- Email: [email protected]
Sudden cardiac death: New approaches for implantable cardioverter-defibrillators (ICDs)
Sudden Cardiac Death New Approaches for Implantable CardioverterDefibrillators (ICD) Riccardo Cappato, Hussam Ali PII: DOI: Reference:
S0167-5273(17)31691-1 doi:10.1016/j.ijcard.2017.03.064 IJCA 24744
To appear in:
International Journal of Cardiology
Received date: Accepted date:
15 March 2017 15 March 2017
Please cite this article as: Cappato Riccardo, Ali Hussam, Sudden Cardiac Death New Approaches for Implantable Cardioverter-Defibrillators (ICD), International Journal of Cardiology (2017), doi:10.1016/j.ijcard.2017.03.064
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Sudden Cardiac Death New Approaches for Implantable Cardioverter-Defibrillators (ICD)
IP
T
Riccardo Cappato1, MD, FESC, FHRS, Hussam Ali2, MD, FESC, FEHRA
SC R
1- Arrhythmia & Electrophysiology Research Center, IRCCS Humanitas Research Hospital, Rozzano (Milan), Italy.
MA
NU
2- Arrhythmia & Electrophysiology Unit II, Humanitas Gavazzeni Clinics, Bergamo, Italy.
CE P
Corresponding Author:
TE
D
Conflict of Interest/Disclosures: Dr. R. Cappato has equity and intellectual property rights with Cameron Health.
Riccardo Cappato, MD, FESC, FHRS
Arrhythmia & Electrophysiology Research Center, Humanitas Research Hospital, Rozzano (Milan), Italy.
AC
E-mail: [email protected] Tel:
+39 02 82244005
Fax:
+39 02 82246453
1
ACCEPTED MANUSCRIPT
Abstract
IP
T
The implantable cardioverter-defibrillator (ICD) has shown its superiority to anti-arrhythmic drugs in the prevention of sudden cardiac death. However, the conventional transvenous ICDs are still associated with
SC R
substantial risks and comorbidities mainly related to the transvenous leads.
The recent advent of an entirely sub-cutaneous ICD (S-ICD) represents an important progress in the
NU
defibrillation technology towards a less invasive approach. Clinical data are growing regarding the safety and efficacy of S-ICD in prevention of sudden cardiac death in selected patients without pacing indications. This
MA
novel technology seems promising and particularly beneficial in young patients with channelopathies, conditions at high risk of infection, or in those who experienced previous complications related to the transvenous leads. The S-ICD technology is still developing regarding the device, diagnostic capabilities, and
TE
D
the surgical implantation technique. Further advancements and potential integration with the leadless pacing technology may realize an outstanding evolution in defibrillation therapy and prevention of sudden cardiac
CE P
death in the near future.
AC
Keywords: subcutaneous ICD; defibrillation technology; ventricular arrhythmias; sudden cardiac death
2
ACCEPTED MANUSCRIPT Introduction The implantable cardioverter-defibrillator (ICD) has shown its superiority to anti-arrhythmic drugs for the primary and secondary prevention of sudden cardiac death.1-3 During the last decades, ICD technologies
IP
T
have evolved dramatically in terms of efficacy and safety. Initially, ICD implantation was accomplished by the placement of epicardial patches and a large abdominal pulse generator during cardiac surgery with non-
SC R
negligible risks and comorbidities.4 The introduction of transvenous (TV) leads, advanced percutaneously, has simplified the implantation procedure and expanded the use of ICD therapy worldwide. Nevertheless,
NU
TV-ICDs are still associated with considerable acute and long-term procedural risks, mainly related to the TV-leads which are considered the weakest link in the TV-ICD system.5,6 Shortcomings related to the TV-
MA
leads include, but are not limited to, late infections or endocarditis, vessel occlusion or thrombosis, valvular dysfunction, and lead failure with secondary inappropriate or ineffective ICD interventions. Moreover, lead extraction of chronic TV-leads is a complex procedure with considerable comorbidity and mortality.7
TE
D
Consequently, an entirely sub-cutaneous ICD (S-ICD) system that leaves the heart and vessels untouched may further simplify the implant procedure and minimize the shortcomings related to the TV-
CE P
leads.
