Left bundle branch area pacing in patients with atrioventricular conduction disease: A prospective multicenter study.

BACKGROUND: The reported success rate of His-bundle pacing (HBP) in patients with infranodal atrioventricular (AV) conduction disease is only 52%-76%. The success rate of left bundle branch area pacing (LBBAP) in this cohort is not well studied. OBJECTIVE: The purpose of this study was to evaluate the feasibility, safety, and electrophysiological characteristics of LBBAP in patients with AV conduction disease. METHODS: Patients with AV conduction disease referred for pacemaker implantation at 2 centers between February 2019 and June 2021 were considered for LBBAP. Baseline demographic characteristics, procedural success rates, electrophysiological parameters, and complications were assessed. RESULTS: LBBAP was successful in 340 of 364 patients (93%). Mean age was 72 ± 13 years, and mean follow-up was 331 ± 244 days. Pacing indications were Mobitz I in 27 patients (7%), Mobitz II or 2:1 AV block or high-grade AV block in 94 patients (26%), complete heart block in 199 patients (55%), and sick sinus syndrome with isolated bundle branch block in 44 patients (12%). Left bundle branch block and right bundle branch block were present in 57 patients (16%) and 140 patients (38%), respectively. Procedural success rates did not differ between indications (92.6%, 93.6%, 92.9%, and 95%, respectively) or between patients with narrow (<120 ms) vs wide QRS (≥120 ms). Mean LBBAP threshold was 0.77 ± 0.34 V at 0.4 ms at implant and remained stable during follow-up. There were 4 (1.2%) acute LBBAP lead dislodgments. CONCLUSION: LBBAP is safe and feasible with high success rates for patients with AV conduction disease. In contrast to HBP, LBBAP success rates remain high over the entire spectrum of AV conduction disease, and lead parameters remain stable during follow-up.

Fluoroless Catheter Ablation of Atrial Fibrillation: Integration of Intracardiac Echocardiography and Cartosound Module.

OBJECTIVE: To evaluate the feasibility, safety, and clinical efficacy of non-fluoroscopic radiofrequency catheter ablation of atrial fibrillation (AF) in comparison to traditional fluoroscopy-guided ablation in a local Canadian community cohort. METHODS: We retrospectively studied consecutive patients with paroxysmal and persistent AF undergoing pulmonary vein isolation (PVI) guided by intracardiac echocardiography (ICE) and Carto system (CartoSound module). ICE-guided PVI without fluoroscopy (Zero-fluoro group) was performed in 116 patients, and conventional fluoroscopy-guided PVI (Traditional group) was performed in 131 patients. RESULTS: Two hundred and forty-seven patients with AF (60.7% male; mean age: 62.2 ± 10.6 years; paroxysmal AF =63.1%) who underwent PVI were studied. Mean procedure times were similar between both groups (136.8±33.4 minutes in the zero-fluoro group vs. 144.3±44.9 minutes in the traditional group; p=0.2). Acute PVI was achieved in all patients. Survival from early AF recurrence was 85% and 81% in the zero-fluoro and traditional groups, respectively (p = 0.06). Survival from late AF recurrence (12-months) between the zero-fluoro and traditional groups was also similar (p=0.1). Moreover, there were no significant differences between complication rates, including hematoma (p = 0.2) and tamponade (p = 1),between both groups. CONCLUSIONS: Zero-fluoroscopy ICE and CartoSound-guided AF ablation may be safe and feasible in patients undergoing PVI compared to conventional fluoroscopy-guided ablation.

Safety and feasibility of left bundle branch area pacing following valvular interventions: Multicenter study.

