Dual-chamber Implantable Cardioverter-defibrillator Research Articles

Abstract 11595: Predicting Appropriate Shocks In Patients With Heart Failure: Patient Level Meta-analysis From SCD-HeFT and Madit II

Background: Some patients implanted with a primary prevention implantable cardioverter defibrillator (ICD) due to heart failure receive an appropriate shock, but no precise tools exist to predict this outcome. Methods: Using patient level data from the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) and the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), we identified patients with any appropriate ICD shock. A variety of clinical and demographic variables were included in a logistic regression model to predict appropriate ICD shocks (Table). Results: There were 1,463 patients randomized to ICD from the two included trials; 285 (19%) had ≥1 appropriate shock over a median follow up of 2.59 years. Compared with patients with no appropriate shocks, patients who received any appropriate ICD shock tended to have NYHA class II or III heart failure symptoms, beta blocker therapy, lower LVEF, wider QRS duration, and a single versus dual chamber ICD (79% of all patients had a single chamber ICD). Other comorbidities were similar between groups. Significant independent predictors of appropriate ICD shocks included NYHA class (NYHA II vs I: OR 1.65, 95% CI 1.07-2.55; NYHA III vs I: OR 1.74, 95% CI 1.10-2.76), LVEF based on one unit change (higher vs lower LVEF: OR 0.96, 95% CI 0.94-0.98), beta blocker therapy (presence vs absence: OR 0.96, 95% CI 0.94-0.98), and single chamber ICD (OR 1.67, 95% CI 1.13-2.45). Conclusion: In this meta-analysis of patient level data from MADIT-II and SCD-HeFT, appropriate ICD shocks were significantly predicted by NYHA class, LVEF, beta blocker therapy, and single chamber ICD. There is a compelling need for a large, prospective study to better define the risk of appropriate ICD shocks in patients meeting criteria for a primary prevention ICD. Until such time, stratification of patients by these factors may better define risk for potentially mortal rhythm events that might be prevented by a primary prevention ICD.

Economic impact of longer battery life of cardiac resynchronization therapy defibrillators in Sweden.

ObjectiveThe objective of this study was to quantify the impact that longer battery life of cardiac resynchronization therapy defibrillator (CRT-D) devices has on reducing the number of device replacements and associated costs of these replacements from a Swedish health care system perspective.MethodsAn economic model based on real-world published data was developed to estimate cost savings and avoided device replacements for CRT-Ds with longer battery life compared with devices with industry-standard battery life expectancy. Base-case comparisons were performed among CRT-Ds of three manufacturers – Boston Scientific Corporation, St. Jude Medical, and Medtronic – over a 6-year time horizon, as per the available clinical data. As a sensitivity analysis, we evaluated CRT-Ds as well as single-chamber implantable cardioverter defibrillator (ICD-VR) and dual-chamber implantable cardioverter defibrillator (ICD-DR) devices over a longer 10-year period. All costs were in 2015 Swedish Krona (SEK) discounted at 3% per annum.ResultsBase-case analysis results show that up to 603 replacements and up to SEK 60.4 million cumulative-associated costs could be avoided over 6 years by using devices with extended battery life. The pattern of savings over time suggests that savings are modest initially but increase rapidly beginning in the third year of follow-up with each year’s cumulative savings two to three times the previous year. Evaluating CRT-D, ICD-VR, and ICD-DR devices together over a longer 10-year period, the sensitivity analysis showed 2,820 fewer replacement procedures and associated cost savings of SEK 249.3 million for all defibrillators with extended battery life.ConclusionExtended battery life is likely to reduce device replacements and associated complications and costs, which may result in important cost savings and a more efficient use of health care resources as well as a better quality of life for heart failure patients in Sweden.

Unusual sequel of dual-chamber ICD implantation

(2016). Unusual sequel of dual-chamber ICD implantation. Acta Cardiologica: Vol. 71, No. 5, pp. 623-624.