The S-ICD concept and early clinical studies During the recent years, awareness has increased of the shortcomings and risks related to the
AC
implantation of TV-leads. This has motivated investigators to conceive an entirely S-ICD system preserving the cardiovascular structures. The first trial was conducted in 78 patients to assess defibrillation threshold according to different configurations of a temporary S-ICD system.8 The results led to the selection of the SICD shock configuration currently available for clinical use, consisting of a left lateral pulse-generator (PG) positioned at the fifth intercostal space, and an 8-cm shock coil positioned parallel to the left parasternal margin. A subsequent trial of permanent S-ICD was conducted in 55 patients showing successful detection and defibrillation (at 65 J) of the induced VF in 100% and 98% of patients, respectively. All 12 episodes of clinical ventricular tachyarrhythmias were detected and terminated effectively by the S-ICD during a relatively short follow-up period (10 ± 1 months). Complications were minor, and inappropriate sensing was rare and could be managed by device reprogramming.8,9 The current S-ICD system 3
ACCEPTED MANUSCRIPT The system consists of a subcutaneous PG and a subcutaneous lead placed along the left side of the sternum. The current PG model (EMBLEM MRI- SICD, Boston Scientific) has a volume of ~ 60 cc, a weight of 130 g and a projected longevity exceeding 7 years. Using 2 sensing electrodes on the subcutaneous
IP
T
lead and the canister itself as the third one, three sensing vectors are available to detect the subcutaneous signals (Figure 1). The system automatically selects the best sensing vector to avoid double QRS counting
AC
CE P
TE
D
MA
NU
SC R
and/or T-wave oversensing.
Figure 1: The subcutaneous ICD. A) Cartoon showing the S-ICD system in its standard anatomical location with the three available sensing vectors. B) Chest radiogram showing correct positioning of the S-ICD. C) An example of appropriate effective shock terminating an episode of fast ventricular tachycardia.
The implantation procedure is basically guided by anatomical landmarks and fluoroscopy use is not routinely required. At the end of the procedure, defibrillation test is still recommended to assess correct detection and defibrillation (at 65 J) of the induced ventricular fibrillation. Two therapy zones are available (> 170 bpm): the shock zone where heart rate is the only used criterion, and the conditional shock zone where additional discriminators are used to differentiate ventricular from supraventricular arrhythmias to reduce inappropriate shocks. The S-ICD cannot provide chronic pacing, but 4
ACCEPTED MANUSCRIPT it is capable of delivering 30 seconds of transcutaneous pacing if bradycardia is detected following shock therapy.9 Clinical performance of the S-ICD:
IP
T
The largest available data on the S-ICD performance were obtained through pooled data from two large registries: IDE (S-ICD System IDE Clinical investigation) and EFFORTLESS (Boston Scientific Post
SC R
Market S-ICD Registry).9,10 Data from these registries were recently published analyzing S-ICD performance in 882 patients followed for 21.7 ± 11.5 months.
NU
Inappropriate shock rate was 13.1% at 3 years, mostly secondary to T-wave oversensing (about 40% of inappropriate therapies). Importantly, in patients with dual-zone programming, the incidence of inappropriate
MA
shocks at 3 years was significantly lower (11.7%) compared to those with single-zone programming (20.5%). The estimated 3-year device-related complications and all-cause mortality were 11.1% and 4.7%, respectively. Notably, no lead failures, neither S-ICD related endocarditis/bacteremia were reported. The
TE
D
incidence of appropriate shock was 5.3% over 1 year and 98.2% of clinical episodes of ventricular tachyarrhythmias were terminated within the 5 available shocks. A recently published retrospective study
CE P
showed comparable outcomes between the S-ICD and TV-ICD in terms of safety and efficacy.11 The PRAETORIAN trial which is an ongoing prospective, multicenter trial, including 700 patients randomized (1:1) to subcutaneous or transvenous ICD therapy, should provide further evidence comparing clinical
AC
outcomes of both technologies.12 Patient selection
Basically, the S-ICD may be considered in most patients candidate for ICD therapy who prove eligible at the pre-implant signals screening and do not require any type of pacing (i.e.; anti-bradycardia or anti-tachycardia pacing, resynchronization therapy). However, few groups of patients seem to benefit more from this technology including, but not limited to, young patients with electrical channelopathies, complex congenital heart disease with intracardiac shunts or limited vascular access, patients who are at increased risk of serious infection, and those who have already experienced complications related to the TV-leads (e.g.; endocarditis, venous occlusion, lead failure, etc).9 However, other non-clinical factors as cost issues and lack of reimbursement do limit the expansion of this technology in the daily clinical practice in many European countries.13 5
ACCEPTED MANUSCRIPT Novel advancement in the S-ICD technology -
The S-ICD Device: The currently available S-ICD device (EMBLEMTM MRI, Boston Scientific) has several favorable features
IP
T
compared to the first S-ICD generation (SQ-RX 1010, Cameron Health).9 There was a substantial decrease in pulse generator size with 15%, 20%, and 10% reduction in volume, thickness, and weight, respectively. Pulse
SC R
generator reduction might play an important role to reduce pocket-related complications particularly in skinny patients with poorly developed subcutaneous tissue. Notably, the current S-ICD is compatible with
NU