OBJECTIVES: To evaluate the safety and feasibility of left bundle branch area pacing (LBBAP) in patients with valvular interventions. METHODS: Eighty-four patients were included in this study. All patients underwent recent surgical or percutaneous valvular interventions. LBBAP was attempted in all patients. Implant success rates, peri- and postprocedure electrocardiogram, pacing parameters, and complications were assessed at implant, and during follow-up. RESULTS: LBBAP implantation was successful in 80/84 (95%) patients. Mean age was 74.1 ± 13.8 years and 56% patients were male. Prior valvular replacements included: percutaneous aortic (26), surgical aortic (36), combined surgical aortic plus mitral (6), MVR (10), tricuspid (1), and pulmonic (1). Average LVEF was 52.6 ± 11%. Majority of patients underwent LBBAP due to atrioventricular block (76%) and sinus node disease (13%). Total procedure duration was 74.1 ± 12.5 min and fluoroscopic duration was 9.7 ± 6.8 min. Pacing parameters were stable during follow-up period of 10.0 ± 6.3 months. Pacing QRS duration was significantly narrower than baseline QRS duration (131.5 ± 31.4 ms vs. 114.3 ± 13.7 ms, p < .001, respectively). No acute complications were observed. Mean follow-up was 10.0 ± 6.3 months (median: 8.4 months, min: 1 and max: 24 months). During follow-up, there were three device infections and two patients had loss of LBBA capture within 1 month of implant. CONCLUSIONS: LBBAP is a feasible and safe pacing modality in patients with prior interventions for valvular heart disease.

Initial Experience, Safety, and Feasibility of Left Bundle Branch Area Pacing: A Multicenter Prospective Study.

OBJECTIVES: This study sought to evaluate the safety and feasibility of conduction system pacing by performing left bundle branch area pacing (LBBAP). BACKGROUND: There are limited data from single centers showing that LBBAP may circumvent the technical and electrophysiological challenges encountered with His bundle pacing. METHODS: Patients referred for pacemaker implantation at 2 centers between February 1, 2019, and March 31, 2020, were considered for LBBAP. LBBAP was performed by implanting a lumen-less, exposed helix lead approximately 2 cm distal to the His bundle and deep into the septum using a specialized delivery sheath. Implant success rates, complications, and electrophysiological parameters were assessed. RESULTS: LBBAP was successful in 305 of 341 patients (89%). Mean age was 72 ± 12 years; 45% were women; and 39% had QRS duration (QRSd) >130 ms, 22% right bundle branch block, 11% left bundle branch block, and 6% intraventricular conduction defect. Pacing indications were sinus node dysfunction in 28.7%, atrioventricular block in 52.5%, cardiac resynchronization therapy in 8.8%, and refractory atrial fibrillation in 10% of patients. Procedural duration was 74.7 ± 34 min and fluoroscopic time was 10.4 ± 8.1 min. The mean baseline QRSd and paced QRSd in the overall cohort was 114 ± 29.8 ms versus 112 ± 11.7 ms (p < 0.001) and in patients with infra-Hisian disease was 144.5 ± 19 ms versus 115 ± 12 ms (p < 0.001), respectively. Mean left ventricular activation time was 71.7 ± 11 ms at high output and 74.7 ± 11 ms at low output. LBB potentials were noted in 41% patients. Pacing threshold and R waves were 0.74 ± 0.3 V at 0.4 ms and 10.7 ± 4.9 mV at time of implantation and were stable at 1-, 3-, 6-, and 12-month follow-ups. The only major complications were 3 LBBAP lead dislodgements, 2 within 24 h and 1 at 2 weeks. CONCLUSIONS: LBBA pacing is safe, feasible, and a reliable alternative to His bundle pacing for providing physiological pacing. Randomized controlled studies are needed to confirm the safety, feasibility, and clinical outcomes of LBBAP.

Contact force sensing for ablation of persistent atrial fibrillation: A randomized, multicenter trial.

BACKGROUND: Impact of contact force sensing (CFS) on ablation of persistent atrial fibrillation (PeAF) is unknown. OBJECTIVE: The purpose of the TOUCH AF (Therapeutic Outcomes Using Contact force Handling during Ablation of Persistent Atrial Fibrillation) randomized trial was to compare CFS-guided ablation to a CFS-blinded strategy. METHODS: Patients (n = 128) undergoing first-time ablation for persistent AF were randomized to a CFS-guided vs CFS-blinded strategy. In the CFS-guided procedure, operators visualized real-time force data. In the blinded procedure, force data were hidden. Wide antral pulmonary vein isolation plus a roof line were performed. Patients were followed at 3, 6, 9, and 12 months with clinical visit, ECG, and 48-hour Holter monitoring. The primary endpoint was cumulative radiofrequency (RF) time for all procedures. Atrial arrhythmia >30 seconds after 3 months was a recurrence. RESULTS: PeAF was continuous for 26 weeks (interquartile range [IQR] 13-52), and left atrial size was 45 ± 5 mm. Force in the CFS-blinded and CFS-guided arms was 12 g [IQR 6-20] and 14 g [IQR 9-20] (P = .10), respectively. Total RF time did not differ between CFS-guided and CFS-blinded groups (49 ± 14 min vs 50 ± 20 min, respectively; P = .70). Single procedure freedom from atrial arrhythmia was 60% in the CFS-guided arm and 63% in the CFS-blinded arm off drugs. Lesions with gaps were associated with significantly less force (11.4 g [IQR 6-19] vs 13.2 g [IQR 8-20], respectively; P = .0007) and less force-time integral (174 gs [IQR 91-330] vs 210 gs [IQR 113-388], respectively; P <.001). CONCLUSION: CFS-guided ablation resulted in no difference to RF time or 12-month outcome. Lower force/force-time integral was associated with significantly more gaps.

