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Ventricular tachycardia (VT) substrate in left ventricular (LV) nonischemic cardiomyopathy (NICM) consists of fibrosis with surviving myocardium.The purpose of this study was to determine whether, in patients with LV NICM and sustained VT, reduced QRS amplitude and QRSf during sinus rhythm can identify the presence and location of abnormal septal (S-NICM) and/or free-wall (FW-NICM) VT substrate.We compared patients with NICM and VT (group 1) with electroanatomic mapping septal (S-NICM; n = 21) or free-wall (FW-NICM; n = 20) VT substrate to a 38-patient reference cohort (group 2) with cardiac magnetic resonance imaging (cMRI) and NICM but no VT referred for primary prevention implantable cardioverter-defibrillator (26 [68.4%] with late gadolinium enhancement).Group 1 had lower QRS amplitude in leads II (0.60 ± 0.22 vs 0.86 ± 0.35, P.001), aVR (0.60 ± 0.24 vs 0.75 ± 0.31, P = .002), aVF (0.48 ± 0.20 vs 0.70 ± 0.28, P.001), and VIn LV NICM, low frontal plane QRS (0.55 mV in aVF) is associated with VT substrate. Although multilead QRS fractionation is associated with the presence and location of VT substrate, it is frequently identified in patients without VT with cMRI abnormalities.

BACKGROUND Substrate-based ventricular tachycardia (VT) ablation is a first-line treatment in patients with structural cardiac disease and sustained VT refractory to medical therapy. Despite technological improvements and increased knowledge of VT substrate, recurrence still is frequent. Published data are lacking on the possible reduction in VT burden after ablation despite recurrence. OBJECTIVE The purpose of this study was to assess VT burden reduction during long-term follow-up after substrate ablation and identify predictors of VT recurrence. METHODS We analyzed 234 consecutive VT ablation procedures in 207 patients (age 63 6 14.9 years; 92% male; ischemic heart disease in 65%) who underwent substrate ablation in a single center from 2013 to 2018. RESULTS After follow-up of 3.14 6 1.8 years, the VT recurrence rate was 41.4%. Overall, a 99.6% reduction in VT burden (median VT episodes per year: preprocedural 3.546 [1.347-13.951] vs postprocedural 0.001 [0-0.689]; P 5 .001) and a 96.3% decrease in implantable cardioverter-defibrillator (ICD) shocks (preprocedural 1.145 [0.118-4.467] vs postprocedural 0.042 [0-0.111] per year; P 5 .017) were observed. In the subgroup of patients who experienced VT recurrences, VT burden decreased by 69.2% (median VT episodes per year: preprocedural 2.876 [1.105-8.801] vs postprocedural 0.882 [0.505-2.283]; P ,.001). Multivariable analysis showed persistence of late potentials (67% vs 19%; hazard ratio 3.18 [2.18- 6.65]; P ,.001) and lower left ventricular ejection fraction (EF) (30 [25-40] vs 39 [30-50]; P 5 .022) as predictors of VT recurrence. CONCLUSION Despite a high recurrence rate during long-term follow-up, substrate-based VT ablation is related to a large reduction in VT burden and a decrease in ICD therapies. Lower EF and persistence of late potentials are predictors of recurrence. KEYWORDS Arrhythmic burden reduction; Implantable cardioverter-defibrillator shock prevention; Ventricular tachycardia ablation; Ventricular tachycardia recurrence predictors; Ventricular tachycardia storm; Ventricular tachycardia substrate ablation

Purpose To report the feasibility of magnetic resonance imaging-guided cardiac single fraction radioablation (MRgRA) in a patient with dilated cardiomyopathy and recurrent sustained ventricular tachycardia (VT) leading to electrical storms (ES). Materials/methods A workflow to perform Stereotactic Arrhythmia Radioablation (STAR) on a hybrid MR-Linac with real-time tracking and beam-gating was established. Challenges of the MRgRA approach included: (a) the safety of a non-MR compatible cardiac implantable electronic device (CIED) in the MR-Linac field, (b) artefacts caused by the CIED and (c) respiratory motion management with cine-tracking of the moving heart. The specific absorption rate and slew rate of the MR-Linac were within the specifications of a MR-conditional CIED. Phantom measurements showed CIED distortion artefacts of less than 1.5 mm. During MR simulation, tracking could be established on the upper liver to avoid interference with the moving heart and CIED extinction artefacts. Areas of anatomical scarring and critical substrate were identified using invasive three-dimensional electroanatomical mapping of the clinical VT during electrophysiological studies and cardiac MR imaging/computed tomography to build a volumetric target. Results A 71-year-old male patient with non-ischemic dilated cardiomyopathy and recurrent therapy-refractory sustained VT with repetitive implantable cardioverter-defibrillator (ICD) shocks was treated with a single fraction of 25 Gy @85% isodose, cine-tracking time was 46 min, beam-on time 24 min. 24 h post intervention the patient developed an aggravation of the clinical VT and prolonged ES. VT ceased following high-dose dexamethasone administration after 48 h. After this point, the patient remained without any episodes of sustained ventricular tachyarrhythmia requiring ICD interventions until the last follow-up at three months. Conclusion Real-time tracking and beam-gating were successfully applied in this first MRgRA to treat sustained VT.

Sudden cardiac death (SCD) is the most common cause of late mortality in tetralogy of Fallot (TOF). Pulmonary regurgitation (PR) was previously found to be the most common hemodynamic abnormality associated with ventricular arrhythmias (VA), but cardiovascular magnetic resonance (CMR)-based studies did not show this association. The aim of this study is to investigate the risk factors for VA in TOF using CMR. Electronic records of TOF patients and their CMR studies between July 2006 and October 2018 in one center were retrospectively reviewed. Demographic, clinical and CMR data of patients were collected. Outcome was defined as sustained ventricular tachycardia (VT), aborted SCD and SCD. From a total of 434 TOF patients with complete CMR studies, 19 (4.4%) patients developed a positive outcome (12 sustained VT, 4 aborted SCD, 3 SCD) at a median age of 24 years. The number of surgical interventions was significantly greater in patients who developed VA. Right ventricular volumes were significantly larger in patients who suffered a positive outcome. Odds ratio for developing VA was 6.905 for RVEDVI ≥ 160 ml/m2 and 6.141 for RVESVI ≥ 80 ml/m2 (P = 0.0014 and 0.0012, respectively). Event-free survival was longer in patients with smaller right ventricular volumes. In conclusion, right ventricular dimensions are the most significant factors associated with the development of VA in TOF. The number of surgical interventions is also related to an increased risk.

