is difficult to evaluate in patients. We hypothesize that such spatial heterogeneities would be detected by non-invasive ECG imaging (ECGi) in sudden cardiac death (SCD) survivors with structurally normal hearts under physiological stress. METHODS: ECGi was applied to 11 SCD survivors, 10 low-risk Brugada Syndrome patients (BrS) and 10 controls undergoing exercise treadmill testing. ECGi provides whole heart activation maps and > 1200 unipolar electrograms over the ventricular surface from which global dispersion of activation recovery interval (ARI) and regional delay in conduction were determined. These were used as surrogates for spatial heterogeneities in repolarization and depolarization. Surface ECG markers of dispersion (QT and Tpeak-end intervals) were also calculated for all patients for comparison. RESULTS: Following exertion, the SCD group demonstrated the largest increase in ARI dispersion compared to BrS and control groups (13±8 ms vs 4±7 ms vs 4±5 ms; p = 0.009), with baseline dispersion being similar in all groups. In comparison, surface ECG markers of dispersion of repolarisation were unable to discriminate between the groups at baseline or following exertion. Spatial heterogeneities in conduction were also present following exercise but were not significantly different between SCD survivors and the other groups. CONCLUSION: Increased dispersion of repolarization is apparent during physiological stress in SCD survivors and is detectable with ECGi but not with standard ECG parameters. The electrophysiological substrate revealed by ECGi could be the basis of alternative risk-stratification techniques. This article is protected by copyright. All rights reserved.
Leong KMW, Ng FS, yao C, et al., 2017, ST-Elevation Magnitude Correlates With Right Ventricular Outflow Tract Conduction Delay in Type I Brugada ECG, Circulation: Arrhythmia and Electrophysiology, Vol: 10, ISSN: 1941-3084
Background: The substrate location and underlying electrophysiological mechanisms that contribute to the characteristic ECG pattern of Brugada syndrome (BrS) are still debated. Using noninvasive electrocardiographical imaging, we studied whole heart conduction and repolarization patterns during ajmaline challenge in BrS individuals.Methods and Results: A total of 13 participants (mean age, 44±12 years; 8 men), 11 concealed patients with type I BrS and 2 healthy controls, underwent an ajmaline infusion with electrocardiographical imaging and ECG recordings. Electrocardiographical imaging activation recovery intervals and activation timings across the right ventricle (RV) body, outflow tract (RVOT), and left ventricle were calculated and analyzed at baseline and when type I BrS pattern manifested after ajmaline infusion. Peak J-ST point elevation was calculated from the surface ECG and compared with the electrocardiographical imaging–derived parameters at the same time point. After ajmaline infusion, the RVOT had the greatest increase in conduction delay (5.4±2.8 versus 2.0±2.8 versus 1.1±1.6 ms; P=0.007) and activation recovery intervals prolongation (69±32 versus 39±29 versus 21±12 ms; P=0.0005) compared with RV or left ventricle. In controls, there was minimal change in J-ST point elevation, conduction delay, or activation recovery intervals at all sites with ajmaline. In patients with BrS, conduction delay in RVOT, but not RV or left ventricle, correlated to the degree of J-ST point elevation (Pearson R, 0.81; P<0.001). No correlation was found between J-ST point elevation and activation recovery intervals prolongation in the RVOT, RV, or left ventricle.Conclusions: Magnitude of ST (J point) elevation in the type I BrS pattern is attributed to degree of conduction delay in the RVOT and not prolongation in repolarization time.
Mirza KB, Zuliani C, Hou B, et al., 2017, Injection moulded microneedle sensor for real-time wireless pH monitoring, 39th Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society (EMBC), Publisher: IEEE, Pages: 189-192, ISSN: 1094-687X
This paper describes the development of an array of individually addressable pH sensitive microneedles using injection moulding and their integration within a portable device for real-time wireless recording of pH distributions in biological samples. The fabricated microneedles are subjected to gold patterning followed by electrodeposition of iridium oxide to sensitize them to 0.07 units of pH change. Miniaturised electronics suitable for the sensors readout, analog-to-digital conversion and wireless transmission of the potentiometric data are embodied within the device, enabling it to measure real-time pH of soft biological samples such as muscles. In this paper, real-time recording of the cardiac pH distribution, during ischemia followed by reperfusion cycles in cardiac muscles of male Wistar rats has been demonstrated by using the microneedle array.