Defining Blanking Period Post-Pulmonary Vein Antrum Isolation.

OBJECTIVES: This study sought to determine the exact period after pulmonary vein antrum isolation (PVI) during which early recurrence of atrial tachyarrhythmia (ERAT) does not predict late arrhythmia recurrence (LR), in order to better define the blanking period. BACKGROUND: Recurrence of atrial fibrillation after PVI is not uncommon. The first 3 months after PVI have been commonly treated as a blanking period, during which ERAT is not thought to predict LR after PVI; however, recent studies have shown that ERAT does predict LR. METHODS: Baseline and follow-up data for 636 patients (mean age: 61.4 ± 10.6 years; 67.1% male; 59% paroxysmal atrial fibrillation; 31.4% ERAT) who underwent PVI between 2010 and 2014 were included. Recurrences were monitored by electrocardiography and Holter monitoring at 1-, 3-, 6-, 9-, and 12-month intervals post-procedure. Receiver-operating characteristic curve analysis was used to define the blanking period after PVI. RESULTS: Overall, 51%, 76%, and 92% of patients who had ERAT in the first, second, and third month post-PVI, respectively, also experienced LR (p = 0.001). Using a logistic regression model, those manifesting ERAT during the first, second, and third month post-PVI were 4.22, 9.03, and 19.43 (p = 0.001) times more likely to experience LR, respectively, compared to those without ERAT. Furthermore, receiver-operating characteristic analysis revealed that 23 days post-PVI is the optimal cutoff date for the blanking period, with area under the curve of 0.7, sensitivity of 69.2%, and specificity of 61.2%. CONCLUSIONS: The likelihood of experiencing LR progressively rises with ERAT after the first month post-PVI. Blanking period after PVI should be limited to the first 23 days clinically and in future studies.

Risk of Stroke and Recurrence After AF Ablation in Patients With an Initial Event-Free Period of 12 Months.

INTRODUCTION: Because of the unclear prognostic effects of ablation of atrial fibrillation (AF), oral anticoagulation (OAC) is often continued after ablation even in asymptomatic patients. We sought to determine the frequency of stroke and AF recurrence in patients on and off therapeutic OAC 1 year after a successful AF ablation. METHODS AND RESULTS: Patients that underwent AF ablation and were free of AF 12 months after ablation were selected from our AF database. During follow-up (FU), patients were screened for recurrence of AF, changes in OAC or antiarrhythmic medication, and the occurrence of stroke or transient ischemic attack (TIA). A total of 398 patients (median age 60.7 years [50.8, 66.8], 25% female) were investigated. The median duration of FU was 529 (373, 111,3.5) days. OAC was discontinued in 276 patients (69.3%). During FU, 4 patients (1%) suffered from stroke and 55 patients (13.8%) experienced a recurrence of AF. Persistent AF was significantly associated with a greater chance of AF recurrence (49.1% vs. 26.8%; P = 0.001). Neither CHADS2 nor CHA2DS2-VASc-Score nor recurrence of AF were significantly different in patients with or without stroke. There was a trend toward a higher percentage of coronary artery disease among patients that experienced stroke (50% vs. 10%; P = 0.057). CONCLUSION: The overall risk of stroke and AF recurrence is low in patients with a recurrence free interval of at least 12 months after AF ablation. Of note, recurrence of AF was not associated with a higher risk of stroke in our study population.

Predictors for Progression of Atrial Fibrillation in Patients Awaiting Atrial Fibrillation Ablation.

