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2 decades of implantable cardiac devices
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Twenty years ago is approximately when the first dual-chamber defibrillators were available for use. Up to that point, defibrillators had undergone some advances, including antitachycardia pacing, biphasic shock waveforms and using the implantable cardioverter defibrillator can as an electrode, but only provided ventricular backup pacing from a single ventricular lead. These were not very good at preventing the heart from going too slow, so sometimes we needed to insert a separate pacemaker and defibrillator in the same patient.
In 1997, patients who received implantable cardioverter defibrillators more commonly needed them for secondary prevention, ie, they previously had cardiac arrest or sustained ventricular tachycardia. We were just beginning to put devices in after we had done an electrophysiologic study to prove that someone had the potential to develop ventricular tachycardia. These primary prevention ICDs were mostly used for patients with coronary disease and poor ejection fraction.
Since that time, there have been huge developments. The first was that we thought that being able to have a dual-chamber pacemaker combined with an ICD, which is crucial in some patients, would be a big advance over the single-chamber pacemaker/ICD combination. Then, we would be able to give patients beta-blockers and other HF therapies, and the pacemaker function would better help support their heart rhythms. But a few trials, including DAVID and DAVID II, both of which I led, showed that dual-chamber pacing in patients who did not necessarily need it actually made outcomes worse. Dual-chamber pacing turned out not to be a good thing when we could avoid it.
Around the same time, we discovered we could resynchronize hearts by cardiac resynchronization therapy or biventricular pacing by putting in a third lead through the coronary sinus.
In 2002, the DAVID trial came out and showed right ventricular pacing was bad and caused more HF hospitalizations and mortality. Shortly thereafter, the MIRACLE trial in pacemakers and the companion MIRACLE ICD trial found that CRT, essentially the opposite of right ventricular pacing, improved ejection fraction, patient symptoms and survival.
In the SCD-HeFT trial, we discovered that it’s not just patients who had an MI or ischemic cardiomyopathy, but also people with nonischemic cardiomyopathy improve with ICD therapy. The number of patients getting defibrillators increased, and the demographics changed. These technologies greatly improved over time.
We next learned that although some patients received lifesaving therapy with these devices, many received shocks when they were not supposed to. The outcomes of these patients were much worse. Slowly, we learned how to strategically program our patients so that they would get fewer therapies, yet live longer. The PREPARE and MADIT-RIT trials were among those demonstrating that patients received fewer therapies but lived longer and did much better. Strategically programming the patients to faster detection rates and using antitachycardia pacing made outcomes better still.
We originally treated patients as though leads lasted for a very long time and that they did not wear out. However, we developed the understanding that pacemaker leads did not last forever and had started to perform transvenous lead extraction to remove either broken or infected leads. Later we found that defibrillator leads were even more vulnerable than pacemaker leads. By 2000, we had the first consensus document on transvenous lead extraction. It was very clear that defibrillator leads would become a major part of the lead failure problem.
Around 2005, we found that even though it didn’t happen at very high rates, recalls of defibrillators and their leads were not going to be the rare event that we thought. So we learned how to manage both the risks and benefits of the devices. The tools and techniques for transvenous lead extraction have changed dramatically. In addition, ICD and particularly cardiac resynchronization therapy devices were larger and did not last as long as pacemakers, leading to more device changes and infections. Consequently, transvenous lead extraction became a much more frequent and better-executed procedure. More lives were being saved and we were learning how to use the devices much better.
The device landscape went from mostly pacemakers to mostly defibrillators. At least 40% of the defibrillators now use CRT. We have also found that many patients who received cardiac resynchronization defibrillators could have had cardiac resynchronization pacemakers instead.
There is now an evolution of defibrillator devices from using transvenous leads to subcutaneous leads, and from transvenous pacemakers to leadless pacemakers. However, the advances eliminated pacing for the subcutaneous ICDs and allowed only single-chamber pacing for the leadless pacemakers.
The demographics of patients who get ICDs have also changed. It used to be that patients with pacemakers sometimes had good-functioning and sometimes poorly functioning ventricles. Now, pacemakers are usually only put in patients with good ventricles, and defibrillators are put in patients with poor ventricles. Originally defibrillators were mostly implanted in patients with ischemic heart disease, and now they are used more in nonischemic disease. CRT is mostly for patients with poorly functioning ventricles in the setting of left bundle branch block or conduction delays. Pacemakers are often used in the very young and the very old.
Twenty years ago, we were nearing the end of the use of epicardial devices, in which sometimes patches were put on the outside of the heart. It’s now very rare that we would perform surgery to put in either a pacemaker or an ICD. We have moved to single-coil defibrillator leads instead of dual-coil ones. Our implantation techniques have changed a bit, but still mostly go through the subclavian or axillary vessels.
Another major change over time is in the way we follow our patients. We perform remote monitoring of our patients to augment our in-person checks. The device telemetry could only travel a few inches, but now it transmits several yards. Most recently, pacemakers use Bluetooth for telemetry. Patients are almost uniformly monitored with a transmitter device plugged in at their bedside that uses long-range telemetry while they sleep. The pacemaker or ICD uplinks to the bedside monitor, which uses cellular technology to link to central databases and uses the internet to send the information to the physicians. The patient does not have to do anything but sleep. This has revolutionized the way we follow the devices and the patients. The patients can travel all over the world and we can still be in touch with what’s going on with them. The devices themselves now alert both the physician and the patient when there is a problem.
Our patients are different, the indications are different, we are programming the devices differently and the outcomes are much better.
References:
Abraham WT, et al. N Engl J Med. 2002;doi:10.1056/NEJMoa013168.
Bardy GH, et al. N Engl J Med. 2005;doi:10.1056/NEJMoa043399.
DAVID Trial Investigators. JAMA. 2002;doi:10.1001/jama.288.24.3115.
Moss AJ, et al. N Engl J Med. 2012;doi:10.1056/NEJMoa1211107.
Wilkoff BL, et al. J Am Coll Cardiol. 2008;doi:10.1016/j.jacc.2008.05.011.
Wilkoff BL, et al. J Am Coll Cardiol. 2009;doi:10.1016/j.jacc.2008.10.057.
Young JB, et al. JAMA. 2003;doi:10.1001/jama.289.20.2685.
Disclosure: Wilkoff reports he is a consultant for Medtronic, Spectranetics and St. Jude Medical.