Volume 14 - Issue 3, 2014 - Matrix

What is New in Implantable Device Technology?

Authors

Stefan Bogdan, MD

Leviev Heart Center,

Sheba Medical Center,

Tel Hashomer, Israel


Prof. Michael Glikson, MD, FACC, FESC;

President-Elect, Israel Heart Society

Director of Davidai Arrhythmia Center

Leviev Heart Center,

Sheba Medical Center,

Tel Hashomer, Israel

[email protected]

 

Key Points

• The leadless pacemaker is the latest breakthrough in bradycardia therapy, as it reaches phase 3 clinical trials.
• Subcutaneous ICD use is supported by early data from large international registries, showing a good safety profile
and non-inferiority by comparison to standard ICD.
• Quadripolar lead and multisite LV pacing have the potential for better CRT delivery, as opposed to
standard bipolar LV pacing.
• Current recommendations encourage conservative strategy when dealing with normally functioning recalled ICD leads.

Cardiovascular implantable electronic devices (CIED) have seen tremendous progress during the last 20 years, in the field of heart failure (HF) treatment, anti-bradycardia pacing and defibrillation. CIED and leads have evolved allowing easier implantation, improved long term reliability and longer battery life.

 

Implantable cardioverter defibrillators (ICD), initially reserved for highly selected patients, where the benefit of secondary prevention outweighed potential side effects, are now a safe and widespread therapy, and have become part of the standard of care in HF patients with severe systolic dysfunction. Cardiac resynchronisation therapy (CRT) is also coming of age. In patients with heart failure, left ventricular systolic dysfunction and wide QRS, CRT improves clinical status, leads to reverse remodelling and reduces mortality.

 

During the last decade, the number of complex device implantations has dramatically increased. Despite an overall low incidence (<5%), the absolute number of device-related complications has increased. The weak spot remains the endovascular lead, which can fail over time, get infected or lead to vein thrombosis.

 

Several new technologies are targeting the reduction of device complication rates, such as the leadless pacemaker or the sub-cutaneous ICD. Others are attempting to improve delivery of therapy, mainly for CRT – like the multipole LV lead or the development of alternative LV lead access.

 

Leadless Pacemakers

Recently, a major technological breakthrough has been made in the field of bradycardia therapy with the development of the leadless pacemaker, by both St. Jude Medical (with the Nanostim) and Medtronic (with the Micra). The miniaturisation of the device allows its direct implantation into the right ventricle, where it is anchored to the inter-ventricular septum, thus eliminating the need for an endovascular lead (see Figure 1). This technology has the potential to completely eliminate pocket and endovascular lead-related complications.

 

The results from the LEADLESS trial have been published this year, confirming the feasibility and safety of the St. Jude device in a cohort of 33 patients (Reddy et al. 2014). While still ongoing, the post-approval European study suffered a temporary setback due to safety issues, after reports of six perforations resulting in two deaths. Those were probably related to the learning curve of the leadless pacemaker implantation technique, and the study has since resumed. While in a more incipient phase, Medtronic has recently announced, during the 2014 Cardiostim conference, the successful implantation of the Micra in the first four patients.

 

Future challenges include the development of a dual chamber version and possibly a bi-ventricular leadless device with wireless connection between the pacing elements. Device removal long after implantation may prove problematic, despite the fact that both manufacturers offer technical solutions in case extraction is needed.

 

Subcutaneous ICD

Despite undisputable benefits, ICD implantation is still associated with considerable risk, as major complication rates stand at around 1.5%. These include infection, pneumothorax, haemorrhage, perforation and death. Additionally, ICD-related risks persist after implantation such as late infection, lead endocarditis, the delivery of inappropriate therapy, vein occlusion, lead dislodgement, valvular dysfunction and lead failure due to intrinsic lead defects.

 

In view of these considerations, a completely subcutaneous ICD (S-ICD) system has been developed, with the first patients implanted in 2008. It has since been approved for commercial use by the European Union in 2009 and by the FDA in 2012. More than 1300 patients were implanted with S-ICD during the last 5 years.

 

The system comprises a pulse generator, which is introduced subcutaneously over the left thorax, in the axillary region, and a single subcutaneous lead placed along the left side of the sternum. The S-ICD can accurately detect ventricular tachy-arrhythmia, which is treated by high-energy shock (maximum 80J) (Gold et al. 2012) (see Figure 2). It can deliver temporary but not chronic pacing, so it cannot be used in patients with symptomatic bradycardia or frequently recurring ventricular tachycardia terminated with anti-tachycardia pacing.

 

Lambiase reported this year on early data from the multicentre EFFORTLESS S-ICD registry (Lambiase et al. 2014). He showed that in a real-life international population of S-ICD recipients, the S-ICD performed appropriately, with clinical event rates and inappropriate shock rates comparable with those reported for conventional ICDs.

 

Although longer follow-up data is still required for assessing lead reliability over time, the S-ICD has emerged as a valuable alternative to standard ICD in patients with no need for ventricular pacing, with the potential to prevent most of the aforementioned complications associated with intravascular ICD leads. Furthermore, it is today the preferred solution for patients in need of ICD, who suffer from vein occlusion, or who have had system extraction for infection. Future technological challenges include downsizing of the device, which is currently bulky, prevention of infections, and improvement of sensing algorithms to prevent inappropriate shocks (Gold et al. 2014).

 
Figure 1.
Leadless pacemaker implantation technique.

Infection Prevention

Infection is the most serious complication following CIED implantation. It risk for sudden cardiac death have been implanted with Fidelis leads. Moreover, evidence suggests that the risk of Fidelis lead fracture is increasing with time (Cheung et al. 2012)