BACKGROUND: Success rates of atrial fibrillation (AF) ablation have been shown to be significantly lower for patients with persistent AF. However, little is known about the risk factors predicting progression to persistent AF in patients awaiting AF ablation. METHODS: We performed a retrospective, single-centre investigation of patients with paroxysmal AF at the time of placement on the ablation waiting list. Patients were defined as having progressed if they had developed self-reported or electrocardiogram-recorded AF durations more than 7 days while awaiting ablation. After ablation, clinical visits at 3, 6, 9, 12, and 18 months were performed with a minimum of a 48-hour-Holter and electrocardiogram. Baseline characteristics including left atrial diameter (LA) and the HATCH score were analyzed by univariable and multivariable analysis for predicting progression to persistent AF. RESULTS: During a median waiting time of 9.7 (6.1, 14.2) months, 60 of 564 patients (11%) progressed to persistent AF. In patients who progressed, ablation took longer (180 [150, 249] minutes vs 157 [125, 210] minutes; P = 0.009) and was associated with a higher rate of recurrence after a median of 12 months (53.3% vs 39.1%; P < 0.001). The HATCH score was a poor predictor of AF progression (area under the curve 0.54), whereas an LA diameter of more than 45 mm (odds ratio 3.46, P < 0.001) and heart failure (odds ratio 3.11, P = 0.036) were strong and independent predictors of AF progression in multivariable analysis. CONCLUSIONS: Patients with an increased LA diameter or heart failure have a significantly increased risk of progression to persistent AF. These characteristics may define patients who should undergo earlier catheter ablation to optimize outcome.

The Impact of Duration of Atrial Fibrillation Recurrences on Measures of Health-Related Quality of Life and Symptoms.

BACKGROUND: Little is known about the relationship between daily atrial fibrillation (AF) burden and quality of life (QOL). We sought to determine the influence of atrial tachycardia (AT) or AF burden on measures of QOL and symptoms. METHODS AND RESULTS: We retrospectively analyzed patients with dual-chamber pacemakers from the Atrial Septal Pacing Efficacy Clinical Trial (ASPECT), Atrial Therapy Efficacy and Safety Trial (ATTEST), and aTRial arrhythmias dEtected by implaNted Device diagnostics Study (TRENDS) trials. All patients underwent at least one QOL evaluation. We predefined four AF burden groups: no AT/AF (group 1), ≤30 minutes (group 2), 30 minutes-2 hours (group 3), and >2 hours (group 4) per day. We compared QOL measures using the 12-item Short-Form Health Survey (SF-12; standard 4 week recall) and the AF Symptom Checklist (SC) severity and frequency between groups 2-4 to those in group 1. A total of 798 patients were analyzed (age 72 ± 11 years, 447 male [56%]). SC frequency and severity and SF-12 physical and mental scores worsened significantly when patients in group 4 were compared to patients with no AF. There were no statistically significant differences for any of the measures when comparing group 2 or 3 patients to group 1. By linear regression, only the 2-hour-cutoff had a significant impact on QOL as measured by SC frequency (+3.15, P < 0.001), severity (+3.23, P < 0.001), SF-12 physical score (-2.42, P = 0.013), and SF-12 mental score (-2.11, P = 0.021). CONCLUSION: A daily AT/AF burden of more than 2 hours had significant impact on QOL. This might influence the choice of appropriate cut-off points to determine the success of an AF treatment.

Substrate-guided ablation of haemodynamically tolerated and untolerated ventricular tachycardia in patients with structural heart disease: effect of cardiomyopathy type and acute success on long-term outcome.

