T-wave Oversensing Research Articles

Long-term follow-up of subcutaneous ICD systems in patients with hypertrophic cardiomyopathy: a single-center experience.

The totally subcutaneous implantable defibrillator (S-ICD) was introduced as a new alternative to conventional implantable defibrillators and is employed worldwide. This system is especially attractive for young patients. However, in patients with hypertrophic cardiomyopathy (HCM), T-wave oversensing may occur. To address the question whether the S-ICD system is suitable for HCM patients, the data of a standard of care prospective single-center S-ICD registry were evaluated. In the present study, 18 HCM patients who received an S-ICD for primary (n = 14) or secondary prevention (n = 4) and a minimal follow-up duration of 6 months were analyzed. The mean follow-up duration was 31.7 ± 15.4 months. Ventricular arrhythmias were adequately detected in 4 patients (22%). In 7 patients (39%), T-wave oversensing was noticed and led to at least one inappropriate shock in 4 patients (22%). Further adverse events included surgical revision due to a mobile sensing electrode and resulting noise detection as well as one case of early battery failure requiring pulse generator change. Patients with HCM and S-ICD systems have an increased risk of T-wave oversensing and inappropriate shock delivery. Thorough monitoring as well as exercise tests may help to improve device settings and thereby prevent T-wave oversensing.

T-wave oversensing in patients with Brugada syndrome: true bipolar versus integrated bipolar implantable cardioverter defibrillator leads: multicenter retrospective study.

It is thought that dedicated bipolar are more susceptible to T-wave oversensing when compared with integrated bipolar leads. This could be of extreme importance in patients with Brugada syndrome (BrS) because T-wave oversensing in this population is more frequent when compared with other implantable cardioverter defibrillator (ICD) recipients without BrS. We aimed to compare the incidence of T-wave oversensing in patients with BrS according to the type of lead (integrated bipolar versus true/dedicated bipolar). All patients diagnosed with BrS with an ICD implant in 10 tertiary hospitals between 1993 and 2013 were included in the study. A total of 480 patients were included (mean age, 45.6±14 years). During a mean follow-up of 74.9±51.7 months (median, 69; range, 2-236), 28 patients had T-wave oversensing (5.8%), leading to inappropriate shock in 18 (3.8%). All these events occurred in patients with true bipolar ICD leads (P=0.01) and in 2 patients it was solved instantaneously by changing the configuration from a dedicated to an integrated bipolar sensing configuration. In the stepwise multivariate models, only integrated bipolar ICD leads (hazard ratio, 0.34; 95% confidence interval, 0.171-0.675; P=0.002) was independent predictor of non-T-wave oversensing. T-wave oversensing is a potential reason of inappropriate shocks in patients with BrS receiving ICDs. In the vast majority it can be solved by reprogramming. However, in some patients it still requires invasive intervention. Importantly, incidence is significantly lower using an integrated bipolar lead system when compared with a dedicated bipolar lead system and hence the latter should be routinely used in BrS cases.

A case of inappropriate implantable cardioverter defibrillator therapy induced by T-wave oversensing due to hyperkalemia

There have been reports of hyperkalemia-induced T-wave oversensing in patients with implantable cardioverter defibrillators (ICDs). However, a comparison of T-wave amplitudes and morphologies between the surface 12-lead electrocardiogram (ECG) and ICD electrogram has not been reported. We present the case of a 70-year-old man who received inappropriate ICD shocks due to hyperkalemia-induced T-wave oversensing. The T-wave amplitudes on both the ICD electrogram and 12-lead ECG corresponded and normalized after normalization of the potassium level.

