I'm Dr. James Allred, electrophysiologist and co-founder of CV Remote Solutions. CV Remote Solutions is excited to partner with MedAxiom for this education series. This is a device clinic essentials for the care team module. Today, I'm excited to talk to you about device technology. Here are my disclosures. Here are today's learning objectives. Today, we will discuss key components of cardiac implantable electronic devices, also referred to as CIEDs, and their primary role in managing cardiac arrhythmias and heart failure. We will differentiate between various CIED devices, including pacemakers, implantable cardioverter defibrillators, also known as ICDs, cardiac resynchronization therapy, or CRT devices, and implantable loop recorders, also known as ILRs. We will also discuss device-specific indications for implantation. Let's begin by talking about pacemakers. Pacemakers are devices implanted to treat bradycardia, or slow heartbeat rhythms. A pacemaker is typically placed in the left chest wall with wires, also called leads, extending into the heart. Though devices can also be placed on the right side, most commonly, they are placed on the left. The leads would go through the axillary vein, into the subclavian vein, into the superior vena cava, then into the right atrium and right ventricle. As you can see, the tip of the lead will come in direct contact with heart tissue, allowing for sensing and recording in this location. The impulses from the heart are sensed, and if inadequate for the patient, then the pacemaker will increase the heartbeat to allow for an adequate heart rhythm. Pacemakers also help keep the heart in synchronization with itself so that heart can pump blood efficiently in conditions such as atrioventricular or AV block. Pacemakers also help treat arrhythmias that are caused by diseases of the electrical system of the heart. An example of this is atrioventricular or AV block. In this situation, a pacemaker will help synchronize the heart so that the heart can beat blood more efficiently. You'll see in this example, here on the patient, that a pacemaker is implanted in the left chest wall. The pacemaker is inserted under the skin, and wires are transversed from the pacemaker through the axillary and subclavian veins into the chambers of the heart. Pacemakers may have only one wire that goes to the atrium, or one wire that goes to the ventricles of the heart, or a pacemaker may have both. A pacemaker with two wires is called a dual-chamber pacemaker. The wires of the heart then insert directly into the muscle tissue of the heart, where they can sense electrical impulse as well as stimulate heart muscle tissue. Let's talk about bradycardia. Bradycardia refers to a slower-than-normal heart rate, typically defined as less than 60 beats per minute in adults. Causes of bradycardia can include aging, heart disease, medications, electrolyte imbalance, or damage from a heart attack. Symptoms of bradycardia include fatigue, dizziness, lightheadedness, fainting, shortness of breath, or chest pain. As we think further about slow heartbeats, or bradyarrhythmias, we think of two different types of arrhythmias. We think of those that result from problems with impulse formation, and then again we think about those related to difficulties with impulse conduction. As we think about this, let's think about the electrical signals of the heart. So normally the electrical impulse starts with the sinus node in the right upper chamber of the heart, or the right atrium. Electrical activity starts with the sinus node, which is the pacemaker that we're born with that determines our heart rate. And that electrical impulse will then go across to the left atrium, as well as down to the middle of the heart to meet up with a structure in the middle of the heart called the AV node. A for atria, V for ventricles. You can think of this AV node as a wire that takes electrical impulses from the upper chambers of the heart to the lower chambers of the heart. So normally the upper chambers beat, and then the lower chambers beat. Upper, lower, lub, dub, and that's what causes a normal heartbeat. If there's a problem related to impulse formation, then that means that the sinus node has not adequately generated an impulse to start the electrical signals across the heart. The sinus node has sort of a thermostat to it, so that when we're resting our heart rate is slow, but when we get excited, or upset, or if we're exercising and we have adrenaline, then the sinus node tells the heart rate to increase. Any difficulties in that pathway are termed sinus node dysfunction. There are situations where the normal electrical impulse does generate from the sinus node, but the problem is that it doesn't conduct throughout the heart. If that happens, then we term this a problem with our impulse conduction. Examples of this are second degree AV block, third degree AV block, also known as complete heart block. Chronotropic incompetence refers to a situation where the heart is not generating a heartbeat fast enough for the body's needs. An example again is if a runner is running and they're exercising, their heart rate should increase appropriately to deliver oxygen to their tissues when they're exercising. If the heartbeat does not generate a fast enough flow of blood throughout the body, then we would refer to this as chronotropic incompetence. I'm often asked, what heartbeat is an appropriate heartbeat that would require a pacemaker? When is the heart too slow? Is there a number that we would refer to to say that this patient's heartbeat is too slow? In reality, there is no exact number that says a person needs a pacemaker. We go by symptoms. If a patient's heart is able to generate a pulse and a blood flow that is fast enough and frequent enough for that patient, then they typically do not need a pacemaker. An example of this is a well-tuned athlete. Lance Armstrong's resting heartbeat is 38 beats per minute. Now, does Lance Armstrong need a pacemaker? The answer is no. His heart is so conditioned that with each stroke, with each contraction of the heart, oxygen is delivered throughout the body to meet his needs. His heart is so conditioned that he does not need a resting heartbeat of 50 or 60 beats per minute. 