ORCID Profile
0000-0001-5043-0787
Current Organisation
John Hunter Hospital
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Publisher: Elsevier BV
Date: 11-2016
Publisher: Radcliffe Group Ltd
Date: 24-12-2020
DOI: 10.15420/AER.2020.25
Abstract: Empirical approaches to targeting the ventricular tachycardia (VT) substrate include mapping of late potentials, local abnormal electrogram, pace-mapping and homogenisation of the abnormal signals. These approaches do not try to differentiate between the passive or active role of local signals as the critical components of the VT circuit. By not considering the functional components, these approaches often view the substrate as a fixed anatomical barrier. Strategies to improve the success of VT ablation need to include the identification of critical functional substrate. Decrement-evoked potential (DeEP) mapping has been developed to elucidate this using an extra-stimulus added to a pacing drive train. With knowledge translation in mind, the authors detail the evolution of the DeEP concept by way of a study of simultaneous panoramic endocardial mapping in VT ablation an in silico modelling study to demonstrate the factors influencing DeEPs a multicentre VT ablation validation study a practical approach to DeEP mapping the potential utility of DeEPs to identify arrhythmogenic atrial substrate and, finally, other functional mapping strategies.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2017
DOI: 10.1161/CIRCINTERVENTIONS.116.004172
Abstract: The therapeutic potential of renal denervation (RDN) for arrhythmias has not been fully explored. Detailed mechanistic evaluation is in order. The objective of the present study was to determine the antiarrhythmic potential of RDN in a postinfarct animal model and to determine whether any benefits relate to RDN-induced reduction of sympathetic effectors on the myocardium. Pigs implanted with single-chamber implantable cardioverter defibrillators to record ventricular arrhythmias (VAs) were subjected to percutaneous coronary occlusion to induce myocardial infarction. Two weeks later, a sham or real RDN treatment was performed bilaterally using the St Jude EnligHTN basket catheter. Parameters of ventricular remodeling and modulation of cardio–renal sympathetic axis were monitored for 3 weeks after myocardial infarction. Histological analysis of renal arteries yielded a mean neurofilament score of healthy nerves that was significantly lower in the real RDN group than in sham controls damaged nerves were found only in the real RDN group. There was a 100% reduction in the rate of spontaneous VAs after real RDN and a 75% increase in the rate of spontaneous VAs after sham RDN ( P =0.03). In the infarcted myocardium, presence of sympathetic nerves and tissue abundance of neuropeptide-Y, an indicator of sympathetic nerve activities, were significantly lower in the RDN group. Peak and mean sinus tachycardia rates were significantly reduced after RDN. RDN in the infarcted pig model leads to reduction of postinfarction VAs and myocardial sympathetic effectors. This may form the basis for a potential therapeutic role of RDN in postinfarct VAs.
Publisher: Elsevier BV
Date: 05-2018
DOI: 10.1016/J.HLC.2018.03.011
Abstract: The most frequent complications from percutaneous electrophysiology procedures relate to vascular access. We sought to perform the first randomised controlled trial for femoral venous haemostasis utilising a simple and novel purse string suture (PSS) technique. We randomised 200 consecutive patients who were referred for electrophysiology procedures at two different hospitals to either 10minutes of manual pressure or a PSS over the femoral vein and determined the incidence of vascular access site complications. The mean age was 61.8±12.1years and 138 (69%) were male. Bleeding requiring addition pressure or a FemStop (Abbott Laboratories, Abbott Park, IL, USA) for complete haemostasis occurred in 17/99 (17%) patients in the PSS arm and 19/101 (19%) patients in the manual pressure arm (p=0.72). There were no cases of haematoma prolonging hospital stay, arterio-venous fistula, pseudoaneurysm or retroperitoneal bleeding. The mean duration to achieve haemostasis was 45seconds in the PSS arm and 10minutes 44seconds in the manual pressure arm (p<0.001). Pain/discomfort associated with haemostasis occurred in 15/99 (15%) patients in the PSS arm and in 29/101 (29%) patients receiving manual pressure (p=0.03). In this randomised trial we demonstrate that an easy to perform PSS is as effective at achieving haemostasis as 10minutes of manual pressure for catheter ablation procedures. The PSS is considerably faster to perform and is more comfortable for patients than manual pressure.
