Electrophysiologist at Northwestern Medicine’ s Bluhm Cardiovascular Institute, Bradley Knight, MD, talks about new technology that could prevent cardiac events and death.
Interview conducted by Ivanhoe Broadcast News in 2023.
It seems like everyone has either had, or knows someone who’s had, a cardiac event. Would you consider them to be a common occurence?
Knight: Cardiac arrests are relatively common. About 350,000 people die in the United States from a sudden cardiac arrest. It’s an epidemic based on the prevalence of heart disease and coronary disease.
People with heart problems tend to use a pacemaker. They’re said to be lifesavers, but is it true that they can boast their own set of problems?
Knight: Yes. Pacemakers are designed to treat very slow heart rates. They’re implanted by making an incision, usually up on the left shoulder, and placing leaves that go down into the heart, usually one in the bottom chamber and one in the upper chamber. A pacemaker is intended to pace the heart with very low energy stimulation that the patient doesn’t feel to prevent the heart rate from getting too slow. It’s a relatively common procedure and the risks are pretty low. An implantable defibrillator is implanted conventionally like a pacemaker, up in the left shoulder area with leads that are placed down inside the heart. Although a defibrillator can also act as a pacemaker to treat slow heart rates, its main goal is to treat life threatening arrhythmias, such as ventricular fibrillation and ventricular tachycardia.
We’ve heard about problems with the leads, but now there’s an alternative, the EV ICD. What is it? How is it different? How does it work?
Knight: A conventional implantable defibrillator is placed transvenously through the veins in the shoulder, down into the heart, much like a pacemaker. They’re highly effective at preventing someone from dying of a cardiac arrest. They’ve also been present and available for patients for probably almost thirty years. The weakest link in that system, however, are the leads. Once the leads have been implanted in the body, they become adherent and become apart of you after a few years. If they ever need to be removed, there could be some significant risks of removal of leads. Defibrillator and pacemaker leads are the weakest link in the system. They are electrical cables surrounded by insulation, and over time, these leads have the potential to break or to fail. In particularly young patients, we really try to avoid putting leads in the heart, if at all possible. With young patients who have heart disease, who have had a cardiac arrest, or are at high risk of having a cardiac arrest — we recommend a defibrillator. One high enough that we can offer them an implantable defibrillator just in case they have a cardiac arrest. The alternative to a standard transvenous defibrillator has been available for almost 10 years and it’s a device called a totally subcutaneous defibrillator. It’s a real advance; if a young person needs a defibrillator, we often consider this option. That subcutaneous defibrillator is implanted under the arm pit, in the left chest area, rather than up under the collar bone. It is twice as big as a standard defibrillator and unable to pace the heart. The battery is not quite as long lasting as a standard defibrillator. There are some trade offs. However, the ability to implant a subcutaneous defibrillator and keep everything under the skin is a long term advantage for some young patients. Now, as I mentioned earlier, that device does have its own limitations. It’s significantly bigger. It’s about an 80 jewel device, or about 80 CCs in size, rather than about half that size for a standard defibrillator. An alternative that’s now been under development is the extra vascular or EV, implantable cardiac defibrillator, or EVICD. The EVICD is about the same size as the transvenous defibrillator. The difference between that and a totally subcutaneous defibrillator is that although the device is placed here and it’s much smaller, the lead is not tunneled under the skin, it’s implanted under the sternum. A major advantage to that approach is that the lead is now under the bone, not on top of the bone. The energy it takes to shock the heart is significantly lower and that allows the device to be smaller. The defibrillator lead is then able to get much closer to the heart and it can actually pace the heart. Pacing the heart can do two things. One, it can prevent slow heart rates. But actually, an implantable defibrillator can also treat some dangerous fast rhythms by pacing the heart very fast. It’s called antitachycardia pacing. That’s not an option in the current subcutaneous defibrillator that the extra vascular or substernal defibrillator can offer.
Is this intended for patients with all types of heart problems?
Knight: Implantable defibrillators are intended for patients who have had a cardiac arrest. We call that secondary prevention and it’s to prevent that patient from dying if they were to have another one. Then there are the patients who have something wrong with the heart muscle – meaning they’ve had a heart attack before, cardiomyopathy, a heart muscle disorder, or they have an electrical problem. There are primary electrical disorders, such as long QT syndrome and Brugada syndrome and these electrical disorders can lead to a cardiac arrest even though the heart muscle looks normal. A cardiac arrest is usually due to a very fast heart rhythm, ventricular fibrillation, or ventricular tachycardia, that leads to the heart not pumping. When the heart stops pumping blood, there’s no blood going to the brain. Within about 5-10 seconds the patient will collapse and the only treatment for a cardiac arrest is a shock to the heart. Typically patients who survive this are administered CPR or cardiopulmonary resuscitation before that shock is delivered. The sooner that shock is delivered, the more likely it’s going to work. That’s why these implantable devices that give a shock within 10 seconds are highly effective.