Is something hidden during tachycardia?

A 61-year-old male patient was referred to our electrophysiology lab for ventricular tachycardia (VT) ablation. The patient had a history of ischaemic cardiomyopathy with impaired left ventricular function and received a dual chamber implantable cardioverter-defibrillator (ICD) after he survived a cardiac arrest. During the past months, the patient suffered from recurrent episodes of monomorphic VT with appropriate ICD therapies. Electrocardiogram suggested an apical origin of the VT. Prior to VT ablation, device interrogation showed a stored supraventricular tracing (Fig. 1).

Detection and discrimination of tachycardia in ICDs manufactured by St. Jude Medical

Modern implantable cardioverter/defibrillator (ICD) systems offer amultitude of algorithms to optimize performance in sensing and tachycardia detection even in difficult circumstances (e. g., ventricular tachycardia during supraventricular tachycardia, fine ventricular fibrillation with intermittent undersensing), to reliably discriminate sustained ventricular tachyarrhythmia from noise, nonsustained and supraventricular tachyarrhythmia, and to limit shock therapy only to those arrhythmias that definitely need to be treated by ashock. Adisadvantage of these multiple algorithms is the complexity of annotated tracings that makes it sometimes difficult to understand why the ICD did what it did. If atachycardia classification was wrong, it may be thus difficult to find the best way to reprogram the device to avoid another misclassification. This review explains in detail the algorithms used for tachycardia detection, discrimination, and prevention of inappropriate therapy in single- and dual-chamber ICDs manufactured by St. Jude Medical. Knowledge of these features may help to optimize ICD treatment in patients fitted with these devices.

16-56: Sleep Apnea Syndrome in a Multicentric Study on Patients with Device Remote Monitoring System

Background: Sleep apnea syndrome (SAS) has up to 60% prevalence in the Pacemaker population, with 80% remaining undiagnosed. The ApneaScan TM is an implanted impedance-based respiratory sensor system embedded with Boston Scientific defibrillator devices: apneic events are expressed with the Apnea Hypopnea Index (AHI) (i.e the average number of events per hour of sleep). The aim of the study was to describe the prevalence of SAS in a french population of patients implanted as well as with a pace-maker or an implanted cardioverter defibrillator using the ApneaScan. Methods: In this 4-centers study, we retrospectively included 118 patients who had a Boston Scientific device with remote monitoring follow-up. The AHI was used to classify the severity of the sleep apnea, mild :5-14 events per hour of sleep, moderate : between 15-29, severe : more than 30. Results: Among the 118 patients (mean age, 68 ±14 years), 55% had a severe sleep apnea (average of AHI 44.9 ± 12.9/h) and 31% a moderate sleep apnea (AHI 22.9 ± 4.3/h); 46 patients were implanted with a dual chamber pace maker, 72 patients with an implantable cardioverter defibrillator (ICD): 41 dual chamber ICD and 31 CRT-D. The AHI was comparable in the CRT-D patients (AHI 29.2 ± 14.7/h), dual chamber ICD patients (32.5 ±17.2/h) or dual chamber pace-maker patients (36.1 ± 18.1/h) (ANOVA p = 0.222). An inverse correlation between the percentage of atrial pacing and the AHI (r = -0.25 p = 0.002) was found. The percentage of patient activity level (% per day) was inversely correlated with the AHI (r = -0.269 p = 0.005). The AHI was correlated with the age of patients (r = 0.2990, p = 0.0010). The percentage of ventricular pacing had no influence on AHI (p = 0.120). Conclusion: High prevalence of sleep apnea syndrome was found in patients implanted with device as well pacemaker or defibrillator. There were no differences of prevalence between patients implanted with pace-maker, ICD or CRT-D. Preliminary results identified a profile of patients at risk.