Publisher: Elsevier BV
Date: 03-2023
Publisher: Springer Science and Business Media LLC
Date: 28-09-2016
DOI: 10.1007/S10840-016-0193-7
Abstract: Pulmonary vein isolation using cryoballoon ablation is an established approach to treating atrial fibrillation. The procedure involves insertion of a 15-Fr sheath into the left atrium across the interatrial septum. This creates an iatrogenic atrial septal defect, which may have important long-term clinical relevance, especially in younger patients. We sought to determine the long-term incidence of these defects and determine the direction of shunt using contrast transesophageal echocardiography. In iduals who had undergone a single pulmonary vein isolation procedure were invited to attend for transesophageal echocardiography (TOE). Patients who had undergone more than one procedure involving puncture of the interatrial septum were excluded. The interatrial septum was interrogated using two-dimensional imaging, color flow Doppler, and microbubble contrast study. A total of 27 patients were recruited with a median follow-up time of 553 days from pulmonary vein isolation to TOE. Seven patients had persistent iatrogenic atrial septal defects with three demonstrating right to left shunt either at rest or with Valsalva. There were no reported adverse events during the study period. Persistent iatrogenic atrial septal defects are relatively common following cryoballoon ablation procedures. Right to left shunting can be observed using microbubble contrast in a subset of patients with iatrogenic atrial septal defect (iASD). Further studies that longitudinally assess shunt fraction, pulmonary artery pressure, and the incidence of paradoxical embolism are needed to better understand the clinical impacts of such defects.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2015
DOI: 10.1161/CIRCEP.115.003083
Abstract: Substrate-based mapping for ventricular tachycardia (VT) ablation is h ered by its inability to determine critical sites of the VT circuit. We hypothesized that those potentials, which delay with a decremental extrastimulus (decrement evoked potentials or DEEPs), are more likely to colocalize with the diastolic pathways of VT circuits. DEEPs were identified in intraoperative left ventricular maps from 6 patients with ischemic cardiomyopathy (total 9 VTs) and were compared with late potential (LP) and activation maps of the diastolic pathway for each VT. Mathematical modeling was also used to further validate and elucidate the mechanisms of DEEP mapping. All patients demonstrated regions of DEEPs and LPs. The mean endocardial surface area of these potentials was 18±4% and 21±6%, respectively ( P =0.13). The mean sensitivity for identifying the diastolic pathway in VT was 50±23% for DEEPs and 36±32% for LPs ( P =0.31). The mean specificity was 43±23% versus 20±8% for DEEP and LP mapping, respectively ( P =0.031). The electrograms that displayed the greatest decrement in each case had a sensitivity and specificity for the VT isthmus of 29±10% and 95±1%, respectively. Mathematical modeling studies recapitulated DEEPs at the VT isthmus and demonstrated their role in VT initiation with a critical degree of decrement. In this preliminary study, DEEP mapping was more specific than LP mapping for identifying the critical targets of VT ablation. The mechanism of DEEPs relates to conduction velocity restitution magnified by zigzag conduction within scar channels.
Publisher: Elsevier BV
Date: 03-2016
DOI: 10.1016/J.HLC.2015.07.012
Abstract: Cryoballoon ablation is an established catheter-based approach to treating atrial fibrillation (AF). There is little data regarding the long-term efficacy of this approach. We enrolled 200 consecutive patients with symptomatic AF who had failed therapy with at least one anti-arrhythmic medication and followed them for five years. The primary efficacy endpoint was symptomatic recurrence of AF after a single cryoballoon ablation procedure. Two hundred patients formed the study group. Median follow-up was 56 months. Following a single procedure, 46.7% of patients with paroxysmal AF remained free of symptomatic recurrence of AF compared to 35.6% of patients with persistent AF. When allowing for repeat ablations, at the end of the follow-up period 53.3% of patients in the paroxysmal group remained free of symptomatic AF compared to 47.5% in the persistent group. The rate of complications was low. Cryoballoon ablation is an effective catheter-based approach for treating symptomatic AF with a low risk of complications.
