Broad and narrow complex tachycardia resulting in cardiorespiratory arrest in a child: what is the optimal treatment strategy?

Background: We describe a child with a broad and narrow complex tachycardia causing haemodynamic collapse. Case summary: A 9-year-old girl (weight 26 kg, height 114 cm) with a 5-year history of refractory 'epilepsy' presented with cardiorespiratory arrest and tonic-clonic seizure, witnessed by her mother. Electrocardiogram documented recurrent episodes of simultaneous broad and narrow tachycardias associated with haemodynamic compromise. Diagnostic electrophysiologic study (EPS) confirmed a dual tachycardia mechanism. The challenge in selecting the optimal treatment strategy is discussed. A diagnosis of dual tachycardia was made with catecholaminergic polymorphic ventricular tachycardia (CPVT) and simultaneous focal atrial tachycardia. Discussion: Bidirectional ventricular tachycardia (VT) induced by isoproterenol in this clinical scenario is strongly suggestive of CPVT. Diagnostic EPS can be useful in challenging clinical situations to understand the mechanism of arrhythmias and to tailor the most appropriate treatment strategy. Combination therapy with nadolol and flecainide is highly effective in ventricular arrhythmia control. Implantable cardioverter defibrillator implantation is not without risk in CPVT as there is a potential of electrical storm driven by shock therapy that increases adrenergic drive. Cervical sympathectomy may be considered if further VTs occur in future despite optimum medical therapy.

Preclinical cardiac perforation reduction in leadless pacing: An update to the Micra leadless pacemaker delivery system.

BACKGROUND: Leadless pacemakers have been developed to avoid some of the complications that are associated transvenous pacemakers. Pericardial effusion is a rare complication of leadless pacemaker implantation, which may result from perforation of the delivery catheter. In this study, we describe preclinical perforation performance of an updated Micra delivery catheter. METHODS: To assess preclinical perforation performance of the updated delivery catheter, three analyses were performed. First, Finite Element Analysis (FEA) computational modeling was performed to estimate the target tissue stress during Micra delivery catheter tenting. Second, benchtop perforation forces of ovine tissue were recorded for the original and updated delivery catheters. Finally, a Monte-Carlo simulation combining human cadaveric Micra implant forces and human ventricular tissue perforation properties was performed to estimate clinical perforation performance. RESULTS: FEA modeling demonstrated a 66% reduction in target tissue stress when using the updated Micra delivery catheter (6.2 vs. 2.2 psi, Original vs. Updated Micra delivery catheter). Updated Micra delivery catheters required 20% more force to perforate porcine ventricular tissues in benchtop testing (µupd  = 26.9N vs. µorg  = 22.4N, p = .01). Monte-Carlo Simulation of catheter performance in human cadaveric tissues predicts 28.5% reduction of catheter-perforated cases with the updated delivery catheter. CONCLUSIONS: This study, using computer modelling and benchtop experimentation, has indicated that increased surface area and rounding of the updated Micra catheter tip significantly improves preclinical perforation performance. It will be important to evaluate the impact of these catheter design changes with robust registry data.

High-density electroanatomic activation mapping to guide slow pathway modification in patients with persistent left superior vena cava.

BACKGROUND: Slow pathway (SP) mapping and modification can be challenging in patients with persistent left superior vena cava (PLSVC) due to anatomic variance of the Koch triangle (KT) and coronary sinus (CS) dilation. Studies using detailed 3-dimensional (3D) electroanatomic mapping (EAM) to investigate conduction characteristics and guide ablation targets in this condition are lacking. OBJECTIVES: The purpose of this study was to describe a novel technique of SP mapping and ablation in sinus rhythm using 3D EAM in patients with PLSVC after validation in a cohort with normal CS anatomy. METHODS: Seven patients with PLSVC and dual atrioventricular (AV) nodal physiology who underwent SP modification with the use of 3D EAM were included. Twenty-one normal heart patients with AV nodal reentrant tachycardias formed the validation group. High-resolution, ultra-high-density local activation timing mapping of the right atrial septum and proximal CS in sinus rhythm was performed. RESULTS: SP ablation targets were consistently identified by an area in the right atrial septum with the latest activation time and multicomponent atrial electrogram adjacent to a region with isochronal crowding (deceleration zone). In PLSVC patients, these targets were located at or within 1 cm of the midanterior CS ostium. Ablation in this area led to successful SP modification, reaching standard clinical endpoints with a median of 43 seconds of radiofrequency energy or 14 minutes of cryoablation without complications. CONCLUSION: High-resolution activation mapping of the KT in sinus rhythm can facilitate localization and safe SP ablation in patients with PLSVC.