38 beats per minute is very sufficient to meet his body's needs. Let's talk about the evolution of pacemakers. The first pacemakers were constructed in the 1950s. As time went on, devices that were battery-powered were invented. These were still larger devices that were wearable, but were much better than the previous generation of devices that required a cord and AC power. In the late 1950s, fully implantable pacemakers were developed, which could be implanted under the skin for the patient, and therefore, they did not have an external wearable type of device. Since that time, we've seen dramatic improvements in technologies for pacemakers. Current pacemaker systems are implanted under the skin. They're much lighter than the older generation of device. Their batteries last much longer. The leads that take electrical activity to the heart have been developed to last much longer and to provide better sensing and impulse delivery. In 2016, we saw an even newer generation of pacemaker. This is a leadless pacemaker. There is not a device implanted under the chest wall with wires going to the heart. With this technology, the entire device is implanted within the heart, a very small device implanted within the heart. There are future technologies coming, which are even more promising in patient care. Let's look at the components of a typical pacemaker system. In front of you are two examples of pacemakers. The one on the left has a clear header with a single port to allow for a single lead to be placed. This is a single chamber pacemaker. The device on the right has a dual header with two ports, one for an atrial lead and one for a ventricular lead. In addition to the header, you'll also see the can, which is the largest part of the pacemaker. Inside of this can, the biggest component is the battery. In addition to the battery are smaller electronic pieces, which form the computer and the brains of the pacemaker. You'll also see behind these pacemakers a wire. This wire is referred to as a pacing lead. This end on the right has an active helix, which can be screwed directly into heart tissue. You'll see here this white outer piece, it's called a suture sleeve. Once the pacing wire has been inserted into the heart through veins, this suture sleeve is used to secure the pacing wire to the body. Here are three different types of pacing leads. The one on the top has an active fixation, meaning that you can screw a little helix out of the end of this lead into heart tissue to actively fix the lead to the heart. This middle lead is called a passive fixation lead. It has barb hooks on it, which allow you to hook this lead into the tissue. Here you will see a J-tipped lead, which is also a passive lead. It has within it a preformed J. The purpose of this J is to redirect the lead upward. This lead would be used for atrial pacing purposes. Here's an x-ray example of a patient's pacemaker. This is a chest x-ray. You'll see the patient's ribs in the background, you'll see their heart here, and then you'll also see their pacemaker. This is a dual-chamber pacemaker. The header has two different ports, one for the atrial lead, one for the ventricular lead, and then you'll see the can here. You'll notice this large portion is actually the battery of the pacemaker, and then here you can see the electrical components. The wires, the pacing wires, go through the axillary vein, the subclavian vein, into the heart, and this lead is actively fixed or screwed into the right atrium, which is here. The second lead is screwed actively into the ventricle here. Here are pictures of leadless pacemakers. The one on the right is a micro device. It is a single lead device. As you can see, it's a very tiny device, the size of a nickel. This device would be inserted directly into the ventricle of a patient, into their right ventricle, and can sense and pace from that location. On the left is a dual-chamber pacing system. You'll notice two separate generators. This one would go into the right atrium, and the second would go into the right ventricle. You'll notice the different components of these devices. The majority of this device is battery technology, and there is a small component of electronics within as well. You'll notice the active fixation helix, and in addition to that, you'll notice a structure here that can be used to maneuver the device. This micro device has a different type of fixation method. It has a more passive barbed hook type of fixation to the heart. Then you'll notice a large component of battery and a smaller component of electrical components. Then on the end, there is again a small knob that can be used to direct the device during employment and retrieval. Here's an example of a leadless pacemaker inserted into the right ventricle of the heart. You'll