Publisher: Wiley
Date: 02-11-2018
DOI: 10.1111/JCE.13773
Publisher: Elsevier BV
Date: 04-2017
DOI: 10.1016/J.HRTHM.2017.01.023
Abstract: Endocardial mapping tools use variable interelectrode resolution, whereas body surface mapping tools use narrow bandpass filtering (BPF) to map fibrillatory mechanisms established by high-resolution optical imaging. The purpose of this study was to study the effect of resolution and BPF on the underlying mechanism being mapped. Hearts from 14 healthy New Zealand white rabbits were Langendorff perfused. We studied the effect of spatial resolution and BPF on the location and characterization of rotors by comparing phase singularities detected by high-resolution unfiltered optical maps and of fibrillating myocardium with decimated and filtered maps with simulated electrode spacing of 2, 5, and 8 mm. As we decimated the maps with 2-mm, 5-mm, and 8-mm interelectrode spacing, the mean ( ± SD) number of rotors detected decreased from 10.2 ± 9.6, 1.6 ± 3.2, and 0.2 ± 0.5, respectively. Lowering the resolution led to synthesized pseudo-rotors that may be inappropriately identified. Applying a BPF led to fewer mean phase singularities detected (248 ± 207 vs 333 ± 130 P<.01), giving the appearance of pseudo-spatial stability measured as translation index (with BPF 3.6 ± 0.4 mm vs 4.0 ± 0.5 mm without BPF P<.01) and pseudo-temporal stability with longer duration (70.0 ± 17.6 ms in BPF maps vs 44.1 ± 6.6 ms in unfiltered maps P<.001) than true underlying fibrillating myocardium mapped. Electrode resolution and BPF of electrograms can result in distortion of the underlying electrophysiology of fibrillation. Newer mapping techniques need to demonstrate sensitivity analysis to quantify the degree of distortion before clinical use to avoid inaccurate electrophysiologic interpretation.
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.HRTHM.2015.05.004
Abstract: Successful activation mapping of ventricular tachycardia (VT) is dependent on the identification of a region of diastolic conduction by use of point-by-point sequential mapping. It is important to identify the site of transition from diastolic conduction to systolic activation of healthy myocardium (exit site) and differentiate this from nonvulnerable regions of the circuit. We sought to determine the temporal and component characteristics of exit-site electrograms using simultaneous multielectrode endocardial mapping and to differentiate them from bystander sites during activation mapping. Sixteen VTs induced in 12 patients with ischemic cardiomyopathy who underwent multielectrode mapping during VT performed with a custom-made 112-bipolar-electrode endocardial array were analyzed retrospectively. The activation sequence in systole and diastole was annotated, and the timing at exit and bystander sites of the near-field component was characterized in relation to surface electrocardiogram activation and to the far-field component. Spectral content of bipolar electrograms recorded at these sites was additionally analyzed to identify the near-field to far-field interval. The mean activation time at exit sites was 60.0 ± 31.5 ms (range 21-113 ms) ahead of surface QRS but was not significantly different from bystander sites (72.0 ± 55.0 ms, P = .63). However, the time delay from local to far-field activity was significantly lower at exit sites than at bystander sites (24.9 ± 15.6 vs. 86.6 ± 92.0 ms, P = .003), which was confirmed by spectral analysis (10.0 ± 13.1 vs. 89.0 ± 64.5 ms, P = .003). Our analysis suggests that temporal-component analysis of diastolic electrograms during activation mapping of VT provides a practical method to differentiate nonvulnerable sites from the exit site without the need for pacing maneuvers.