Sustained ventricular tachycardia (VT) in the early postoperative period following intracardiac repair for tetralogy of Fallot is rare. In stable VT, amiodarone forms the mainstay of management. However, where amiodarone and other antiarrhythmic drugs are contraindicated, suppressive overdrive atrial pacing can be used as a safe and efficient alternative to maintain cardiac output. We present a case of 1-year 5-month-old child who developed VT with low cardiac output syndrome with deranged hepatic function, who was managed efficiently using suppressive atrial pacing to ameliorate the effects of sustained VT.

Background Premature ventricular contractions (PVCs) may be found in any stage of arrhythmogenic right ventricular cardiomyopathy (ARVC) and have been associated with the risk of sustained ventricular tachycardia (VT). Objective To investigate the role of PVC ablation in ARVC patients. Methods We studied consecutive ARVC patients who underwent PVC ablation due to symptomatic high PVC burden. Mean daily PVC burden and AAD use were assessed before and after the procedure. Complete long-term success was defined as > 80% reduction in PVC burden off of membrane-active AADs. Results Eight patients (37±15yo; 4 males) underwent PVC ablation. The mean daily PVC burden before ablation ranged from 5.4% to 24.8%. Seven (87.5%) patients underwent epicardial ablation. Complete acute elimination of PVCs was achieved in 4 (50%) patients (no complications). The mean daily PVC burden variation ranged from an 87% reduction to a 26% increase after the procedure. Over a median follow-up of 345 days (range: 182-3004 days), only one (12.5%) patient presented complete long-term success, and 6 (75%) patients either maintained or increased the need for Class I or Class III AADs. Two (25%) patients experienced sustained VT for the first time following the ablation procedure, requiring repeat ablation. No death or heart transplantation occurred. Conclusion PVC ablation was not associated with a consistent reduction of the PVC burden in ARVC patients with symptomatic, frequent PVCs. PVC ablation may be reserved for highly symptomatic patients who failed AADs. Additional investigation is required to improve the efficacy of PVC ablation in ARVC patients. This article is protected by copyright. All rights reserved.

Ventricular arrhythmias (VAs) occurring in the absence of structural heart disease or ion channelopathies are referred to as idiopathic. They can clinically present with frequent monomorphic premature ventricular contractions, nonsustained ventricular tachycardia (VT), or sustained VT, and generally share a benign prognosis. Approximately 4% to 10% of idiopathic VAs have an epicardial site of origin, represented in most cases by the left ventricular summit and, less frequently, by the cardiac crux. Epicardial foci can be addressed by catheter ablation via the coronary venous system tributaries. In rarer instances, a direct epicardial access from a subxiphoid approach is needed.

Idiopathic ventricular arrhythmia (IVA) is a term used to describe a spectrum of ventricular arrhythmia without structural heart disease (SHD). IVAs contain premature ventricular contractions (PVCs), nonsustained monomorphic ventricular tachycardia (VT), and sustained VT. Electrocardiography is a fundamental and important tool to diagnose and localize IVAs. More detailed, IVAs originating from different origins exhibit characterized ECGs due to their specific anatomic backgrounds. As catheter ablation becomes widely used to eliminate these arrhythmias, its high success rate is based on accurate localization of their origins. Therefore, these ECG characteristics show great importance for precise localization of their origins and subsequently successful ablation. This review aims to sum up ECG characteristics of IVAs based on anatomy and give brief introduction of mechanisms and treatment of IVAs.

We herein report a woman diagnosed with cardiac sarcoidosis (CS) based on the presence of epithelioid granulomas in non-cardiac organs and clinical findings including sustained ventricular tachycardia (VT) and cardiac dysfunction. She stopped oral corticosteroid after 4 years of treatment, and an abnormal myocardial uptake of fluorine-18 fluorodeoxyglucose and sustained VT recurred 3.5 years later. There is no consensus concerning whether or not corticosteroid therapy should be discontinued in the treatment of CS. As a relapse of sarcoidosis-related inflammation may be associated with life-threatening arrhythmia, some patients should continue corticosteroid therapy, even at low doses.

Objective Amiodarone is commonly used in the treatment of stable ventricular tachycardia (VT), but its efficacy has not been empirically examined in the prehospital setting. The objective of this study was to examine the safety and efficacy of amiodarone administered by paramedics to patients with stable VT. Methods Patient records from Victoria, Australia between 1 May 2007 and 30 June 2017 were examined retrospectively. Patients attended by Ambulance Victoria with stable sustained VT who were administered amiodarone by paramedics as the initial treatment were included. Data were used to determine the prevalence of treatment with amiodarone, the incidence of VT termination prior to transfer of care, and the incidence of progression to electrical cardioversion. Results Sixty-one patients were identified who met the inclusion criteria. The mean age was 72 years (standard deviation = 14) with 77% (n = 47) being male. Of the patients treated with amiodarone, 52% (n = 32) reverted successfully during paramedic care while 48% (n = 29) did not. Two patients required cardioversion for haemodynamic instability after amiodarone administration. One patient experienced cardiac arrest after receiving amiodarone and was successfully resuscitated by paramedics. Conclusions Approximately half of the patients treated with amiodarone reverted from VT while under paramedic care. Patient deterioration was rare, with cardiac arrest or requirement for cardioversion occurring very infrequently. Amiodarone was relatively safe and moderately effective for the treatment of sustained stable VT. However, given recent evidence of increased efficacy of procainamide for stable VT, further studies are required in the prehospital setting to compare these two drugs.

Idiopathic sustained focal right ventricular tachycardia (VT) is most frequently due to outflow tract (OT) tachycardia. This arrhythmia is recognized by its characteristic ECG pattern and sensitivity to adenosine. However, there are other forms of idiopathic, focal sustained VT that originate from the right ventricle (RV), which are less well appreciated and easily overlooked. This review will identify the characteristic features and electrophysiologic properties of these forms of RV VT, including those originating from the tricuspid annulus, right ventricular papillary muscles, and moderator band as well as variants of classic RVOT tachycardia and those due to microreentry in the presence of preclinical disease. Recognition of these subtypes of focal RV tachycardia should facilitate targeted therapy.

Background Ventricular arrhythmias in adult patients following surgical repair of tetralogy of Fallot (TOF) may be challenging to manage and life-threatening. Ventricular tachycardia (VT) is the leading cause of sudden cardiac death in this patient population. Radiofrequency catheter ablation (RFCA) constitutes an important treatment modality for VT. Aim The present study summarizes the outcomes of repaired TOF patients undergoing RFCA for resistant VT. Methods A systematic literature search of the PubMed and Cochrane databases was performed with respect to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Results Eight studies including 106 patients were analyzed. Mean patient age at the time of RFCA was 39.0 ​± ​15.9 years, male:female ratio was 1.97:1. Programmed ventricular stimulation induced sustained VT in 81.6% (95%CI: 72.7–88.1) of patients. VT recurred shortly after the procedure in 16% (95%CI: 10.2–24.3) and during follow-up in 12.2% (95%CI: 6.3–21.7). The post-procedural use of amiodarone and beta-blockers therapy was decreased from 40% (95%CI: 30.3–51.1) to 20% (95%CI: 8.4–39.6) and from 58% (95%CI: 44.2–70.6) to 28% (95%CI: 14.1–47.8) of patients, respectively. A repeat RFCA procedure was required in 17.5% (95%CI: 11.1–26.4). No in-hospital deaths occurred, while overall mortality rate during a mean follow-up of 73.5 ​± ​61.4 months was 3% (95%CI: 0.2–10.9). Conclusion RFCA can control ventricular dysrhythmias in over 80% of the cases, with zero in-hospital and low overall mortality, while substantially reducing the need for antiarrhythmic drugs.