Outcomes From Pediatric Ablation: A Review of 20 Years of National Data.

OBJECTIVES: This study set out to examine outcomes from pediatric supraventricular tachycardia ablations over a 20-year period. This study sought to examine success rates and repeat ablations over time and to evaluate whether modalities such as 3-dimensional (3D) mapping, contact force, and cryotherapy have improved outcomes. BACKGROUND: Ablation of supraventricular tachycardia in pediatric patients is commonly performed in most congenital heart centers with excellent long-term results. METHODS: Data were retrieved from the NICOR (National Institute of Clinical Outcomes Research) database in the United Kingdom. Outcomes over time were evaluated, and procedure-related details were compared. RESULTS: There were 7,069 ablations performed from January 1, 1999, to December 31, 2018, at 10 centers. Overall, ablation success rates were 92% for accessory pathways, 97% for atrioventricular node re-entry tachycardia, and 89% for atrial tachycardia. There was an improvement in procedural success rates over time (p < 0.01). The use of 3D mapping did not alter success or need for repeat ablation but was associated with a higher proportion of lower fluoroscopy cases; 55% of 3D mapping cases used <5 min of fluoroscopy (p < 0.01). Patients needing a repeat ablation were 341 (12%) for accessory pathways, 128 (7%) for atrioventricular node re-entry tachycardia, and 35 (7%) for atrial tachycardia. Overall, the risk of complete heart block was low (n = 12, <0.01%). The use of cryotherapy was associated with an increased risk of needing a repeat ablation. CONCLUSIONS: Overall success rates from pediatric ablations are excellent and compare favorably to other registries. Introduction of newer technologies have likely made procedures safer and reduced radiation exposure, but they have not changed success rates or the need for a repeat procedure.

Machine learning detection of Atrial Fibrillation using wearable technology.

BACKGROUND: Atrial Fibrillation is the most common arrhythmia worldwide with a global age adjusted prevalence of 0.5% in 2010. Anticoagulation treatment using warfarin or direct oral anticoagulants is effective in reducing the risk of AF-related stroke by approximately two-thirds and can provide a 10% reduction in overall mortality. There has been increased interest in detecting AF due to its increased incidence and the possibility to prevent AF-related strokes. Inexpensive consumer devices which measure the ECG may have the potential to accurately detect AF but do not generally incorporate diagnostic algorithms. Machine learning algorithms have the potential to improve patient outcomes particularly where diagnoses are made from large volumes or complex patterns of data such as in AF. METHODS: We designed a novel AF detection algorithm using a de-correlated Lorenz plot of 60 consecutive RR intervals. In order to reduce the volume of data, the resulting images were compressed using a wavelet transformation (JPEG200 algorithm) and the compressed images were used as input data to a Support Vector Machine (SVM) classifier. We used the Massachusetts Institute of Technology (MIT)-Beth Israel Hospital (BIH) Atrial Fibrillation database and the MIT-BIH Arrhythmia database as training data and verified the algorithm performance using RR intervals collected using an inexpensive consumer heart rate monitor device (Polar-H7) in a case-control study. RESULTS: The SVM algorithm yielded excellent discrimination in the training data with a sensitivity of 99.2% and a specificity of 99.5% for AF. In the validation data, the SVM algorithm correctly identified AF in 79/79 cases; sensitivity 100% (95% CI 95.4%-100%) and non-AF in 328/336 cases; specificity 97.6% (95% CI 95.4%-99.0%). CONCLUSIONS: An inexpensive wearable heart rate monitor and machine learning algorithm can be used to detect AF with very high accuracy and has the capability to transmit ECG data which could be used to confirm AF. It could potentially be used for intermittent screening or continuously for prolonged periods to detect paroxysmal AF. Further work could lead to cost-effective and accurate estimation of AF burden and improved risk stratification in AF.

