Author + information
- Received July 19, 2018
- Revision received October 11, 2018
- Accepted November 1, 2018
- Published online December 26, 2018.
- Lucas V.A. Boersma, MD, PhDa,b,∗ (, )
- Béla Merkely, MD, PhDc,
- Petr Neuzil, MD, PhDd,
- Ian G. Crozier, MDe,
- Devender N. Akula, MDf,
- Liesbeth Timmers, MDg,
- Zbigniew Kalarus, MD, PhDh,i,
- Lou Sherfesee, PhDj,
- Paul J. DeGroot, MSj,
- Amy E. Thompson, MS, MBAj,
- Daniel R. Lexcen, PhDj and
- Bradley P. Knight, MDk
- aDepartment of Cardiology, St. Antonius Hospital, Nieuwegein, the Netherlands
- bAcademic Medical Center (AMC), University of Amsterdam, Amsterdam, the Netherlands
- cSemmelweis University, Heart and Vascular Center, Budapest, Hungary
- dDepartment of Cardiology, Na Homolce Hospital, Prague, Czech Republic
- eDepartment of Cardiology, Christchurch Hospital, Christchurch, New Zealand
- fLourdes Cardiology Center, Voorhees, New Jersey
- gDepartment of Cardiology, Ghent University Hospital, Ghent, Belgium
- hSMDZ, Zabrze, Poland, Medical University of Silesia, Katowice, Poland
- iDepartment of Cardiology, Silesian Center for Heart Diseases, Zabrze, Poland
- jMedtronic, Minneapolis, Minnesota
- kNorthwestern University, Feinberg School of Medicine, Chicago, Illinois
- ↵∗Address for correspondence:
Dr. Lucas V. A Boersma, Department of Cardiology, St. Antonius Hospital, PO 2500, 3430 EM, Nieuwegein, The Netherlands.
Objectives The ASD2 (Acute Extravascular Defibrillation, Pacing, and Electrogram) study evaluated the ability to adequately sense, pace, and defibrillate patients with a novel implantable cardioverter-defibrillator (ICD) lead implanted in the substernal space.
Background Subcutaneous ICDs are an alternative to a transvenous defibrillator system when transvenous implantation is not possible or desired. An alternative extravascular system placing a lead under the sternum has the potential to reduce defibrillation energy and the ability to deliver pacing therapies.
Methods An investigational lead was inserted into the substernal space via a minimally invasive subxiphoid access, and a cutaneous defibrillation patch or subcutaneous active can emulator was placed on the left mid-axillary line. Pacing thresholds and extracardiac stimulation were evaluated. Up to 2 episodes of ventricular fibrillation were induced to test defibrillation efficacy.
Results The substernal lead was implanted in 79 patients, with a median ± SD implantation time of 12.0 ± 9.0 min. Ventricular pacing was successful in at least 1 vector in 76 of 78 patients (97.4%), and 72 of 78 (92.3%) patients had capture in ≥1 vector with no extracardiac stimulation. A 30-J shock successfully terminated 104 of 128 episodes (81.3%) of ventricular fibrillation in 69 patients. There were 7 adverse events in 6 patients causally (n = 5) or possibly (n = 2) related to the ASD2 procedure.
Conclusions The ASD2 study demonstrated the ability to pace, sense, and defibrillate using a lead designed specifically for the substernal space.
- anterior mediastinum
- defibrillation lead
- implantable cardioverter-defibrillator
Subcutaneous implantable cardioverter-defibrillators (SQ ICDs) provide an alternative to managing patients at risk for sudden cardiac death when implantation of a transvenous implantable cardioverter-defibrillator (TV ICD) is not possible or desired (1). Although the SQ ICDs may reduce long-term complications associated with transvenous leads, the current models are larger in size and do not provide antitachycardia pacing (ATP) or bradycardia pacing support, except for limited post-shock pacing (2,3). A potential solution to these limitations is to place the lead closer to the heart but still in the extravascular space.
