Entirely Subcutaneous Cardiac Defibrillator Implant: Initial Experience in a Single Spanish Centre

. Escrito en Volumen VII - Número 1


RevElectro y Arritmias

2014;7: 8-12

Miguel A. Arias, Marta Pachón, Alberto Puchol, Finn Akerström, Luis Rodríguez-Padial

Unidad de Arritmias y Electrofisiología Cardiaca, Servicio de Cardiología, Hospital Virgen de la Salud, Toledo, España

Correspondence to: Dr. Miguel Ángel Arias
Unidad de Arritmias y Electrofisiología Cardiaca, Servicio de Cardiología. Hospital Virgen de la Salud, Avenida de Barber 30, 45004, Toledo
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Recibido: 13/10/2013 Aceptado: 05/11/2013


Objectives. A new system of automatic defibrillation completely subcutaneous, which has recently been introduced in Spain, was developed in order to avoid the clinical issues associated to intracavitary leads in patients with transvenous implanted defibrillators (ICD). The work of the Spanish center with the widest experience up-to-date is presented.

Materialand Methods. We expose the initial experience in a Spanish center, which has a large experience with conventional ICD implants, with completely subcutaneous defibrillators, providing data of induction test, defibrillation and initial patients follow-up.

Results. tytyt completely subcutaneous defibrillation system was implanted in three patients with risk of presenting malignant ventricular arrhythmias, no susceptible of treatment through antitachycardia pacing, without the need of permanent pacing. There were no complications peri-implant or during initial follow-up. Induction of ventricular fibrillation; detection and defibrillation were successful without significant complications.

Conclusions. The subcutaneous defibrillator is going to be defined as an effective and safety option in a certain group of patients with an indication of ICD. The initial experience in our center during the implant and the efficacy of defibrillation in the induced arrhythmias is very favorable.

Keywords: subcutaneous defibrillator; sudden death; malignant arrhythmias; ventricular fibrillation


The benefit of the implantable cardioverter defibrillator (ICD) for primary and secondary prevention of sudden cardiac death in certain high risk subgroups has been demonstrated in several international clinical multicenter trials in the lasts two decades, deriving its results to diverse indications of ICD included in the clinical guides of the most relevant international scientific societies. The need to implant transvenous leads in order to detect the cardiac rhythm and apply effective programmable treatments represents the fundamental limitation of these devices, considering they are associated to frequent complications during the implant procedure and follow-up. Thus, increasing the survival of ICD patients, the long-term risk of infection of devices and dysfunction of leads becomes a problem of great relevance. Approximately one fifth of patients with an ICD have a dysfunction of these elements after 10 years from the implant, with the inherent risks in such problems, including the need of surgical revisions, infections, inappropriate therapies and even increased mortality related with such processes. It is in this context that appeared the need to develop an implantable defibrillation system that does not require transvenous leads.

Thus, a completely subcutaneous defibrillation system was developed; the first clinical results were reported in 2011 and in September 2012 received the approval by the U.S. FDA for clinical use in certain subgroups of patients. In Spain, the subcutaneous ICD system has not been introduced in the market until very recently and our experience is very limited. The aim of this paper is to report the initial experience with the entirely subcutaneous ICD implant in a Spanish center with extensive experience in conventional implanted devices.

Material and methods


Three consecutive patients with indication for ICD implantation due to risk of malignant ventricular arrhythmias, without the need for permanent pacing and characteristics of the disease not a priori subsidiary to benefit from the ICD antitachycardia pacing(low risk of presenting sustained uniformed arrhythmias) ere selected in order to implant an entirely subcutaneous ICD in our center. The general characteristics of the three patients are summarized in Table 1. They were three young patients with no history of uniform sustained ventricular tachycardia, stable sinus rhythm and without organic disorders of the specific cardiac conduction system. The advantages and disadvantages of this new form of therapy were discussed with all patients and their families; they gave an oral and written consent to undergo the procedure.

Patient 1

Patient 2

Patient 3

Age (years)








Height (cm)




Weight (Kg)




Cardiac disease

Brugada Syndrome

Undetermined with a relative with SCD

Brugada Syndrome

Ventricular Function


Slightly depressed



Primary Prevention

Primary Prevention

Primary Prevention


Sinus Rhythm

Sinus Rhythm

Sinus Rhythm

Previous supraventricular arrhythmias




Table 1. General patient characteristics.

