Martin C. Burke

Safety and Efficacy of a Totally Subcutaneous Implantable-Cardioverter Defibrillator

Background— The most frequent complications associated with implantable cardioverter-defibrillators (ICDs) involve the transvenous leads. A subcutaneous implantable cardioverter-defibrillator (S-ICD) has been developed as an alternative system. This study evaluated the safety and effectiveness of the S-ICD System (Cameron Health/Boston Scientific) for the treatment of life-threatening ventricular arrhythmias (ventricular tachycardia/ventricular fibrillation). Methods and Results— This prospective, nonrandomized, multicenter trial included adult patients with a standard indication for an ICD, who neither required pacing nor had documented pace-terminable ventricular tachycardia. The primary safety end point was the 180-day S-ICD System complication-free rate compared with a prespecified performance goal of 79%. The primary effectiveness end point was the induced ventricular fibrillation conversion rate compared with a prespecified performance goal of 88%, with success defined as 2 consecutive ventricular fibrillation conversions of 4 attempts. Detection and conversion of spontaneous episodes were also evaluated. Device implantation was attempted in 321 of 330 enrolled patients, and 314 patients underwent successful implantation. The cohort was followed for a mean duration of 11 months. The study population was 74% male with a mean age of 52±16 years and mean left ventricular ejection fraction of 36±16%. A previous transvenous ICD had been implanted in 13%. Both primary end points were met: The 180-day system complication-free rate was 99%, and sensitivity analysis of the acute ventricular fibrillation conversion rate was >90% in the entire cohort. There were 38 discrete spontaneous episodes of ventricular tachycardia/ventricular fibrillation recorded in 21 patients (6.7%), all of which successfully converted. Forty-one patients (13.1%) received an inappropriate shock. Conclusions— The findings support the efficacy and safety of the S-ICD System for the treatment of life-threatening ventricular arrhythmias. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT01064076.

Safety and Efficacy of the Totally Subcutaneous Implantable Defibrillator: 2-Year Results From a Pooled Analysis of the IDE Study and EFFORTLESS Registry

BACKGROUND The entirely subcutaneous implantable cardioverter-defibrillator (S-ICD) is the first implantable defibrillator that avoids placing electrodes in or around the heart. Two large prospective studies (IDE [S-ICD System IDE Clinical Investigation] and EFFORTLESS [Boston Scientific Post Market S-ICD Registry]) have reported 6-month to 1-year data on the S-ICD. OBJECTIVES The objective of this study was to evaluate the safety and efficacy of the S-ICD in a large diverse population. METHODS Data from the IDE and EFFORTLESS studies were pooled. Shocks were independently adjudicated, and complications were measured with a standardized classification scheme. Enrollment date quartiles were used to assess event rates over time. RESULTS Eight hundred eighty-two patients who underwent implantation were followed for 651±345 days. Spontaneous ventricular tachyarrhythmia (VT)/ventricular fibrillation (VF) events (n=111) were treated in 59 patients; 100 (90.1%) events were terminated with 1 shock, and 109 events (98.2%) were terminated within the 5 available shocks. The estimated 3-year inappropriate shock rate was 13.1%. Estimated 3-year, all-cause mortality was 4.7% (95% confidence interval: 0.9% to 8.5%), with 26 deaths (2.9%). Device-related complications occurred in 11.1% of patients at 3 years. There were no electrode failures, and no S-ICD-related endocarditis or bacteremia occurred. Three devices (0.3%) were replaced for right ventricular pacing. The 6-month complication rate decreased by quartile of enrollment (Q1: 8.9%; Q4: 5.5%), and there was a trend toward a reduction in inappropriate shocks (Q1: 6.9% Q4: 4.5%). CONCLUSIONS The S-ICD demonstrated high efficacy for VT/VF. Complications and inappropriate shock rates were reduced consistently with strategic programming and as operator experience increased. These data provide further evidence for the safety and efficacy of the S-ICD. (Boston Scientific Post Market S-ICD Registry [EFFORTLESS]; NCT01085435; S-ICD® System IDE Clinical Study; NCT01064076).