Recent studies and human case reports have shown that a lead can be placed successfully under the sternum in the substernal space (anterior mediastinum) for pacing and defibrillation, although these evaluations and their results have been limited by the use of commercially available leads and/or catheters not designed for substernal therapy delivery (4–10). Development of an ICD lead designed for the substernal space may provide a more durable extravascular solution to address some of the inherent limitations of the current systems, but further investigation is needed before this approach is adopted for a broad population of ICD patients. The objective of the ASD2 (Acute Extravascular Defibrillation, Pacing, and Electrogram) study was to evaluate the feasibility of sensing, pacing, and defibrillation from a lead designed specifically for the substernal space.
The ASD2 study was a prospective multicenter, worldwide, nonrandomized, acute, proof-of-concept clinical study. This study complied with the Declaration of Helsinki (11) and was approved by the ethics committees and associated regulatory authorities of the participating centers. Informed consent was obtained from all patients before study enrollment.
Eligible patients were those who underwent a surgical procedure that required a midline sternotomy or implantation of a TV ICD or SQ ICD. Exclusion criteria included previous pericarditis or sternotomy, significant right ventricular dilatation, New York Heart Association functional class IV, oxygen-dependent chronic obstructive pulmonary disease, myocardial infarction within 6 weeks, and active cardiac or noncardiac device implantations. Patients underwent a baseline visit, acute testing visit, and a follow-up visit.
The ASD2 study was conducted with the patient under general anesthesia, conscious sedation, or monitored anesthesia care sedation, per investigator discretion. A small incision (∼1 to 3 cm) was made adjacent to the left aspect of the xiphoid process or just inferior to the xiphoid tip. Using lateral and anteroposterior fluoroscopy, blunt dissection was performed to and through the diaphragmatic attachments to facilitate substernal entry. A hemostatic peel-away sheath was placed over a tunneling tool (Figure 1) and together advanced through the diaphragmatic attachments into the substernal space. The tunneling tool was angulated toward the posterior face of the sternum, and during advancement, care was taken to maintain close contact between the tip of the tunneling tool and the sternum. The tunneling tool was advanced medial to the left lateral border of the sternum and no farther than the top of the cardiac silhouette. Once tunneling was complete, the sheath was retained, and the tunneling tool was removed.
An investigational lead (Figure 2) designed for substernal therapy delivery was introduced through the peel-away sheath and advanced under fluoroscopy until the distal pacing ring electrode (ring 1) was approximately centered over the cardiac silhouette. The curved defibrillation coil segments were oriented toward the right lateral border and the pacing electrodes toward the left lateral border of the sternum.
Two different tunneling tools (both malleable 3.1-mm diameter stainless steel tunneling rods with blunt tip) were available for use within the ASD2 study, per investigator discretion: a commercially available tunneling tool (Model 6996T, Medtronic, Minneapolis, Minnesota) or a similarly designed tool with an added polymer guide rod and overmolded handle (not commercially available) (Figure 1).
An investigational lead designed for substernal therapy delivery was used (Figure 2). The lead contained 2 ring electrodes for pacing and sensing, and 2 coil electrodes for pacing, sensing, ventricular fibrillation (VF) induction, and defibrillation: ring 1 (distal ring), ring 2 (proximal ring), coil 1 (distal coil), and coil 2 (proximal coil). The coil electrodes (coils 1 and 2) could be coupled to form an overall 8-cm defibrillation coil for defibrillation purposes.
The investigational lead was connected via surgical cables to an external research defibrillator (Figure 3) capable of delivering 40 J, with the 40-J maximum output reflective of the anticipated design of a future system. The external research defibrillator used custom firmware to provide pacing and VF induction capabilities unique to the ASD2 study, but otherwise had the sensing and defibrillation capabilities used in conventional TV ICDs. A 79-cm2 defibrillation patch electrode (Model 1010P, Medtronic) or 23.9-cm3 subcutaneous active can emulator (ACE; Model 5719U, Medtronic) was placed on the chest of the patient along the left mid-axillary line near the fifth intercostal space.