Inappropriate shocks in the subcutaneous ICD: Incidence, predictors and management

BackgroundThe entirely subcutaneous implantable cardioverter-defibrillator (S-ICD) eliminates the need for transvenous leads, and therefore has the potential to improve lead-longevity and reduce lead-related complications. The S-ICD has a morphology-based sensing algorithm of which inappropriate shocks have been reported. MethodsWe analyzed the incidence, predictors and management of inappropriate shocks in the EFFORTLESS S-ICD Registry, which collects S-ICD implantation information and follow-up data from clinical centers in Europe and New Zealand. ResultsDuring a follow-up of 21±13months, 48 out of 581 S-ICD patients (71% male, age 49±18years) experienced 101 inappropriate shocks (8.3%). The most common cause was cardiac signal oversensing (73%), such as T-wave oversensing. Eighteen shocks (18%) were due to supraventricular tachycardias (SVT), of which 15 occurred in the shock-only zone. Cox-proportional hazard modeling using time-dependent covariates demonstrated that patients with a history of atrial fibrillation (HR 2.4) and patients with hypertrophic cardiomyopathy (HR 4.6) had an increased risk for inappropriate shocks, while programming the primary vector for sensing (from xyphoid to V6) reduced the risk. Reprogramming or optimization of SVT treatment after the first clinical event of inappropriate shock was successful in preventing further inappropriate shocks for cardiac oversensing and SVT events. ConclusionsInappropriate shocks, mainly due to cardiac oversensing, occurred in 8.3% of the S-ICD patients. Patients with hypertrophic cardiomyopathy or a history of atrial fibrillation were at increased risk, warranting specific attention for sensing and programming in this population.

Recent advances in the entirely subcutaneous ICD System.

The entirely subcutaneous implantable cardioverter defibrillator (S-ICD®) is emerging as a widely accepted therapeutic alternative to a conventional implantable cardioverter defibrillator (ICD) for prevention of sudden cardiac death. Essentially, the S-ICD® is promising in terms of reduction of electrode-related complications such as lead failure and infections. The conventional transvenous ICD has proven efficacy in various randomized clinical trials. The first results of S-ICD® studies confirm efficacy and safety in primary and secondary prevention as well. Owing to basic differences between S-ICD® and transvenous ICD—such as limited programming options and lack of pacing—not all patients are eligible for the S-ICD®. Concerns exist regarding inappropriate shocks due to T-wave oversensing, dimensions of the device, and shorter battery longevity. However, the S-ICD® should be considered a useful supplementation of ICD therapy in those patients at risk for sudden cardiac death who are not expected to require pacing due to bradycardia or antitachycardic pacing.

Myocardial Ischemic Hyperacute T-Wave Oversensing Leading to a Defibrillator Shock Storm

Appropriate sensing is essential for the normal functioning of an implantable cardioverter defibrillator (ICD). T-wave oversensing is a potential clinical problem in ICD patients that may result in inappropriate shocks. Oversensing may have various underlying causes and can be treated with noninvasive or invasive means. We present the case of a 45-year-old man presenting with shock storm as a result of T-wave oversensing. Workup revealed a hemodynamically significant stenosis of the left anterior descending artery treated with percutaneous coronary intervention and drug-eluting stent placement. This resulted in the resolution of T-wave missensing and restoration of normal ICD functioning.

Inappropriate ICD shocks in pediatrics and congenital heart disease patients: Risk factors and programming strategies.

Inappropriate implantable cardioverter-defibrillator (ICD) shocks are a common and significant problem in pediatric patients and patients with congenital heart disease (CHD). The purpose of this study was to evaluate the effect of programming high detection rates and long detection duration on inappropriate shocks in this population. We performed a retrospective review of all patients with ICDs at a single pediatric center. Inappropriate shocks were defined as a shock for any rhythm except ventricular tachycardia or fibrillation. A total of 144 patients were included, 63 (44%) with CHD. At implant, mean age and weight were 17 ± 10 years and 57 ± 23 kg. ICDs were single chamber in 35 (24%), dual chamber in 97 (67%), and biventricular in 12 (8%). The mean follow-up duration was 42 ± 39 months. Appropriate shocks occurred in 29 (20.1%) and inappropriate shocks in 14 (9.7%). Causes of inappropriate shocks were supraventricular tachycardia (n = 6), lead malfunction (n = 4), sinus tachycardia (n = 3), and T-wave oversensing (n = 1). The mean ventricular fibrillation detection rate was 222 ± 15 beats/min, and the detection duration was 18 ± 12 beats. Patients with shocks programmed in the ventricular tachycardia zone were more likely to receive an inappropriate shock (P = .03). There were no associations between inappropriate shocks and age or weight at implant, presence of CHD, dual-chamber vs single-chamber device, history of supraventricular tachycardia, or antiarrhythmic use. There were no adverse events as a result of programming. Programming high detection rates and long detection duration resulted in a low rate of inappropriate shocks without associated adverse events in this large cohort of pediatric and CHD patients with ICDs.

