A cluster of inappropriate shocks in a pediatric S-ICD patient - how to troubleshoot?

We present the case of a 16-year-old male pediatric patient diagnosed with hypertrophic cardiomyopathy (HCM, identified as having a high risk of sudden cardiac death (SCD), who underwent a successful subcutaneous implantable cardiac defibrillator (S-ICD) implantation as a primary prevention measure in 2018. His past medical history included ADHD, Autism, and panic attacks. The patient experienced appropriate shocks that successfully terminated VF episodes. However, he also experienced multiple inappropriate shocks from the S-ICD, triggered by anxiety-induced tachycardia during panic episodes. Meticulous assessment of S-ICD tracings and electrocardiograms (ECGs) revealed the erroneous classification of sinus tachycardia as sustained ventricular tachycardia, leading to unwarranted therapeutic interventions. Clinical intervention involved reprogramming of the S-ICD, emphasizing the pivotal role of personalized device configuration in pediatric cases where fine margins matter. While literature on S-ICD use in pediatric populations remains limited, emerging registries underscore the efficacy and safety of S-ICDs in preventing sudden cardiac death while reducing complications associated with intravascular leads. This case underscores the critical nature of customized device programming in pediatric patients, underscoring S-ICDs as a practical defibrillation alternative that addresses distinct concerns within this cohort of patients.

Ripple mapping: Initial multicenter experience of an intuitive approach to overcoming the limitations of 3D activation mapping.

BACKGROUND: Ripple mapping (RM) displays electrograms as moving bars over a three-dimensional surface displaying bipolar voltage, and has shown in a single-center series to be effective for atrial tachycardia (AT) mapping without annotation of local activation time or window-of-interest assignment. We tested the reproducibility of these findings in operators naïve to RM, using it for the first time in postablation AT. METHODS: Maps were collected with multielectrode catheters and CARTO ConfiDENSE. A diagnosis of the tachycardia mechanism was made using RM and an assessment of operator confidence was made according to a three-grade scale (1 highest-3 lowest). RESULTS: The first 20 patients (64 ± 9 years, median two previous ablations) undergoing RM-guided AT ablation across five sites were studied. High-density maps (2,935 ± 1,328 points) in AT (CL = 296 ± 95 milliseconds) were collected. Macroreentrant ATs bordered by scar or anatomical obstacles were identified in n = 12 (60%), small reentrant ATs around scar in n = 3 (15%), and focal ATs from scar in n = 5 (25%). Diagnostic confidence with RM was grade 1 in n = 13 (65%), where operators felt confident to proceed to ablation without entrainment. Ablation offered the correct diagnosis n = 18 (90%). Retrospective review of the accompanying LAT maps demonstrated potential sources for error related to the window of interest selection, interpolation, and differentiating regions of scar during tachycardia on the voltage map. CONCLUSION: RM was easy to adopt by operators using it for the first time, and identified the correct target for ablation with high diagnostic confidence in most cases of complex AT.

Open Window Mapping of Accessory Pathways: A Literature Review and Practical Guide.

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 randomized sham-controlled study of pulmonary vein isolation in symptomatic atrial fibrillation (The SHAM-PVI study): Study design and rationale.

INTRODUCTION: Pulmonary vein (PV) isolation has been shown to reduce atrial fibrillation (AF) burden and symptoms in patients. However, to date previous studies have been unblinded raising the possibility of a placebo effect to account for differences in outcomes. HYPOTHESIS & METHODS: The objective of this study is to compare PV isolation to a sham procedure in patients with symptomatic AF. The SHAM-PVI study is a double blind randomized controlled clinical trial. 140 patients with symptomatic paroxysmal or persistent AF will be randomized to either PV isolation (with cryoballoon ablation) or a sham procedure (with phrenic nerve pacing). All patients will receive an implantable loop recorder. The primary outcome is total AF burden at 6 months postrandomisation (excluding the 3 month blanking period). Key secondary outcomes include (1) time to symptomatic and asymptomatic atrial tachyarrhythmia (2) total atrial tachyarrhythmia episodes and (3) patient reported outcome measures. RESULTS: Enrollment was initiated in January 2020. Through April 2023 119 patients have been recruited. Results are expected to be disseminated in 2024. CONCLUSION: This study compares PV isolation using cryoablation to a sham procedure. The study will estimate the effect of PV isolation on AF burden.

Ripple-AT Study: A Multicenter and Randomized Study Comparing 3D Mapping Techniques During Atrial Tachycardia Ablations.