remote-monitoring (LATTITUDE) which is becoming the standard of care for all ICD systems allowing a closer follow-up of patients. Battery-longevity has also been improved significantly (about ↑40 % from 5.1
MA
to 7.3 years) that should reduce replacement interventions and their associated costs and infection risks. Importantly, patients with the EMBLEM MRI (or the previous EMBLEM) devices may undergo 1.5 Tesla full-body MRI under controlled conditions. Interestingly, the advanced INSIGHT algorithm with « Smart
TE
D
Pass Filter » seems promising to reduce T wave oversensing and consequent inappropriate shocks. The new S-ICD system is also provided with AF monitoring capability to early detect and manage silent atrial
CE P
fibrillation. Finally, pre-implant patient screening is now digitalized using the programmer and signals eligibility is assessed automatically by the software. This digital screening should reduce the inter-observer variability and the percentage of ineligible patients since the digital screening is provided with the advanced
-
AC
smart filter similar to the EMBLEM generator itself. S-ICD programming:
The current recommendation is to activate the optional conditional shock zone (programmable between 170240 bpm) to enhance detection of supraventricular arrhythmias since this approach showed up to 50% reduction in inappropriate shocks.10 There is tendency to program a high cut-off for the therapy zones, particularly the VF zone. This is in harmony with the results of MADIT-RIT trial that showed how a more conservative programming may reduce the incidence of unnecessary therapies.14
-
The surgical implantation technique
6
ACCEPTED MANUSCRIPT The standard surgical implantation technique is accomplished by three surgical incisions.8 The longest incision (~ 6 cm) is made at the lateral thorax to position the device in a subcutaneous pocket at the level of the 5th or 6th intercostal space and the mid-axillary line. Two smaller parasternal incisions are performed in
IP
T
proximity of the xiphoid process and sternal angle to tunnelize the lead placing it subcutaneously along the left margin of the sternum. After a learning curve and experience maturation regarding surgical techniques
SC R
that approach a new anatomical area for most electrophysiologists, and with the aid of surgeons’ skills, a few modifications of the implantation technique have been utilized through the last years with promising results.
NU
Of note, a two incisions technique has been successfully performed using an 11-French splittable sheath being inserted over the tunneling tool from the xiphoid incision superiorly and thus avoiding the need for the
MA
superior parasternal incision.15 This approach may further simplify the implantation procedure and reduce pocket infections. More importantly, an intermuscular technique has been adopted to implant the S-ICD generator between the anterior surface of serratus anterior and the posterior surface of latissimus dorsi. In
TE
D
small studies, this implant technique showed optimal cosmetic results and very low rates of pocket complications. By obtaining a more dorsal positioning of the canister and avoiding most of the fat tissue
CE P
beneath the device, the shock impedance and defibrillation threshold are expected to be optimal. 16 The intermuscular implantation technique could be particularly beneficial in obese patients to optimize the defibrillation threshold, in skinny patients to improve cosmetic aspects and reduce local complications, and
-
AC
also in patients with previous pocket infections by protecting the device between tow muscles layers. S-ICD and concomitant pacing therapy The major limitation of current the S-ICD system is the lack of pacing capabilities, excluding 30 seconds of post-shock backup pacing. Interestingly, the combined use of S-ICD and a permanent pacemaker was successful in limited number of patients and in varying unique conditions including complex congenital heart disease and limited vascular access.17 Clinical research is ongoing to integrate the S-ICD system with the novel leadless pacing technology. Recent preclinical and preliminary results showed encouraging data regarding the feasibility of this combination.18 Realizing such advancement in the future would be a first step to abandon the intracardiac leads and their associated shortcomings. However, safety and long-term data are still unavailable and caution should be taken that novel technologic advancements might compromise the simplicity and the less invasive nature of the S-ICD that was the original concept behind its invention. 7
ACCEPTED MANUSCRIPT S-ICD and the current guidelines: The first inclusion of the S-ICD in the guidelines was in the ESC guidelines 2014 on hypertrophic cardiomyopathy (class IIb indication).19 Subsequently, with growing data on clinical performance of this
IP
T
novel technology in terms of safety and efficacy, the ESC guidelines 2015 on management of ventricular arrhythmias and sudden cardiac death have addressed the S-ICD as a viable alternative to TV-ICD (class IIa
SC R
indication) when pacing therapies are not required.20 Conclusions
NU
After more than 15 years of continuous research and studies, the S-ICD has become a real life clinical practice for both primary and secondary prevention of SCD unless pacing is required. The S-ICD avoids
MA
procedural complications associated with TV- leads, and does not require routine fluoroscopy use. It is particularly beneficial in young patients, those with electrical syndromes, patients who had already experienced complications related to the TV-leads. Further technology innovations as leadless pacing, if
TE
D
integrated with the S-ICD, might offer an attractive therapeutic approach in the future and probably it might
CE P
expand the population of patients that may benefit from this therapy.