Early failure of the Biotronik Linox implantable cardioverter defibrillator lead.

The Linox and Durata implantable cardioverter defibrillator (ICD) leads were introduced to British Columbia (BC) in 2008. We determined their performance and the potential risk factors for lead failure in a large population-based patient registry. We used the BC Cardiac Registry, a mandatory Governmental database of ICD implants, to identify all recipients of Linox and Durata leads in BC between October 2008 and April 2012, and those subsequently undergoing reoperation. Lead failure was defined as recurrent nonphysiological high-rate sensing unrelated to external electromagnetic interference or T-wave oversensing; a sudden rise in impedance unrelated to perforation or lead dislodgement; or abnormal lead parameters with definite evidence of lead fracture or insulation failure. We determined the estimated cumulative lead survival by the Kaplan-Meier method, and the risk factors for lead failure in a proportional hazards model. Over a median of 39 (27-50) months, the Linox failed more frequently than the Durata (16/477 [3.4%] vs. 4/838 [0.4%]; P < 0.001), and had a significantly lower estimated cumulative survival (91.6 [80.6-96.5]% vs. 99.4 [98.4-99.8]% at 5 years; P < 0.0001). Linox failure was characterized by high-rate nonphysiological sensing (11 cases), and/or a sudden impedance rise (7 cases). Insulation failure was clearly confirmed in 6 cases of Linox failure. Female sex was a significant risk factor for Linox failure (adjusted HR = 2.1[1.3-3.4]; P = 0.004). This multicenter registry indicates a high rate of Linox lead failure, particularly in female patients. Ongoing surveillance of the Linox ICD lead performance is recommended.

Maneuvers to eliminate loss of biventricular pacing due to T-wave oversensing

Maneuvers to eliminate loss of biventricular pacing due to T-wave oversensing

Catheter ablation of atrial tachyarrhythmias causing inappropriate implantable cardioverter-defibrillator shocks.

Inappropriate shocks have been an important issue post-implantable cardioverter-defibrillator (ICD) implantation. Moreover, inappropriate ICD shocks are associated with increased mortality. The objective of this study was to evaluate the feasibility of catheter ablation therapy for atrial tachyarrhythmias (ATa) responsible for inappropriate ICD shocks. Among 108 consecutive patients who underwent ICD implantations, 22, 5, and 3 experienced inappropriate ICD shocks due to ATa, sinus tachycardia, and T-wave oversensing, respectively. Among the 22 patients with ATa, 18 patients (55 ± 10 years, 15 men, structural heart disease in 9) underwent catheter ablation of ATa causing inappropriate shocks. The median duration between the ICD implantation and first inappropriate shock was 10.0 (3.0-24.5) months. The ATa were atrial fibrillation (AF), atrial flutter (AFL), and atrioventricular nodal reentrant tachycardia in 14, 2, and 2 patients, respectively. One patient underwent an atrioventricular nodal ablation for persistent AF associated with a venous anomaly. Among 13 patients who underwent pulmonary vein antrum isolation, 10 (76.9%) were free from AF for a median of 21.0 (13-37.3) months after an average of 1.3 ± 0.5 procedures. In four patients with AFL or a supraventricular tachycardia, none had any arrhythmia recurrence for a median of 6.0 (3.3-93.5) months after a cavotricuspid isthmus or slow pathway ablation, respectively. There were no procedural complications. During the median follow-up of 19.0 (9.5-37.3) months after the last procedure, no patients experienced any inappropriate shocks. Catheter ablation is a feasible therapeutic option for treating ATa responsible for inappropriate shock(s) in patients with ICD.