Entirely subcutaneous defibrillation system and electrocardiographic screening pre-implant

The S-ICD is a system consisting of a generator (S-ICD®, SQ-RX 1010, Boston Scientific) with a weight of 145 grams and estimated 5-year life longevity (Figure 1), which delivers high-energy shocks of 80 Joules (a lower energy is programmable during test of ventricular fibrillation induction during the implant, to ensure minimum safety margin to follow-up) and up to 30 seconds of post-shock pacing using a transthoracic biphasic current of 200 miliamperes. For detection and defibrillation it has a lead (Q Trak 3010, Boston Scientific) with a 8 cm coil between the two sensing electrodes, that is placed parallel to the sternum in the subcutaneous tissue. The heart rate is detected by the signal obtained with one of the three possible vectors using the two electrodes of the lead and the generator can (proximal electrode – can, distal electrode – can and distal electrode – proximal electrode).


Figure 1. Generator and system lead.


Figure 2. Transparent ruler with printed profiles used for the screening process that selects which patients are suitable for an S-ICD implant.


Figure 3. Electrode position in order to perform the three lead ECG, placed in the theoretical position of the ICD can, distal and proximal electrodes.


Figure 4. Successful screening leads for patient 1, confirming that in both supine and seated positions, one of the profiles accomplishes the requisites.


Figure 5. Image of the tunneling tool.

To ensure proper detection after implantation, a pre-implant morphology analysis of QRS complexes and T waves should be performed. This electrocardiographic suitability of patients was evaluated with a strip of printed profiles (Figure 2). A three-lead electrocardiogram was performed by placing the electrodes on the theoretical positions where the sensing electrode and the generator would eventually be, and therefore corresponding to the three vectors which make the possible detection (Figure 3): 1) Proximal electrode – can (lead III, equivalent to primary vector); 2) Distal electrode – can (lead II, equivalent to secondary vector), and 3) distal electrode – proximal electrode (Lead I, which corresponds to the alternative vector). It was recorded at 5, 10 and 20 mm/mV, both in supine and standing position. The three electrodes are placed at the position where the future generator (mid-axillary line), detection electrode (para-xifoid left region) and distal electrode (14 cm cranial to the prior (Fig. 4)) would be. If at least one of the three leads is suitable, the patient is considered suitable for the S-ICD implant. One lead is considered suitable if in both supine and standing position, aligning baseline electrocardiogram with the strip, the QRS complex and the T wave do not exceed any of the profiles of the screening tool, with at least one peak of the QRS end content in between a dashed dotted line that exists at each end of the printed profile (Figure 5). If only one lead is appropriate, it is recommended to repeat the ECG recording during exercise and check that this lead is also suitable during the exercise test.

Implant system

The implants were performed with patients in supine position, the left upper limb was situated at an angle of approximately 90 degrees to the long axis of the thorax. A wide-subcutaneous pocket was made to place the device in the vicinity of the mid-axillary line upon the sixth rib. Then, two-small left parasternal incisions at the site of the xiphoid process and at the manubrium-sternal junction were performed. An initial tunneling was performed from the incision where the proximal electrode would be located (xiphoid process) to the pocket, by means of a specific insertion tool whose distal tip is tied to the defibrillation electrode, once emerged at the device pocket. The lead was tunneled by pulling back the tool towards the xiphoid incision, leaving the proximal end in the pocket in order to be connected to the generator. Next, both parasternal incisions and the lead´s tip were connected with the tunneling tool until it emerged at the manubrium-sternal incision, removing the tool and anchoring the distal electrode to the fascia. The proximal electrode was secured with a suture sleeve. Incisions were closed, the generator was connected to the proximal end and the wound was closed using standard procedures for the implantation of subclavian devices. Once the system was placed an induction of ventricular fibrillation testing was performed to evaluate detection and defibrillation functions of the system. In order to do that, induction was performed with 50 Hz stimulation from the lead, one shock zone above 170 beats per minute programmed, and an initial shock from the subcutaneous ICD set at 65 J. In case of being unsuccessful, a high energy shock from the external defibrillator would have been applied.


Regarding the pre-implantation screening electrocardiogram, two ECG leads were optimal for patients 1 and 3. For patient 2, only one of them was useful, thus it was suggested by the manufacturer to perform the same analysis recording the electrocardiogram during intense exercise loads (recommended to be close to the submaximal heart rate), providing a favorable outcome for the lead fitted at resting.