BACKGROUND: Ripple mapping (RM) is an alternative approach to activation mapping of atrial tachycardia (AT) that avoids electrogram annotation. We tested whether RM is superior to conventional annotation based local activation time (LAT) mapping for AT diagnosis in a randomized and multicenter study. METHODS: Patients with AT were randomized to either RM or LAT mapping using the CARTO3v4 CONFIDENSE system. Operators determined the diagnosis using the assigned 3D mapping arm alone, before being permitted a single confirmatory entrainment manuever if needed. A planned ablation lesion set was defined. The primary end point was AT termination with delivery of the planned ablation lesion set. The inability to terminate AT with this first lesion set, the use of more than one entrainment manuever, or the need to crossover to the other mapping arm was defined as failure to achieve the primary end point. RESULTS: One hundred five patients from 7 centers were recruited with 22 patients excluded due to premature AT termination, noninducibility or left atrial appendage thrombus. Eighty-three patients (pts; RM=42, LAT=41) completed mapping and ablation within the 2 groups of similar characteristics (RM versus LAT: prior ablation or cardiac surgery n=35 [83%] versus n=35 [85%], P=0.80). The primary end point occurred in 38/42 pts (90%) in the RM group and 29/41pts (71%) in the LAT group (P=0.045). This was achieved without any entrainment in 31/42 pts (74%) with RM and 18/41 pts (44%) with LAT (P=0.01). Of those patients who failed to achieve the primary end point, AT termination was achieved in 9/12 pts (75%) in the LAT group following crossover to RM with entrainment, but 0/4 pts (0%) in the RM group crossing over to LAT mapping with entrainment (P=0.04). CONCLUSIONS: RM is superior to LAT mapping on the CARTO3v4 CONFIDENSE system in guiding ablation to terminate AT with the first lesion set and with reduced entrainment to assist diagnosis. CLINICAL TRIALS REGISTRATION: https://www.clinicaltrials.gov. Unique identifier: NCT02451995.

Inappropriate implantable cardioverter defibrillator shocks in fractured Sprint Fidelis leads associated with 'appropriate' interrogation.

We present two patients with fractures within the pace-sense circuit of their Medtronic Sprint Fidelis leads who received inappropriate shocks from their Medtronic defibrillators during device interrogation. This was not simply a coincidence, but due to electromagnetic interference induced within the Sprint Fidelis lead by the device programmer during two-way communication with the defibrillator. Our subsequent investigations have uncovered at least two other similar incidents in Canada. We have also discovered that the Medtronic 'Auto-resume' feature may leave future patients uniquely vulnerable to such inappropriate shocks in the future.

Experience of atrial fibrillation ablation in a new cardiac centre using three-dimensional mapping and multielectrode duty-cycled radiofrequency ablation.

BACKGROUND: Catheter ablation is widely used to treat symptomatic atrial fibrillation (AF) refractory to drug therapy; and can be facilitated by a number of different techniques. AIMS: To evaluate our performance as a new centre for AF ablation and to evaluate the efficacy of different AF ablation techniques. METHODS: We employed three techniques in AF ablations; the three-dimensional (3D) mapping approaches (CARTO or Ensite NavX) or multielectrode catheter duty-cycled radiofrequency ablation (pulmonary vein ablation catheter [PVAC]). The immediate restoration of sinus rhythm was considered as acute success; while success at 6 months was determined by the maintenance of sinus rhythm on Holter monitoring. RESULTS: Between March 2008 and March 2010, 109 patients underwent AF ablations (mean age: 58 years; 72% male). Six-month success rates did not differ significantly between CARTO and NavX (40% vs 38%; P=0.81), but the PVAC group achieved greater success than the two 3D-mapping groups combined (68% vs 39%; P=0.004). Paroxysmal AF patients demonstrated greater 6-month success than persistent AF patients (P=0.005); and although the ratio of paroxysmal to persistent AF patients was slightly higher among the PVAC group, logistic regression confirmed PVAC and paroxysmal AF as predictors of success. Single-procedure success at 6 months was 48%. Including redo-ablations, some performed beyond the study period, our overall success rate at 6 months was 65%. Four patients experienced complications, but there were no deaths. CONCLUSION: Despite being a new centre with relative inexperience, we achieved success rates comparable to those of established tertiary centres. PVAC performed significantly better than the two 3D-mapping approaches.

Accelerating risk of Fidelis lead fracture.

BACKGROUND: Sprint Fidelis (Medtronic Inc., Minneapolis, Minnesota) is a 6.6-F implantable cardioverter-defibrillator lead. In October 2007 the manufacturer suspended distribution of Sprint Fidelis leads secondary to high early fracture rates. Reprogramming of lead impedance alerts was recommended to try to reduce inappropriate shocks. OBJECTIVE: This study sought to assess how the hazard of Fidelis fracture varies with time, whether lead impedance alert thresholds programmed after recall have prevented inappropriate shocks, and predictors of lead fracture. METHODS: We collected clinical and device interrogation data on all lead fractures and performed a Kaplan-Meier analysis. We performed a case control study to examine univariate and multivariate predictors of lead fracture. RESULTS: There have been 17 lead fractures in our cohort of 480 Sprint Fidelis (model 6949) leads, median follow-up 19.8 months. The hazard of fracture increased significantly with time by a power of 2.74 (95% confidence interval: 2.57 to 2.91, P <.0001). Reprogrammed lead impedance thresholds prevented inappropriate shocks in only 1 of 6 patients. Independent predictors of lead fracture were greater left ventricular ejection fraction (P = .0011) and noncephalic venous access (P = .0224). CONCLUSION: The risk of lead fracture increased with time by a power of 2.74. Reprogrammed lead impedance thresholds prevented inappropriate shocks in only 1 of 6 patients. Independent predictors of lead fracture were greater left ventricular ejection fraction and noncephalic access.