BACKGROUND Implanted cardioverter defibrillators (ICDs) clearly improve survival in patients with prior cardiac arrest without reversible cause, and in those with sustained ventricular tachycardia (VT) with significantly impaired left ventricular ejection fraction (EF). This ‘secondary prevention’ approach is well supported by evidence from large clinical trials. However, it is not clear from the evidence whether patients with a minimally reduced ejection fraction (35-50%) who experience sustained VT that is hemodynamically tolerated benefit from ICD therapy. ICD implant entails some risk and these devices can malfunction or become infected in a small proportion of patients, making the comparison of benefit to risk clinically important to ICD decision making. We set out to describe a cohort of patients that have received an ICD in London for 'walk-in' VT with preserved ejection fraction, and assess whether they have received therapy from their ICD for ventricular arrhythmias. METHODS AND RESULTS We queried our clinical database to identify patients who received an ICD from May 2015 to December 2019 for treatment of a hemodynamically stable episode of VT with ejection fraction minimally impaired at 35-50%. Patient demographics, medications and comorbidities were recorded, along with their history of ICD therapy for ventricular arrhythmias. The timing and nature of ICD therapies was documented. A blanking period was applied to the 7 days after ICD implant to ensure that the presenting episode of VT had subsided was not counted as a follow-up event. Local REB approval was obtained for this project. Among 423 ICDs implanted for secondary prevention during this time period, 64 patients met the enrollment criteria and were included. Average age was 68 (±12) and ejection fraction at time of implant 40%(±4.4). 28 patients (44%) were taking sotalol or amiodarone during follow-up. Over a mean follow-up time of 961 days (±589, range 14-3025) ICD therapy was delivered to 36 (56%) patients. ICD shocks were delivered to 18 (28%) patients over a mean 370 (±347, range 12-1080) days. ATP was delivered to 32 (50%) patients over a mean 239 (±277, range 11-933) days. CONCLUSION ICD therapies are delivered to approximately half of patients with a minimally reduced ejection fraction and an ICD for hemodynamically well tolerated VT, over a period of several years after implant. Guidelines are unclear on ICD indication for these patients due to lack of trial data. Our findings suggest that further study is warranted.

Indications for AICD implantation include previous history of monomorphic or polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) resulting in cardiac arrest or syncope and sustained VT with structural heart disease and cardiomyopathy with low ejection fraction, as this is a significant risk factor for developing VT (Epstein et al., Circulation. 117:e350–408, 2008). Approximately 50–75% of AICD discharges result from an appropriate device response to a malignant ventricular arrhythmia, either VT of VF. More than 30% of patients with a history of VT or VF experience an appropriate AICD discharge for a malignant ventricular dysrhythmia within the initial 2 years of AICD implantation.

Andersen-Tawil syndrome (ATS) is an inherited disorder characterised by the triad of ventricular arrhythmias (VAs), periodic paralysis and dysmorphic features. A 31-year-old woman diagnosed with ATS caused by a KCNJ2 mutation (p.R228ins) was urgently admitted to our hospital following an episode of syncope during exercise. Electrocardiography revealed frequent premature ventricular complexes and non-sustained ventricular tachycardias (VTs) with pleomorphic QRS patterns. During the intravenous flecainide test (30 mg), the frequent VAs were inhibited completely. After oral flecainide (100 mg) was started, VAs, except for a brief bigeminy, were suppressed during the exercise test. On 24-hour Holter recordings, the VAs decreased from 50 133 to 13 363 beats/day (−73%). Sustained VT and syncope were not observed during a 3-year follow-up period. Intravenous flecainide challenge test may be useful in predicting the efficacy of oral flecainide treatment for patients with ATS.

A recent increase in the incidence of ventricular arrhythmias has been observed with the consumption of large dosages of the anti-diarrheal agent, loperamide. Our case is unique in that our patient not only displayed ventricular tachycardia (VT) but sustained VT (known as a VT storm). In this era of the opioid crisis, clinicians should be aware of all of the over-the-counter medications that have opioid-like side effects.

Key Clinical Message The Revivent‐TC™‐system is able to restore LV volumes in patients with severe ischemic cardiomyopathy. We are presenting a case report of successful implantation of the Revivent‐TC™‐system, but postprocedural development of sustained VT. This case report is presenting one way to successfully treat patients with postprocedural frequent VT.

Non-compaction myocardium syndrome of the left ventricle (NCM) is relatively new diagnosis. There is no consensual approach to classification, diagnostics, as treatment and management of patients with NCM till recently. Predictive value of the observed genetic mutations is not studied good enough too. Aim. The article is focused on a clinical case of female patient with NCM and lifethreatening ventricular rhythm disorders, revealed two independent mutations in genes coding sarcomere proteins of myocardium. Material and methods. Clinical and instrumental study, except standard methods, included serological diagnostics of myocarditis, defining a genome of cardiotropic viruses in blood, and MSCT of the heart; genetic study included sequencing on the platform Ion Torrent of the coding sequences and attached inthrone regions on 16 genes, which mutations might lead to NCM. Results. In current study we performed clinical, instrumental and genetic investigation of 59-year old female patient with NCM and sustained VT paroxysms of unknown duration that had been being registered since her 47 age, with frequent VE (up to 24 thousands per day). Ventricular dysrhythmias did not resolve regardless two interventions on RFA of the focus of arrhythmia and drug treatment. At the age 56 cardioverter-defibrillator was implanted, and during 3 years of follow-up there were 13 relevant shocks. There were high titers of antimyocardial antibodies. Differential diagnostics was about myocarditis, ACRV and NCM. Genetic test revealed two mutations heterozygous: p.Q1233* gene MYBPC3 and p.R237W in gene MYH7. These genes’ mutations are common findings in NCM. If two mutations found, it is a factor of higher risk of SCD and progradient course of the disease. Conclusion. Genetic changes (mutations) that influence morphology of myocardium proteins, determine primary cardiomyopathies. However, the velocity of a disease course and real conditions of a patient do determine non-genetic factors as well, including sex, age, comorbidities, infectious or immune myocarditis, range and effectiveness of treatment.