Implants were performed under general anesthesia because they were the first ones in our group and we were unfamiliar with the technique, requiring external technical assistance. In all three cases, implant was performed by two electrophysiologists (operator and assistant) with extensive experience in conventional implant devices. In addition, only in the first case, under the supervision of an operator with extensive experience in subcutaneous ICD implants. No fluoroscopy was used for implants, but before beginning the procedure it was used to determine the ideal anatomic landmarks, already with the patient supine and using a non-sterile system. The implantation technique described thoroughly in the methods section was followed uneventful. Implants were performed without incidents and a clear signal was obtained within the device in all cases (Figure 6). The device did an automatically set up in all patients, choosing the primary configuration as the best sensing vector (patient 1) and secondary configuration (patient 2 and 3). Ventricular fibrillation was induced in a single attempt with 50 Hz current for 2 seconds, which was properly detected and reverted to sinus rhythm with a single shock of 65 J in all three cases (Figure 7). Time for induction therapy and value of shock impedance for patients 1, 2 and 3 was 3,4, 16,5 and 13,5 seconds, and 61, 51 and 61 ohms, respectively. A 240 beats per minute single shock zone was programmed in all three patients. The postoperative course was favorable, being discharged the next day, after performing a thorax x-ray that showed no complications, except slight subcutaneous emphysema in patients 1 and 3 (Figure 8). At a mean follow-up of 45 days post-implant, no complications were observed, lead sensing and impedance were adequate and patients remained asymptomatic with surgical wounds in perfect conditions.


Figura 6. A: Post-implant thorax X-ray; B: Above, programmed ICD signal; below, equivalent surface ECG of the same lead; C: Induction test and defibrillation registered with an external defibrillator.


The development of S-ICD represents a major technological innovation that, compared with conventional ICD, avoids potential issues, both periprocedural and long term, related to the need for having vascular access and to implant transvenous leads. Several early clinical studies have reported a limited rate of complications related to the implant, and although up-to-date there are no randomized-comparative trials between the S-ICD and the conventional ICD, currently available data supports the S-ICD as a very effective device for detecting, discriminating and terminating malignant ventricular arrhythmias4. The IDE trial is the largest multicenter study published to date5. Data of 314 patients was analyzed with standard indication for ICD in which an S-ICD was implanted and a mean follow-up of 11 months took place. In this group, patients’ rate free of complications after 180 days was 99%, and of 899 episodes of malignant arrhythmias generated in the induction tests, 897 were properly detected and defibrillated. During follow-up, the rate of inappropriate shocks was 13,1%, and there were 119 episodes of spontaneous malignant arrhythmias in 21 patients, with a 92,1% effectiveness of the first shock, none of the episodes were associated to mortality and no external shocks were needed to terminate any of the episodes5.

The fact that the implant is performed following anatomical landmarks also obviates the need to use fluoroscopy, with subsequent benefits for both patient and operators. Some authors have evaluated simplifying the procedure, obviating the incision of the manubrium-sternal junction to minimize surgical complications6.

The device’s detection feature uses a vector among the two electrodes or each one of them to can. The vector that more adequately avoids double counting of QRS or T-wave oversensing should be programmed, avoiding events that can cause inappropriate therapies of the S-ICD. In an attempt to avoid these problems in some patients, a pre-implant screening electrocardiogram is required. Olde Nordkamp et al7, in a series of 230 patients candidates for S-ICD who completed the previous screening, found that it was inappropriate in 7,3% of them, and some variables such as major overweight, hypertrophic cardiomyopathy, prolonged QRS or a R/T ratio less than 3 in the electrocardiographic lead with the highest T wave in the 12-lead electrocardiogram, were independent variables for the screening to be unacceptable.

One of the main limitations of S-ICD is its inability to provide permanent pacing, thus it is not indicated for patients who require it, including candidates for cardiac resynchronization therapy, or those who present uniform ventricular tachycardia repeatedly qualifying for the antitachycardia pacing. On the other hand, it is an attractive alternative for patients with difficult vascular access or null, with high risk of infection (patients on hemodialysis or with previous infected devices) or youths with various forms of congenital heart disease, cardiomyopathy, or channelopathies, in which the likelihood of problems related with electrodes will be high due to the elevated number of years that an ICD will be carried. In this context, Brugada syndrome, as was the case in two of our patients, is emerging as an ideal pathology due to the usual lack of need for pacing, patients’ not advanced age and the absence of treatable spontaneous arrhythmias by antitachycardia pacing8.

Therefore, indications, real benefits and true potential of S-ICD will be clarified in the coming years mainly as a result of data from current multicenter studies9, 10 as well as implementing additional technical improvements in these devices.


The entirely subcutaneous ICD is emerging as an effective and safe option in selected groups of patients with indication for ICD. The initial experience at our center in the implant and the defibrillation efficacy of induced arrhythmias has been very favorable.


Our acknowledgement to Carlos Briz and Alexis Herrera, from Boston Scientific, Spain, for their outstanding technical support.


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