A simple pacing maneuver to overcome T-wave oversensing and ensure complete biventricular pacing

I have read with great interest the article entitled ‘Loss of biventricular pacing due to T wave oversensing: Case report and review of the literature’ by Korantzopoulos et al. [ [1] Korantzopoulos P. Kyrlas K. Goudevenos J.A. Loss of biventricular pacing due to T wave oversensing: case report and review of the literature. Int J Cardiol. 2013; 168: 1626-1628 Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar ]. They have represented a case with the loss of biventricular pacing due to T-wave oversensing (TWOS) and the restoration of biventricular pacing was accompanied by lowering the ventricular sensitivity. They have also mentioned about potential solutions to overcome TWOS problem. Atrial tachycardia/atrial fibrillation accounted for the majority of cardiac resynchronization therapy (CRT) loss. However, many programmable causes of CRT loss such as TWOS might also be detected.

Implantable cardioverter-defibrillators in patients with arrhythmogenic right ventricular cardiomyopathy: the course of electronic parameters, clinical features, and complications during long-term follow-up.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a progressive cardiomyopathy characterized by myocardial atrophy and fibro-fatty replacement of the right ventricle (RV) and ventricular tachyarrhythmias in young patients. Our aim was to evaluate clinical course and electronic parameters in patients with implantable cardioverter-defibrillator (ICD) and ARVC, during long-term follow-up. We report on 12 patients with ARVC (mean age 40 ± 13 years) who were treated with ICD implantation in our center. Although several RV sites were tested for proper lead positions, the amplitude of R-wave at implantation was quite low (7.4 ± 3.0 mV). After a mean follow-up of 91 ± 28 months, R-wave amplitude significantly decreased to a mean value of 5.4 ± 2.5 mV (p=0.03). We also found a noticeable, nearly significant increase in pacing threshold (p=0.052) and a moderate increase in defibrillation impedance (p=0.07). Six patients (46 %) experienced at least one appropriate ICD therapy; three patients (23 %) experienced inappropriate ICD shocks secondary to the supraventricular tachycardia, T-wave oversensing, and electromagnetic interference. ICD in patients with ARVC has been demonstrated to be feasible and safe. In our case series, we found low R-wave amplitudes at implantation and a significant R-wave decrease during follow-up; a considerable and nearly significant increase in pacing threshold was also observed. These findings may be related to the progressive fibro-fatty replacement of RV myocardium. Multiple sites should be tested in the right ventricle if sensing or pacing values are not optimal, and all the electronic parameters should be carefully monitored throughout the entire follow-up.

Use of an electrocardiographic screening tool to determine candidacy for a subcutaneous implantable cardioverter-defibrillator

An electrocardiographic (ECG) screening test has been developed to identify patients being considered for a totally subcutaneous implantable cardioverter-defibrillator (S-ICD) at risk for T-wave oversensing. The purpose of this study was to determine the proportion of potential S-ICD recipients who fail the ECG screening test and to identify predictors of failure. Patients who already have an ICD but are not receiving antibradycardia pacing are representative of patients who might be considered for an S-ICD. One hundred such outpatients were enrolled in the study. Surface rhythm strips were recorded along the sensing vectors of the S-ICD system and the screening template applied. Clinical and standard ECG characteristics of patients who failed the test were compared to those who passed. Patients had the following characteristics: 72% male, age 57 ± 16 years, body mass index 29 ± 6 kg/m(2), left ventricular ejection fraction 43% ± 17%, QRS duration 109 ± 23 ms, QTc interval 447 ± 39 ms, 44% had coronary disease, and 55% had heart failure. Among the 100 patients, 8% failed the screening test. There were no differences in patient clinical characteristics and most standard ECG measurements. However, patients with T-wave inversions in standard ECG leads I, II, and aVF had a 45% chance of failing. Eight percent of potential S-ICD patients were not eligible for the S-ICD after failing the screening test designed to identify patients susceptible to T-wave oversensing. Patients with T-wave inversions in leads I, II, and aVF on a standard ECG were 23 times more likely to fail. More work is needed in S-ICD sensing algorithms to increase patient eligibility for the S-ICD.