Sustained VT is associated with death, which risk can be reduced by medical intervention. Early and accurate detection of VT, therefore has the potential to reduce deaths. Standard evaluation of VT is often limited to 24-48h ECG monitoring, and it is not known what proportion of sustained VT is

Scar-mediated ventricular tachycardia (VT) is a recognized cause of morbidity and mortality in patients with ischemic cardiomyopathy and other cardiomyopathies such as nonischemic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and cardiac sarcoidosis. Implantable cardioverter-defibrillator (ICD) therapy improves survival but does not prevent the onset of recurrent VT or associated morbidity from ICD shocks. While randomized controlled trials have demonstrated advantages of scar-mediated VT ablation in comparison with antiarrhythmic drugs, procedural success has remained overall modest at between 50% and 70%. Standard scar-mediated VT ablation has relied on the use of activation and entrainment mapping during sustained VT to identify critical isthmuses for ablation. Substrate-based approaches have emerged as options to address hemodynamically unstable VT and have focused on identifying electrograms characteristic of critical isthmuses (eg, late potentials, local abnormal ventricular activities, conducting channels) within dense scar during sinus rhythm. Scar homogenization, a more recent approach, relies minimally on mapping and focuses on complete substrate modification. Core isolation, on the other hand, another recent development, relies heavily on mapping to identify regions within scar that are "cores" for arrhythmogenicity and then concentrates ablation to these areas. At this time, scar-mediated VT ablation appears to be at a crossroads wherein evolving substrate-based approaches are exploring whether to rely less or increasingly more on mapping. This review will therefore discuss the evolution of substrate-based, scar-mediated VT ablation and in the process try to answer whether there is still a role for mapping.

Idiopathic ventricular premature contractions (VPCs), defined as VPCs in the absence of obvious structural heart disease, are one of the common types of arrhythmia in clinical practice. They are sometimes complicated with non-sustained ventricular tachycardia (VT), and/or sustained VT with almost same QRS morphology in 12 leads ECG. Idiopathic VT (IVT) commonly occurs by focal mechanisms and the origins are distributed in a variety of sites in both ventricles. In this article, the clinical characteristics of IVT/IVPCs, the diagnostic algorithm, and how to ablate them will be reviewed.

Objectives This study sought to demonstrate the prevalence, mechanism, and electrocardiographic and electrophysiological characteristics of upper septal idiopathic left fascicular ventricular tachycardia (US-ILVT). Background ILVT is classified into left anterior and posterior types with no clear data about US-ILVT. Methods Among 193 ILVT patients, we identified 12 patients (6.2%; age 41 ± 22 years, 7 men) with US-ILVT. Results Of 12 patients with US-ILVT, 6 patients (50%) had previous history of radiofrequency catheter ablation for common ILVT. Sustained VT (cycle length: 349 ± 53 ms) was seen in all patients with a QRS interval slightly wider (104 ± 18 ms) than that during sinus rhythm (90 ± 19 ms). The VT exhibited an identical QRS configuration as sinus rhythm in 6 (50%) and incomplete right bundle branch block configuration in another 6. His-ventricular interval during VT was always shorter than that during sinus rhythm (27 ± 5 ms vs. 47 ± 10 ms). Purkinje potentials were activated in a reverse direction to that of common ILVT; namely, the diastolic potential (P1) was activated retrogradely but the pre-systolic potential (P2) was activated antegradely. At the left upper-middle ventricular septum, P1 potential was recorded during VT, preceding the QRS by 54 ± 20 ms. Radiofrequency catheter ablation at that site eliminated the VT with no recurrence during a 58 ± 35 months of follow-up. Conclusions US-ILVT is an identifiable VT that shares common criteria with ILVT and has a narrow QRS interval. Some US-ILVT cases appeared after common ILVT ablation. It is a reverse type of common ILVT (orthodromic form) with baseline morphological abnormalities that might provide a potential substrate for such VT.

This study sought to examine the relationship between the number of oral antiarrhythmic drug (AAD) failures before referral for ventricular tachycardia (VT) ablation and subsequent clinical outcomes.Failure of AADs prompts referral for VT ablation.Consecutive patients (n = 669) with sustained VT who were referred for a first-time ablation were divided into 2 groups according to the number of oral Class 1 or 3 AAD failures before referral: single-drug failure (≤1 AAD; n = 256) or multidrug failure (1 AADs; n = 413). Outcomes were stratified according to underlying disease type (no structural heart disease [SHD] [n = 87]; ischemic cardiomyopathy [ICM] [n = 368]; and ischemic cardiomyopathy [NICM] [n = 214]) and reported at a mean follow-up of 35 ± 46 months.Patients with multidrug failure, compared with patients with single-drug failure, had more advanced SHD and required more extensive ablation to control arrhythmia. Multidrug failure, compared with single-drug failure, was associated with lower ventricular arrhythmia-free survival in ICM (46 ± 4% vs. 58 ± 6%; p = 0.03) and NICM (26 ± 5% vs. 49 ± 6%; p = 0.008), but not in the absence of SHD (71 ± 8% vs. 85 ± 7%; p = 0.10). Overall survival was lower in multidrug failure versus single-drug failure groups in patients with ICM (71 ± 3% vs. 84 ± 4%; p = 0.03) and NICM (70 ± 5% vs. 88 ± 4%; p 0.001). Multidrug failure was independently associated with a higher risk of ventricular arrhythmia recurrence (hazard ratio: 1.6; p = 0.01) and mortality in NICM (hazard ratio: 2.6; p = 0.008), but not in ICM.Patients with SHD and failure of multiple oral AADs before VT ablation referral have more advanced heart disease and worse clinical outcomes following ablation, especially in NICM.

Objective: Electrical storm (ES) is not uncommon among patients with an implantable cardioverter defibrillator (ICD) in situ. Catheter ablation (CA) may suppress the arrhythmia in the acute setting and prevent ES recurrence. Methods: Nineteen consecutive patients with an ICD in situ presenting with ES underwent electrophysiologic studies followed by CA. CA outcome was classified as a complete success if both clinical and non-clinical tachycardia were successfully ablated, partial success if ≥1 non-clinical tachycardia episodes were still inducible post–CA, and failure if clinical tachycardia could not be abolished. Patients were followed for a median period (IQR) of 5.6 (1.8-13.7) months. The primary endpoint was event-free survival from ES recurrence. The secondary endpoint was event-free survival from a composite of ES and/or sustained ventricular tachycardia (VT) recurrence. Results: Clinical arrhythmia was successfully ablated in 14 out of 19 (73.7%) cases after a single CA procedure. A completely successful CA outcome was associated with significantly increased ES-free survival compared with a partially successful or failed procedure (Log rank P=0.039). Nevertheless, patients with acute suppression of all tachycardia episodes (n=11), relative to those with a partially successful or a failed CA procedure (n=8), did not differ in incidence of the composite endpoint of sustained VT or ES (Log rank P=0.278). Conclusion: A single CA procedure can acutely suppress clinical arrhythmia in three-quarters of cases. A completely successful CA outcome can prolong ES-free survival; however, sporadic ICD therapies cannot be abrogated. Keywords: Electrical storm, Catheter ablation, Implantable cardioverter defibrillator