Sensing data were collected during intrinsic rhythm using commercially available recording equipment. Sensing data were collected from the ring 1 to ring 2 vector to confirm adequacy of lead placement. Sensing parameters were adjusted to avoid T-wave, P-wave, or other extracardiac oversensing.
Pacing capture was evaluated from 3 vectors (Figure 3): ring 1 to ring 2 (low-voltage vector), ring 1 to coil 2 (low-voltage vector), and coil 1 to coil 2 (high-voltage vector). The pacing rate was set to approximately 20 beats/min above the intrinsic rate of patient. Pacing capture was defined as 3 consecutive beats of capture.
For the coil-to-coil vector at 10-ms pulsewidth (PW), pacing capture was determined starting from a voltage of 10 V and increased to 16, 20, 30, and 40 V until capture was achieved. If capture was observed, PW was shortened to 2 ms, and the protocol repeated. For both low-voltage vectors at 8-ms PW, voltage increased from 2 to 8 V in 2-V increments. If capture was observed, PW was shortened to 2 ms, and the protocol was repeated.
During pacing, the level of extracardiac muscle stimulation was recorded qualitatively as none, low, or high. None was defined as no visible or palpable extracardiac stimulation; low as visible, mild extracardiac stimulation (e.g., muscle twitching); and high as visible, strong extracardiac stimulation. Descriptive statistics were used to summarize the prevalence of extracardiac stimulation for each vector.
Following pacing testing, defibrillation efficacy was evaluated, with termination of ventricular tachycardia (VT)/VF defined as a return to supraventricular tachycardia or intrinsic rhythm. Up to 2 episodes of VT/VF could be induced per patient, with a single 30-J shock delivered after each successful induction, and external rescue shocks were delivered from a transthoracic defibrillator immediately thereafter, if needed. In the event of first-shock failure and termination of ventricular arrhythmia with external rescue shocks, the second induction and 30-J shock was conducted per physician discretion. All 30-J shocks were delivered between the ACE and/or patch and the investigational lead coil electrodes (coil 1 and coil 2) tied together. Electrograms were collected for all induced rhythms, and each electrogram was reviewed by the site, sponsor, and/or independent physician to adjudicate whether the rhythm was VT or VF.
Study end procedures
Following data collection, the ASD2 research system was removed before the planned procedure of the patient. All patients underwent an in-person follow-up 7 to 50 days post-procedure. Adverse events and outcomes were collected and adjudicated by an independent committee to determine association with either the ASD2 implant and/or system or the final surgery and/or system of the patient (e.g., TV ICD implant), using the Guidelines on Medical Devices (MEDDEV 2.7/3 Revision 3) classification system for causality (not related, unlikely, possible, probable, and causal). Serious and nonserious adverse events were reported to regulatory bodies and ethics committees. Serious adverse events, defined as adverse events that led to death or a serious deterioration in the health of the patient, which were also associated with the ASD2 system, are reported in the following.
SAS 9.4 (SAS Institute, Cary, North Carolina) was used for all analyses. Descriptive statistics were used to summarize baseline demographics, procedure characteristics, number of induced VF episodes, and presence of extracardiac stimulation. Because patients might have had multiple R-wave amplitude measures taken at the final lead position, the multiple measurements were averaged so that each patient contributed 1 measure to descriptive statistics. Because patients had multiple episodes induced, a generalized estimating equation logistic regression model was fit to assess defibrillation efficacy of VF episodes to account for within-patient correlation, whereas 1-sided 95% lower exact binomial confidence bounds were used to summarize pacing capture at different vectors.