Abnormal Cellular Repolarization due to Implantable Cardioverter Defibrillator Shock: A Case Report

Implantable cardioverter-defibrillators (ICDs) have a considerable impact on the therapy of patients with threatening ventricular arrhythmias, significantly reducing the risk of sudden death. Even though newest devices have achieved a remarkable reliability, the delivery of inappropriate shocks is still possible. In this paper a singular case of T-wave oversensing is described, associated with a high number of inappropriate shocks and consequent rapid depletion of ICD battery. Persistent abnormalities of cellular repolarization following a first appropriate shock were believed to be at the origin of T-wave oversensing. J Med Cases. 2014;5(2):92-97 doi: http://dx.doi.org/10.14740/jmc1642w

Cardiology News /Recent Literature Review / Fourth Quarter 2013

ACC Congress 2014: Washington, DC, 29-31/3/2014 Athens Cardiology Update 2014 : Athens (Crown Plaza Hotel), 10-12/4/2014 HRS Meeting: San Francisco, 7-10/5/2014 EuroPCR : Paris, 20-23/5/2014 CardioStim 2014: Nice, 18-21/6/2014 ESC Congress 2014 (Barcelona, 30/8-3/9/14) O nly One Fifth of the Sudden Cardiac Arrest Victims in the Community are Eligible for a Primary Prevention ICD Before the Event, but Among These, a Small Proportion (13%) are Actually Implanted According to data from the Oregon Sudden Unexpected Death study, among 2093 victims of sudden cardiac arrest (SCA) over a decade, of 448 having information about left ventricular ejection fraction (LVEF), 92 (20.5%) were eligible for primary ICD implantation, 304 (67.9%) were ineligible because of LVEF>35%, & the remainder (52, 11.6%) had LVEF ≤35% but were ineligible on the basis of clinical criteria. Among eligible subjects, only 12 (13%) received a primary ICD. Compared with recipients, ICD nonrecipients were older (age at LVEF assessment, 67.1±13.6 vs 58.5±14.8 years, P =0.05), with 20% aged ≥80 years (vs 0% among recipients, P =NS). Additionally, a subgroup (26%) had either a clinical history of dementia or were undergoing chronic dialysis. The authors concluded that only one fifth of the SCA cases in the community were eligible for a primary prevention ICD before the event, but among these, a small proportion (13%) were actually implanted. Although older age and comorbidity may explain nondeployment in a subgroup of these cases, other determinants such as socioeconomic factors, health insurance, patient preference, and clinical practice patterns may play a role (Narayanan K, et al, Circulation 2013;128:1733-1738). Appropriate ICD Therapies over 10 Years are More Prevalent in Symptomatic Brugada Syndrome (19-48%) but Still Occur in Asymptomatic Patients (12%) A total of 378 patients (310 men; aged 46±13 years) with a type 1 Brugada ECG pattern were implanted with an implantable cardioverter-defibrillator-ICD; 31 for aborted sudden cardiac arrest, 181 for syncope, and 166 asymptomatic. During a mean follow-up of 77±42 months for 363 patients, 7 patients (2%) died (1 as a result of an inappropriate shock), and 46 patients (12%) had appropriate device therapy (5±5 shocks per patient). Appropriate device therapy rates at 10 years were 48% for patients whose ICD indication was aborted sudden cardiac arrest, 19% for those with syncope, and 12% for the asymptomatic patients. At 10 years, rates of inappropriate shock and lead failure were 37% and 29%, respectively. Inappropriate shock occurred in 91 patients (24%) because of lead failure (n=38), supraventricular tachycardia (n=20), T-wave oversensing (n=14), or sinus tachycardia (n=12). Reduced inappropriate shocks were noted with introduction of remote monitoring, programming a high single ventricular fibrillation zone (>210–220 bpm), and a long detection time. The authors concluded that appropriate therapies are more prevalent in symptomatic Brugada syndrome but are not insignificant in asymptomatic patients (1%/y). Optimal ICD programming and remote monitoring dramatically reduce inappropriate shocks. However, lead failure remains a major problem in this population (Sacher F et al, Circulation 2013;128: 1739-1747)... (excerpt)

Inappropriate subcutaneous implantable cardioverter-defibrillator shocks due to T-wave oversensing can be prevented: Implications for management