notice here the right atrium and the right ventricle. Here you see a leadless pacemaker inserted into the right ventricle. This would be a single device within the heart, as opposed to a dual chamber pacing system where one device would be inserted into the right atrium and a second device would be inserted into the right ventricle. This again is a dual chamber leadless pacing system. So what are the indications for pacing? As we've discussed already, sick sinus syndrome, which is inappropriate function of the sinus node is an indication for a pacemaker, Mobitz II second degree heart block, high grade AV block, and complete heart block. Let's turn our attention now to implantable cardioverter defibrillators or ICDs. These are devices implanted similarly into the left chest of the patient with wires into the heart, which can be used to treat sustained ventricular arrhythmias, such as ventricular tachycardia, ventricular fibrillation, or to prevent sudden cardiac death. As with our pacemaker example, the device is implanted into the left chest wall under the skin with wires going through the left axillary vein, subclavian vein, into the right atrium and right ventricle of the heart, again with the tips of the electrodes coming in contact with heart tissue to allow for sensing and pacing from these locations. Defibrillators can be single lead devices with a single lead going to the right ventricle, or they could be dual chamber devices with one lead going to the right atrium and the other lead going to the right ventricle. In addition, we'll also talk about cardiac resynchronization therapy shortly, which would include three wire devices. Let's understand sudden cardiac death. Sudden cardiac death is unexplained death resulting from sudden loss of heart function, also known as a cardiac arrest. This is typically caused by a ventricular heart rhythm, such as ventricular tachycardia or ventricular fibrillation, where the lower chamber of the heart, the ventricle, is racing very fast, and when that happens, it's unable to contract in an organized way. This causes blood pressure to drop and for the patient to lose consciousness. Risk factors include heart disease, a family history of sudden cardiac death, certain hereditary heart conditions, smoking, obesity, high blood pressure, and diabetes. When someone has a cardiac arrest, the most important thing is to get to this person as fast as possible to restore a normal heart rhythm. Chance of successful resuscitation is reduced 7% to 10% with each passing minute. The longer it takes to defibrillate someone, the less likely it is that they will survive. Here on the left, you'll see a picture of a very old implanted cardiac defibrillator. Initial devices were actually implanted in the lower abdominal wall. These were very large and heavy devices with a battery often lasting only one to two years. On the right, you'll see a new version of these devices. These are devices that are implanted today. With these devices, they're much lighter. They're implanted into the left upper chest. These devices will typically last 10 years or more. In addition to a typical transvenous system, as we have discussed with a defibrillator can in the left chest with wires going into the heart, there are newer types of defibrillators which do not require leads to be placed inside of the heart. One example is called a subcutaneous ICD, sometimes abbreviated SICD. Here the can is placed into the outer left side of the flank and the wires are sent just under the skin in an area near the heart to allow for defibrillation. The final example here is a very new device called an EV or extravascular ICD. Again, the can of the device is placed in the flank on the left side and the wire is now sent up near the sternum so that there is a pathway for electrical current between the device and the wire to allow for defibrillation. What are the components of an ICD? As you can see here, the clear portion is called the header. This is what allows the lead to attach to the device. Here you can see that portions of the lead will attach to portions of the device and there's a set screw here that can be used to tighten to allow the lead to be secured to the device or untighten to allow the lead to be withdrawn. In addition to the header, you'll notice here a large battery component within the device, a large capacitor, which will allow for the shock to be generated, as well as high and low voltage circuits. This entire portion is referred to as the CAN. Here's a chest x-ray from a patient with an implanted defibrillator. Again, you'll notice the defibrillator CAN here with the capacitor and battery components, as well as the electrical components. You'll notice here the header with wires going into the heart. A defibrillator lead is different from a pacemaker lead in that there are often one or two coils. These allow for current to be generated to defibrillate the patient. What are indications for an ICD? One indication is sustained ventricular arrhythmias. A patient who has ventricular tachycardia or ventricular fibrillation. Another indication is a history of sudden cardiac death. Cardiomyopathies, including ischemic cardiomyopathy, non-ischemic cardiomyopathy, or certain hereditary cardiomyopathies, such as hypertrophic cardiomyopathy, can also be indications for an ICD, as well as channelopathies, such as long QT syndrome. When we think about an ICD indication, we think about the primary indication versus secondary prevention indications. Primary prevention means