AC
-
References: [1] Bardy GH, Lee KL, Mark DB, et al: Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med 2005;352:225-237. 8
ACCEPTED MANUSCRIPT [2] Moss AJ, Zareba W, Hall WJ, et al: Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med 2002;346:877-883. [3] Moss AJ, Hall WJ, Cannom DS, et al: Improved survival with an implanted defibrillator in patients with
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T
coronary disease at high risk for ventricular arrhythmia. Multicenter Automatic Defibrillator Implantation Trial Investigators. N Engl J Med 1996;335:1933-1940.
SC R
[4] Saksena S: Defibrillation thresholds and perioperative mortality associated with endocardial and epicardial defibrillation lead systems. PACE 1993;16:202-207.
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[5] Kleemann T, Becker T, Doenges K, et al: Annual rate of transvenous defibrillation lead defects in implantable cardioverter-defibrillators over a period of 10 years. Circulation 2007;115:2474-2480.
MA
[6] Kron J, Herre J, Renfroe EG, et al: Lead- and device-related complications in the antiarrhythmics versus implantable defibrillators trial. Am Heart J 2001;141:92-98. [7] Buiten MS, van der Heijden AC, Schalij MJ, et al. How adequate are the current methods of lead
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D
extraction? A review of the efficiency and safety of transvenous lead extraction methods. Europace 2015;17:689-700.
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[8] Bardy GH, Smith WM, Hood MA, et al. An entirely subcutaneous implantable cardioverter-defibrillator. N Engl J Med 2010;363:36-44.
[9] Ali H, Lupo P, Cappato R. The entirely subcutaneous defibrillator - A new generation and future
AC
expectations. Arrhythm Electrophysiol Rev 2015;4:116-121. [10] Burke MC, Gold MR , Knight BP, et al. Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry. J Am Coll Cardiol 2015;65:1605-1615. [11] Brouwer TF, Yilmaz D, Lindeboom R, et al. Long-term clinical outcomes of subcutaneous versus transvenous implantable defibrillator therapy. J Am Coll Cardiol 2016;68:2047-2055. [12] Olde Nordkamp LR, Knops RE, Bardy GH, et al. Rationale and design of the PRAETORIAN trial: a Prospective, RAndomizEd comparison of subcuTaneOus and tRansvenous ImplANtable cardioverter-defibrillator therapy. Am Heart J 2012;163:753-760.
9
ACCEPTED MANUSCRIPT [13] Boveda S, Lenarczyk R, Haugaa K, et al. Implantation of subcutaneous implantable cardioverter defibrillators in Europe: results of the European Heart Rhythm Association survey. Europace 2016;18:1434-1439.
defibrillator
Implantation Trial-Reduce
programming Inappropriate
in
Therapy
the
Multicenter
(MADIT-RIT).
2014;7:785-792.
Automatic
Defibrillator
Circ Arrhythm
Electrophysiol
SC R
cardioverter
IP
T
[14] Ruwald AC, Schuger C, Moss AJ, et al. Mortality reduction in relation to implantable
implantation
of
the
subcutaneous
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[15] Knops RE, Olde Nordkamp LR, de Groot JR, Wilde AA. Two-incision technique for implantable
MA
2013;10:1240-1243.
cardioverter-defibrillator.
Heart
Rhythm
[16] Winter J, Siekiera M, Shin DI, et al. Intermuscular technique for implantation of the subcutaneous
implantable
cardioverter
defibrillator:
long-term
performance
and
complications.
TE
D
Europace 2016. pii: euw297. doi: 10.1093/europace/euw297. [Epub ahead of print] [17] Huang J, Patton KK, Prutkin JM. Concomitant use of the subcutaneous implantable
1245.
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cardioverter defibrillator and a permanent pacemaker. Pacing Clin Electrophysiol 2016;39:1240-
[18] Tjong FV, Brouwer TF, Smeding L, et al. Combined leadless pacemaker and subcutaneous
1747.