In total, 87 patients were enrolled across 16 sites in Europe (n = 54), the United States (n = 19), New Zealand (n = 10), Hong Kong (n = 3), and Australia (n = 1). Among them, 68 were scheduled for TV ICD or SQ ICD, 14 for coronary artery bypass grafting, 2 for valve replacement and/or repair, and 1 for patent foramen ovale closure. Eight patients were excluded before the ASD2 procedure. There were 79 patients (86.1% male; age 62.0 ± 10.9 years) who had a mean left ventricular ejection fraction of 36.9 ± 13.8%, and 79.7% of whom were indicated for or received ICDs and who underwent the ASD2 tunneling procedure (Table 1). Sixty-eight (86.1%) patients received general anesthesia, 3 patients (3.8%) underwent conscious sedation, and 8 (10.1%) patients underwent monitored anesthesia care. Thirty-eight patients (48.1%) did not receive muscle paralytics, which included 27 patients who received general anesthesia and all patients who underwent conscious sedation or monitored anesthesia care sedation. Patients who underwent the procedure reflected cohorts typically presented in ICD trials (Figure 4). Seventy-seven patients (97.5%) completed the follow-up visit. There were 2 reported deaths (2.5%) during the follow-up period.
The investigational lead was placed in all 79 patients who underwent the implantation procedure. Total median ± SD lead placement time was 12.0 ± 9.0 min (time from first incision to final lead placement). The investigational lead deployed successfully during the first insertion attempt in 66 patients (83.5%) and was redeployed (in 1 to 4 attempts) to achieve the preferred orientation in all remaining patients.
Electrogram collection and sensing
A total of 78 patients had R-wave amplitudes tested in normal sinus rhythm in the final lead position, and the median R-wave amplitude was 2.4 mV (interquartile range: 1.8 to 3.6 mV). There were 130 induced episodes with electrocardiograms adjudicated as VF in 70 patients.
Pacing thresholds and extracardiac stimulation
Of the 79 patients who underwent the ASD2 testing procedure, 78 completed pacing testing in ≥1 vector. Ventricular pacing capture was successful in ≥1 vector for 76 of 78 patients (97.4%), and capture was successful in all vectors at all PWs for 31 patients (39.2%).
Across the 3 vectors, capture success was best with the high-voltage coil 1 to coil 2 vector, with capture achieved in this vector (mean capture voltage: 10.8 ± 2.2 V and 10-ms PW) in 97.4% of patients. However, 64 of 78 patients (82.1%) had capture in at least 1 of the low-voltage vectors (ring 1 to ring 2 or ring 1 to coil 2), whereas mean capture voltages were at 8-ms PW and 5.4 ± 2.0 and 4.6 ± 2.0 V, respectively (Table 2).
Extracardiac stimulation during pacing was assessed qualitatively as none, low, or high (Table 3). Extracardiac stimulation was absent in most of the 78 patients for all vectors and PWs. Capture was achieved in ≥1 vector without extracardiac stimulation in 92.3% of patients.
There were 130 induced episodes of VF in 70 patients. Two episodes (1.5%) in 1 patient were not shocked because of sensing issues related to suboptimal lead positioning. The remaining episodes were shocked from the external research defibrillator, after a mean episode duration of 16.6 ± 2.4 s. Of the 128 episodes in 69 patients included in the analysis cohort, the 30-J shock successfully terminated 104 episodes (81.3%), which included 55 of 69 first episodes (79.7%) and 49 of 59 second episodes (83.1%). Shock impedance was 88.1 ± 21.7 ohms. The generalized estimating equation−adjusted estimated overall defibrillation efficacy and 95% 1-sided lower confidence bounds were 80.0% and 72.0%, respectively.
All shock failures were observed among the 61 patients in whom a defibrillation cutaneous patch electrode was used, whereas no shock failures were observed among the 8 patients with an ACE in a device pocket. All 8 patients with an ACE had successful termination of the first episode (100%) compared with 47 of 61 patients (77.1%) with the cutaneous patch (p = 0.19; Fisher’s exact test).