Publisher: Elsevier BV
Date: 05-2015
Publisher: Elsevier BV
Date: 08-2021
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 04-2015
Publisher: Elsevier BV
Date: 06-2015
DOI: 10.1016/J.JACEP.2015.04.003
Abstract: This study sought to determine the characteristics of human LDVF, particularly as it contrasts with short-duration VF (SDVF), and evaluate the role of Purkinje fibers in its maintenance. The electrophysiological mechanisms of long-duration ventricular fibrillation (LDVF) have not been studied in the human heart. VF was induced in 12 human Langendorff hearts, and the hearts were examined from initiation to LDVF (10 min). Endocardial, epicardial, and transmural plunge needle mapping were performed on the hearts. Simulated LDVF was studied in canine hearts to determine the potential role of Purkinje fiber automaticity. The mean age at transplant was 48 ± 20 years, and the mean ejection fraction was <20%. The mean cycle length of local activation times on the endocardium was 252 ± 66 ms in SDVF and 441 ± 80 ms in LDVF (p = 0.0002). On the endocardium and the epicardium in LDVF, cycle length was 441 ± 80 ms and 590 ± 88 ms, respectively (p = 0.0002). No endocardial to epicardial activation frequency gradient was seen in SDVF. Simultaneous transmural needle activation was most common in SDVF, whereas endocardial to epicardial activation was most common in LDVF (47.7% and 38.8% of activations, respectively [p = 0.031]). Re-entry was less common in LDVF, and over time, wave break (i.e., nontransmural propagation of wave fronts) developed. Isochronal maps of the left ventricular endocardium in LDVF identified Purkinje potentials as preceding and predominating endocardial activations. In explanted canine heart preparations, rapid pacing led to spontaneous Purkinje fiber activity that was dependent on pacing rate and duration. LDVF in human hearts is characterized by focal endocardial activity with mid-myocardial wave break and not by re-entry. This arrhythmia is modulated by rapid activations in early VF that lead to spontaneous Purkinje fiber activity.
Publisher: Elsevier BV
Date: 06-2020
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1016/J.HRTHM.2016.01.018
Abstract: Renal denervation (RDN) was primarily developed to treat hypertension and is potentially a new method for treating arrhythmias. Because of the lack of a standardized protocol to measure renal sympathetic nerve activity, RDN is administered in a blind manner. This inability to assess efficacy at the time of treatment delivery may be a large contributor to the ambiguity of RDN outcomes reported in the hypertension literature. The advancement of RDN as a treatment of hypertension or arrhythmias will be h ered by the lack of delivery assessment, a deficiency that the cardiovascular electrophysiology community, with its expertise in recording and mapping, may have a role in addressing and overcoming. The development of endovascular recording of renal nerve action potentials may provide a useful accessory tool for RDN. Innovation in this area will be crucial as we as a community reconsider the therapeutic value of RDN.