AC
implantable defibrillator therapy: feasibility, safety, and performance. Europace 2016;18:1740-
[19] Elliott PM, Anastasakis A, Borger MA, et al. 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy. Eur Heart J 2014;35:2733-2779. [20] Priori SG, Blomström-Lundqvist C, Mazzanti A, et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J 2015;36:2793-2867.
10
S0167-5273(17)31691-1 doi:10.1016/j.ijcard.2017.03.064 IJCA 24744
To appear in:
International Journal of Cardiology
Received date: Accepted date:
15 March 2017 15 March 2017
Please cite this article as: Cappato Riccardo, Ali Hussam, Sudden Cardiac Death New Approaches for Implantable Cardioverter-Defibrillators (ICD), International Journal of Cardiology (2017), doi:10.1016/j.ijcard.2017.03.064
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Sudden Cardiac Death New Approaches for Implantable Cardioverter-Defibrillators (ICD)
IP
T
Riccardo Cappato1, MD, FESC, FHRS, Hussam Ali2, MD, FESC, FEHRA
SC R
1- Arrhythmia & Electrophysiology Research Center, IRCCS Humanitas Research Hospital, Rozzano (Milan), Italy.
MA
NU
2- Arrhythmia & Electrophysiology Unit II, Humanitas Gavazzeni Clinics, Bergamo, Italy.
CE P
Corresponding Author:
TE
D
Conflict of Interest/Disclosures: Dr. R. Cappato has equity and intellectual property rights with Cameron Health.
Riccardo Cappato, MD, FESC, FHRS
Arrhythmia & Electrophysiology Research Center, Humanitas Research Hospital, Rozzano (Milan), Italy.
AC
E-mail: [email protected] Tel:
+39 02 82244005
Fax:
+39 02 82246453
1
ACCEPTED MANUSCRIPT
Abstract
IP
T
The implantable cardioverter-defibrillator (ICD) has shown its superiority to anti-arrhythmic drugs in the prevention of sudden cardiac death. However, the conventional transvenous ICDs are still associated with
SC R
substantial risks and comorbidities mainly related to the transvenous leads.
The recent advent of an entirely sub-cutaneous ICD (S-ICD) represents an important progress in the
NU
defibrillation technology towards a less invasive approach. Clinical data are growing regarding the safety and efficacy of S-ICD in prevention of sudden cardiac death in selected patients without pacing indications. This
MA
novel technology seems promising and particularly beneficial in young patients with channelopathies, conditions at high risk of infection, or in those who experienced previous complications related to the transvenous leads. The S-ICD technology is still developing regarding the device, diagnostic capabilities, and
TE
D
the surgical implantation technique. Further advancements and potential integration with the leadless pacing technology may realize an outstanding evolution in defibrillation therapy and prevention of sudden cardiac
CE P
death in the near future.
AC
Keywords: subcutaneous ICD; defibrillation technology; ventricular arrhythmias; sudden cardiac death
2
ACCEPTED MANUSCRIPT Introduction The implantable cardioverter-defibrillator (ICD) has shown its superiority to anti-arrhythmic drugs for the primary and secondary prevention of sudden cardiac death.1-3 During the last decades, ICD technologies
IP
T
have evolved dramatically in terms of efficacy and safety. Initially, ICD implantation was accomplished by the placement of epicardial patches and a large abdominal pulse generator during cardiac surgery with non-
SC R
negligible risks and comorbidities.4 The introduction of transvenous (TV) leads, advanced percutaneously, has simplified the implantation procedure and expanded the use of ICD therapy worldwide. Nevertheless,
NU
TV-ICDs are still associated with considerable acute and long-term procedural risks, mainly related to the TV-leads which are considered the weakest link in the TV-ICD system.5,6 Shortcomings related to the TV-
MA
leads include, but are not limited to, late infections or endocarditis, vessel occlusion or thrombosis, valvular dysfunction, and lead failure with secondary inappropriate or ineffective ICD interventions. Moreover, lead extraction of chronic TV-leads is a complex procedure with considerable comorbidity and mortality.7
TE
D
Consequently, an entirely sub-cutaneous ICD (S-ICD) system that leaves the heart and vessels untouched may further simplify the implant procedure and minimize the shortcomings related to the TV-
CE P
leads.