Right Ventricular Outflow Versus Apical Pacing in Pacemaker Patients with Congestive Heart Failure and Atrial Fibrillation

Introduction: Prior studies suggest that right ventricular apical (RVA) pacing has deleterious effects. Whether the right ventricular outflow tract (RVOT) is a more optimal site for permanent pacing in patients with congestive heart failure (CHF) has not been established.

Atrial Fibrillation After Radiofrequency Ablation of Type I Atrial Flutter Time to Onset, Determinants, and Clinical Course

BACKGROUND The occurrence of atrial fibrillation after ablation of type I atrial flutter remains an important clinical problem. To gain further insight into the pathogenesis and significance of postablation atrial fibrillation, we examined the time to onset, determinants, and clinical course of atrial fibrillation after ablation of type I flutter in a large patient cohort. METHODS AND RESULTS Of 110 consecutive patients with ablation of type I atrial flutter, atrial fibrillation was documented in 28 (25%) during a mean follow-up of 20.1+/-9.2 months (cumulative probability of 12% at 1 month, 23% at 1 year, and 30% at 2 years). Among 17 clinical and procedural variables, only a history of spontaneous atrial fibrillation (relative risk 3.9, 95% confidence intervals 1.8 to 8.8, P=0.001) and left ventricular ejection fraction <50% (relative risk 3.8, 95% confidence intervals 1.7 to 8.5, P=0.001) were significant and independent predictors of subsequent atrial fibrillation. The presence of both these characteristics identified a high-risk group with a 74% occurrence of atrial fibrillation. Patients with only 1 of these characteristics were at intermediate risk (20%), and those with neither characteristic were at lowest risk (10%). The determinants and clinical course of atrial fibrillation did not differ between an early (< or = 1 month) compared with a later onset. Atrial fibrillation was persistent and recurrent, requiring long-term therapy in 18 patients, including 12 of 19 (63%) with prior atrial fibrillation and left ventricular dysfunction. CONCLUSIONS Atrial fibrillation after type I flutter ablation is primarily determined by the presence of a preexisting structural and electrophysiological substrate. These data should be considered in planning postablation management. The persistent risk of atrial fibrillation in this population also suggests a potentially important role for atrial fibrillation as a trigger rather than a consequence of type I atrial flutter.

Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: The START study

Arrhythmia Detection with S‐ICD Versus Transvenous ICDs.

Atypical Atrial Flutter Originating in the Right Atrial Free Wall

BACKGROUND Data from experimental models of atrial flutter indicate that macro-reentrant circuits may be confined by anatomic and functional barriers remote from the tricuspid annulus-eustachian ridge atrial isthmus. Data characterizing the various forms of atypical atrial flutter in humans are limited. METHODS AND RESULTS In 6 of 160 consecutive patients referred for ablation of counterclockwise and/or clockwise typical atrial flutter, an additional atypical atrial flutter was mapped to the right atrial free wall. Five patients had no prior cardiac surgery. Incisional atrial tachycardia was excluded in the remaining patient. High-density electroanatomic maps of the reentrant circuit were obtained in 3 patients. Radiofrequency energy application from a discrete midlateral right atrial central line of conduction block to the inferior vena cava terminated and prevented the reinduction of atypical atrial flutter in each patient. Atrial flutter has not recurred in any patient (follow-up, 18+/-17 months; range, 3 to 40 months). CONCLUSIONS Atrial flutter can arise in the right atrial free wall. This form of atypical atrial flutter could account for spontaneous or inducible atrial flutter observed in patients referred for ablation and is eliminated with linear ablation directed at the inferolateral right atrium.

Myocardial damage in patients with sarcoidosis and preserved left ventricular systolic function: an observational study

Late gadolinium enhanced cardiovascular magnetic resonance (LGE‐CMR) is a valuable test to detect myocardial damage in patients with sarcoidosis; however, the clinical significance of LGE in sarcoidosis patients with preserved left ventricular ejection fraction (LVEF) is not defined. We aim to characterize the prevalence of LGE, its associated cardiac findings, and its clinical implications in sarcoidosis patients with preserved LVEF.