Inappropriate shocks (IASs) complicate implantable cardioverter-defibrillator (ICD) therapy. The management of IASs in patients with a subcutaneous ICD (S-ICD) differs from that in patients with a conventional ICD because of different sensing algorithms and programming options. To describe the management of IASs in patients with an S-ICD. Patients were implanted with an S-ICD between February 2009 and July 2012. The prevalence data and clinical determinants of IASs were prospectively collected. In the case of T-wave oversensing (TWOS), an exercise test was performed, and all possible sensing vectors were screened for TWOS. The absence of TWOS defined a suitable vector. Eleven of 69 patients (54% men; mean age 39 ± 14 years; 73% primary prevention) received IASs after 8.9 ± 10 months of implantation (10.8% annual incidence rate). In 8 cases, TWOS caused IASs. Seven of these IASs occurred during exercise and 1 during atrial fibrillation with a high ventricular rate. To manage TWOS, in 7 of 8 patients the sensing vector was changed and in 5 of 8 patients the (un)conditional zone was changed. Hereafter, IASs recurred in 3 of 8 patients, in 2 because of programming errors. Hence, after reprogramming, we observed no IASs in 87.5% of the patients with TWOS during a follow-up of 14.1 ± 13 months. IASs due to TWOS in the S-ICD can be managed by reprogramming the sensing vector and/or the therapy zones of the device using a template acquired during exercise. Exercise-optimized programming can reduce future IASs, and standard exercise testing shortly after the implantation of an S-ICD may be considered in patients at an increased risk for TWOS.

Who Should Receive the Subcutaneous Implanted Defibrillator?

On September 28, 2012, the US Food and Drug Administration approved the totally subcutaneous implantable cardioverter defibrillator (S-ICD) for the treatment of life-threatening ventricular tachyarrhythmias in patients who do not have symptomatic bradycardia, incessant ventricular tachycardia (VT), or spontaneous, frequently recurring VT that is reliably terminated with antitachycardia pacing (ATP). These devices hold the promise of life-saving defibrillation without some of the known problems of transvenous defibrillator systems (TV-ICD), including limited vascular access, transvenous lead durability, hazardous lead extractions, and risks of bloodstream infections. There are trade-offs with the S-ICD devices including reports of increased infections and the inability to deliver ATP. The subcutaneous position of the electrodes requires higher energy delivery with longer charge times. In addition, sophisticated signal processing is required for accurate arrhythmia detection and diagnosis. As we consider the appropriate patient population for S-ICD therapy, it is important to review the trade-offs of this system compared with traditional TV-ICD systems. Response by Poole and Gold on p 1251 Unlike transvenous ICDs that sense the local ventricular myocardial depolarization with an endocardial bipolar electrode, the S-ICD records a signal from 2 of its 3 subcutaneous electrodes. These are the distal sensing electrode located at the lead tip, a proximal sensing electrode located 14 cm proximal to the distal electrode, and the pulse generator itself. By their nature, the S-ICD signals are more susceptible to external and myopotential noise, as well as T-wave oversensing. Thus, sophisticated algorithms have been developed to filter noise from the true cardiac signals.1 Nevertheless, oversensing is responsible for the majority of inappropriate shocks in these systems as reported in a recent multicenter case–control study.2 The competing concern is that of undersensing true arrhythmias that can lead to delays in therapies. The best data available on S-ICD time to therapy come from …

Outcome After Implantation of a Cardioverter-Defibrillator in Patients With Brugada Syndrome

Background— Implantable cardioverter-defibrillator indications in Brugada syndrome remain controversial, especially in asymptomatic patients. Previous outcome data are limited by relatively small numbers of patients or short follow-up durations. We report the outcome of patients with Brugada syndrome implanted with an implantable cardioverter-defibrillator in a large multicenter registry. Methods and Results— A total of 378 patients (310 male; age, 46±13 years) with a type 1 Brugada ECG pattern implanted with an implantable cardioverter-defibrillator (31 for aborted sudden cardiac arrest, 181 for syncope, and 166 asymptomatic) were included. Fifteen patients (4%) were lost to follow-up. During a mean follow-up of 77±42 months, 7 patients (2%) died (1 as a result of an inappropriate shock), and 46 patients (12%) had appropriate device therapy (5±5 shocks per patient). Appropriate device therapy rates at 10 years were 48% for patients whose implantable cardioverter-defibrillator indication was aborted sudden cardiac arrest, 19% for those whose indication was syncope, and 12% for the patients who were asymptomatic at implantation. At 10 years, rates of inappropriate shock and lead failure were 37% and 29%, respectively. Inappropriate shock occurred in 91 patients (24%; 4±4 shocks per patient) because of lead failure (n=38), supraventricular tachycardia (n=20), T-wave oversensing (n=14), or sinus tachycardia (n=12). Importantly, introduction of remote monitoring, programming a high single ventricular fibrillation zone (&gt;210–220 bpm), and a long detection time were associated with a reduced risk of inappropriate shock. Conclusions— Appropriate therapies are more prevalent in symptomatic Brugada syndrome patients but are not insignificant in asymptomatic patients (1%/y). Optimal implantable cardioverter-defibrillator programming and follow-up dramatically reduce inappropriate shock. However, lead failure remains a major problem in this population.