Electrical heart disease: Genetic and molecular basis of cardiac arrhythmias in normal structural hearts.

Purely electrical heart diseases, defined by the absence of any structural cardiac defects, are responsible for a large number of sudden, unexpected deaths in otherwise healthy, young individuals. These conditions include the long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia and the short QT syndrome. Collectively, these conditions have been referred to as channelopathies. Ion channels provide the molecular basis for cardiac electrical activity. These channels have specific ion selectivity and are responsible for the precise and timely regulation of the passage of charged ions across the cell membrane in myocytes, and the summation of their activity in cardiac muscle defines the surface electrocardiogram. Impairment in the flow of these ions in heart cells may mean the difference between a normal, prosperous life and the tragedy of a sudden, unexpected death due to ventricular arrhythmia. The present paper reviews the current clinical and molecular understanding of the electrical diseases of the heart associated with sudden cardiac death.

The clinical impact of implantable loop recorders in patients with syncope.

AIMS: Implantable loop recorders (ILR) provide an opportunity to record ECG data from a spontaneous syncopal event. We conducted a randomized study to investigate the impact of the Reveal Plus ILR on an unselected population of patients with recurrent syncope. Initial follow-up (at least 6 months) did not demonstrate a reduction in syncopal events or an improvement in quality of life. We report the planned extension of follow-up to 18 months. METHODS AND RESULTS: All patients presenting acutely with recurrent unexplained syncope over a 16-month period, following a basic clinical work-up, were randomized to receive the ILR or conventional investigation and management. A total of 421 patients presented, 201 were eligible, median age 74, (IQ range 61-81) 54% female, with median syncopes 3 (IQ range 2-6). Median follow-up 17 months (IQ range 9-23). 42 (43%) of ILR patients and 8 (6%) of conventional patients received an ECG diagnosis (hazard ratio 6.53, 95% CI 3.73-11.4, P<0.001). Time to second syncope was significantly longer for ILR patients, although of borderline significance (P=0.04). A greater variety of diagnoses and treatments were seen in ILR patients. ILR patients had fewer post-randomization investigations and fewer days in hospital; however, cost savings were not statistically significant. There was improved quality of life in the ILR group (visual analogue scales, P=0.03) for general wellbeing. Overall mortality was 12% with no difference between the two groups. CONCLUSION: Investigation by the ILR significantly increases the diagnostic rate and ECG directed treatments in a typical unselected syncopal population. Long-term follow-up has demonstrated a significant subsequent reduction in syncopal events with improved quality of life.

How do we diagnose syncope?

INTRODUCTION: The Eastbourne Syncope Assessment Study aims to increase diagnostic yield in unexplained syncope while reducing investigational costs. The initial study phase was a retrospective analysis of every presentation to the Eastbourne General Hospital (a busy nontertiary center in the United Kingdom serving a population of 250,000; 24% are older than 65 years) with syncope for the year 1998. METHODS AND RESULTS: A total of 1,334 cases with syncopal codes were identified. Six hundred sixty patients (mean age 64 years) had actually suffered an episode of syncope. Forty percent had recurrent syncope, with a mean of 4.7 previous episodes. Twenty-nine percent of syncope cases remained undiagnosed. Forty-four percent were diagnosed as vasovagal, 12% neurologic, 6% due to an arrhythmia, 2% drug related, and 2% due to hemorrhage. Thirteen different types of investigation were undertaken, with an overall total of 3,264 investigations performed at a cost of Pound Sterling 104,285. Diagnosis was achieved by history and examination alone in 61% of cases. Excluding history and examination, the most cost-effective diagnostic tools were the 7-day patient-activated recorder (R test) and tilt testing (Pound Sterling 260 and Pound Sterling 401 per diagnosis, respectively). Investigations also were graded by their relative diagnostic power. Hospital admission alone accounted for 67% of the cost of investigating syncope. CONCLUSION: In syncope, diagnostic rates can be improved and investigational costs reduced by concentrating on the most specific, sensitive, and cost-effective investigations and by minimizing hospital stay. Such a protocol currently is under investigation at our institution.