Leong KMW, Ng FS, Patil S, et al., 2017, An electrocardiogram opinion from an National Health Service walk-in centre, Emergency Medicine Journal, Vol: 34, Pages: 631-632, ISSN: 1472-0205
Roney CH, Cantwell CD, Bayer JD, et al., 2017, Spatial resolution requirements for accurate identification of drivers of atrial fibrillation, Circulation-Arrhythmia and Electrophysiology, Vol: 10, ISSN: 1941-3084
Background—Recent studies have demonstrated conflicting mechanisms underlying atrial fibrillation (AF), with the spatial resolution of data often cited as a potential reason for the disagreement. The purpose of this study was to investigate whether the variation in spatial resolution of mapping may lead to misinterpretation of the underlying mechanism in persistent AF.Methods and Results—Simulations of rotors and focal sources were performed to estimate the minimum number of recording points required to correctly identify the underlying AF mechanism. The effects of different data types (action potentials and unipolar or bipolar electrograms) and rotor stability on resolution requirements were investigated. We also determined the ability of clinically used endocardial catheters to identify AF mechanisms using clinically recorded and simulated data. The spatial resolution required for correct identification of rotors and focal sources is a linear function of spatial wavelength (the distance between wavefronts) of the arrhythmia. Rotor localization errors are larger for electrogram data than for action potential data. Stationary rotors are more reliably identified compared with meandering trajectories, for any given spatial resolution. All clinical high-resolution multipolar catheters are of sufficient resolution to accurately detect and track rotors when placed over the rotor core although the low-resolution basket catheter is prone to false detections and may incorrectly identify rotors that are not present.Conclusions—The spatial resolution of AF data can significantly affect the interpretation of the underlying AF mechanism. Therefore, the interpretation of human AF data must be taken in the context of the spatial resolution of the recordings.
Luther V, Sikkel M, Bennett N, et al., 2017, Visualizing Localized Reentry With Ultra-High Density Mapping in Iatrogenic Atrial Tachycardia Beware Pseudo-Reentry, CIRCULATION-ARRHYTHMIA AND ELECTROPHYSIOLOGY, Vol: 10, ISSN: 1941-3149
Background—The activation pattern of localized reentry (LR) in atrial tachycardia remains incompletely understood. We used the ultra–high density Rhythmia mapping system to study activation patterns in LR.Methods and Results—LR was suggested by small rotatory activations (carousels) containing the full spectrum of the color-coded map. Twenty-three left-sided atrial tachycardias were mapped in 15 patients (age: 64±11 years). 16 253±9192 points were displayed per map, collected over 26±14 minutes. A total of 50 carousels were identified (median 2; quartiles 1–3 per map), although this represented LR in only n=7 out of 50 (14%): here, rotation occurred around a small area of scar (<0.03 mV; 12±6 mm diameter). In LR, electrograms along the carousel encompassed the full tachycardia cycle length, and surrounding activation moved away from the carousel in all directions. Ablating fractionated electrograms (117±18 ms; 44±13% of tachycardia cycle length) within the carousel interrupted the tachycardia in every LR case. All remaining carousels were pseudo-reentrant (n=43/50 [86%]) occurring in areas of wavefront collision (n=21; median 0.5; quartiles 0–2 per map) or as artifact because of annotation of noise or interpolation in areas of incomplete mapping (n=22; median 1, quartiles 0–2 per map). Pseudo-reentrant carousels were incorrectly ablated in 5 cases having been misinterpreted as LR.Conclusions—The activation pattern of LR is of small stable rotational activations (carousels), and this drove 30% (7/23) of our postablation atrial tachycardias. However, this appearance is most often pseudo-reentrant and must be differentiated by interpretation of electrograms in the candidate circuit and activation in the wider surrounding region.