that the patient has never had an episode of symptomatic ventricular tachycardia or ventricular fibrillation. They've never passed out in the past. They've never had cardiac arrest or arrhythmias. But we're worried that they might. And so we would implant a device for primary prevention. Secondary prevention means that someone has experienced symptomatic life-threatening arrhythmias, such as ventricular tachycardia or ventricular fibrillation. And we're worried that it might recur. And we want to prevent recurrence of such arrhythmias. Now let's talk about CRT devices, or cardiac resynchronization therapy devices. These are devices which could be pacemakers or defibrillators. But they have three wires. So one wire would go to the atrium. One wire would go to the right ventricle, just like with the pacemaker and defibrillators that we've talked about already. And then there's a third wire that would typically go through the coronary sinus vein into coronary sinus branches, which will allow for an additional vector of pacing from the left wall, typically of the left ventricle. CRT is delivered either by a pacemaker or a defibrillator. Electrical impulses are delivered to both right and left ventricles of the heart to treat heart failure symptoms and to prevent worsening heart failure in patients requiring ventricular pacing. You'll notice here examples of CRT devices. This is an example of a CRT-P, or a CRT pacemaker. And here's an example of a CRT-D, or CRT defibrillator. These devices will, as I said, typically have three wires. Within this header, you can see that the upper pin will allow for the atrial lead. The lower pin would allow for the right ventricular lead. And the middle header would allow for the left ventricular lead. Here's a chest X-ray example of a patient with a CRT-D device. And so again, you'll see the can here with wires into the heart. Here's a wire going to the right atrium. A second wire or lead, the same, going to the right ventricle. And then if you'll look closely, you see the third wire here going out through the coronary sinus branch to allow for the LV lead to capture the left ventricle for resynchronization therapy. What are the benefits of CRT? So compared to optimal pharmacologic therapy, CRT therapy in heart failure patients improves ejection fraction, New York Heart Association class, and six-minute hallwalk results. Reduced rates of all calls in cardiac and heart failure hospitalization are also seen. Compared to traditional ICD therapy, CRT in patients with heart failure will decrease hospitalizations and reduce risk of death. What are indications for CRT? A class 1 indication means that it should be done if possible. Patients with a left ventricular ejection fraction of less than 35%, left bundle branch block with a QRS duration of greater than 150 milliseconds, and a New York Heart Association class 3 or 4 should have a CRT device considered. Class 2A means in most situations, this is the right thing to do. So a class 2A indication for CRT implant would include a left ventricular ejection fraction of less than 35% with a left bundle branch block, but with a QRS between 130 and 150 milliseconds. With that, also a New York Heart Association class of 2, 3, or 4. Another class 2A indication includes a left ventricular ejection fraction of less than 35%, a non-left bundle branch block with a QRS of greater than 150 milliseconds, and New York Heart Association class 2, 3, or 4. And finally, indications according to the study BlockHF would suggest that for patients with a left ventricular ejection fraction of less than 50% with anticipated RV pacing of greater than 40%, CRT should be considered. Now let's take our attention to conduction system pacing. So what is conduction system pacing? So this involves pacing of the heart in a way that uses and takes advantage of the normal conduction system. And so you'll see in this example, there is an atrial lead, but instead of a right ventricular lead going down to the apex portion of the heart, you'll see that this lead has been implanted into the septum between the right ventricle and the left ventricle. And you'll notice that the active helix, which is screwed out from the lead, will go into the septum to engage the electrical system of the heart. And so with conduction system pacing, we can pace directly to the his bundle, or we can pace into the septum to try to selectively or non-selectively pace the left bundle of the heart. So as you can see here, we can pace the his bundle, we can pace the distal his, or we can pace the left bundle branch portion of the heart. And the purpose of this is to try to use as much of the intrinsic conduction system of the heart as we can, because that's more physiologic for patients and often better tolerated. Conduction system pacing indications would include heart failure patients with CRT indication, but in whom CRT cannot be achieved for one reason or another, such as difficulties in implanting an LV lead. Another indication would be patients with pacing-induced cardiomyopathy and whom conduction system pacing is expected to improve their heart failure. A left ventricular ejection fraction of less than 50% with anticipated RV pacing would be an indication for conduction system pacing. And then there are more indications underway with current research studies ongoing. Now let's talk about implantable loop recorders. An ILR or implantable loop recorder is a diagnostic cardiac device implanted under the skin, which continuously records electrical