The short answer is maybe.
Advances in the field of defibrillation have brought to practice different types of devices that include the transvenous implantable cardioverter-defibrillator (ICD) with or without cardiac resynchronization therapy, the subcutaneous ICD (S-ICD), and the wearable cardioverter-defibrillator. To ensure optimal use of these devices and to achieve best patient outcomes, clinicians need to understand how these devices work, learn the characteristics of patients who qualify them for one type of device versus another, and recognize the remaining gaps in knowledge surrounding these devices.
The transvenous ICD has been shown in several randomized clinical trials to improve the survival of patients resuscitated from near-fatal ventricular fibrillation and those with sustained ventricular tachycardia with syncope or systolic heart failure as a result of ischemic or nonischemic cardiomyopathy despite receiving guideline-directed medical therapy. Important gaps in knowledge regarding the transvenous ICD involve the role of the ICD in patient subgroups not included, or not well represented, in clinical trials and the need to refine the selection criteria for the ICD in patients who are indicated for it.
S-ICD was recently introduced into the clinical arena as another option for many patients who have an approved indication for a transvenous ICD. The main advantage of the S-ICD is a lower risk of infection and lead-related complications; however, the S-ICD does not offer bradycardia or antitachycardia pacing. The S-ICD may be ideal for patients with limited vascular access, high infection risk, or some congenital heart diseases. However, more data are needed regarding the efficacy and effectiveness of the S-ICD in comparison to transvenous ICDs, the extent of defibrillation testing required, and the use of the S-ICD with other novel technologies, including leadless pacemakers.
Cardiac resynchronization therapy-defibrillators are indicated in patients with a left ventricular ejection fraction 35 percent, QRS width 130 m, and New York Heart Association class II, III, or ambulatory IV symptoms despite treatment with guideline-directed medical therapy. Multiple randomized controlled trials have shown that the cardiac resynchronization therapy-defibrillator improves survival, quality of life, and several echocardiographic measures. One main challenge related to cardiac resynchronization therapy-defibrillators is the 30 percent nonresponse rate. Many initiatives are underway to address this challenge, including improved cardiac resynchronization therapy and imaging technologies, and enhanced selection of patients and device programming.
Technology moves incredibly fast in the 21st century. Look at the difference in cell phones from just 10 years ago and today! We went from boxy phones with antennas and the standard phone keypad to the slick, slim phones currently ruling our lives.
Medical technology has also moved quickly. Surgeons can now perform heart bypass surgery via robotic fingers through five small slits in a person’s chest rather than making a long incision and then cracking open the chest to reach the heart. Bluetooth-enabled bionic limbs have moved out of 1970’s television into the real world. Even the complete human genome has been mapped!
It would seem something as important as a portable device which can reset the heart of someone who is technically dead would have gone through many technological advances over the past 16 years. Strangely, though, automated external defibrillators (AEDs) have not really changed all that much in this century. The biggest advance was the switch from monophasic to biphasic waveforms. After that, real changes have occurred in the areas of only cases, batteries, and user interface.
Leadless Pacing. Leadless pacing is an emerging technology with the potential to significantly improve outcomes associated with the need for long-term pacing. Specifically, the major advantage of leadless systems is abolishing the need for transvenous leads and subcutaneous pockets, both of which account for most adverse events associated with traditional pacemakers. Over a half of century later, leadless pacemakers and defibrillation systems are just reaching the clinical arena. Despite the remarkable advantages of leadless pacing systems, the data are still quite limited and broad implementation of these technologies need to occur in a cautious and deliberate fashion as the peri-procedural risks remain high. Two of the three systems – nanostim and micra transcatheter pacing system – have shown the greatest applicability, although they are currently only limited to single-chamber pacing and procedural risks are modest. The WiCS-LV system is anatomically limited and benefits a small subset of patients. Leadless implantable cardioverter-defibrillator (ICD) therapy, the subcutaneous ICD, has demonstrated encouraging short-term safety and efficacy data supporting its use. Since its introduction, modifications to the implant procedure, pre-screening of patients, and programming of the devices have reduced procedural-related complications and inappropriate shocks. The S-ICD is a promising technology, but it is premature to conclude that it will supplant conventional ICDs. At this current time, the S-ICD may benefit select patients, such as those with recurrent bacteremia, vascular access limitations, and who may be prone to transvenous lead failure.
Advances in Battery Technology. Over the past five decades, the ICD technology has seen many developments, focused on improving battery shelf-life and ensuring a more seamless remote monitoring of patient data. The introduction of automatic external defibrillators and wearable defibrillators that are markedly more compact and easy to store has boosted the adoption of ICD devices. Additionally, significant improvements in the battery technology such as the optimization of the active cathode materials and the introduction of SVO nanomaterials possessing high cell potential of discharge have helped improve the functioning of CRM devices. For efficient functioning, ICD devices need to be continuously powered by high-current pulses to manage well the heart monitoring functions throughout the lifetime of the patient. Factors preventing adoption of these devices are systemic infections and the failure of the intravascular lead. In such cases, the extraction of lead may involve significant expenses and additional complications. Recent technological advancements have sought to address these limitations.
Wireless Remote Monitoring. Wireless remote monitoring (RM) has fundamentally changed the paradigm of how physicians and allied professionals manage patients with cardiovascular implantable electronic devices (CIEDs). Wireless RM transceivers now include wireless data transmission capability, eliminating the need for patients to connect to home phone lines or cable modems. This dramatically simplifies the home setup for patients, removing what was previously a significant barrier. This also makes it easier for clinics to implement RM technology for all of their patients, regardless of the device brand. Wireless RM of CIEDs represents the beginning of a fundamental change in how patients and healthcare providers will collaborate in the future. Sensors that silently monitor physiological data will provide warning to healthcare providers, enabling intervention at earlier points in the disease process, thereby reducing morbidity and mortality, as has been demonstrated for CIED remote monitoring. As technology and scientific evidence advances, it will be the responsibility of healthcare providers to implement these new and disruptive treatment paradigms into clinical practice.