Ng FS, Guerrero F, Luther V, et al., 2017, Microreentrant left atrial tachycardia circuit mapped with an ultra-high-density mapping system, HeartRhythm Case Reports, Vol: 3, Pages: 224-228, ISSN: 2214-0271
Micro-reentrant tachycardias are well described and are thought to be responsible for a small proportion of atrial tachycardias post-atrial fibrillation ablation. However, due to the small size of these re-entrant circuits and the poor spatial resolution of conventional mapping tools, they have not previously been mapped accurately in vivo in humans, and have therefore been difficult to distinguish from non-reentrant focal tachycardias. The newly-developed Rhythmia electroanatomical mapping system allows for the rapid creation of activation maps of ultra-high resolution. In this case report, we provide the first images of a micro-reentrant atrial tachycardia circuit in a post-atrial fibrillation setting, mapped with the high resolution Rhythmia mapping system.
Sikkel MB, Luther V, Sau A, et al., 2017, High-Density Electroanatomical Mapping to Identify Point of Epicardial to Endocardial Breakthrough in Perimitral Flutter, JACC: Clinical Electrophysiology, Vol: 3, Pages: 637-639, ISSN: 2405-500X
Rajkumar CA, Qureshi N, Ng F, et al., 2017, Adenosine induced ventricular fibrillation in a structurally normal heart: a case report, Journal of Medical Case Reports, Vol: 11, ISSN: 1752-1947
BackgroundAdenosine is the first-line pharmacotherapy for termination of supraventricular tachycardia through its action on the atrioventricular node. However, pro-arrhythmic effects of adenosine are also recognised, most notably in the presence of pre-excited atrial fibrillation. In this case report, we describe the induction of ventricular fibrillation in a patient with no demonstrable accessory pathway, nor any other structural heart disease. This rare, idiosyncratic reaction has never previously been reported and is of relevance given the widespread and routine use of adenosine in clinical practice.Case presentationA 26-year-old woman of Cypriot origin presented to our emergency department with a sudden onset of palpitations and chest discomfort. She was healthy, with no previous medical history and no regular medications. An electrocardiogram demonstrated a narrow complex tachycardia with a rate of 194 beats per minute. Following failure of vagal maneuvers to terminate the tachycardia, the assessing physician administered a single intravenous dose of 6 mg adenosine. Our patient instantaneously developed coarse ventricular fibrillation and circulatory collapse. Cardiopulmonary resuscitation was initiated and our patient was rapidly defibrillated to sinus rhythm with a single 150 J direct current shock. A 900-mg loading dose of intravenous amiodarone was commenced and our patient was managed in the cardiac high dependency unit. No further arrhythmias were identified on continuous cardiac monitoring.On review, her presenting electrocardiogram had demonstrated rapidly conducted atrial fibrillation with no evidence of ventricular pre-excitation. Concordantly, her resting electrocardiogram was not suggestive of any accessory pathway. This was conclusively excluded on invasive electrophysiology study, with negative programmed ventricular stimulation up to three extrastimuli. Extensive laboratory investigations were unremarkable and failed to identify an underlying cau
Roney CH, Cantwell CD, Qureshi NA, et al., 2016, Rotor tracking using phase of electrograms recorded during atrial fibrillation, Annals of Biomedical Engineering, Vol: 45, Pages: 910-923, ISSN: 1573-9686
Extracellular electrograms recorded during atrial fibrillation (AF) are challenging to interpret due to the inherent beat-to-beat variability in amplitude and duration. Phase mapping represents these voltage signals in terms of relative position within the cycle, and has been widely applied to action potential and unipolar electrogram data of myocardial fibrillation. To date, however, it has not been applied to bipolar recordings, which are commonly acquired clinically. The purpose of this study is to present a novel algorithm for calculating phase from both unipolar and bipolar electrograms recorded during AF. A sequence of signal filters and processing steps are used to calculate phase from simulated, experimental, and clinical, unipolar and bipolar electrograms. The algorithm is validated against action potential phase using simulated data (trajectory centre error <0.8 mm); between experimental multi-electrode array unipolar and bipolar phase; and for wavefront identification in clinical atrial tachycardia. For clinical AF, similar rotational content (R (2) = 0.79) and propagation maps (median correlation 0.73) were measured using either unipolar or bipolar recordings. The algorithm is robust, uses standard signal processing techniques, and accurately quantifies AF wavefronts and sources. Identifying critical sources, such as rotors, in AF, may allow for more accurate targeting of ablation therapy and improved patient outcomes.