Of the 14 patients in whom the first-episode shock failed, 5 patients (35.7%) did not have a second episode induced. Of the remaining 9 patients with a second episode, 3 patients (33.3%) had a second episode successfully terminated by the research defibrillator. Only 6 of 69 patients (8.7%) had shock failures on both the first and second episode.
Of the 69 patients in the analysis, 18 had at least 1 30-J first or second shock failure. Specifically, 15 (25.4%) of 59 subjects who received an ICD and 3 (30%) of 10 subjects who underwent some other surgical procedure experienced at least 1 shock failure.
Of the 79 patients who underwent the ASD2 study, there were 7 adverse events in 6 patients adjudicated as causally (n = 5) or as possibly (n = 2) related to the ASD2 procedure.
Four of the 5 adverse events adjudicated as being causally related to the ASD2 procedure resolved with no lasting effect on the patient; these included bleeding at the incision site, mild erythema at the incision, an episode of transient atrial fibrillation that occurred during VF induction, and reaction to anesthesia that resulted in low oxygen saturation. The fifth event was a pericardial effusion with tamponade in a 62-year-old patient with ischemic cardiomyopathy who was referred for an ICD generator change and addition of an atrial lead. During an improper substernal tunneling procedure, the patient developed tamponade physiology and prolonged hypotension intraoperatively. Hemodynamic stability was restored, but prolonged hypotension resulted in hypoxic cerebral injury. After 72 h, supportive care was withdrawn at the request of the family, and the patient died.
Two adverse events adjudicated as being possibly related to either the ASD2 procedure or to the final planned procedure and/or system included 1 episode of pericarditis and 1 episode of asystolic cardiac arrest. The patient with pericarditis received a de novo dual-chamber TV ICD with active fixation leads after the ASD2 procedure but presented with chest pain and a pericardial effusion without tamponade physiology 3 days post-procedure. The patient underwent uneventful pericardiocentesis with resolution of complaints and no further sequelae. The patient with asystolic cardiac arrest was an 81-year-old patient with diabetes, chronic kidney disease, peripheral vascular disease post-lower right limb amputation, and ischemic cardiomyopathy, who was admitted for decompensated heart failure, persistent atrial fibrillation, and systemic inflammatory response syndrome in the setting of urosepsis. The patient was medically managed and eventually underwent the ASD2 study procedure and planned dual-chamber TV ICD implantation. The procedures occurred uneventfully, and the patient was transferred in stable condition to a secondary center without complaints. Approximately 36 h post-procedure, the patient developed asystole. Despite cardiopulmonary resuscitation and pacing attempts by the ICD, there was failure to capture the myocardium, and the patient died.
The ASD2 study demonstrated the ability to position a substernal defibrillation lead and to achieve high effectiveness for acute defibrillation and pacing capture. The main findings of the study are presented in Figure 5.
In the present study, 104 of 128 (81.3%) induced and sensed episodes of VF were terminated by a single 30-J defibrillation shock, and only 6 patients had shock failures at both the first and second episodes. In these 6 patients, 1 had probable inappropriate connection of the research system, 1 had a body mass index of 39 kg/m2, and 4 had suboptimal and/or challenging lead or patch positioning.
Because the ASD2 study was a feasibility evaluation, system modification between shocks was not specified per protocol, although a polarity change between shocks was allowed at investigator discretion. Despite that limitation, the measured defibrillation efficacy in ASD2 was comparable to other studies of defibrillation testing during ICD implantation, when first-shock defibrillation efficacy was observed to range from 77% to 93% (12,13). Using conventional ICD sensing and detection, VF was adequately detected in all patients, except for 1 patient with suboptimal lead placement, with time to therapy (detection and charging) of 16.6 ± 2.4 s.
