Catheter ablation is the treatment of choice for patients with symptomatic accessory pathways (APs) causing recurrent atrioventricular reciprocating tachycardia or in situations where APs conduct rapidly, posing a risk of sudden cardiac death. Conventional AP mapping relies on point-by-point assessment of local electrograms looking closely for pathway electrograms or early atrial or ventricular electrograms, which may be challenging and time consuming. Recently, open window mapping (OWM) using 3D navigational systems has emerged as a novel technique to help localise and ablate APs. OWM has significant advantages over conventional point-by-point mapping techniques. The purpose of this review is to summarise the currently available literature on the OWM technique and to highlight the technical aspects and mapping considerations for OWM, including specific cases demonstrating its utility.

A 73-year-old gentleman with dilated cardiomyopathy, left bundle branch block and a left ventricular (LV) ejection fraction of 20% was implanted with two LV leads in a tri-ventricular cardiac resynchronisation therapy defibrillator (CRT-D) trial. As a part of the trial he was programmed with fusion-based CRT therapy with dual LV lead only pacing. The patient presented to local heart failure service 12 years after implant, after a positive response to CRT therapy, with increase in fatigue, shortness of breath and bilateral pitting oedema. The patient sent a remote monitoring transmission that suggested loss of capture on one of the LV leads. This coupled with atrial ectopics was producing a high burden of pacemaker-mediated tachycardia (PMT) that was not seen when both LV leads had been capturing. What is the mechanism for this? Dual LV-lead tri-ventricular leads have been shown to have variable improvements in CRT response but with an increased complexity of implant procedure. This is the first case report of PMT-induced heart failure exacerbation in a tri-ventricular device following loss of LV capture of one lead.

Background: ECG imaging (ECGI) has been used to guide treatment of ventricular ectopy and arrhythmias. However, the accuracy of ECGI in localizing the origin of arrhythmias during catheter ablation of ventricular tachycardia (VT) in structurally abnormal hearts remains to be fully validated. Methods: During catheter ablation of VT, simultaneous mapping was performed using electroanatomical mapping (CARTO, Biosense-Webster) and ECGI (CardioInsight, Medtronic) in 18 patients. Sites of entrainment, pace-mapping, and termination during ablation were used to define the VT site of origin (SoO). Distance between SoO and the site of earliest activation on ECGI were measured using co-registered geometries from both systems. The accuracy of ECGI versus a 12-lead surface ECG algorithm was compared. Results: A total of 29 VTs were available for comparison. Distance between SoO and sites of earliest activation in ECGI was 22.6, 13.9 to 36.2 mm (median, first to third quartile). ECGI mapped VT sites of origin onto the correct AHA segment with higher accuracy than a validated 12-lead ECG algorithm (83.3% versus 38.9%; P =0.015). Conclusions: This simultaneous assessment demonstrates that CardioInsight localizes VT circuits with sufficient accuracy to provide a region of interest for targeting mapping for ablation. Resolution is not sufficient to guide discrete radiofrequency lesion delivery via catheter ablation without concomitant use of an electroanatomical mapping system but may be sufficient for segmental ablation with radiotherapy.

IntroductionThe European Society of Cardiology 2016 atrial fibrillation (AF) guidance suggests atrioventricular node (AVN) ablation and pacemaker implantation in patients with AF unresponsive to rate and rhythm control therapies.1 For patients with conventional cardiac resynchronisation therapy (CRT) indications and AF, the recommendations are clear. However, in patients with normal left ventricular (LV) function and a pace and ablate strategy, there is limited evidence to support biventricular pacing (CRT) in favour of conventional right-ventricular permanent pacemakers (PPM). We audited our practice of AVN ablation to evaluate the current practice in our institution, and to observe for differences between pacing groups.MethodsOur devices database was searched for patients who underwent AV node ablation between June 2016 to September 2018. Descriptive and statistical analysis were performed, using t-test and Chi-squared methods.Results142 patients underwent AV node ablation, and 56 patients were identified with preserved LV function (LVEF > 50%) with a pace and ablate management strategy. Of these patients, 35 had a PPM, and 21 a CRT implanted prior to ablation. Comparing these groups, patients undergoing pacemaker implantation were significantly older (PPM 76± 14 vs CRT 67± 11, p= 0.014). There was also a significant difference in male gender, (PPM 8 (22.9%) vs CRT 13 (61.9%), p= 0.0035). Mean LVEF was similar between PPM and CRT groups (56±4% vs. 53±3%). There was a trend in higher background ischaemic heart disease in the CRT group (CRT 3 (14.2%) vs. PPM 1 (2.9%), p=0.108). At initial device implantation, two patients intended for CRT had a failed attempt at LV lead placement (5.7%), therefore a PPM was implanted. Device procedure time appears longer in the CRT group (CRT 132.1 mins ± 40.9, vs. PPM 85.8 mins ± 34.8). Total mean follow-up period was 345 days (± 197). Two patients (5.7%) in the PPM group required lead revisions, compared to none in the CRT group. A total of two patients required repeat procedures for failed ablations, with no other procedural complications. There was a trend in higher all cause mortality in the PPM group compared with the CRT group (4 (11.4%) vs. 1 (4.8%), p= 0.397).Discussion and conclusionThe BLOCK HF trial demonstrated that biventricular pacing was superior to right-ventricular pacing in patients with an LVEF <50%.2 The role of prophylactic CRT implantation in patients with preserved LV was addressed in the BIOPACE trial, however these results were not formally published and controversy still exists about the type of device to implant in patients with near normal LV function.3 Our study describes the variability in our clinical practice given the split in PPM vs CRT in patients with near normal LV function. The increased age and mortality trend in the PPM group may reflect an increased frailty or co-morbidity compared with the CRT group. However, long term clinical outcomes are required in order to provide clarity on this important clinical decision.Conflict of InterestNone