Ng FS, Efimov IR, 2016, Letter by Ng and Efimov regarding article, "Electrophysiological effects of selective atrial coronary artery occlusion in humans"., Circulation, Vol: 134, Pages: e397-e398, ISSN: 0009-7322
Ng FS, Rashid M, Lim E, et al., 2016, Mapping signatures of ventricular ectopy of endocavitary origin, JACC: Clinical Electrophysiology, Vol: 3, Pages: 186-188, ISSN: 2405-5018
A 53-year-old man with very frequent ventricular ectopic activity (39.4% burden) and a structurally normal heart was admitted for percutaneous ablation. Electrocardiography showed a bigeminal unifocal ventricular ectopic pattern, with a right bundle branch block configuration and superior axis, indicating likely origin at the inferior left ventricle.During mapping at the inferior left ventricle, multiple sites with good morphological match to the ectopic beats during pace mapping, and with early local electrograms relative to the QRS complex, were identified. Despite this, the proximal electrograms at these sites consistently preceded the distal bipolar electrograms (Figure 1A) with the mapping catheter oriented perpendicularly to the inferior left ventricular wall (Figures 1B and 1C). Figure 1D shows the good pace matches obtained from these sites. The locations of these sites were roughly in a circle (Figure 1B), presumed to represent sites encircling the posteromedial papillary muscle, with the origin of the ectopic activity at the mid–papillary muscle, which would account for the consistent finding of proximal electrograms preceding distal electrograms at the surrounding sites.
Leong KMW, Chow J-J, Ng FS, et al., 2016, Risk Stratification in Hypertrophic Cardiomyopathy: Evaluation of the European Society of Cardiology Sudden Cardiac Death Risk Scoring System, Annual Conference of the British Cardiovascular Society (BCS) on Prediction and Prevention, Publisher: BMJ Publishing Group, Pages: A104-A105, ISSN: 1355-6037
Leong KMW, Ng FS, Yao C, et al., 2016, Contribution of Conduction and Repolarisation Abnormalities to the Type I Brugada Pattern: A Study Using Non-Invasive Electrocardiographic Imaging, Annual Conference of the British Cardiovascular Society (BCS) on Prediction and Prevention, Publisher: BMJ Publishing Group, Pages: A105-A106, ISSN: 1468-201X
Luther V, Linton NW, Jamil-Copley S, et al., 2016, A prospective study of ripple mapping the post-infarct ventricular scar to guide substrate ablation for ventricular tachycardia, Circulation-Arrhythmia and Electrophysiology, Vol: 9, ISSN: 1941-3084
BACKGROUND: Post-infarct ventricular tachycardia is associated with channels of surviving myocardium within scar characterized by fractionated and low-amplitude signals usually occurring late during sinus rhythm. Conventional automated algorithms for 3-dimensional electro-anatomic mapping cannot differentiate the delayed local signal of conduction within the scar from the initial far-field signal generated by surrounding healthy tissue. Ripple mapping displays every deflection of an electrogram, thereby providing fully informative activation sequences. We prospectively used CARTO-based ripple maps to identify conducting channels as a target for ablation. METHODS AND RESULTS: High-density bipolar left ventricular endocardial electrograms were collected using CARTO3v4 in sinus rhythm or ventricular pacing and reviewed for ripple mapping conducting channel identification. Fifteen consecutive patients (median age 68 years, left ventricular ejection fraction 30%) were studied (6 month preprocedural implantable cardioverter defibrillator therapies: median 19 ATP events [Q1-Q3=4-93] and 1 shock [Q1-Q3=0-3]). Scar (<1.5 mV) occupied a median 29% of the total surface area (median 540 points collected within scar). A median of 2 ripple mapping conducting channels were seen within each scar (length 60 mm; initial component 0.44 mV; delayed component 0.20 mV; conduction 55 cm/s). Ablation was performed along all identified ripple mapping conducting channels (median 18 lesions) and any presumed interconnected late-activating sites (median 6 lesions; Q1-Q3=2-12). The diastolic isthmus in ventricular tachycardia was mapped in 3 patients and colocated within the ripple mapping conducting channels identified. Ventricular tachycardia was noninducible in 85% of patients post ablation, and 71% remain free of ventricular tachycardia recurrence at 6-month median follow-up. CONCLUSIONS: Ripple mapping can be used to identify conduction channels within scar to guide functional substrate
Ng FS, Ariff B, Punjabi PP, et al., 2016, Pyopneumopericardium Secondary to Pericardioesophageal Fistula After Radiofrequency Ablation of Atrial Fibrillation, JACC: Clinical Electrophysiology, Vol: 2, Pages: 397-399, ISSN: 2405-500X