Screening for Atrial Fibrillation Using Economical and Accurate Technology (From the SAFETY Study).

The prevalence of atrial fibrillation (AF) is estimated at more than 3% in the adult population and there has been increased interest in screening for AF. In the SAFETY trial we chose to evaluate if inexpensive, wearable, consumer electrocardiography (ECG) sensing devices (Polar-H7 [PH7] and Firstbeat Bodyguard 2 [BG2]), could be used to detect AF accurately. We undertook a case-control study of 418 participants aged >65 (82 with AF and/or flutter at the study visit and 336 without) attending 3 general practice surgeries in Hampshire, UK for a single screening visit. The PH7 and BG2 devices were tested alongside 2 established AF detection devices (AliveCor and WatchBP) in random order and the diagnosis of AF was confirmed by 12-Lead ECG interpreted by a panel of cardiologists. The sensitivity (95% confidence interval [CI] range), specificity (95% CI range), and overall accuracy (95% CI range) of the 4 devices were: AliveCor: 87.8% (78.7% to 94.0%), 98.8% (97.0% to 99.7%), 96.7% (94.4% to 98.2%); WatchBP: 96.3% (89.7% to 99.2%), 93.5% (90.3% to 95.9%), 94.0% (91.3% to 96.1%): PH7: 96.3% (89.7% to 99.2%), 98.2% (96.2% to 99.3%), 97.9% (96.0% to 99.0%). BG2: 96.3% (89.7% to 99.2%), 98.5% (96.6% to 99.5%), 98.1% (96.3% to 99.2%). The PH7 and BG2 devices were highly reliable (the devices acquired sufficient data and obtained a diagnostic result in all but 1 participant on the first attempt). In conclusion, inexpensive, consumer heart rate monitoring devices (PH7 and BG2) can be used to detect AF accurately with sensitivity and specificity >95%. The consumer devices performed as well or better than WatchBP and AliveCor and have the capability to store or transmit ECG data which could be used to confirm AF.

Monitoring of arrhythmia and sudden death in a hemodialysis population: The CRASH-ILR Study.

INTRODUCTION: It has been suggested that sudden cardiac death (SCD) contributes around 50% of cardiovascular and 27% of all-cause mortality in hemodialysis patients. The true burden of arrhythmias and arrhythmic deaths in this population, however, remains poorly characterised. Cardio Renal Arrhythmia Study in Hemodialysis (CRASH-ILR) is a prospective, implantable loop recorder single centre study of 30 established hemodialysis patients and one of the first to provide long-term ambulatory ECG monitoring. METHODS: 30 patients (60% male) aged 68±12 years receiving hemodialysis for 45±40 months with varied etiology (diabetes 37%, hypertension 23%) and left ventricular ejection fraction (LVEF) 55±8% received a Reveal XT implantable loop recorder (Medtronic, USA) between August 2011 and October 2014. ECG data from loop recorders were transmitted at each hemodialysis session using a remote monitoring system. Primary outcome was SCD or implantation of a (tachy or bradyarrhythmia controlling) device and secondary outcome, the development of arrhythmia necessitating medical intervention. RESULTS: During 379,512 hours of continuous ECG monitoring (mean 12,648±9,024 hours/patient), there were 8 deaths-2 SCD and 6 due to generalised deterioration/sepsis. 5 (20%) patients had a primary outcome event (2 SCD, 3 pacemaker implantations for bradyarrhythmia). 10 (33%) patients reached an arrhythmic primary or secondary end point. Median event free survival for any arrhythmia was 2.6 years (95% confidence intervals 1.6-3.6 years). CONCLUSIONS: The findings confirm the high mortality rate seen in hemodialysis populations and contrary to initial expectations, bradyarrhythmias emerged as a common and potentially significant arrhythmic event.