Mechanism Specific Effects of Adenosine on VT Introduction There is no universally accepted method by which to diagnose clinical ventricular tachycardia (VT) due to cAMP-mediated triggered activity. Based on cellular and clinical data, adenosine termination of VT is thought to be consistent with a diagnosis of triggered activity. However, a major gap in evidence mitigates the validity of this proposal, namely, defining the specificity of adenosine response in well-delineated reentrant VT circuits. To this end, we systematically studied the effects of adenosine in a model of canine reentrant VT and in human reentrant VT, confirmed by 3-dimensional, pace- and substrate mapping. Methods and Results Adenosine (12 mg [IQR 12–24]) failed to terminate VT in 31 of 31 patients with reentrant VT due to structural heart disease, and had no effect on VT cycle length (age, 67 years [IQR 53–74]); ejection fraction, 35% [IQR 20–55]). In contrast, adenosine terminated VT in 45 of 50 (90%) patients with sustained focal right or left outflow tract tachycardia. The sensitivity of adenosine for identifying VT due to triggered activity was 90% (95% CI, 0.78–0.97) and its specificity was 100% (95% CI, 0.89–1.0). Additionally, reentrant circuits were mapped in the epicardial border zone of 4-day-old infarcts in mongrel dogs. Adenosine (300–400 μg/kg) did not terminate sustained VT or have any effect on VT cycle length. Conclusion These data support the concept that adenosine's effects on ventricular myocardium are mechanism specific, such that termination of VT in response to adenosine is diagnostic of cAMP-mediated triggered activity.

Objective The purpose of the present study was to determine the incidence of ventricular arrhythmias before and after alcohol septal ablation (ASA). Background In patients with hypertrophic obstructive cardiomyopathy (HOCM), gradient reduction by ASA is an alternative for surgical myectomy. However, concerns exist about whether the induction of a myocardial scar during ASA may create substrate for ventricular arrhythmias. Methods The study group consisted of 44 patients in whom ASA was performed for symptomatic, drug-refractory hypertrophic cardiomyopathy. Continuous rhythm monitoring was obtained by implantable loop recorder (n=30) or pacemaker (n=14). Occurrence of ventricular and supraventricular arrhythmias before and after ASA was noted, retrospectively. Results The ASA procedure was considered successful (resting gradient 30 days after ASA. No cardiac deaths occurred during follow-up. Conclusions In a low-risk cohort of patients who underwent ASA, in which continuous rhythm monitoring was performed, sustained VT or VF within 30 days occurred in 3 patients (7%) while no VT/VF was observed before ASA. During long-term follow-up, no sustained VT or VF was observed >30 days after ASA

An effective treatment for scar-related ventricular tachycardia (VT) is to interrupt the circuit by catheter ablation. If activation sequence and entrainment mapping can be performed during sustained VT, the exit and isthmus of the circuit can often be identified. However, with invasive catheter mapping, only monomorphic VT that is hemody namically stable can be mapped in this manner. A non-invaive approach to fast mapping of unstable VTs can potentially allow an improved identification of critical ablation sites. In this pilot study, noninvasive ECG-imaging were carried out on patients with unstable scar-related VT. The reconstructed reentry circuits correctly revealed both epicardial and endocardial origins of activation, consistent with locations of exit sites found during ablation procedures. The results also indicated that some reentry circuits involve both epicardial and endocardial layers, and can only be properly interpreted by mapping both layers.

Category: 27. Clinical Electrophysiology—Ventricular ArrhythmiasSession-Poster Board Number: 1057-381 Authors: Yoshihiro Yamashina, Tetsuo Yagi, Akio Namekawa, Akihiko Ishida, Hirokazu Sato, Takashi Nakagawa, Manjirou Sakuramoto, Eiji Sato, Tomoyuki Yambe, Sendai City Hospital, Sendai, Japan, Tohoku University School of Medicine, Sendai, Japan Background: The relationship between J waves during sinus rhythm and idiopathic ventricular tachycardia (VT) or premature ventricular complexes (PVCs) originating from the right ventricular outflow tract (RVOT) has not been reported. The aim of this study was to investigate the prevalence and characteristics of idiopathic RVOT-VT/PVCs associated with J waves. Methods: The study enrolled 121 consecutive idiopathic RVOT-VT/PVC patients (mean age 45 ± 16 years, 46 males) undergoing radiofrequency catheter ablation (RFCA). The prevalence of J waves was assessed. The clinical and electrophysiological data were compared between the patients with J waves (J-wave group) and those without (Non-J-wave group). Results: J waves were present in 53 (43.8%) idiopathic RVOT-VT/PVC patients. The distribution of the J waves was as follows: Inferior leads = 62%, inferior-lateral leads = 24.5% and lateral leads = 13.2%. The J-wave group had a higher incidence of sustained VT (22.6% vs. 3.5%, P

Epicardial RF Ablation After Endocardial Approach. Introduction: Management of recurrent ventricular tachycardia (VT) remains difficult. Neither medical treatments nor conventional endocardial radiofrequency (RF) ablation are efficient to prevent some recurrences. In these cases, a percutaneous pericardial approach may be required. Methods: Among all the patients referred to our center between 1998 and 2007 for a VT ablation, 276 endocardial and 35 epicardial procedures were performed, the latter in case of failure of the conventional approach. We report in this study the efficacy and the safety of these 35 interventions analyzed retrospectively. Results: Thirty-five epicardial procedures were attempted in 32 patients. An electric storm was present in 5 of 32 (16%) patients, with other individuals presenting with a recurrent VT despite drug therapy and a previous endocardial ablation. Pericardial space was reached in 28 of 32 patients by a xyphoidian puncture. An immediate success of RF on clinical VT was obtained in 22 of 29 (76%) cases. During a mean follow-up of 384 ± 405 days, only 9 patients (26%) experienced a recurrence of a sustained VT. One patient died from tamponade during the procedure despite surgical drainage. Other complications had no significant consequences. Conclusion: Percutaneous epicardial puncture is feasible and relatively safe in patients with recurrent VT in whom conventional endocardial RF ablation failed. Epicardial RF ablation offers a high success rate in these challenging patients with only few severe complications. (J Cardiovasc Electrophysiol, Vol. 21, pp. 56–61, January 2010)