Do patients report feeling better when using this device rather than when using a traditional defibrillator?
Knight: Implantable defibrillators in general don’t make patients feel any better. They’re really there to make them live longer, to prevent them from dying suddenly or from a cardiac arrest. There are some implantable defibrillators that can also provide special pacing therapy. There are some patients who have, for example, congestive heart failure and an abnormality of the electrical system that can benefit from cardiac resynchronization therapy or cardiac resynchronization pacing. That can be delivered through a pacemaker with three leads or a defibrillator, a standard transvenous defibrillator with three leads.
Is there anyone this device wouldn’t be good for?
Knight: Well, there are some patients who wouldn’t qualify for an extravascular ICD because of the need to tunnel under the sternum. In the Global Extravascular, or EVICD pivotal trial, that included 46 centers around the world, we did not enroll patients who had had previous open heart surgery, were significantly obese, or had significant lung disease, making access to that substernal or space under the chest bone difficult.
Thank you. Let’s discuss that study.
Knight: Sure, the global pivotal trial for the extravascular ICD was a multi-center international trial. The results of the six-month data were published in the New England Journal last year. The 18-month data was presented at the Annual Heart Rhythm Meeting in May. There were 46 centers. There were 23 centers in the United States, including Northwestern. We were the only center in Chicago who participated in this trial. We enrolled 316 patients and 299 patients actually either underwent the procedure or attempted to implant the device. 299 patients had the device successfully implanted. There were specific predetermined safety and efficacy endpoints that were predetermined with the FDA. The safety endpoints were met, as were the performance and efficacy endpoints. The main efficacy endpoint was successful defibrillation at the time of the procedure where we induced a cardiac arrest and tested the device. That was effective in 98.7% of patients at an energy of 30 joules or less. I mention that because the device has a maximum amount that determines the size, and this device is the same size as a typical transvenous defibrillator and it’s capable of giving a 40 joule shock. When we know it works at 30 joules, we’re quite confident that if this were to happen at home, for example, that it would be effective. In the patients where the ventricular fibrillation was induced and a shock was delivered, it was effective 98.7% of the time. We also know that over the next year and a half, about 7% of patients had an effective shock for a cardiac arrest on their own. They had a spontaneous, what we call spontaneous episode of ventricular fibrillation or ventricular tachycardia, and the shocks were effective in all those patients. Actually, in half of those patients a shock did not need to be delivered because it was able to terminate the arrhythmia with antitachycardia pacing. Half the patients who had a cardiac arrest after the device was implanted were spared a painful shock because of the effectiveness of antitachycardia pacing, something that this device can deliver, as well as a transvenous device. But a subcutaneous defibrillator is not able to do that. In this trial, 12% of the patients received an inappropriate shock. Most of these were due to shocks delivered for what was not an abnormal rhythm because of over sensing non arrhythmia events. When the device is implanted, that lead is under the sternum and it will detect other things, muscle noise and activity from the upper chambers of the heart. In the last few months, the device has been significantly improved by adding additional discriminating software or special software in the device that helps to be smarter about when it should deliver a shock. In fact, this was approved in Europe and before it was released, the manufacturer of the Extravascular ICD has put things on hold until this software is actually placed in the device before it’s commercially available. In addition to the safety data at six months, we know that at 18 months, only 12% of patients had a device or procedure related complication.
When you met Joseph Mulligan, he had just had his second cardiac event, correct?
Knight: Yes.
What happened?
Knight: Joseph was referring mainly to his cardiac event. Meaning, a myocardial infarction or a coronary event. He had not had a cardiac arrest, but because of the injury to the heart from his two cardiac events, he was considered at a significantly increased risk of having a cardiac arrest on his own. An implantable defibrillator was a reasonable option for him to treat a cardiac arrest if it were to happen. He’s exactly the type of patient we’d like to identify early on who would be an excellent candidate for an implantable defibrillator; And he would have been a candidate for a standard conventional transvenous defibrillator too. Fortunately, he was willing and able to participate in this clinical trial and underwent implantation of the extravascular ICD.