Use of the CHA2DS2VASc score to reduce utilisation of transoesophageal echocardiography prior to ablation for atrial fibrillation.

Transoesophageal echocardiography (TOE) is frequently performed prior to atrial fibrillation (AF) ablation to exclude left atrial appendage (LAA) thrombus. However, patients undergoing AF ablation are usually anticoagulated, thus making the presence of thrombus unlikely in most cases. This study aimed to determine whether the CHA2DS2VASc scoring system can be used to identify patients that do not require TOE prior to AF ablation. In this single-centre retrospective study, local institutional and primary care databases and electronic patient records were searched to identify patients that had undergone TOE prior to AF ablation. Patient demographics, CHA2DS2VASc score, TOE findings and anticoagulation status were collected for analysis. Over a 7-year period (2008-2014), 332 patients (age 57 ± 10 years; 74% male) underwent TOE prior to proposed AF ablation. CHA2DS2VASc scores of 0, 1, 2 and >2 were found in 39, 34, 15 and 12% of patients, respectively. The prevalence of LAA thrombus was 0.6% (2 patients) and these 2 patients had risk scores of 2 and 4. No patients with a score of 0 or 1 had LAA thrombus. Patients that are classed as low risk by the CHA2DS2VASc score do not require a pre-ablation TOE to screen for LAA thrombus provided they are adequately anticoagulated. This would lead to a significant reduction in health care expenditures by reducing unnecessary TOE requests and thereby improve patient experience.

The relationship between left ventricular scar and ventricular repolarization in patients with coronary artery disease: insights from late gadolinium enhancement magnetic resonance imaging.

AIMS: The markers of ventricular repolarization corrected QT interval (QTc), QT dispersion (QTD) and Tpeak-to-Tend interval (Tpeak-end) have shown an association with sudden cardiac death (SCD) in the general population. However, their mechanistic relationship with SCD is unclear. The study aim was to evaluate the relationship between QTc, QTD, and Tpeak-end, and the extent and distribution of left ventricular (LV) scar in patients with coronary artery disease at high SCD risk. METHODS AND RESULTS: We included 64 consecutive implantable cardioverter defibrillator (ICD) recipients (66 ± 11 years, 80% male, median left ventricular ejection fraction 30%) who had undergone late gadolinium enhancement cardiac magnetic resonance (CMR) imaging prior to device implantation over 4 years. Scar was quantified using the CMR images and characterized in terms of percent LV scar and number of LV segments with subendocardial/transmural scar. Repolarization parameters were measured on an electrocardiogram performed prior to ICD implantation. After adjustment for potential confounders there was a strong association between the number of limited subendocardial (1-25% transmurality) scar segments and QTc (P = 0.003), QTD (P = 0.002), and Tpeak-end (P = 0.008). However, there was no association between the repolarization parameters and percent LV scar or the amount of transmural scar. During a mean follow-up of 19 ± 10 months 19 (30%) patients received appropriate ICD therapy, but none of the repolarization parameters were associated with its occurrence. CONCLUSION: In this pilot study there was a strong association between limited subendocardial LV scar and prolonged QTc, QTD, and Tpeak-end. However, there was no association between any of these repolarization markers and the delivery of appropriate ICD therapy.

Rates of upgrade of ICD recipients to CRT in clinical practice and the potential impact of the more liberal use of CRT at initial implant.