16-60: A New Approach to analyze ICD therapy Efficacy. Single-Centre Experience of Discovery™ Link TachyMed (Medtronic, USA)

The goal: to analyze an ICD therapy efficacy using an application Discovery™ Link TachyMed (Medtronic, USA). Materials and Methods: We enrolled 154 patients connected to the remote monitoring network Carelink (Medtronic, USA) who had an implanted dual (46) and triple chamber ICDs (108). Device programming parameters and intracardiac electrograms were studied. To carry out quantitative analysis of ICD therapy efficacy an application Discovery™ Link TachyMed was used. Statistical data are presented as Median (IQR 25%; 75%). Results: A dual zone ICD programming is frequently used (68%) in our center. A choice of single or triple ICD configuration is made rarely (in 22% and 10%, respectively). A zone of slow VT (sVT) corresponds to 179 (168; 182) bpm. A zone of fast VT (fVT) is programed in the range over 182 (176; 240) bpm and a zone of VF is detected in case of tachycardia equal or above 200 (188; 200) bpm. In most cases standard manufacturer discrimination algorithm is used. 690 episodes of VT were analyzed: 43 in VF zone (11 patients), 565 (12 patients) and 82 episodes (6 patients) in sVT and fVT zones respectively. ATP strategy was used in 78% cases (538 VT events). It was effective in 85% of initial VTs. These episodes were frequently referred to sVT and fVT. In 11% of analyzed VTs (76 events) a sinus rhythm was restored after ICD shock. It was usually due to VF events detection (75%). The vast majority of ICD shocks were delivered with submaximal values of energy (less than 35 Joules). Other episodes stopped spontaneously. Inappropriate shocks were delivered in 8 patients: in 5 of them due to atrial flutter with 1:1 conduction, in 2 patients because of atrial fibrillation with fast ventricular rate. In 1 case an electrical noise detected by a defibrillation lead was a reason for an appropriate shock. Conclusions: A low percent of inappropriate shocks was registered (7%). In most cases VT episodes were stopped by ATP, in cases of ICD shocks low values of energy were effective. Remote monitoring system provides facilities for early identification of the reasons of inappropriate ICD therapy. Discovery™ Link TachyMed application allows to carry out a quantitative analysis of ICD therapy efficacy which is especially necessary in centers with a high volume of ICD implantations.

Reducing ICD Test Shocks with a Simplified Upper Limit of Vulnerability.

Determination of an adequate defibrillation safety margin or defibrillation threshold can be a challenge in patients with implantable defibrillators (ICDs). The upper limit of vulnerability (ULV) has been shown to be highly correlated with measured defibrillation thresholds. The peak of the latest peaking monophasic T wave measured from the pacing spike of the induction train of S1 via the surface electrocardiogram (ECG) is generally accepted to approximate the vulnerable period of the cardiac cycle. The purpose of this study was to determine whether a single electrogram-derived coupling interval could provide an accurate determination of the vulnerable period for a simplified test method to approximate the defibrillation safety margin. We used a single electrogram-derived coupling interval for the timing of the T shock. We compared the measured intracardiac electrogram coupling interval to the latest peaking T wave on the surface ECG. A total of 72 patients were studied: single-chamber ICD (n = 28), dual-chamber ICD (n = 26), or cardiac resynchronization therapy-defibrillator (n = 18). The coupling intervals were greater on the electrograms versus the surface ECG: 365 ms ± 27 versus 347 ms ± 26 (P < 0.0001). Almost all of the patients tested, 69/72 (96%), were indeed defibrillated with the T-shock energy that failed to induce ventricular fibrillation (VF). Only three (4%) of the patients failed the hypothesis when 500 V failed to induce VF but subsequently also failed to defibrillate a forced induction of VF. A simplified ULV testing protocol, using a single electrogram channel, accurately separates low from high defibrillation threshold testing patients.