Publisher: Elsevier BV
Date: 11-2019
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 07-2016
DOI: 10.1161/CIRCEP.116.004107
Abstract: With its inherent limitations, determining local activation times has been the basis of cardiac mapping for over a century. Here, we introduce omnipolar electrograms that originate from the natural direction of a travelling wave and from which instantaneous conduction velocity litude and direction can be computed at any single location without first determining activation times. We sought to validate omnipole-derived conduction velocities and explore potential application for localization of sources of arrhythmias. Electrograms from omnipolar mapping were derived and validated using 4 separate models and 2 independent signal acquisition methodologies. We used both electric signals and optical signals collected from monolayer cell preparations, 3-dimensional constructs built with cardiomyocytes derived from human embryonic stem cells, simultaneous optical and electric mapping of rabbit hearts, and in vivo pig electrophysiology studies. Conduction velocities calculated from omnipolar electrograms were compared with wavefront propagation from optical and electric-mapping studies with a traditional local activation time–based method. Bland–Altman analysis revealed that omnipolar measurements on optical data were in agreement with local activation time methods for wavefront direction and velocity within 25 cm/s and 30°, respectively. Similar agreement was also found on electric data. Furthermore, mathematical operations, such as curl and ergence, were applied to omnipole-derived velocity vector fields to locate rotational and focal sources, respectively. Electrode orientation–independent cardiac wavefront trajectory and speed at a single location for each cardiac activation can be determined accurately with omnipolar electrograms. Omnipole-derived vector fields, when combined with mathematical transforms may aid in real-time detection of cardiac activation sources.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2016
Publisher: Elsevier BV
Date: 08-2012
DOI: 10.1016/J.HLC.2012.03.123
Abstract: Cryoballoon ablation is a recently introduced technique to isolate the pulmonary veins in patients with atrial fibrillation (AF). It can potentially reduce procedural times and serious complications associated with radiofrequency ablation. We present data for 200 consecutive patients who underwent cryoballoon ablation for symptomatic AF with a mean follow-up of 16 months. Over 214 procedures that involved cryoballoon technique the mean procedure and fluoroscopy times fell to 130 and 30 min, respectively. 93.6% of pulmonary veins targeted were isolated with the cryoballoon only and 97.7% could be isolated with the addition of a radiofrequency ablation catheter. At one year 70% of patients in the paroxysmal AF group and 59% of patients in the persistent AF group were free from symptomatic recurrence. Three percent of patients experienced phrenic nerve palsy that persisted beyond the procedure. The major complication rate in this study was 0.9%. This represents the earliest and largest experience with cryoballoon ablation for AF in Australia. The major complication rate was low with no pulmonary vein stenosis, atrio-oesophageal fistula, stroke or cardiac t onade in this series. The majority of patients were free from symptomatic recurrence at two years follow up.
Publisher: Wiley
Date: 30-05-2016
DOI: 10.1002/HED.24495
Publisher: Elsevier BV
Date: 03-2018
DOI: 10.1016/J.JACEP.2017.12.005
Abstract: The authors conducted a multicenter study of decrement-evoked potential (DEEP)-based functional ventricular tachycardia (VT) substrate modification to evaluate if such a mechanistic and physiological strategy is feasible and efficient in clinical practice and provides reduction in the VT burden. Only a fraction of the myocardium targeted in current VT substrate modification procedures is involved in the initiation and perpetuation of VT. The physiological basis of the DEEP strategy for identification of areas of initiation and maintenance of VT was recently established. We included 20 consecutive patients with ischemic cardiomyopathy. During substrate mapping, fractionated and late potentials (LPs) were tagged, and an extra stimulus was performed to determine which LPs displayed decrement (DEEPs). All patients underwent DEEP-focused ablation: elimination of DEEP + further radiofrequency (RF) if VT was still inducible. Patients were followed during 6 months. Patients were predominantly male (95%), and their mean age was 64.6 ± 17.1 years. Mean left ventricular ejection fraction was 33.4 ± 11.4%. Mean ablation time was 30.6 ± 20.4 min. Specificity of DEEPs to detect the isthmus of VT was better than that of LPs (0.97 [95% confidence interval [CI]: 0.95 to 0.98] vs. 0.82 [95% CI: 0.73 to 0.89]), without significant differences in terms of sensitivity (0.61 [95% CI: 0.52 to 0.69] vs. 0.60 [95% CI: 0.44 to 0.74], respectively). Fifteen of 20 (75%) patients were free of any VT after DEEP-RF at 6 months of follow-up and there was a strong reduction in VT burden compared to 6 months pre-ablation. In a multicenter prospective study, DEEP substrate mapping identified the functional substrate critical to the VT circuit with high specificity. DEEP-guided VT ablation, by its physiological nature, may enable greater access to focused ablation therapy for patients requiring VT treatment.
No related grants have been discovered for Nicholas Jackson.