The S-ICD concept and early clinical studies During the recent years, awareness has increased of the shortcomings and risks related to the
AC
implantation of TV-leads. This has motivated investigators to conceive an entirely S-ICD system preserving the cardiovascular structures. The first trial was conducted in 78 patients to assess defibrillation threshold according to different configurations of a temporary S-ICD system.8 The results led to the selection of the SICD shock configuration currently available for clinical use, consisting of a left lateral pulse-generator (PG) positioned at the fifth intercostal space, and an 8-cm shock coil positioned parallel to the left parasternal margin. A subsequent trial of permanent S-ICD was conducted in 55 patients showing successful detection and defibrillation (at 65 J) of the induced VF in 100% and 98% of patients, respectively. All 12 episodes of clinical ventricular tachyarrhythmias were detected and terminated effectively by the S-ICD during a relatively short follow-up period (10 ± 1 months). Complications were minor, and inappropriate sensing was rare and could be managed by device reprogramming.8,9 The current S-ICD system 3
ACCEPTED MANUSCRIPT The system consists of a subcutaneous PG and a subcutaneous lead placed along the left side of the sternum. The current PG model (EMBLEM MRI- SICD, Boston Scientific) has a volume of ~ 60 cc, a weight of 130 g and a projected longevity exceeding 7 years. Using 2 sensing electrodes on the subcutaneous
IP
T
lead and the canister itself as the third one, three sensing vectors are available to detect the subcutaneous signals (Figure 1). The system automatically selects the best sensing vector to avoid double QRS counting
AC
CE P
TE
D
MA
NU
SC R
and/or T-wave oversensing.
Figure 1: The subcutaneous ICD. A) Cartoon showing the S-ICD system in its standard anatomical location with the three available sensing vectors. B) Chest radiogram showing correct positioning of the S-ICD. C) An example of appropriate effective shock terminating an episode of fast ventricular tachycardia.
The implantation procedure is basically guided by anatomical landmarks and fluoroscopy use is not routinely required. At the end of the procedure, defibrillation test is still recommended to assess correct detection and defibrillation (at 65 J) of the induced ventricular fibrillation. Two therapy zones are available (> 170 bpm): the shock zone where heart rate is the only used criterion, and the conditional shock zone where additional discriminators are used to differentiate ventricular from supraventricular arrhythmias to reduce inappropriate shocks. The S-ICD cannot provide chronic pacing, but 4
ACCEPTED MANUSCRIPT it is capable of delivering 30 seconds of transcutaneous pacing if bradycardia is detected following shock therapy.9 Clinical performance of the S-ICD:
IP
T
The largest available data on the S-ICD performance were obtained through pooled data from two large registries: IDE (S-ICD System IDE Clinical investigation) and EFFORTLESS (Boston Scientific Post
SC R
Market S-ICD Registry).9,10 Data from these registries were recently published analyzing S-ICD performance in 882 patients followed for 21.7 ± 11.5 months.
NU
Inappropriate shock rate was 13.1% at 3 years, mostly secondary to T-wave oversensing (about 40% of inappropriate therapies). Importantly, in patients with dual-zone programming, the incidence of inappropriate
MA
shocks at 3 years was significantly lower (11.7%) compared to those with single-zone programming (20.5%). The estimated 3-year device-related complications and all-cause mortality were 11.1% and 4.7%, respectively. Notably, no lead failures, neither S-ICD related endocarditis/bacteremia were reported. The
TE
D
incidence of appropriate shock was 5.3% over 1 year and 98.2% of clinical episodes of ventricular tachyarrhythmias were terminated within the 5 available shocks. A recently published retrospective study
CE P
showed comparable outcomes between the S-ICD and TV-ICD in terms of safety and efficacy.11 The PRAETORIAN trial which is an ongoing prospective, multicenter trial, including 700 patients randomized (1:1) to subcutaneous or transvenous ICD therapy, should provide further evidence comparing clinical
AC
outcomes of both technologies.12 Patient selection
Basically, the S-ICD may be considered in most patients candidate for ICD therapy who prove eligible at the pre-implant signals screening and do not require any type of pacing (i.e.; anti-bradycardia or anti-tachycardia pacing, resynchronization therapy). However, few groups of patients seem to benefit more from this technology including, but not limited to, young patients with electrical channelopathies, complex congenital heart disease with intracardiac shunts or limited vascular access, patients who are at increased risk of serious infection, and those who have already experienced complications related to the TV-leads (e.g.; endocarditis, venous occlusion, lead failure, etc).9 However, other non-clinical factors as cost issues and lack of reimbursement do limit the expansion of this technology in the daily clinical practice in many European countries.13 5
ACCEPTED MANUSCRIPT Novel advancement in the S-ICD technology -
The S-ICD Device: The currently available S-ICD device (EMBLEMTM MRI, Boston Scientific) has several favorable features
IP
T
compared to the first S-ICD generation (SQ-RX 1010, Cameron Health).9 There was a substantial decrease in pulse generator size with 15%, 20%, and 10% reduction in volume, thickness, and weight, respectively. Pulse
SC R
generator reduction might play an important role to reduce pocket-related complications particularly in skinny patients with poorly developed subcutaneous tissue. Notably, the current S-ICD is compatible with
NU
remote-monitoring (LATTITUDE) which is becoming the standard of care for all ICD systems allowing a closer follow-up of patients. Battery-longevity has also been improved significantly (about ↑40 % from 5.1