activity of the heart and stores this information in the device when it is triggered by certain cardiac events when they occur. You'll notice here that the device is fairly small and is typically implanted over the heart around the area of the left chest wall. The importance of this technology is that it allows a patient to be more active and for us to record over a long period of time. You'll see on the left, a picture of Norman Holter with one of the first recording devices ever discovered. And with his discovery and with his technology, we could record the electrical activity of the heart, but as you'll see, this large battery pack would be very limiting for someone's quality of life or activity. Early, we were able to implant the Reveal XT type of device. This was a larger device and had to be implanted in an electrophysiology lab or an operating room. Subsequently, a much smaller device, as you can see here, has been developed with a battery lasting between three and five years, allowing for continuous recording. And with these devices, they can be implanted in the office or hospital settings. What are indications for an implantable loop recorder? Recurrent unexplained syncope. Recurrent loss of consciousness of an unknown source is one indication for an implantable loop recorder. Palpitations or other transient heart symptoms in the arrhythmogenic and etiology would also be an indication. A patient who has a stroke of an unknown source called a cryptogenic stroke is a patient in whom we would be worried about atrial fibrillation as a possible cause for their stroke. An implantable loop recorder could be implanted to follow that patient for a longer period of time to evaluate for an AFib or an arrhythmogenic cause for their stroke. And then finally, atrial fibrillation management can be an indication for implantation of this device. What are some other technology considerations when we think of these devices? Certainly battery longevity is very important. Lithium iodine batteries are typically what we're seeing in use today. These have a long battery life. They're very reliable. And that is very important because with the longer battery life comes a reduction in the frequency in which we have to replace these devices. And that's important for patient safety and reduction in infection. With battery longevity comes enhanced patient confidence and the reliability and longevity of their device. And we're always looking for ways to make these batteries last longer to optimize the duration of therapy for a patient. At the same time, reducing the size of the battery because typically as you've seen from the examples the battery might be the largest part of the device. And so if we can make the battery smaller then typically we'll see devices that are also smaller. MRI conditionality has also become important. Patients with implanted cardiac devices often have requirements for an MRI for various reasons not related to their device. And years past between the device and the lead there were often concerns about damage to the device during an MRI. Over the past few years we've been able to develop devices that are MRI conditional which means that they are safe for the MRI scanner. That means that the integrity of the system will be upheld but also patient safety can be assured with these devices during an MRI. There are lots of different features to allow for patient activity, reduction in heart failure symptoms and these are certainly important. Accelerometers are tools within the device to allow for increasing heart rates as the patient becomes more active. The typical type of accelerometer is a piezoelectric accelerometer. And with these accelerometers, when a patient is moving the device senses that movement and says I think this patient is active so I'm going to increase the heart rate. That is one type of accelerometer. Minute ventilation accelerometers detect respiration within the patient and say while this patient is breathing a little harder and a little bit faster I think we need to increase their heart rate. Closed loop stimulation is another type of technology that senses within the right ventricle from the right ventricular lead that the heart is contracting faster and harder and says maybe we need to increase heart rates related to this. There are also other sensors that are allowing for accelerometer therapy as well within MICRA and AVERE, the leadless pacemakers. They have very unique sensors that allow for increasing heart rate. With MICRA you see the 3D accelerometer and with AVERE you see a temperature based accelerometer. For patients who have heart failure there is also technology within the device to sense changes in impedance and other things which will suggest that a patient might be having trouble with heart failure. When this is sensed the device clinic team will see this information and can manage the patient accordingly. Examples include thoracic impedance, heart logic, triage HF, as well as interstitial impedance. Here's an example of a patient with an implanted cardiac device and you can see from this the thoracic impedance is recorded. If thoracic impedance is high then the patient is dry and does not have difficulties at that time based on the device with heart failure. But as impedance goes down then the suggestion is that this person could be accumulating chest wall fluid and may be having trouble with their heart failure. You can see that this generates an increase in the index which will allow for the clinical team to evaluate the