All observed shock failures occurred in patients in whom a cutaneous patch electrode was used, and none occurred when an ACE was used. The 30-J shock energy was chosen to provide the contemporary 10-J safety margin used in testing TV ICDs, anticipating a 40-J output in a future substernal ICD system. In contrast, the SQ ICD delivered up to 80 J using a subcutaneous defibrillation coil and lateral can with an average defibrillation threshold of 36.6 ± 19.8 J (2). The present strategy with a similar left lateral ICD can but substernal lead position seems to offer potential for lower thresholds and lower energy requirements that can positively influence longevity, as well as patient comfort associated with a smaller device size.
With the substernal lead near the right ventricle, the 3 tested pacing vectors demonstrated capture in ≥1 vector in >97% of patients. Capture was achieved in 1 of 2 low-voltage vectors for 82.1% of patients. Extracardiac stimulation was absent in 97.4% of patients in each low-voltage vector, even at longer PW. Importantly, patients with capture at 2 V in a low-voltage vector or at 10 V in the high-voltage vector were not tested at lower voltage outputs to determine true pacing capture threshold or to further minimize potential for extracardiac stimulation, thus potentially overestimating both. Despite that, 92.3% of ICDs could be programmed to achieve pacing capture in ≥1 vector while avoiding extra-cardiac stimulation. Although thresholds were higher than in traditional contact-pacing systems, the ability to pace the heart from a substernal lead location was an important finding. Although a different platform might be required, the data suggested a means to deliver ATP in patients with ventricular arrhythmias and might also provide an option for backup stimulation in patients with intermittent bradycardia. The present SQ ICD platform offered limited pacing options, which unavoidably led to symptomatic muscle stimulation.
Substernal lead implantation
In the present study, 1 patient death was adjudicated as causally related to the procedure due to pericardial effusion and tamponade after an improper tunneling procedure. Following this event, prescriptive methods were detailed for pre-procedural and procedural imaging with anteroposterior and lateral fluoroscopic approaches to ensure that the tool remained close to the posterior face of the sternum upon initial entry and throughout the procedure. No other encroachments of the pericardial space were observed following these modifications. Future investigation will be necessary to evaluate the safety of substernal lead implantation against objective performance criteria and to report on long-term patient follow-up.
These data build on the ASD and SPACE (Substernal Pacing Acute Clinical Evaluation Study) human feasibility studies, which evaluated substernal defibrillation and pacing feasibility, respectively, using commercially available equipment not specifically designed for substernal use (4,5).
Substernal alternative to the transvenous lead
Although the traditional TV ICD has proven its value in >3 decades of clinical trials, morbidity associated with TV ICD systems has led to a desire for extravascular and/or extracardiac options (14–19). In the past decade, the SQ ICD has been developed as a viable alternative to the TV ICD in certain patients with good effectiveness to terminate ventricular arrhythmias; however, it has limitations that include higher effective defibrillation energy, which requires a larger can with shortened battery life, and no option of delivering ATP for termination of re-entrant arrhythmias with a single device implantation (2,3,20).
A substernal ICD lead may solve several of the TV ICD- and SQ ICD-related issues. The energy required for substernal defibrillation should be lower underneath the sternum, whereas the proximity of the lead to the epicardial surface offers options for direct cardiac stimulation (4–6,8). The substernal lead is neither in the bloodstream nor connected to a continuously contracting heart, which potentially limits the incidence of systemic infection and accompanying risks, as well as lead durability issues. The ability to eliminate shocks via ATP and deliver lower energy shocks when necessary should improve morbidity and may improve the mortality benefit of ICD therapy (21,22).
The ASD2 research system included the use of a cutaneous patch electrode or an ACE to simulate the performance of an ICD generator, and most patients had a patch electrode. A patch electrode applied to the skin might not have been representative of a fully implanted ICD and might have led to energy loss that underestimated the true efficacy of a 30-J shock. Moreover, electrode placement was not strictly specified in the protocol and could have resulted in a large degree of variation. Optimization of lead and generator placement was shown to be of importance in SQ ICD device performance (23).