AIMS: The purpose of this study was to evaluate the outcomes of purely substrate-guided ventricular tachycardia (VT) ablation in patients with non-ischaemic dilated cardiomyopathy (NIDCM) and ischaemic cardiomyopathy (ICM) and the impact of acute procedural success on long-term outcome. METHODS AND RESULTS: One hundred and forty-two patients (65 ± 12 years old, 72% male) with ICM (n = 87) and with NIDCM (n = 55) underwent substrate-guided VT ablation. The ablation approach involved eliminating all LP regions and ablating all scar border zone regions with 10 or more out of 12 pace-matching. All patients were followed with regular implantable defibrillator interrogations for mean 641 ± 301 days. Complete acute success (no inducible VT) was achieved in 60 patients with ICM (69%) and in 29 patients with NIDCM (53%) (P = 0.03). Partial success (elimination of clinical VT only) was obtained in nine patients with ICM (10%) and in four patients with NIDCM (7%) (P = 0.14). Procedural failure (clinical VT still inducible) occurred in 18 patients within the ICM group (21%) and in 22 patients of the NIDCM (40%) (P = 0.04). Overall, 51 patients presented with recurrence of ventricular arrhythmias: 23 in the group with ICM (26%) and 28 in the group with NIDCM (51%) (P = 0.03). Long-term success was related to acute procedural outcome. CONCLUSIONS: Substrate-guided ablation is an effective approach in the treatment of VT with long-term outcome directly related to acute procedural success. Success rates are significantly lower in patients with NIDCM compared with those with ICM.

Comparison of outcomes after cardioversion or atrial fibrillation ablation in patients with differing periprocedural anticoagulation regimens.

BACKGROUND: There is a paucity of data that compare traditional vitamin K antagonist (VKA) with novel oral anticoagulant regimens in periprocedural management of cardioversion or ablation of atrial fibrillation (AF). We sought to compare outcomes of use of VKA, dabigatran (DABI), and rivaroxaban (RIVA) anticoagulation around the time of intervention. METHODS: We studied consecutive patients undergoing cardioversion or ablation of AF at our centre from October 2010 to October 2013. There were 3 different anticoagulation groups: warfarin (VKA), DABI, and RIVA. Safety was assessed according to number of strokes, transient ischemic attacks (TIAs), and clinically important and not important bleeding events. RESULTS: Baseline characteristics were well balanced between the groups. Average follow-up was 6 months (± 4 months). A total of 901 patients who underwent cardioversion were studied (VKA [n = 471], DABI [n = 288] and RIVA [n = 141]). In these patients there were no strokes seen during follow-up and 2 TIAs in the DABI group. Bleeding rates were low, with no significant difference between the 3 groups. A total of 680 patients who underwent ablation were studied (VKA [n = 319], DABI [n = 220] and RIVA [n = 171]). There were no strokes reported during follow-up and 3 TIAs: 2 in the VKA group and 1 in the DABI group not resulting in a significant difference between the groups. Bleeding rates were low, with no significant difference between the groups. CONCLUSIONS: Overall, there was a low incidence of adverse events for all anticoagulation regimens. Warfarin, DABI, and RIVA use around the time of the procedure are safe and reasonable options for patients who undergo cardioversion or AF ablation.

Cardiac resynchronization therapy modulation of exercise left ventricular function and pulmonary O2 uptake in heart failure.

To better understand the mechanisms contributing to improved exercise capacity with cardiac resynchronization therapy (CRT), we studied the effects of 6 mo of CRT on pulmonary O(2) uptake (Vo(2)) kinetics, exercise left ventricular (LV) function, and peak Vo(2) in 12 subjects (age: 56 ± 15 yr, peak Vo(2): 12.9 ± 3.2 ml·kg(-1)·min(-1), ejection fraction: 18 ± 3%) with heart failure. We hypothesized that CRT would speed Vo(2) kinetics due to an increase in stroke volume secondary to a reduction in LV end-systolic volume (ESV) and that the increase in peak Vo(2) would be related to an increase in cardiac output reserve. We found that Vo(2) kinetics were faster during the transition to moderate-intensity exercise after CRT (pre-CRT: 69 ± 21 s vs. post-CRT: 54 ± 17 s, P < 0.05). During moderate-intensity exercise, LV ESV reserve (exercise - resting) increased 9 ± 7 ml (vs. a 3 ± 9-ml decrease pre-CRT, P < 0.05), and steady-state stroke volume increased (pre-CRT: 42 ± 8 ml vs. post-CRT: 61 ± 12 ml, P < 0.05). LV end-diastolic volume did not change from rest to steady-state exercise post-CRT (P > 0.05). CRT improved heart rate, measured as a lower resting and steady-state exercise heart rate and as faster heart rate kinetics after CRT (pre-CRT: 89 ± 12 s vs. post-CRT: 69 ± 21 s, P < 0.05). For peak exercise, cardiac output reserve increased significantly post-CRT and was 22% higher at peak exercise post-CRT (both P < 0.05). The increase in cardiac output was due to both a significant increase in peak and reserve stroke volume and to a nonsignificant increase in heart rate reserve. Similar patterns in LV volumes as moderate-intensity exercise were observed at peak exercise. Cardiac output reserve was related to peak Vo(2) (r = 0.48, P < 0.05). These findings demonstrate the chronic CRT-mediated cardiac factors that contribute, in part, to the speeding in Vo(2) kinetics and increase in peak Vo(2) in clinically stable heart failure patients.