AIMS In patients presenting with spontaneous sustained ventricular tachycardia (VT) from the outflow-tract region without overt structural heart disease ablation may target premature ventricular contractions (PVCs) when VT is not inducible. We aimed to determine whether inducibility of VT affects ablation outcome. METHODS AND RESULTS Data from 54 patients (31 men; age, 52 ± 13 years) without overt structural heart disease who underwent catheter ablation for symptomatic sustained VT originating from the right- or left-ventricular outflow region, including the great vessels. A single morphology of sustained VT was inducible in 18 (33%, SM group) patients, and 11 (20%) had multiple VT morphologies (MM group). VT was not inducible in 25 (46%) patients (VTni group). After ablation, VT was inducible in none of the SM group and in two (17%) patients in the MM group. In the VTni group, ablation targeted PVCs and 12 (48%) patients had some remaining PVCs after ablation. During follow-up (21 ± 19 months), VT recurred in 46% of VTni group, 40% of MM inducible group, and 6% of the SM inducible group (P = 0.004). Analysis of PVC morphology in the VTi group further supported the limitations of targeting PVCs in this population. CONCLUSION Absence of inducible VT and multiple VT morphologies are not uncommon in patients with documented sustained outflow-tract VT without overt structural heart disease. Inducible VT is associated with better outcomes, suggesting that attempts to induce VT to guide ablation are important in this population.

A 33-year-old man was referred to our center due to sustained ventricular tachycardia (VT).

UNLABELLED This study examined the relation between heart rate variability (HRV) and baroreflex sensitivity (BRS) and subsequent major arrhythmic events (MAE), defined as sustained VT, VF or sudden death, in 263 patients with idiopathic dilated cardiomyopathy (IDC) in sinus rhythm. The predefined measure of HRV was the standard deviation of all normal-to-normal RR intervals (SDNN) on baseline 24-hour ambulatory ECG. BRS was determined by the phenylephrine method. Over 52 +/- 21 months of follow-up, MAE occurred in 38 patients (14%). SDNN at baseline 24-hour ambulatory ECG (106 +/- 46 vs 109 +/- 45, ns) and BRS (7.9 +/- 5.5 vs 7.7 +/- 5.3 ms/mmHg, ns) were both similar in patients with versus without MAE during follow-up. In contrast, left ventricular ejection fraction was significantly lower in patients with versus without MAE (24%+/- 7% vs 31%+/- 10%, P < 0.019. CONCLUSIONS Neither HRV nor BRS predicted MAE in patients with IDC.

VT Ablation in a Patient with Peripartum Cardiomyopathy A 38-year-old female with prior failed endocardial ablation for ventricular tachycardia (VT) was referred for further treatment. She had been diagnosed with peripartum cardiomyopathy 7 years before and had persistent left ventricular dysfunction with an ejection fraction of 20%. Epicardial voltage mapping showed extensive epicardial scar despite absence of endocardial scar. Five distinct VT morphologies were induced. Ablation was aided by electrogram characteristics, pace mapping, entrainment mapping, and establishing electrical inexcitability along areas of epicardial scar. After epicardial ablation no sustained VT was induced. She had been doing well without VT occurrence but died 1 year later unexpectedly at home.

Ventricular tachycardia (VT) is considered to be the most common precursor of ventricular fibrillation (VF). However, the mechanisms underlying the transition from VT to VF remain unclear. Here, we investigated whether and how perfusion of the heart with verapamil, a blocker of L-type calcium channels, changed the macro-dynamics of the heart between VT and VF. The experiments were performed with Langendorff perfused isolated rat hearts, in which left ventricular pressure and left ventricular cardiomyogram were measured. Sustained VT or VF was induced by burst pacing of the left ventricular muscles. During sustained VF, verapamil perfusion resulted in the conversion of VF to VT. A cross-correlation analysis between left ventricular cardiomyogram and left ventricular pressure revealed that the correlation coefficient was small during VF, but became larger during VT. This study showed that inactivation of L-type Ca 2+ channels occurred during verapamil-induced conversion of pacing-induced sustained VF to VT, and characterized the changes in macro-dynamics of the heart associated with the transition.

Ventricular tachycardia (VT), especially when the patient presents with multiple episodes (storm) or when it is sustained, is a life-threatening emergency and requires prompt diagnosis and management. Our initial approach to the patient with ventricular tachycardia involves the assessment of several clinical issues: If the patient is in sustained VT, the arrhythmia should be urgently controlled with cardioversion and antiarrhythmic medications; the clinical dictum of assuming any wide complex rhythm to be VT until proven otherwise is a safe bet. Once stability is achieved, we typically look at the following issues carefully

The accuracy of information retrievable from the memories of DDDR pacing systems has been limited by the absence of actual electrograms confirming the proper sensing of spontaneous cardiac activity versus that of extraneous signals. This study examined the diagnostic power of a new arrhythmia interpretation scheme, which includes the recording and storage of high resolution endocavitary atrial and ventricular electrograms (HREGM). HREGM stored in the memories of new generation pacemakers (PM) in response to nonsustained ventricular tachycardia (NSVT), sustained VT, and atrial arrhythmias were analyzed in a follow-up registry of 520 patients at 1 month, and 3 to 6 months after implantation of a PM for standard indications. For each sequence of stored HREGM, the accuracy of the PM response was examined, classified as accurate (true positive), versus inaccurate (false positive), versus undetermined, and the relative contribution of the HREGM in verifying the PM diagnosis was measured. During a follow-up of 4.9 +/- 2 months, 256 (49%) of the 520 patients had an event recorded, which was confirmed to be arrhythmic on the basis of HREGM. Overall, approximately 34% of atrialtachy response (ATR) episodes were confirmed to be appropriate. Similar percentages of episodes were prompted by oversensing of signals unrelated to cardiac arrhythmias, while nearly 12% of the episodes could not be clarified because of such brief duration as to preclude recording of their onset. Approximately one-third of NSVT, and one-half of VT detections were false positive. Ventricular oversensing, most often due to myopotential interference in presence of unipolar sensing, and atrial undersensing were both identified as sources of false-positive detections of ventricular events. The proportion of true-positive detections was significantly higher in the bipolar (83%) than unipolar configuration. Among 520 PM recipients, miscellaneous episodes of atrial arrhythmias were confirmed by HREGM in 37% of patients within 3 to 6 months of follow-up. Atrial fibrillation was confirmed in only 6% of patients, of whom over 50% already had histories of atrial fibrillation. The prevalence of unsuspected atrial arrhythmia in this unselected population was lower than previously reported.

Some implantable cardioverter-defibrillators (ICD) are designed with a ventricular rate stabilization (VRS) algorithm triggered by sensing a pacemaker-defined ventricular premature complex, for the prevention of "short-long-short" sequences that may predispose to ventricular tachycardia (VT). The VRS algorithm initiates AV sequential pacing at a relatively fast and decreasing rate according to a programmable sequence. This report describes a complex manifestation of ICD function where activation of the VRS algorithm produced AV sequential pacing during sustained VT. This response occurs when there is an appropriate relationship between the timing cycles of the ICD and a relatively slow VT.