Although the rate of pacing capture was high and the rate of extracardiac stimulation was low, the limited pacing protocol might have overestimated the pacing threshold and the rate of extracardiac stimulation. Also, the anesthesia method was not prescribed by the ASD2 protocol but was at the discretion of the implanting physician. With a large proportion of patients (86.1%) under general anesthesia and paralytics used in 51.9% of patients overall, extracardiac stimulation might have been affected if paralytics were active during the time of pacing testing.
Most enrolled patients in ASD2 received an ICD; however, approximately 20% of patients who underwent the research procedure might have not needed an ICD and were enrolled for a surgical procedure that required midline sternotomy (e.g., coronary artery bypass grafting), which potentially affected electrical results.
ASD2 was an acute feasibility study; therefore, long-term performance data were missing. The impacts on pacing and defibrillation of factors such as lead stability, patient movement or posture, and chronic tissue encapsulation, as well as long-term system management issues related to infection, system modification, or extraction, require further evaluation. Ultimately, data from ambulatory patients implanted with a substernal lead for the long term will need to be collected to determine durability of the acute ASD2 findings and to further evaluate safety and efficacy.
The ASD2 study was the first reported human clinical study of pacing, sensing, and defibrillation from a lead designed specifically for the substernal space. The proximity of the lead to the pericardium resulted in R-wave amplitudes amenable to ICD sensing, a high rate of pacing capture, and a low degree of extracardiac stimulation during pacing. Moreover, defibrillation efficacy was >80% with a single 30-J shock. Further investigation in ambulatory patients is needed, but taken together, these results demonstrated the feasibility of a novel extravascular approach to ICD therapy delivery.
COMPETENCY IN MEDICAL KNOWLEDGE 1: The substernal space may provide an anatomic alternative for lead placement that can be reached reliably with a defibrillator lead.
COMPETENCY IN MEDICAL KNOWLEDGE 2: Custom-built leads in the substernal space are able to pace and defibrillate the heart in the large majority of patients.
TRANSLATIONAL OUTLOOK 1: Although long-term data are required for the novel extravascular ICD system, a substernal lead strategy may overcome the substantial morbidity and mortality associated with the introduction and long-term position of transvenous leads in the heart.
TRANSLATIONAL OUTLOOK 2: Current SQ defibrillator technology does not allow pacing and requires high-energy shock with a large device. The future novel extravascular ICD platform may enable physicians to provide bradycardia and ATP options, as well as defibrillate the heart with energy levels similar to current TV ICD platforms.
The authors would like to thank all the ASD2 study investigators, as well as the patients who consented to be enrolled; Griet Wouters of Medtronic for co-authorship of the ASD2 clinical protocol; and Aimee Pol and Koen J.P. Verhees of Medtronic for their editorial and logistical support and the critical appraisal of this manuscript.
This study was sponsored in its entirety by Medtronic.
Dr. Boersma is a consultant with Boston Scientific Corp., Medtronic, and Abbott; and has received research grants from Medtronic and fellowship support from Boston Scientific Corp. Dr. Merkely has received lecture fees from Medtronic, Biotronik, and Abbott. Dr. Neuzil has been a consultant for and is a member of the Advisory Board for Medtronic. Dr. Crozier has been a consultant for and has received research grants and fellowship support from Medtronic. Ms. Thompson holds stock in Medtronic. Dr. Knight has been a consultant for and has received lecture fees and fellowship support from Medtronic. All other authors have reported that they have no relationships relevant to the content of this paper to disclose.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
- Abbreviations and Acronyms
- active can emulator
- antitachycardia pacing
- SQ ICD
- subcutaneous implantable cardioverter-defibrillator
- TV ICD
- transvenous implantable cardioverter-defibrillator
- ventricular fibrillation
- ventricular tachycardia
- Received July 19, 2018.
- Revision received October 11, 2018.
- Accepted November 1, 2018.
- 2018 The Authors
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