HRS 2017: New implantable string subcutaneous defibrillator shows promise for sudden cardiac death prevention

Petr Neuzil

The use of a novel implantable string subcutaneous defibrillator (ISSD, Newpace) that has no can, and has been designed to be placed without the need for a surgical pocket, may allow improved patient compliance and aesthetics, is less invasive, and has optimal implantation time. 

The results from a first-in-man feasibility study on subcutaneous defibrillation utilising an integrated flexible string shaped defibrillator were presented at the Heart Rhythm Society’s 38th Annual Scientific Sessions (10‒13 May, Chicago, USA) by Petr Neuzil from Na Homolce Hospital in Prague, Czech Republic.

Current subcutaneous defibrillators require an electrically active, metal encased implantable pulse generator of about 60cm3 volume, which is placed over the ribs. The ISSD is an integrated device which has no can. The ICD components and functionality are in a single flexible string shaped device that is inserted subcutaneously. However, there have been concerns that the surface area of the defibrillation coil is insufficient for effective defibrillation of patients.

Neuzil told delegates: “The configuration consists of an integrated and flexible structure with a string which is 45fr, including the active segment, and two shocking coils of 10cm each at 15fr and 9fr. The two coils are to the mid sternum and lateral axillary line. These are connected to the cable string, which contains all the batteries, capacitors, and communication system. So it is one body. This is implanted subcutaneously.”

He continued: “The main questions for the feasibility trial were: can this system defibrillate in this configuration, and how complex is the procedure? All patients were discharged from hospital without any complications. So, in conclusion, based on our first results, I would say that this defibrillator can defibrillate successfully.”

The acute non-randomised single-arm, single-centre study was conducted at Na Homolce Hospital in Prague. The patient population consisted of patients who were indicated for ICD implantation for primary and secondary prevention of sudden cardiac death prior to implant. The patient cohort included 22 enrolled patients aged 69.5±8.9 years, 82% were male, left ventricular ejection fraction (LVEF) was 28.9±8.2, 18% had non-ischaemic cardiomyopathy, 14% had prior cardiac surgery, and 91% were primary prevention patients. Endpoint was the defibrillation time (DFT) values.

Among the exclusion criteria were chronic obstructive pulmonary disease, renal failure, bleeding disorders, pulmonary hypertension, antiarrhythmic drugs, and antibiotics. Rapid pacing was used to induce ventricular fibrillation (VF), and defibrillation attempts started at 50J. When 50J was successful, after a rest period, repeated VF induction occurred, followed by a 70J or 30J shock, then possibly 20J, depending on shock success. Preliminary results indicated an average DFT of 26J, with a standard deviation of 11J in successfully screened patients, thus the researchers concluded that a defibrillation shock of 60J has a 99.87% chance of success.

Neuzil explained: “After all this testing, we got very exciting results, because the majority of the patients succeeded with 30J and less. Seven patients were done with 20J, and four patients succeeded with 30J. The average DFT we got was 25.8J. Which means if you go to a 60J defibrillation shock, we could statistically be able to defibrillate nearly 100% patients. If you compare it with a traditional S-ICD [subcutaneous implantable cardioverter defibrillator], they are really fascinating data.”

He added: “The procedure was extremely fast. We did all of these procedures in around 20 minutes average implantation time. The shortest time, including tunnelling the subcutaneous pathway for this defibrillator, was 11 minutes. The timing was excellent, even if you used an off-the-shelf system for tunnelling.”

Neuzil noted that, in order for this configuration to defibrillate successfully, the device must be positioned according to the guidelines, and using pre-operative fluoroscopy. And, although the procedure was easy and fast, it could be made shorter with tailored implant tools.

Neuzil said: “I think we need to work on much more dedicated tools to make it shorter and much more adaptable. We also hope to use this device for chronic implants. If we are able to implant in this kind of patients, then I think they are easily able to get several sizes; for example, for younger patients and kids. I would be extremely positive about several sizes. We were not using sensing as a parameter for defibrillation. We defibrillated manually using externally connected defibrillation. There are four elements for sensing, and actually, we can choose in the future what you want to use as the best amplitude for sensing.”

And he predicted: “This study indicated that we really would be able to get for the patient great comfort and also [satisfy] cosmetic issues. This is a unique system. For the next generation, when we want to implant, if all the processes are going well we expect the lifespan to be around 10 years, and this system should be the first ICD that would be rechargeable.”

Implantable string subcutaneous defibrillator (ISSD)