KORHONEN, P., ET AL.: Relation of Magnetocardiographic Arrhythmia Risk Parameters to Delayed Ventricular Conduction in Postinfarction Ventricular Tachycardia. Time-domain late field and intra-QRS fragmentation parameters in magnetocardiography (MCG) identify patients prone to VT after myocardial infarction. This study investigated if they are related to slow ventricular conduction and affected by arrhythmia surgery. Twenty-two patients with old myocardial infarction undergoing map-guided subendocardial resection to treat sustained VT were included. Bipolar electrograms were recorded during operation using an epicardial jacket and endocardial balloon electrode array. The time from the QRS onset to the end of local ventricular excitation in each electrogram was measured during sinus rhythm. Multichannel MCG was recorded before and after operation and filtered QRS duration (QRSd), root mean square amplitude of the magnetic field strength during the last 40 ms of the QRS complex (RMS 4 0 ), duration of the low amplitude signal < 300 fT (LAS 3 0 0 ), fragmentation index M (M), and fragmentation score S (S) were determined. All patients had one or two VT foci localized and resected. MCG parameters correlated with time to the latest end of ventricular excitation; r = 0.45 for QRSd (P = 0.035), r = 0.64 for M (P = 0.001), and r = 0.73 for S (P < 0.001). The correlations were even better in patients with anterior infarction (e.g., r = 0.87 for QRSd, P < 0.001; r = 0.91 for M, P < 0.001). The operation reduced the abnormalities in MCG parameters and 20 of the 21 patients tested postoperatively became noninducible. MCG parameters indicating postinfarction arrhythmia propensity are related to delayed ventricular conduction. Abolition of the arrhythmia substrate reverses the abnormality of these parameters.

Background — The reentrant mechanism of postinfarct ventricular tachycardia (VT) has been documented by surgical mapping analysis, but little is known about postinfarct VT circuits and the characteristics of their related protected isthmus with the use of 3D catheter mapping systems. Methods and Results — A 3D electroanatomic mapping was performed in 21 patients with well-tolerated, postinfarct, sustained VT. In total, 33 episodes of tachycardia (mean cycle length 432±74 ms) were induced and mapped. Complete maps demonstrated macroreentrant circuits with 1 loop (n=8) or 2 loops (n=25) rotating around a protected isthmus bounded by 2 approximately parallel conduction barriers that consisted of a line of double potentials, a scar area, or the mitral annulus. A total of 26 critical isthmi were identified for the 33 VTs mapped, with the same isthmus being shared by 2 to 4 different tachycardic morphologies in 5 patients. On average, isthmi were 31±7 mm long (ranging from 18 to 41 mm) and 16±8 mm wide (ranging from 6 to 36 mm) and harbored diastolic electrograms. The isthmus axis was oriented parallel to the mitral annulus plane in perimitral circuits and perpendicular to the mitral annulus plane in all other circuits. Linear radiofrequency ablation performed across the most accessible part of the isthmus prevented the recurrence of tachycardia in 19 patients (90%) with a follow-up at 16±8 months. Conclusions — Detailed 3D electroanatomic mapping is helpful in reconstructing postinfarct VT circuits and in defining the characteristics of their related protected isthmi. The wide range of isthmus width values supports the need of linear radiofrequency lesions to eliminate the reentrant substrate of postinfarct VTs.

and Management of Ventricular Arrhythmias in the Child With a Structurally Normal Heart Jane E. Crosson, MD, FACC (Chair), David J. Callans, MD, FHRS, FACC, FAHA (Chair), David J. Bradley, MD, FACC, FAAP, Anne Dubin, MD, FHRS, FAHA, FACC, Michael Epstein, MD, FACC, CCDC, Susan Etheridge, MD, FHRS, FACC, FAAP, CEPS, Andrew Papez, MD, FHRS, CCDS, John R. Phillips, MD, FAAP, FHRS, FACC, Larry A. Rhodes, MD, FAAP, FHRS, FACC, Philip Saul, MD, FHRS, FACC, FAHA, Elizabeth Stephenson, MD, MSc, FHRS, CCDS, CEPS, William Stevenson, MD, FAHA, FHRS, FACC, Frank Zimmerman, MD, FAHA, FHRS From the Bloomberg Children’s Center, Johns Hopkins University School of Medicine, Baltimore, Maryland, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, C.S. Mott Children’s Hospital, Anne Arbor, Michigan, Lucile Packard Children’s Hospital, Stanford School of Medicine, Stanford, California, Maine Medical Center, Portland, Maine, University of Utah and Primary Children’s Medical Center, Salt Lake City, Utah, Phoenix Children’s Hospital/Arizona Pediatric Cardiology Consultants Phoenix, Arizona, WVUH Children’s Hospital, Morgantown, West Virginia, Nationwide Children’s Hospital, Ohio State University, Columbus, Ohio, University of Toronto, Toronto, Ontario, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, and Advocate Heart Institute for Children Advocate Children’s Hospital, Oak Lawn, Illinois.

Sudden cardiac death is the main cause of mortality in patients affected by chronic heart failure (CHF) and with history of myocardial infarction. No study yet investigated the intra-QT phase spectral coherence as a possible tool in stratifying the arrhythmic susceptibility in patients at risk of sudden cardiac death (SCD). We, therefore, assessed possible difference in spectral coherence between the ECG segment extending from theqwave to theTwave peak (QTp) and the one fromTwave peak to theTwave end (Te) between patients with and without Holter ECG-documented sustained ventricular tachycardia (VT). None of the QT variability indexes as well as most of the coherences and RR power spectral variables significantly differed between the two groups except for theQTp-Tespectral coherence. The latter was significantly lower in patients with sustained VT than in those without (0.508±0.150versus0.607±0.150,P<0.05). Although the responsible mechanism remains conjectural, theQTp-Tespectral coherence holds promise as a noninvasive marker predicting malignant ventricular arrhythmias.