A case of elderly dextroveusional heart patient with hypertrophic cardiomyopathy and incomplete densification undergo dual chamber implantable cardioverter defibrillator therapy

A case of elderly dextroveusional heart patient with hypertrophic cardiomyopathy and incomplete densification undergo dual chamber implantable cardioverter defibrillator therapy

Patient Activity Decreases and Mortality Increases After the Onset of Persistent Atrial Fibrillation in Patients With Implantable Cardioverter-Defibrillators.

The study sought to determine the effect of persistent atrial fibrillation (AF) on device-measured activity and mortality. Patients with AF often complain of fatigue, which may be reflected in patient activity. Daily activity can be objectively measured by implanted devices. We retrospectively studied patients (n= 266, 88% male, 69 ± 10 years of age) from the deidentified Medtronic CareLink database with persistent AF (≥28 consecutive days with≥23 h of AF/day), dual-chamber implantable cardioverter-defibrillators (ICDs) capable of monitoring daily activity and AF burden, no AF between months 1 and 6 post-implant, and≥1 year of data. The first persistent AF episode occurred 980 ± 534 days after implant and lasted a median of 87 days (interquartile range: 49 to 161 days). Average daily activity over a week just prior (baseline) to the first persistent AF episode was compared to each of the 4 weeks during the AF episode and to each of the weeks following termination ofthe persistent AF episode. Daily activity decreased significantly from the baseline week (135 min/day) compared to each of the 4 consecutive weeks after AF onset (8%, 11%, 14%, and 17% decrease, p< 0.001). Mortality at 4 years was increased in patients with persistent AF compared to a matched group with no persistent AF (20.6% vs. 8.6%, p<0.01). Patients with ICDs have a significant reduction in activity following the onset of persistent AF andasignificant increase in mortality when compared to a matched group without persistent AF. Objective measuresofactivitymay more accurately reflect the impact of persistent AF on patients' functional status.

Acute Myocardial Infarction with Isolated Congenitally Corrected Transposition of the Great Arteries

Congenital cardiac abnormalities diagnosed at the time of acute coronary syndrome are rare. A 43-year-old man presented to the emergency department complaining of recurring, severe chest pain. Subsequent emergent coronary angiography demonstrated unusual coronary anatomy: 1) one small caliber bifurcating vessel originating from the right sinus of Valsalva; 2) one very large vessel arising from the posterior sinus; and 3) no coronary artery from the normal left sinus of Valsalva. The large vessel from the posterior sinus was totally occluded in its midportion and was treated with intravascular ultrasound-guided percutaneous coronary intervention. Further diagnostic workup, including two-dimensional transthoracic echocardiogram and computed tomographic coronary angiography, demonstrated isolated corrected transposition of the great arteries with a dilated systemic ventricle and systolic dysfunction with an ejection fraction of 30%. The patient's clinical course was complicated by recurrent nonsustained ventricular tachycardia, treated with medical therapy and a dual-chamber implantable cardioverter defibrillator. This case is an example of a common clinical presentation with a very uncommon congenital heart disorder. Similar cases may become more frequent as the number of adult congenital heart patients increases in the population.

Safety of Bioelectrical Impedance Analysis in Patients Equipped With Implantable Cardioverter Defibrillators.

Current guidelines warn of potential electromagnetic interferences (EMI) when using bioelectrical impedance analysis (BIA) to measure body composition in patients equipped with implantable cardioverter-defibrillators (ICDs). We aimed to test the occurrence of EMI in a setting where this risk was experimentally maximized. Outpatients scheduled for routine ICD controls simultaneously underwent a BIA measurement using an electrical current of 0.8 mAmp at frequencies from 5-100 kHz. ICD sensitivity levels were set to maximum levels while therapies were temporarily inactivated. The device electrograms were monitored in real time to detect sensed and/or visible EMI during BIA measurement. A total of 63 patients equipped with single-chamber (n = 13), dual-chamber (n = 18), or biventricular (n = 32) ICDs from 5 major manufacturers were included. No EMI were detected by the ICDs in these patients, nor were any artifacts visualized during real-time electrogram recordings. BIA can be safely performed in patients equipped with ICDs without cardiac monitoring. Current guidelines should be updated accordingly.