A novel mutation in the RYR2 gene leading to catecholaminergic polymorphic ventricular tachycardia and paroxysmal atrial fibrillation: dose-dependent arrhythmia-event suppression by ß-blocker therapy.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic condition that presents with exercise-induced polymorphic arrhythmias. We describe a case report of a 25-year-old woman who had a cardiac arrest due to ventricular fibrillation. Genetic analysis revealed a novel missense mutation in exon 90 of the ryanodine receptor (RyR2) gene resulting in substitution of arginine for serine at residue 4153 (S4153R). The patient received an implantable cardioverter-defibrillator and low-dose ß-blocker therapy. She had recurrent polymorphic ventricular arrhythmias treated with appropriate cardioverter-defibrillator shocks and paroxysmal atrial fibrillation. Titration of ß-blocker to a much higher dose suppressed further episodes of ventricular arrhythmia and paroxysmal atrial fibrillation, resulting in reduction in device therapies.

Transesophageal echocardiography for the prevention of embolic complications after catheter ablation for atrial fibrillation.

BACKGROUND: Thromboembolic complications during left-sided ablations range between 1.5 and 5.4%. Preprocedural TEE has been used to exclude the presence of left atrial thrombi in order to minimize risk. The use of TEE is empiric and it has not been evaluated in contemporary practice. METHODS AND RESULTS: A multicenter national survey describing the practice at 11 Canadian teaching hospitals. A total of 2,225 patients underwent elective catheter ablation for symptomatic AF. Transesophageal echocardiography (TEE) was used either routinely or selectively as a preablative strategy in patients. There were 996 patients in a routine preprocedure TEE strategy and 1,190 in a selected TEE strategy; 1 center (n = 39 patients) did not perform TEE. Twelve of 996 (1.2%) in the routine unselected cohort had thrombi identified. TEEs were performed in 200 of 1,190 in the selected cohort; 4 (2.0%) left atrial thrombi were observed; there was no significant difference in the prevalence of thrombi (P = 0.34). A total of 11 embolic events occurred inclusive of all groups. There was no difference in event rates between the 2 strategies (0.6% and 0.4%, P = 0.54). Events were unrelated to AF duration (persistent vs paroxysmal, r = 0.03, N = 2,225, P = 0.9). CONCLUSION: The selection criteria employed to perform TEEs did not increase the chance of identifying LA thrombi in a patient cohort with primarily nondilated left atria and paroxysmal AF. The overall thromboembolic event rate was low (0.49%) and was not significantly different between the 2 TEE strategies.

Proportion of patients followed in a specialized heart failure clinic needing an implantable cardioverter defibrillator as determined by applying different trial eligibility criteria.

Numerous trials have demonstrated survival benefits using implantable cardioverter defibrillators (ICDs) for primary prevention in selected patients with left ventricular (LV) systolic dysfunction. However, eligibility criteria differed across these trials. Without a risk stratification scheme that clearly identifies those who will benefit, there remains debate about which patients with heart failure (HF) should receive ICDs for primary prevention. To explore the implications of applying different eligibility criteria, this study evaluated all patients seen in a specialized HF clinic from August 2003 to January 2004. Of the 309 consecutive patients in the cohort, 46 were excluded because their HF complicated recent myocardial infarcts (n = 3); their LV ejection fractions were not measured (n = 9); or their HF was due to valvular disease, myocarditis, or peripartum cardiomyopathy (n = 34). The Multicenter Automatic Defibrillator Implantation Trial-II criteria were met by 85 patients (32%), and 134 patients (51%) met the Sudden Cardiac Death in Heart Failure Trial criteria. Even allocation decisions based on randomized trial evidence can have vastly different resource implications depending on which trial is chosen. Thus, the development and validation of a risk stratification scheme to identify those patients most likely to benefit from ICDs for primary prophylaxis should be a research priority.