KULAKOWSKI, P., et al.: QT Interval Dispersion in Ventricular Beats: A Noninvasive Marker of Susceptibility to Sustained Ventricular Arrhythmias. Increased QT dispersion (QTd) calculated from sinus beats has been shown to identify patients prone to sustained VT. However, predictive accuracy of this parameter is limited. Electrophysiological properties of the myocardium may be altered by a premature ventricular beats, which is a well-established trigger for sustained VT. Therefore, the author hypothesised that QTd in spontaneous or paced ventricular beats may improve identification of patients with inducible sustained VT. In 28 consecutive patients (men, mean age 61 ± 13 years) who underwent programmed ventricular stimulation, the values of QTd calculated in sinus and ventricular beats were compared between inducible and noninducible patients. The mean QTd values obtained using three different methods differed significantly, QTd in paced ventricular beats being the highest, QTd in spontaneous ventricular beats was intermediate, and QTd in sinus beats was the lowest (83.9 ± 30 vs 63.0 ± 29 ms vs 53.9 ± 27 ms, P < 0.0001 and P < 0.004, respectively). In 13 (46%) patients sustained VT was induced. QTd values were significantly higher in inducible than noninducible patients (QTd sinus beats: 67.5 ± 31 vs 42.1 ± 11 ms, P = 0.02; QTd spontaneous ventricular beats: 79.3 ± 35 vs 46.7 ± 13 ms, P = 0.008, and QTd-paced ventricular beats: 104.8 ± 32 vs 65.9 ± 9 ms, P = 0.0009). The receiver operator characteristic curves showed that at a sensitivity level of 100%, the highest specificity for identification of inducible patients had QTd measured in paced ventricular beats (87%) followed by QTd in spontaneous ventricular beats (45%), and QTd in sinus beats (40%). In conclusion, (1) QTd in ventricular beats is greater than in sinus beats, and (2) QTd calculated from paced ventricular beats identifies patients with inducible sustained VT better than QTd measured during sinus rhythm.

Between 1980 and 1996, 89 unselected consecutive patients with repaired tetralogy of Fallot (TOF) underwent examination, including a prospective right ventricular programmed stimulation with the same protocol (S1 S2, S3, S4). Age at surgery was 4.2 +/- 3.5 years and age at electrophysiologic study was 10.9 +/- 6.5 years. Follow-up since surgery was 14.4 +/- 4.8 years and patient follow-up after programmed stimulation was 7.8 +/- 4.2 years. The aim of this study was to evaluate the main predictors of the inducibility of a sustained monomorphic ventricular tachycardia (VT) and its significance to identify a group of patients at risk of sudden death: 21 (group A) had and 68 (group B) had no induced sustained VT. The induction of VT was related to older age at programmed stimulation, prolonged QRS duration, presence of complex ventricular arrhythmia, symptoms, right ventricular overload, and increased right ventricular systolic pressure. Predictors of induced VT selected by multivariate analysis were age at electrophysiologic study (p0.0001), previous palliative shunts (p0.001), right ventricular systolic pressure (p0.007), and symptoms (p0.005). Among group A patients, 4 had previous sustained VT before stimulation, and 1 had sustained VT only during follow-up after stimulation. No patients of group B had clinical sustained VT. Late mortality was low but similar between both groups. A negative electrophysiologic study may be helpful for the management of patients after surgical repair of TOF, but because the arrhythmic event rate is low, the findings of even a positive electrophysiologic study should be interpreted with caution.

Procainamide and T-Wave Alternans. Introduction: The measurement of microvolt level T wave alternans (TWA) is a technique for detecting arrhythmia vulnerability. Previous studies demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of antiarrhythmic drugs on TWA are unknown. Methods and Results: This was a prospective evaluation of intravenous procainamide on TWA in 24 subjects with inducible sustained ventricular tachycardia (VT). Measurements of TWA were performed at baseline in the drug-free state and after procainamide loading (1,204 ± 278 mg). Recordings were made in normal sinus rhythm, and during atrial pacing at 100 heats/min and 120 heats/min. The magnitude of TWA in the vector magnitude lead was decreased by procainamide at all heart rates: 0.6 ± 0.8 to 0.3 ± 0.4 μV in sinus rhythm, 2.0 ± 1.6 to 0.7 ± 0.7 μV at 100 beats/min, and 3.0 ± 2.0 to 1.7 ± 1.8 μV at 120 beats/min (P < 0.001 by analysis of variance). The sensitivity of TWA for the induction of VT at baseline was 5% in sinus, 60% at 100 beats/min, and 87% at 120 beats/min, while it decreased with procainamide to 5%, 19%, and 60%, respectively. Decreases in TWA in response to procainamide were independent of the antiarrhythmic effects on VT inducibility. Conclusions: These results indicate that the magnitude of TWA decreases with acute procainamide loading and this effect decreases the sensitivity of TWA for the induction of sustained VT.

Radiofrequency catheter ablation has been useful in the treatment of ventricular tachycardia (VT) in selected patients with healed myocardial infarction. Previous studies have demonstrated success rates of 60% to 96% for targeted VT morphologies; however, these studies included patients only after they have had successful mapping procedures and have received radiofrequency lesions. All patients referred for VT ablation from July 1992 to November 1996 were included in this analysis on an intention-to-treat basis. Ninety-five procedures were performed in 66 patients for 77 distinct presentations with tolerated, sustained VT. Fifty-five procedures were successful (58%) and 40 procedures failed. Reasons for procedural failure included failed radiofrequency application despite adequate VT mapping (21 procedures), no tolerated VT induced (12), and aborted procedures due to complications or technical difficulties (7). Fifty-five patients (71%) eventually had a successful VT ablation, although 10 required >1 procedure. This analysis revealed factors that contribute to failure of VT ablation procedures in addition to inadequate mapping and lesion formation. Procedural difficulties, particularly the inability to induce tolerated VT, frequently prevent successful catheter ablation in patients who present with tolerated, sustained VT.

Unnecessary shocks by ICDs for rhythms other than sustained VT or VF have been described as the most frequent adverse event in ICD patients. To avoid unnecessary shocks for self-terminating arrhythmias, the third-generation Jewel PCD defibrillators 7202, 7219, and 7220 Plus use a specially designed VF confirmation algorithm after charge end. The purpose of this study was to determine the ability of this VF confirmation algorithm to recognize nonsustained VT, and to analyze the reasons for failure of the PCD device to abort shock therapy for nonsustained VT despite use of this VF confirmation algorithm. Analysis of stored electrograms of electrical events triggering high voltage capacitor charging in the programmed VF zone of the device showed 36 spontaneous episodes of nonsustained VT (227 +/- 21 beats/min) during 18 +/- 7 months follow-up in 15 patients who had a Jewel PCD implanted at our hospital. Intracardiac electrogram recordings and simultaneously retrieved marker channels demonstrated that the ICD shock was appropriately aborted according to the VF confirmation algorithm in 24 (67%) of 36 episodes of nonsustained VT. Twelve episodes (33%) of nonsustained VT, however, were followed by spontaneous ICD shock in 6 (40%) of the 15 study patients. The only reason for all 12 shocks for sustained VT was the inability of the device to recognize the absence of VT after charge end due to shortcomings of the VF confirmation algorithm: 11 of the 12 shocks for nonsustained VT were triggered by the occurrence of paced beats during the VF confirmation period and 1 shock for nonsustained VT was triggered by the occurrence of 2 premature beats after charge end. Thus, better VF confirmation algorithms need to be incorporated in future PCD devices to avoid unnecessary shocks for nonsustained VT.