Successful dual chamber ICD implantation via a persistent left superior vena cava after ratchet syndrome

Device implantations may be challenging in patients with venous abnormalities. The most common congenital variation, frequently associated with other congenital abnormalities, is a persistent left superior vena cava (PLSVC), and successful atrial and ventricular lead implantation via a PLSVC have both been reported [1]. “Ratchet syndrome” has also been reported as a rare complication after a newly implanted pacemaker or implantable cardioverter-defibrillator (ICD) and involves lead dislodgement and retraction due to a ratchet-like movement through the suture sleeve that causes a continuous short pull [2], [3]. Here, we present a rare case in which successful dual-chamber ICD implantation via a PLSVC was achieved after the occurrence of ratchet syndrome.

Battery drain in daily practice and medium-term projections on longevity of cardioverter-defibrillators: an analysis from a remote monitoring database.

AimsThe longevity of generators is a crucial determinant of the cost-effectiveness of therapy with implantable cardioverter-defibrillators (ICDs) and cardiac resynchronization therapy defibrillators (CRT-D). We evaluated the trend of device-measured residual battery capacity and longevity projections over 5-year follow-up. We also investigated possible factors associated with battery drain.Methods and resultsData from 4851 patients in the European LATITUDE® database who were followed up for a minimum of 3 years were analysed. The factors associated with battery drain (i.e. year-to-year decrease in residual battery capacity), and thus potentially impacting on device longevity, were mainly the pacing parameters in CRT-D devices and the number of shocks delivered and diverted in both ICD and CRT-D (all P < 0.01 on linear regression analysis). Over the first 5 years, the longevity estimates provided by devices showed low intra-patient variability and increased with time. The estimates exceeded 10 years for CRT-D and 13 and 12 years for single- and dual-chamber ICDs, respectively. In CRT-D patients, the expected patient age on replacement was 80 ± 12 years, and the expected probability of undergoing device replacement was 63 ± 13% for New York Heart Association (NYHA) II patients and 37 ± 16% for NYHA III patients. For comparison, the probabilities of replacing a CRT-D lasting 5 years were 78 ± 8 and 59 ± 13%, respectively (both P < 0.001).ConclusionBattery drain was mainly associated with pacing output in CRT-D devices and with the number of capacitor charges in both ICD and CRT-D devices. The longevity estimates provided by the devices were consistent and conservative. According to these estimates, among CRT-D recipients a low proportion of patients should require device replacement.

Relation between detection rate and inappropriate shocks in single versus dual chamber cardioverter-defibrillator--an analysis from the OPTION trial.

The programming of implantable cardioverter-defibrillators (ICDs) influences inappropriate shock rates. The aim of the study is to analyse rates of patients with appropriate and inappropriate shocks according to detection zones in the OPTION trial. All patients received dual chamber (DC) ICDs randomly assigned to be programmed either to single chamber (SC) or to DC settings including PARAD+ algorithm. In a post-hoc analysis, rates of patients with inappropriate and appropriate shocks were calculated for shocks triggered at heart rates ≥170 bpm (ventricular tachycardia zone) and at rates ≥200 bpm (ventricular fibrillation zone). In the SC group, higher rates of patients with total and inappropriate shocks were delivered at heart rates ≥170 bpm than at rates ≥200 bpm (total shocks: 21.1% vs. 16.6%; p = 0.002; inappropriate shocks: 7.6% vs. 4.5%, p = 0.016; appropriate shocks: 15.2% vs. 13.5%; p = n.s.). No such differences were observed in the DC group (total shocks: 14.3% vs. 12.6%; p = n.s.; inappropriate shocks: 3.9% vs. 3.6%; p = n.s.; appropriate shocks: 12.2% vs. 10.4%; p = n.s.). The higher frequency of patients with total shocks with SC settings than with DC settings that benefit from PARAD+ was driven by a higher percentage of patients with inappropriate shocks in the VT zone (170–200 bpm) in the SC population.