Research Update – Defibrillators Could Save Lives with Light Pulses
Scientists think that beams of red light could restore normal heartbeat functions in humans, replacing the use of painful electric shocks. Researchers have already tested this on animals and hope to make – incredibly – an optical defibrillator. Biomedical engineering professor Natalia Trayanova, based at John Hopkins University said that with this tech, “Light will be given to a patient who is experiencing cardiac arrest, and we will be able to restore the normal functioning of the heart in a gentle and painless manner.”
Typical defibrillators use electric pulses that can damage heart tissue – light would be a safer (not to mention gentler) way of tackling a patient’s irregular heartbeat. The science is based around optogenetics, where light-sensitive proteins are attached to living tissues. When light hits these proteins, they can modify the electrical activity inside the human cells.
A team from Germany’s University of Bonn tested mouse hearts whose cells had been genetically engineered to produce proteins that could be triggered by light. One-second light pulses were all that was needed to restore a regular heartbeat.
Scientists at John Hopkins then designed a human heart sim, noting that the blue light used by the German team on the smaller mouse hearts was not strong enough for human heart tissue. Red light, with a longer wavelength, was more effective – at least according to their computer simulation. Optical defibrillators are not coming any time soon; it will still take around 5 to 10 years before the technology is ready for human patients.
The Road Ahead
Are there new technologies on the horizon when it comes to defibrillation technology? The short answer is maybe. As stated by Trayanova, the future will be optical defibrillation but how soon can we expect to see ICDs which use light instead of electricity? Until implantable optical defibrillators can be developed for the treatment of patients, it will still take at least 5 to 10 years.
And that is for the implantable application. Can this technology be applied to external defibrillators? That question cannot be answered at this time, but one can be sure AED manufacturers are watching this new development very, very closely.
Another possibility is ultrasound technology. Still in the early stages of research, researchers at Drexel University released findings that ultrasound could be used to change the beat frequency of heart muscle. This is advantageous on two levels. One, AEDs on the market today cannot affect a heart in asystole (flatline) as there has to be some electrical activity in the heart to begin with in order to be reset. If an ultrasound AED can cause heart muscle contractions, it could possibly reduce the need for CPR, as well as getting the heart beating again. Ultrasound’s second advantage would be the non-invasive nature of the treatment. It could be delivered externally, much the same way existing AEDs deliver an electrical current, and unlike the optical defibrillators which are more effective as an implanted device.
Envision a future AED as a cell phone-sized device, small and light enough to be carried in a pocket. The device could be placed on the victim’s sternum to analyze the patient and administer treatment, if needed. Today’s AEDs are considered simple to use, but these could be even simpler – merely emitting a sound wave or light strong enough to penetrate clothing, as well as the sternum bone, and reset the heart. Even better, what if it was simply an app one could download onto their cell phone? Everyone could literally have everyone else’s lives in their hands.
Advances in ICD
Implantable cardiac defibrillators are life-saving devices, which use an electrical shock to terminate ventricular fibrillation or pulseless ventricular tachycardia and reset the electrical state of the heart so that it may beat to normal intrinsic or paced rhythm. There have been several recent advancements in ICD technology to extend battery life, improvements in patient monitoring to avoid needless shocks, the introduction of quadripolar lead devices to improve device programming and to improve therapy effectiveness, and development of magnetic resonance imaging (MRI)-safe ICDs.
ICDs are incorporated into cardiac resynchronization therapy defibrillator (CRT-D) devices, which resynchronize contractions of both ventricles and have defibrillation capabilities. Quadripolar leads with four electrodes allow more programming options for pacing and overcoming issues with lead placement. This can help optimize CRT-D therapy and decrease the number of patients who do not respond.
Newer ICDs offer wireless remote monitoring/interrogation of the device data with bedside sending units, so patients do not need to come in for regular physician visits.
Battery longevity has long been an issue with ICDs and as patients live longer, they may need to undergo multiple battery replacements with increased risk of infections and added expenses. Newer devices developed with high-performance chemistry and advanced manufacturing capabilities provide up to double the battery capacity and many manufacturers now claim a projected battery life of 11–12 years.
Subcutaneous ICD (S-ICD) sits entirely just below the skin without the need for intracardiac implantable leads. This leaves the heart and blood vessels untouched, offering patients an alternative to transvenous ICDs, and is being increasingly used in pediatric population and patients with lead failures and device-related infections. For patients at risk for sudden cardiac arrest, who are being evaluated for a permanent ICD, a wearable external defibrillator is now available as a temporary solution. Patients with older devices have been contraindicated from receiving MRI scans because of potential interactions between the MRI and device function. There are several MRI-compatible ICDs now available in the market, which allow for whole-body MRI scans up to 3T.
Newer ICDs include technology to help reduce inappropriate shocks. Newer algorithms with more anti-tachycardia pacing options can convert many fast ventricular arrhythmias painlessly and avoid the need for high-voltage shocks. These newer advancements, though adding to cost, have been shown to reduce mortality and morbidity in patients who are implanted with ICDs.
Co-authored by Dr Aman Makhija, Senior Consultant Electrophysiologist, Sir Ganga Ram Hospital, New Delhi
Dr JPS Sawhney,
HOD-Department of Cardiology,
Sir Ganga Ram Hospital, New Delhi