Outcomes of defibrillator therapy in catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterized by adrenergically induced ventricular arrhythmias in patients with structurally normal hearts. Initiating triggered arrhythmias, such as bidirectional ventricular tachycardia, often degenerate into reentrant arrhythmias, such as ventricular fibrillation (VF). To determine whether the effectiveness of implantable cardioverter-defibrillator (ICD) shocks is dependent on rhythm type. It is a retrospective study of patients with CPVT who had undergone ICD implantation. Thirteen patients received ICDs (median age 15 years; range 9-43 years): 7 of 13 (54%) for cardiac arrest and 6 of 13 (46%) for syncope despite drug therapy. The median follow-up duration was 4.0 years (range 1.7-19.9 years). Nineteen reinterventions occurred, excluding generator replacements. Ten patients received 96 shocks (median 4 shocks; range 1-30 shocks). Eighty-seven shock electrograms were reviewed. Sixty-three (72%) shocks were appropriate, and 24 (28%) were inappropriate (T-wave oversensing 7 [29%], supraventricular arrhythmia 16 [67%], after self-terminating VF 1 [4%]). Among appropriate shocks, 20 (32%) were effective in terminating sustained arrhythmia and 43 (68%) were ineffective. Shocks delivered to triggered arrhythmias nearly always failed (1 of 40 [3%] effective), while shocks delivered to VF were usually successful (19 of 23 [83%] effective; P < .001). Four patients received 17 appropriate antitachycardia pacing therapies for ventricular tachycardia: only 2 (12%) were effective. No patient died. The effectiveness of ICD shock therapy in CPVT depends on the mechanism of the rhythm treated. Shocks delivered to initiating triggered arrhythmias nearly always fail, whereas those for subsequent VF are usually effective. ICD programming in these patients is exceptionally challenging.

United Kingdom national experience of entirely subcutaneous implantable cardioverter-defibrillator technology: important lessons to learn

The aim of this study was to describe the early phase United Kingdom (UK) clinical experience with a novel entirely subcutaneous implantable cardioverter-defibrillator (S-ICD). A questionnaire was sent to all UK hospitals implanting S-ICDs. Nineteen of 25 (76%) hospitals responded with the details of 111 implanted patients [median 5/hospital (range 1-18)]. Mean duration of follow-up was 12.7 ± 7.1 months. Median patient age was 33 years (range 10-87 years). Underlying pathology was primary electrical disease in 43%, congenital heart disease 12%, hypertrophic cardiomyopathy 20%, ischaemic cardiomyopathy 14%, idiopathic dilated cardiomyopathy 5%, and other cardiomyopathies 7% patients. Nineteen (17%) patients required 20 re-operations, including permanent device explantation in 10 (9%). Twenty-four appropriate shocks were delivered in 13 (12%) patients, including 10 for ventricular fibrillation. One patient suffered arrhythmic death, but there were no failures to detect or terminate ventricular arrhythmias above the programmed detection rate. Fifty-one inappropriate shocks were delivered in 17 (15%) patients. Forty-one (80%) were for T-wave over-sensing and 1 (2%) for atrial flutter-wave over-sensing. The 11 patients who received inappropriate shocks due to T-wave over-sensing were significantly younger than patients who did not (24 ± 10 vs. 37 ± 19 years; P = 0.02). The S-ICD is an important innovation in ICD technology. However, these data indicate that adverse event rates are significant during early clinical adoption. Important lessons in patient selection, implant technique, and device programming can be learnt from this experience.