MA
to 7.3 years) that should reduce replacement interventions and their associated costs and infection risks. Importantly, patients with the EMBLEM MRI (or the previous EMBLEM) devices may undergo 1.5 Tesla full-body MRI under controlled conditions. Interestingly, the advanced INSIGHT algorithm with « Smart
TE
D
Pass Filter » seems promising to reduce T wave oversensing and consequent inappropriate shocks. The new S-ICD system is also provided with AF monitoring capability to early detect and manage silent atrial
CE P
fibrillation. Finally, pre-implant patient screening is now digitalized using the programmer and signals eligibility is assessed automatically by the software. This digital screening should reduce the inter-observer variability and the percentage of ineligible patients since the digital screening is provided with the advanced
-
AC
smart filter similar to the EMBLEM generator itself. S-ICD programming:
The current recommendation is to activate the optional conditional shock zone (programmable between 170240 bpm) to enhance detection of supraventricular arrhythmias since this approach showed up to 50% reduction in inappropriate shocks.10 There is tendency to program a high cut-off for the therapy zones, particularly the VF zone. This is in harmony with the results of MADIT-RIT trial that showed how a more conservative programming may reduce the incidence of unnecessary therapies.14
-
The surgical implantation technique
6
ACCEPTED MANUSCRIPT The standard surgical implantation technique is accomplished by three surgical incisions.8 The longest incision (~ 6 cm) is made at the lateral thorax to position the device in a subcutaneous pocket at the level of the 5th or 6th intercostal space and the mid-axillary line. Two smaller parasternal incisions are performed in
IP
T
proximity of the xiphoid process and sternal angle to tunnelize the lead placing it subcutaneously along the left margin of the sternum. After a learning curve and experience maturation regarding surgical techniques
SC R
that approach a new anatomical area for most electrophysiologists, and with the aid of surgeons’ skills, a few modifications of the implantation technique have been utilized through the last years with promising results.
NU
Of note, a two incisions technique has been successfully performed using an 11-French splittable sheath being inserted over the tunneling tool from the xiphoid incision superiorly and thus avoiding the need for the
MA
superior parasternal incision.15 This approach may further simplify the implantation procedure and reduce pocket infections. More importantly, an intermuscular technique has been adopted to implant the S-ICD generator between the anterior surface of serratus anterior and the posterior surface of latissimus dorsi. In
TE
D
small studies, this implant technique showed optimal cosmetic results and very low rates of pocket complications. By obtaining a more dorsal positioning of the canister and avoiding most of the fat tissue
CE P
beneath the device, the shock impedance and defibrillation threshold are expected to be optimal. 16 The intermuscular implantation technique could be particularly beneficial in obese patients to optimize the defibrillation threshold, in skinny patients to improve cosmetic aspects and reduce local complications, and
-
AC
also in patients with previous pocket infections by protecting the device between tow muscles layers. S-ICD and concomitant pacing therapy The major limitation of current the S-ICD system is the lack of pacing capabilities, excluding 30 seconds of post-shock backup pacing. Interestingly, the combined use of S-ICD and a permanent pacemaker was successful in limited number of patients and in varying unique conditions including complex congenital heart disease and limited vascular access.17 Clinical research is ongoing to integrate the S-ICD system with the novel leadless pacing technology. Recent preclinical and preliminary results showed encouraging data regarding the feasibility of this combination.18 Realizing such advancement in the future would be a first step to abandon the intracardiac leads and their associated shortcomings. However, safety and long-term data are still unavailable and caution should be taken that novel technologic advancements might compromise the simplicity and the less invasive nature of the S-ICD that was the original concept behind its invention. 7
ACCEPTED MANUSCRIPT S-ICD and the current guidelines: The first inclusion of the S-ICD in the guidelines was in the ESC guidelines 2014 on hypertrophic cardiomyopathy (class IIb indication).19 Subsequently, with growing data on clinical performance of this
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novel technology in terms of safety and efficacy, the ESC guidelines 2015 on management of ventricular arrhythmias and sudden cardiac death have addressed the S-ICD as a viable alternative to TV-ICD (class IIa
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indication) when pacing therapies are not required.20 Conclusions
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After more than 15 years of continuous research and studies, the S-ICD has become a real life clinical practice for both primary and secondary prevention of SCD unless pacing is required. The S-ICD avoids
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procedural complications associated with TV- leads, and does not require routine fluoroscopy use. It is particularly beneficial in young patients, those with electrical syndromes, patients who had already experienced complications related to the TV-leads. Further technology innovations as leadless pacing, if
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integrated with the S-ICD, might offer an attractive therapeutic approach in the future and probably it might
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expand the population of patients that may benefit from this therapy.