Background We describe a case series of patients for a gradual rise in daily, low-voltage sub-threshold measurement (LVSM) of shock (high-voltage, HV) impedance in a group of patients with Boston Scientific implantable cardioverter-defibrillators (ICDs) and investigate the cause of the abnormality. Case summary Six patients presented with a gradual rise in HV impedance above normal range (132.5 +/- 20.8 Omega). Patients were young with a mean age of 29 +/- 11 years, four patients had hypertrophic cardiomyopathy, one left ventricular non-compaction, and one long QT. All lead designs were silicon body with GORE polytetrafluoroethylene (ePTFE) coated coils, and a lower true shock impedance (TSI) was seen in all cases with full output synchronized shock. We compared the rate of HV impedance rise with our historical cohort of Boston ICDs using an unpaired t-test. The change in impedance per month was significantly higher amongst our six patients when compared with our cohort of Boston Scientific ICDs (3.2 +/- 1.9 Omega/month vs. 0.0008 +/- 0.005 Omega/month, P < 0.001). Patients were individually investigated and management discussed in a dedicated device multi-disciplinary team meeting (MDT). Discussion There are distinct differences between TSI and LVSM. The TSI is derived from a full output shock, whilst LVSM is calculated from a small current output. These cases highlight the inaccuracies of the LVSM measurement. The gradual rise in LVSM is significantly higher than the value for TSI in these patients we propose the most likely mechanism is encapsulation fibrosis surrounding the right ventricular shock coil. Management for these patients requires vigorous testing to rule out electrical failure, and replacement maybe necessary.

Background: The accuracy of ECG imaging (ECGI) in structural heart disease remains uncertain. This study aimed to provide a detailed comparison of ECGI and contact-mapping system (CARTO) electrograms. Methods: Simultaneous epicardial mapping using CARTO (Biosense-Webster, CA) and ECGI (CardioInsight) in 8 patients was performed to compare electrogram morphology, activation time (AT), and repolarization time (RT). Agreement between AT and RT from CARTO and ECGI was assessed using Pearson correlation coefficient, ρ AT and ρ RT , root mean square error, E AT and E RT , and Bland-Altman plots. Results: After geometric coregistration, 711 (439–905; median, first-third quartiles) ECGI and CARTO points were paired per patient. AT maps showed ρ AT =0.66 (0.53–0.73) and E AT =24 (21–32) ms, RT maps showed ρ RT =0.55 (0.41–0.71) and E RT =51 (38–70) ms. The median correlation coefficient measuring the morphological similarity between the unipolar electrograms was equal to 0.71 (0.65–0.74) for the entire signal, 0.67 (0.59–0.76) for QRS complexes, and 0.57 (0.35–0.76) for T waves. Local activation map correlation, ρ AT , was lower when default filters were used (0.60 (0.30–0.71), P =0.053). Small misalignment of the ECGI and CARTO geometries (below ±4 mm and ±4°) could introduce variations in the median ρ AT up to ±25%. Minimum distance between epicardial pacing sites and the region of earliest activation in ECGI was 13.2 (0.0–28.3) mm from 25 pacing sites with stimulation to QRS interval <40 ms. Conclusions: This simultaneous assessment demonstrates that ECGI maps activation and repolarization parameters with moderate accuracy. ECGI and contact electrogram correlation is sensitive to electrode apposition and geometric alignment. Further technological developments may improve spatial resolution.