patient and manage their heart failure accordingly. Finally, let's think about remote monitoring technologies. The implanted cardiac devices of today generate lots of data. This data talks about the integrity of the system that has been implanted as well as certain features related to the patient such as their activity level. Are they having atrial fibrillation? Are they having heart failure and other things? And so by managing these patients with remote monitoring we are able to harness the technology, find data coming from these devices and manage our patients often on a day-to-day. What are the benefits of remote monitoring? Increasing clinical efficiencies, reduction in healthcare utilization, expediting clinical decision-making and even increasing patient survival are benefits of remote monitoring. There's also opportunity for patients to get feedback from their device. As technology continues to evolve, you'll see here part of a clinical trial that data can be presented to patients through their smartphone. So this patient has a pacemaker implanted and from their device through their cell phone, they're able to receive information about their active movement, the daytime heart rates and whether or not a transmission has been received by their care team. So you see here trends in their heart rates with average heart rates for daytime and night, you'll see active movement for this patient and they'll also be able to see when their transmissions have been processed. As this technology continues, we will see more and more features open for patients to allow them to be active participants in their own care. So let's look at a couple of questions together. Here's a 25-year-old male who's visiting the emergency department with nausea, vomiting and diarrhea for two days. When getting up to go to the bathroom, he gets nauseated and he passes out. The patient had one prior episode of passing out when donating blood previously. When he's in the emergency department and passes out, he is wearing a monitor and we see the following. Based on this strip, what would your recommendation be? A, single chamber pacemaker, B, conduction system pacing, C, reassurance and observation or D, loop recorder implantation? The correct answer is C, reassurance and observation. Why is that? Well, this is a transient and reversible event. This patient had his pause and what you'll see here is this is Mobitz 1 heart block followed by transient complete heart block. But this occurs in a reversible setting and someone who's having nausea and vomiting. This would be called vagal syncope for this patient. And so a pacemaker would not help this patient. They would not require conduction system pacing. And because we've seen this on the monitor and we know what's going on, there would not be a benefit for a loop recorder placement for this patient. Let's look at another example. A 52 year old male has a history of hypertension and diabetes. He had a myocardial infarction at age 47 and is known to have an ischemic cardiomyopathy with an ejection fraction of 28% despite optimal medical therapy. He has frequent palpitations with dizziness and his EKG is shown here. Would you recommend A, a single chamber defibrillator, B, conduction system pacing, C, an implantable loop recorder or D, a biventricular ICD or CRTD device? The correct answer here is D, a biventricular ICD device. The reason for that, this patient on EKG has a left bundle branch block with a cure restoration of greater than 150 milliseconds. They also have an ejection fraction of less than 35% despite optimal medical therapy. This would be a class one indication for a biventricular ICD device. One more question. The previous patient did receive a biventricular ICD without complications and you see him back for a wound check. You're providing him with general education. Which aspects of education are most important to highlight at this time? Would you recommend A, stressing the importance of avoiding the use of a microwave oven, B, stress the importance of remote monitoring starting three months after device implantation, C, review a shock plan with the patient alerting him to the next step should he receive a shock from his defibrillator or D, remind the patient to keep his arm in a sling for 10 more days? The correct answer here is C, review a shock plan with the patient alerting him to next steps should he receive a shock from his defibrillator. Wound checks and office follow-up visits are always great times to educate patients about their device. Take advantage of this opportunity whenever you can. There's no contraindication of using a microwave oven if you have an implanted cardiac device. We want remote monitoring ideally to start from the day that the patient leaves the hospital after implant. And so waiting three months for beginning remote monitoring is not something we would encourage. We would encourage it prior to that, immediately after implantation. And then if a patient has had a recent implant, we typically don't want them wearing a sling for a prolonged period of time as this can cause frozen shoulder and other things. Here are references from this module. Thank you so much for your time today. It has been my privilege to talk to you about cardiac device technology. I look forward to spending more time with you on our next module.

Dr. James Allred

electrophysiologist

CV Remote Solutions

MedAxiom

device clinic essentials

cardiac implantable electronic devices

pacemakers

implantable cardioverter defibrillators