A New Algorithm to Reduce Inappropriate Therapy in the S-ICD System

The subcutaneous ICD system (S‐ICD) has been shown to be a safe and effective treatment for patients at risk for sudden cardiac death. This device reliably detects ventricular tachyarrhythmias with a low incidence of inappropriate shocks for supraventricular arrhythmias. However, T‐wave oversensing (TWOS) is more common with the S‐ICD compared with transvenous systems. We developed a novel discrimination algorithm to reduce TWOS without compromising tachyarrhythmia discrimination.

Use of a discrimination algorithm to reduce inappropriate shocks with a subcutaneous implantable cardioverter-defibrillator

BACKGROUND The subcutaneous implantable cardioverter-defibrillator system (S-ICD) uses a novel detection algorithm previously shown to discriminate induced tachyarrhythmias (ventricular vs supraventricular) effectively. OBJECTIVE The purpose of this study was to evaluate the role of the S-ICD discrimination algorithm in reducing the incidence of spontaneous inappropriate shocks. METHODS A total of 314 subjects underwent implantation with an S-ICD system as part of the S-ICD Clinical Investigation (IDE Trial). Subjects were grouped according to programming at discharge to either a single shock zone or 2 shock zones, with a discrimination algorithm in the lower rate zone. RESULTS This cohort had 226 subjects (72%) with dual zone programming and 88 subjects (28%) with single zone programming. Over a mean follow-up period of 661 ± 174 days, inappropriate shocks occurred in 23 subjects from the dual zone subgroup (10.2%) and 23 subjects from the single zone subgroup (26.1%, P < .001), with 2-year inappropriate shock-free rates of 89.7% vs. 73.6%;,respectively (hazard ratio 0.38, P = .001). Freedom from appropriate shocks did not differ between subgroups (92.2% vs. 90.3%, hazard ratio 0.82, P = .64). Moreover, mean time to appropriate therapy did not differ between subgroups, and there was only 1 episode of arrhythmic syncope in the cohort. CONCLUSION The addition of a second shock zone with an active discrimination algorithm was strongly associated with a reduction in inappropriate shocks with the S-ICD system and did not result in prolongation of detection times or increased syncope. These data support the use of dual zone programming as a standard setting for S-ICD patients.

Implications and outcome of permanent coronary sinus lead extraction and reimplantation

Objective: We examined the implications and outcome of coronary sinus (CS) lead removal including the feasibility of laser use within the CS. Background: Cardiac anatomy and lead interactions are more complex with the advent of biventricular pacemakers and atrial cardioverters requiring permanent lead/shocking coil placement in the coronary sinus and its branches. Methods: Fifty‐five permanent cardiac leads were extracted during 2003 in 28 consecutive patients. Our study population included a 10/55 (18%) subset (all males; age 73 ± 6 years; EF = 0.24 ± 0.09) that underwent CS (1/10) or vein branch (9/10) lead extraction. Leads were extracted with an excimer laser sheath (n = 4) or by direct traction (n = 6). Median times between implantation and lead removal were 9.5 months (range 5–59) in the laser group and 3 months (range 3–4) in the direct traction group. Indication for extraction was infection (n = 4), dislodgement (n = 3), diaphragm stimulation (n = 2), and elevated threshold (n = 1). The CS was divided into distal, mid, and proximal segments by venogram. Results: Entry of the laser sheath into the CS was necessary in three of four laser patients. The two distal CS laser cases (left lateral CS coil and anterior‐lateral left ventricular (LV) lead) required both 14‐ and 12‐Fr sheaths, separately. The proximal CS laser case (posterior‐lateral LV lead) required a 12 Fr sheath. The remaining laser patient required a 12‐Fr sheath to pass to the mid SVC. There were no procedural complications as a result of CS lead extraction. Reimplantation of a CS lead was attempted in 7/10 patients at a median of 4 days (range 1–300). CS venograms were available for review in patients before initial implantation (6/10) and after extraction (7/10). The postextraction venograms demonstrated complete occlusion of the vein from which the lead was extracted, and its distal branches, which were unusable in 5/10 (50%). The vein occlusions were present in patients with indwelling leads for greater than 3 months and were independent of extraction method. Conclusions: Laser lead extraction in the coronary sinus appears feasible in carefully selected cases with mandatory indications. However, special intraoperative monitoring and echocardiographic imaging with surgical backup ready is strongly recommended. Target vein selection may be limited for the purpose of reimplantation when leads are indwelling for greater than 3 months.