BACKGROUND: Many implantable cardioverter defibrillator (ICD) recipients may develop indications for cardiac resynchronization therapy (CRT) during follow-up. However, the actual upgrade rate during follow-up in clinical practice is not known. METHODS: We performed a single center retrospective observational study of all new ICD implants over 5 years (2003-2007). The rate of CRT upgrade of patients initially implanted with a single-/dual-chamber ICD during follow-up was assessed. The impact of using alternative criteria on the need for CRT in ICD recipients at initial implant was also evaluated. RESULTS: During the study period, there were 549 new ICD implants. The initial implant was a single/dual-chamber ICD in 73% (n = 399) and a CRT-D in 27% (n = 150). During follow-up (48±20 months) of the 399 ICD recipients, 70 (17.5%) died and 15 (3.8%) were upgraded to CRT, including eight cases where left ventricular lead implant had been initially unsuccessful. Upgrade rates at 1, 3, and 5 years were 0.03%, 2.4%, and 5.1%, respectively. Using alternative CRT criteria (left ventricular ejection fraction [LVEF]≤30%, QRS ≥130 ms, New York Heart Association I-IV) 42.6% (n = 234) of ICD recipients met criteria for CRT at initial implant. CONCLUSION: In this retrospective single center study, rates of CRT upgrade in ICD recipients over the medium term were low, which may reflect underuse in otherwise appropriate candidates. The more liberal use of CRT at initial implant in patients with a reduced LVEF, a broad QRS, but only mild heart failure symptoms would require approximately 50% increase in CRT use in ICD recipients at initial implant, and may help address some of the suggested underutilization.

Transseptal left ventricular endocardial pacing reduces dispersion of ventricular repolarization.

BACKGROUND: Cardiac resynchronization therapy (CRT) may be proarrhythmic in some patients. This may be due to the effect of left ventricular (LV) epicardial pacing on ventricular repolarization. The purpose of this study was to evaluate the effect of endocardial versus epicardial LV biventricular pacing on surface electrocardiogram (ECG) parameters that are known markers of arrhythmogenic repolarization. METHODS: ECG markers of repolarization (QT dispersion, QTD; T peak to end, T(peak-end) ; T(peak-end) dispersion, T(peak-end) D; QTc) were retrospectively measured before and after CRT in seven patients with transseptal LV endocardial leads (TS group), 28 matched patients with coronary sinus (CS) LV leads (CS group), and eight patients with surgical LV epicardial leads (SUR group). All ECGs were scanned and analyzed using digital callipers. RESULTS: Compared to the CS group, the TS group CRT was associated with a significant postpacing reduction in QTD (-45.2 ± 35.6 vs -4.3 ± 43.6 ms, P = 0.03) and T(peak-end) (-24.2 ± 22.1 vs 3.4 ± 26.7 ms, P = 0.02). There was a nonsignificant post-CRT reduction in both T(peak-end) D (-11.3 ± 31.0 vs 2.4 ± 28.9 ms, P = 0.27) and QTc (-50.0 ± 46.4 vs 4.4 ± 70.2 ms, P = 0.06) in the TS versus the CS group. In contrast, there were no differences between the SUR and CS groups in terms of the effect of CRT on these repolarization parameters. CONCLUSIONS: CRT with (atrial transseptal) endocardial LV lead placement is associated with repolarization characteristics that are considered to be less arrhythmogenic than those generated by CS (epicardial) LV lead placement. Further work is needed to determine whether these changes translate to a reduction in proarrhythmia.

Permanent transvenous left ventricular endocardial pacing in a patient with univentricular atrioventricular connection.

Chronotropic incompetence is associated with poorer effort tolerance and worse mortality outcomes, not only in the general cardiac population but also in patients with congenital heart disease. When present in complex patients, pacing options may be limited by difficult pacing access, and an open surgical approach for epicardial lead placement may not always be desirable. We describe a case of symptomatic chronotropic incompetence in a patient with tricuspid atresia, valvar and subpulmonary stenosis, normally related great vessels, and a modified Blalock-Taussig shunt, awaiting cardiac transplantation, whom we palliated with a transvenous endocardial pacing strategy. This technique may provide an alternative pacing strategy for highly selected patients, where few other treatment options are available.