Why did you go that route with him and how does he seem to be doing?
Knight: Well, he’s doing very well. He’s been a really great enrollee in this clinical trial. He’s provided a lot of useful information. I think not only has he done well, but he’s actually brought information that can be shared with other patients like him. The extra vascular ICD was a good option for him as an alternative to a transvenous ICD, which avoided placing any leads down in the heart.
How long will it last?
Knight: The extra vascular ICD has a battery longevity, I believe, of about 11.5 years. This is a little bit more than the subcutaneous ICD and close to the battery longevity of a transvenous ICD. When these devices are replaced, when the battery is depleted, we don’t just take it out and replace the batteries. We take out basically that whole generator, but the leads that have been implanted stay in place. We test them to make sure that they’re intact and that there’s no problems with them. But the leads are left in place when we do a battery replacement or what we call a generator change.
Can you tell us about your other patient, Joe? If I understood him correctly, he has to sleep within close proximity to the device. Why is that?
Knight: Sure. In the past, all of our patients who had pacemakers and defibrillators would have to come to our office for us to check the device. We would check the battery status and we would check all of the diagnostic information collected by the device, which is pretty extensive. That would tell us whether the patients had a shock or therapy from their device. We then would check the integrity of the leads. We measured the ability to sense the heart rhythm and measured the energy it takes to capture the heart with pacing. We also measured the resistance or the impedance. Unfortunately, this process was somewhat of a burden for patients as they’d have to come see us every three months. A big advance in all device therapy now is what’s called home remote monitoring. Most patients who have a pacemaker and defibrillator have a device at home that’s constantly communicating with their implantable defibrillator or pacemaker. The extra vascular ICD has that same home remote option. This not only allows us to get information sent to us remotely every three months, which during COVID was a huge benefit to patients, but also gives us earlier warnings. If there’s some premature battery depletion or the device detects that there’s something wrong with the lead, it will notify us and within a business day we can identify this problem earlier than we would have if the patient had to come in. We can then contact the patient and decide if this is something that needs attention or not.
Joe went on to mention that at one point his heart stopped and he died. In his words, he “died, found out, and didn’t even know it”. He believes this device saved his life — tell us what you know about that event.
Knight: All implantable defibrillators are capable of delivering a shock or sometimes pacing to prevent the arrhythmia. Most patients, if they experience a cardiac arrest, will collapse and the therapy will be delivered within about 10 seconds. People sometimes wake up from that and don’t know what happened, sometimes they remember the shock. On the other hand, there are patients who receive inappropriate shocks while they’re awake, that can be quite painful. But interestingly, there are patients who receive a shock either while they’re sleeping or they’ve passed out and woken up and didn’t really remember what happened. They’re unaware they got a shock. In fact, when we check patients remotely, we’ll often identify that they received an appropriate shock or therapy from the device. When we call them regarding it, they are unaware of it, which is pretty striking. There are patients who have dangerous arrhythmia and the therapy is delivered so quickly, we can’t be sure that it actually saved their life. The arrhythmia might have stopped on its own. But in general, most patients who receive an appropriate shock for a cardiac arrest it’s life saving. They would not have survived that event without an implantable defibrillator.
Did they get a warning?
Knight: There are some patients who get a warning before they get therapy. There are patients who will have ventricular attack of cardia and the heart rate’s not quite fast enough that they will collapse. The heart rate, for example, will be 220 beats per minute, which is quite fast. But everybody is a little bit different and some people tolerate that. They’ll receive a shock of low energy from the device so that it’s not quite as uncomfortable. But there are some patients who receive a shock that is effective, that they will certainly feel. There are patients who unfortunately receive multiple shocks. When patients receive multiple shocks it’s because either the first one or two didn’t work, or because the arrhythmia stopped and recurred. This can be quite traumatizing for the patient, but the reality is in most of those cases they are life saving shocks.
Is there anything else of pertinence you’d like to discuss further?
Knight: The extra vaster ICD is currently not FDA approved. It’s not commercially available. The anticipation is that this fall, this would be available for patients. I believe this will be a consideration in almost all patients who are candidates for an implantable defibrillator.
END OF INTERVIEW
This information is intended for additional research purposes only. It is not to be used as a prescription or advice from Ivanhoe Broadcast News, Inc. or any medical professional interviewed. Ivanhoe Broadcast News, Inc. assumes no responsibility for the depth or accuracy of physician statements. Procedures or medicines apply to different people and medical factors; always consult your physician on medical matters.
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