Outcomes of single- or dual-chamber implantable cardioverter defibrillator systems in Japanese patients

BackgroundThere are no criteria for selecting single- or dual-chamber implantable cardioverter defibrillators (ICDs) in patients without a pacing indication. Recent reports showed no benefit of the dual-chamber system despite its preference in the United States. As data on ICD selection and respective outcomes in Japanese patients are scarce, we investigated trends regarding single- and dual-chamber ICD usage in Japan. MethodsData from a total of 205 ICD recipients with structural heart disease (median age, 63 years) in two Japanese university hospitals were reviewed. Patients with bradycardia with a pacing indication and permanent atrial fibrillation at implantation were excluded. ResultsSingle- and dual-chamber ICDs were implanted in 36 (18%) and 169 (82%) patients, respectively. Non-ischemic cardiomyopathy dominated both groups. Seventeen dual-chamber patients developed atrial pacing-dependency over 4.5 years, and it developed immediately after implantation in 14. Although preoperative testing showed no sign of bradycardia in these patients, their pacing rate was set higher than it was in patients who were pacing-independent (61 vs. 46 paces per min, p<0.01). Two single-chamber patients (5%) underwent atrial lead insertion.While inappropriate shock equally occurred in both groups (7 vs. 21 patients, single- vs. dual-chamber, P=0.285), device-related infection occurred only in dual-chamber patients (0 vs. 9 patients, P=0.155). No differences in death or heart failure hospitalization were observed between groups. ConclusionsDual-chamber ICDs were four-fold more common in Japanese patients without a pacing indication. No benefit over single-chamber ICD was observed. Newly developed atrial pacing-dependency seemed to be limited and could have been overestimated due to higher pacing rate settings in dual-chamber patients.

Attitudes of older adults with serious competing health risks toward their implantable cardioverter-defibrillators: a pilot study.

BackgroundIn elderly heart failure patients, the survival benefit of implantable cardioverter-defibrillators (ICDs) may be attenuated due to competing health risks, and the risk of adverse outcomes magnified. Our objective was to examine older adults’ attitudes towards ICD implantation in the context of competing health risks, exploring the determinants of ICD decision-making among a group of patients who had faced the decision in the past.MethodsTelephone survey with a qualitative component. Patients were age ≥70 with single- or dual-chamber ICDs from a single academic cardiac device clinic. Health status was assessed with the Vulnerable Elders Survey (VES-13). Responses to open-ended questions were transcribed verbatim; an “editing analysis” approach was used to extract themes.ResultsForty-four ICD recipients participated (mean age 77.5 years). Nineteen participants (43 %) had VES-13 scores ≥3, indicating a 50 % likelihood of death or functional decline within 2 years. Twenty-one participants (48 %) had received prior ICD shocks. Forty participants (91 %) said they would “definitely” choose to get an ICD again in their current health. By and large, patients revealed a strong desire to extend life, expressed complete confidence in the lifesaving capabilities of their ICDs, and did not describe consideration of competing health risks.ConclusionsIn this pilot telephone survey with a qualitative component, nearly all older adults with ICDs would still choose to get an ICD despite high short-term risk of death or health deterioration. These findings suggest the need to partner more effectively with patients and families to decide how best to use medical technologies, particularly for older adults with competing risks.