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References: [1] Bardy GH, Lee KL, Mark DB, et al: Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med 2005;352:225-237. 8
ACCEPTED MANUSCRIPT [2] Moss AJ, Zareba W, Hall WJ, et al: Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med 2002;346:877-883. [3] Moss AJ, Hall WJ, Cannom DS, et al: Improved survival with an implanted defibrillator in patients with
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coronary disease at high risk for ventricular arrhythmia. Multicenter Automatic Defibrillator Implantation Trial Investigators. N Engl J Med 1996;335:1933-1940.
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[4] Saksena S: Defibrillation thresholds and perioperative mortality associated with endocardial and epicardial defibrillation lead systems. PACE 1993;16:202-207.
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[5] Kleemann T, Becker T, Doenges K, et al: Annual rate of transvenous defibrillation lead defects in implantable cardioverter-defibrillators over a period of 10 years. Circulation 2007;115:2474-2480.
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[6] Kron J, Herre J, Renfroe EG, et al: Lead- and device-related complications in the antiarrhythmics versus implantable defibrillators trial. Am Heart J 2001;141:92-98. [7] Buiten MS, van der Heijden AC, Schalij MJ, et al. How adequate are the current methods of lead
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extraction? A review of the efficiency and safety of transvenous lead extraction methods. Europace 2015;17:689-700.
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[8] Bardy GH, Smith WM, Hood MA, et al. An entirely subcutaneous implantable cardioverter-defibrillator. N Engl J Med 2010;363:36-44.
[9] Ali H, Lupo P, Cappato R. The entirely subcutaneous defibrillator - A new generation and future
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expectations. Arrhythm Electrophysiol Rev 2015;4:116-121. [10] Burke MC, Gold MR , Knight BP, et al. Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry. J Am Coll Cardiol 2015;65:1605-1615. [11] Brouwer TF, Yilmaz D, Lindeboom R, et al. Long-term clinical outcomes of subcutaneous versus transvenous implantable defibrillator therapy. J Am Coll Cardiol 2016;68:2047-2055. [12] Olde Nordkamp LR, Knops RE, Bardy GH, et al. Rationale and design of the PRAETORIAN trial: a Prospective, RAndomizEd comparison of subcuTaneOus and tRansvenous ImplANtable cardioverter-defibrillator therapy. Am Heart J 2012;163:753-760.
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ACCEPTED MANUSCRIPT [13] Boveda S, Lenarczyk R, Haugaa K, et al. Implantation of subcutaneous implantable cardioverter defibrillators in Europe: results of the European Heart Rhythm Association survey. Europace 2016;18:1434-1439.
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[14] Ruwald AC, Schuger C, Moss AJ, et al. Mortality reduction in relation to implantable
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[15] Knops RE, Olde Nordkamp LR, de Groot JR, Wilde AA. Two-incision technique for implantable
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cardioverter-defibrillator.
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[16] Winter J, Siekiera M, Shin DI, et al. Intermuscular technique for implantation of the subcutaneous
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Europace 2016. pii: euw297. doi: 10.1093/europace/euw297. [Epub ahead of print] [17] Huang J, Patton KK, Prutkin JM. Concomitant use of the subcutaneous implantable
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cardioverter defibrillator and a permanent pacemaker. Pacing Clin Electrophysiol 2016;39:1240-
[18] Tjong FV, Brouwer TF, Smeding L, et al. Combined leadless pacemaker and subcutaneous
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implantable defibrillator therapy: feasibility, safety, and performance. Europace 2016;18:1740-
[19] Elliott PM, Anastasakis A, Borger MA, et al. 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy. Eur Heart J 2014;35:2733-2779. [20] Priori SG, Blomström-Lundqvist C, Mazzanti A, et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J 2015;36:2793-2867.
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