Ng FS, Kalindjian JM, Cooper SA, et al., 2016, Enhancement of Gap Junction Function During Acute Myocardial Infarction Modifies Healing and Reduces Late Ventricular Arrhythmia Susceptibility, JACC. Clinical electrophysiology, Vol: 2, Pages: 574-582, ISSN: 2405-5018
Objectives: To investigate the effects of enhancing gap junction (GJ) coupling during acute myocardial infarction (MI) on the healed infarct scar morphology and late post-MI arrhythmia susceptibility. Background: Increased heterogeneity of myocardial scarring after MI is associated with greater arrhythmia susceptibility. We hypothesized that short-term enhancement of GJ coupling during acute MI can produce more homogeneous infarct scars, reducing late susceptibility to post-MI arrhythmias. Methods: Following arrhythmic characterisation of the rat 4-week post-MI model (n=24), a further 27 Sprague-Dawley rats were randomised to receive rotigaptide to enhance GJ coupling (n=13) or saline control (n=14) by osmotic minipump immediately prior to, and for the first 7 days following surgical MI. At 4 weeks post-MI, hearts were explanted for ex vivo programmed electrical stimulation (PES) and optical mapping. Heterogeneity of infarct border zone (IBZ) scarring was quantified by histomorphometry. Results: Despite no detectable difference in infarct size at 4 weeks post-MI, rotigaptide-treated hearts had reduced arrhythmia susceptibility during PES (Inducibility score: rotigaptide 2.40.8, control 5.00.6, p=0.02) and less heterogeneous IBZ scarring (standard deviation of IBZ Complexity Score: rotigaptide 1.10.1, control 1.40.1, p=0.04), associated with an improvement in IBZ conduction velocity (rotigaptide 43.13.4 cm/s, control 34.82.0 cm/s, p=0.04). Conclusions: Enhancement of GJ coupling for only 7 days at the time of acute MI produced more homogeneous IBZ scarring and reduced arrhythmia susceptibility at 4 weeks post-MI. Short-term GJ modulation at the time of MI may represent a novel treatment strategy to modify the healed infarct scar morphology and reduce late post-MI arrhythmic risk.
Zuliani C, Ng FS, Alenda A, et al., 2016, An array of individually addressable micro-needles for mapping pH distributions, Analyst, Vol: 141, Pages: 4659-4666, ISSN: 1364-5528
This work describes the preparation of an array of individually addressable pH sensitive microneedles which are sensitized by electrodepositing iridium oxide. The impact of the deposition potential, storage conditions and interferents on the sensor characteristics such as slope, offset, intra- and inter-batch reproducibility is investigated. The device may be a useful tool for carrying out direct pH measurements of soft and heterogeneous samples such as tissues and organs. For example, we demonstrated that the microneedle array can be employed for real-time mapping of the cardiac pH distribution during cycles of global ischemia and reperfusion.
Luther V, Linton NW, Koa-Wing M, et al., 2016, A Prospective Study of Ripple Mapping in Atrial Tachycardias: A Novel Approach to Interpreting Activation in Low-Voltage Areas., Circulation: Arrhythmia and Electrophysiology, Vol: 9, ISSN: 1941-3149
BACKGROUND: Post ablation atrial tachycardias are characterized by low-voltage signals that challenge current mapping methods. Ripple mapping (RM) displays every electrogram deflection as a bar moving from the cardiac surface, resulting in the impression of propagating wavefronts when a series of bars move consecutively. RM displays fractionated signals in their entirety thereby helping to identify propagating activation in low-voltage areas from nonconducting tissue. We prospectively used RM to study tachycardia activation in the previously ablated left atrium. METHODS AND RESULTS: Patients referred for atrial tachycardia ablation underwent dense electroanatomic point collection using CARTO3v4. RM was played over a bipolar voltage map and used to determine the voltage "activation threshold" that differentiated functional low voltage from nonconducting areas for each map. Ablation was guided by RM, but operators could perform entrainment or review the isochronal activation map for diagnostic uncertainty. Twenty patients were studied. Median RM determined activation threshold was 0.3 mV (0.19-0.33), with nonconducting tissue covering 33±9% of the mapped surface. All tachycardias crossed an isthmus (median, 0.52 mV, 13 mm) bordered by nonconducting tissue (70%) or had a breakout source (median, 0.35 mV) moving away from nonconducting tissue (30%). In reentrant circuits (14/20) the path length was measured (87-202 mm), with 9 of 14 also supporting a bystander circuit (path lengths, 147-234 mm). In breakout tachycardias, splitting of wavefronts resulted in 2 to 4 incomplete circuits. RM-guided ablation interrupted the tachycardia in 19 of 20 cases with the first ablation set. CONCLUSIONS: RM helps to define activation through low-voltage regions and aids ablation of atrial tachycardias.