Superior Vena Cava Syndrome and Infectious Endocarditis Associated with Dual Chamber ICD Implantation

Se presenta un caso de paciente portador de DAI que debuta con clinica compatible de sindrome de vena cava superior, y posterior desarrollo de endocarditis infecciosa sobre cable del dispositivo

Abstract 17946: How Common is New Onset Atrial Fibrillation in Single Chamber ICD Patients? Sub-analysis From the PainFree SST Study

Introduction: Nearly 75% of ICD recipients have no history of atrial fibrillation (AF) at the time of initial implantation. Yet, many of these patients will develop new onset AF after implant which can lead to serious consequences if not detected and treated. To date, detection algorithms in single-chamber ICDs are not able to detect AF. We investigate how common is new onset AF in single chamber (SC) ICD recipients compared to CRT-D and dual chamber (DC) ICD recipients. Methods: A total of 924 patients with no history of AF from the PainFree SST study (CRT-D: N=321, DC ICD: N=303, SC ICD: N=300) were investigated. We used data from dual-chamber ICDs to estimate the incidence of new-onset AT/AF in SC ICD patients. A propensity score weighted analysis was performed using DC ICD data to match the baseline data of SC ICD patients. Patients with pacing indication were excluded from this evaluation because they would not be indicated for SC ICD. AT/AF-related complications include AT/AF-related serious adverse events, thromboembolic events, progress to AF lasting 7 days or more as well as inappropriate shocks due to AT/AF. Simulated SC ICD results were compared to actual DC and CRT-D results. Results: For AF episodes lasting 6 minutes or more, the incidence rates in CRT-D, DC ICD, and the estimated SC ICD were 28.0%, 23.4%, and 20.5% at 24 months, respectively (Table). The estimated incidence rates of AT/AF episodes in patients with SC ICD were comparable to those of DC ICD in each episode duration. Once the patients experienced first AT/AF episode, the complications were common (Table). Conclusions: AT/AF was frequently detected following implant in patients with no AF history receiving ICD or CRT-D and is associated subsequent AT/AF-related complications even in SC ICD recipients. Therefore, AT/AF monitoring in all ICDs patients may identify those at risk for these complications.

Abstract 15992: Ventricular Tachyarrhythmia Sensing Following Magnetic Resonance Imaging in Patients With an ICD System Designed for the MRI Environment

Objective: To evaluate the impact of MRI on ICD sensing of ventricular tachyarrhythmias. Methods: The Evera MRI study is the first randomized trial of an ICD designed specifically to be MRI safe. This was a world-wide trial of 263 pts implanted with an Evera MRI single or dual chamber ICD in 42 centers. Patients were randomized to either undergo an MRI scan (MRI group) or to not receive a study MRI scan. Per protocol, 156 MRI group pts underwent an MRI procedure at 9-12 weeks post-implant. Device detected spontaneous and induced VT/VF episodes in the MRI group occurring prior to and following MRI were evaluated by an independent Episode Review Committee blinded to the timing of events. Detection delay was computed as the sum of RR intervals of under sensed beats. A ≥5 second delay in detection due to under sensing was prospectively defined as clinically significant. P-values are adjusted for multiple episodes within a patient. Results: There were a total of 34 post-MRI VT/VF episodes in 24 pts, with 16 of those pts having 27 VT/VF episodes prior to MRI. The mean detection delay due to under sensing in the 23 pre-MRI treated episodes was 0.37 ± 0.57 seconds, compared to 0.25 ± 0.57 in 27 treated post-MRI episodes (p=0.29). The maximum detection delay was 2.19 seconds pre-MRI and 2.87 seconds post-MRI. Monomorphic VT and non-sustained VT/VF rarely had any under sensing with 1/11 (9%) pre-MRI episodes and 1/14 (7%) post-MRI episodes (p=0.81) having 2 and 1 under sensed beats, respectively. For polymorphic VT/VF episodes, 13/16 (81%) pre-MRI episodes had some detection delay vs. 10/20 (50%) in post-MRI episodes (p=0.052), but no detection delay was clinically significant. The duration of delay was 0.54 ± 0.61 vs 0.32 ± 0.64, respectively, p=0.28). Conclusion: Detection of VT/VF was excellent with no significant impact of MRI with this system.