Kim M-Y, Ng FS, Ariff B, et al., 2015, Extensive Intramural Esophageal Hematoma After Transesophageal Echocardiography During Atrial Fibrillation Ablation, CIRCULATION, Vol: 132, Pages: 1847-1849, ISSN: 0009-7322
Boukens BJ, Sulkin MS, Gloschat CR, et al., 2015, Transmural APD gradient synchronizes repolarization in the human left ventricular wall, CARDIOVASCULAR RESEARCH, Vol: 108, Pages: 188-196, ISSN: 0008-6363
Cantwell CD, Roney CH, Ng FS, et al., 2015, Techniques for automated local activation time annotation and conduction velocity estimation in cardiac mapping, Computers in Biology and Medicine, Vol: 65, Pages: 229-242, ISSN: 0010-4825
Measurements of cardiac conduction velocity provide valuable functional and structural insight into the initiation and perpetuation of cardiac arrhythmias, in both a clinical and laboratory context. The interpretation of activation wavefronts and their propagation can identify mechanistic properties of a broad range of electrophysiological pathologies. However, the sparsity, distribution and uncertainty of recorded data make accurate conduction velocity calculation difficult. A wide range of mathematical approaches have been proposed for addressing this challenge, often targeted towards specific data modalities, species or recording environments. Many of these algorithms require identification of activation times from electrogram recordings which themselves may have complex morphology or low signal-to-noise ratio. This paper surveys algorithms designed for identifying local activation times and computing conduction direction and speed. Their suitability for use in different recording contexts and applications is assessed.
Ng FS, Lyon AR, Shadi IT, et al., 2010, Gap Junctional Uncoupling with Carbenoxolone Slows Conduction and Increases Vulnerability to Ventricular Arrhythmias in Structurally Normal Hearts: An Optical Mapping Study, British Cardiovascular Society Annual Conference 2010, Pages: A5-A6
Ng FS, Lyon AR, Shadi IT, et al., 2010, Modulation of Gap Junctional Coupling as an Anti-Arrhythmic Strategy to Prevent Reperfusion Ventricular Fibrillation, SET for Britain 2010 (House of Commons, UK Parliament)
Tzortzis KN, Roney CH, Qureshi NA, et al., 2015, Influence of left atrial geometry on rotor core trajectories in a model of atrial fibrillation, Computing in Cardiology, Publisher: IEEE, Pages: 481-484, ISSN: 2325-8861
Left atrial anatomy and myocardial architecture areknown to influence rotor initiation and maintenance.However, identifying their relative contribution clinicallyis challenging. The present study aims to investigate insilico the effect of left atrial geometry in isolation onrotor generation and evolution through thespatiotemporal tracking of phase singularities. Aftermeandering for a short period of time, rotors areattracted to specific areas of the chamber where there ishigh curvature, primarily near the base of the left atrialappendage and the junctions of the pulmonary veins. Thissuggests that the left atrial anatomy could play a key rolein the perpetuation of fibrillatory activity.
Ng FS, Behradfar E, Debney MT, et al., 2015, Activation of normally quiescent Purkinje-myocardial junctions during acute myocardial ischaemia - an unexplored arrhythmogenic mechanism, Congress of the European-Society-of-Cardiology (ESC), Publisher: OXFORD UNIV PRESS, Pages: 214-214, ISSN: 0195-668X
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