Implantable Medical Devices: Basics about the ICD (2008)

Learning Objectives: After reading this article, the physician should be able to: Describe the use of implantable cardioverter-defibrillators (ICD) in patients. Define how ICDs function. Explain how to clinically evaluate patients with ICDs. Release Date: August 2008 Emergency physicians often must evaluate and treat patients with sophisticated, complex, and sometimes totally inscrutable implantable devices designed to assist the heart, treat diseases, control pain, and thwart muscle spasm or diabetes. The technology is awesome but surely not foolproof. While some of these devices are akin to miracles, others get mixed reviews, and of course, they can misbehave so the consequences of their intended and sometimes erratic technology must be evaluated and addressed by the clinician. This month's column discusses a relatively recent device that may show up in your ED: the implantable cardioverterdefibrillator (ICD). Although this device would intuitively seem lifesaving, only the naive or neophyte clinician will conclude that it is the Holy Grail for the failing and electrically challenged heart or that it will be free of problems. Its foibles and functions are not out of the clinical scope or the requisite knowledge base of the emergency clinician. One needs to know what exactly these boxes can and cannot do and how to troubleshoot clinical issues. Amiodarone or an Implantable Cardioverter-Defibrillator for Congestive Heart Failure Bardy GH, et al New Engl J Med 2005;352(3):225 This article is a random prospective study of about 2500 patients with significant congestive heart failure (NYHA class 2 or 3) and a left ventricular injection fraction (LVEF) of 35% or less. There were three patient groups, and all received conventional treatment for CHF. The variable was placebo in the first group, amiodarone drug therapy in the second group, and a shock-only single-lead ICD in the third. The aim of the study was to determine if any of these regimens were superior to conventional drug therapy for preventing sudden death from VF/VT cardiac arrest in patients with advanced CHF. The concept is that patients with CHF can die suddenly and often unpredictably from an arrhythmia despite current drug therapies such as amiodarone and/or beta blockers. Although one would intuit that amiodarone in particular would be helpful, this drug's ability to reduce sudden death in CHF patients is somewhat unknown. Most patients in the study were taking ACE inhibitors, beta blockers, diuretics, digoxin, aspirin, and statins prior to enrollment.Figure: This subcutaneous device can be an ICD-pacemaker or one of a variety of pacemakers. The patient should have a card identifying the device and a phone number for interrogation, but overexposing a chest x-ray may show an identification code. Interrogation can tell exactly what happened when an ICD discharged, rendering moot any question about potential malignant rhythms.The study took place from 1997 to 2001. Patients with CHF from ischemic or nonischemic causes had an LVEF of no more than 35%. Most had advanced major coronary artery disease or history of MI. Nonischemic CHF was defined as LV dysfunction without marked coronary artery stenosis. The primary endpoint of the trial was death from any cause. The study drug, amiodarone, was administered by a loading dose of 800 mg/day for one week, 400 mg/day for three weeks, and then either 200 mg or 300 mg a day based on weight for the remainder of the study. The ICD (Medtronic) was a single-lead shock-only device designed to treat only rapid sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). There were no patients with dual chamber or biventricular pacing devices in this study, and unlike currently implanted devices, the ICD has no pacing ability. Interestingly, 27 percent of the patients discontinued drug therapy, including placebo. A small number of patients on amiodarone developed hypothyroidism, a known complication. About four percent of the patients had their ICD removed during the study. The mortality rate was 29 percent in the placebo group, 28 percent in the amiodarone group, and 22 percent in the ICD group. The authors concluded that amiodarone had no favorable effect on survival in patients with severe CHF compared with placebo. The shock-only ICD resulted in an absolute reduction in death of seven percent in five years, so the number needed to treat to make a significant difference in death rates was about 15. The lack of benefit of amiodarone was an important finding in this study because it is often used for this purpose. There was an approximate five percent rate of acute device-related complications, and 10 percent of patients experience some long-term chronic complications. In the ICD group, 31 percent received a shock from the device from a variety of causes. About 48 percent of those shocked received it for VT/VF. Atrial tachyarrhythmias accounted for other discharges for arrhythmia, termed “inappropriate.” The average five-year annual ICD shock rate was about eight percent. The authors caution that there was no cardiac pacing in this study, currently cutting-edge technology. It was pointed out that ICD therapy should not be considered a single intervention given the complexity of end-stage CHF. This was considered a positive study demonstrating that the ICD could improve survival in end-stage CHF, albeit somewhat minimally, beyond the current state-of-the-art drug therapy. Comment: This was one of the first studies to champion the use of the ICD, although its benefit was not spectacular unless you were one in 15 who escaped sudden death. Since this study, many patients have had the device implanted, and they are now relatively common. Our small community hospital sees about one to two patients a week with device-related visits. The poor showing of amiodarone in this study is discouraging. Note that amiodarone can cause both hypothyroidism and hyperthyroidism, so keep that in mind even in the absence of an ICD. Most patients with an ICD also are treated prophylactically with beta blockers, but amiodarone is usually reserved for those with specific post-ICD arrhythmias. Although patients may not know why they have 12-centimeter scars on their abdomens, they are usually well versed on the device implanted in their chest wall. They should carry a card describing the specifics of the ICD, and hopefully also have a cardiologist who follows them regularly. That hard bulge in the patient's upper pectoral area, if it occurred within the past three or four years, is usually a pacemaker or pacemaker-defibrillator combination. Older ICD models had a single defibrillator lead, but technology has advanced to include multichamber pacing so that a single implantable device can treat arrhythmias, congestive heart failure, and a plethora of deranged cardiac functions. The ICD will certainly make its presence known when it functions as expected. A few will actually fail and some will become infected, but the technology is now quite sophisticated, and pacemaker failure is rare. ICD failure rates are a bit of an unknown and not well documented (reporting events is not mandatory), but with better surveillance methods and programming techniques, potential disasters are usually averted in the cardiologist's office. The ICD is implanted transvenously in the pectoral region (some were in the abdomen previously), with the primary electrode in the apex of the right ventricle. At the time of implantation, the required defibrillation energy is determined for the individual. The ICD patient can undergo subsequent defibrillation function testing (DFT) in the office. In this high-tech procedure, VT is induced, and one observes if the ICD appropriately senses the VT and delivers a shock. This is repeated until the correct electrical output is established and then programmed. Interestingly, the addition of amiodarone will actually raise the threshold for defibrillation, and some recommend performing ICD testing after such medications are added. Some ICDs can deliver as much as 40 joules, but most top out at 30 joules. My experience with the ICD has only been an ED visit for a prior shock or shock in progress, an impressive scenario to be reviewed next month. Infection is a devastating complication, and usually calls for complete removal of the ICD. Bacteremia is not uncommon with infection, and obviously is very problematic in these high-risk patients. I would intuit that the device would fare better in young patients with nonischemic cardiac failure. Most of the patients I see are on a boatload of cardiac medications (drug toxicity is always a possibility), and there is little to offer them as an alternative to the ICD. Implantable Cardioverter-Defibrillators DiMarco JP New Engl J Med 2003;349(19):1836 This is a review article highlighting advances in preventing cardiac arrest and a summary of clinical experience with the ICD. The author begins by stating that most patients with out-of-hospital cardiac arrest will not survive, and most of them who do have been quickly defibrillated. This is the theory behind implantable defibrillators and defibrillators in public places that can be used by laypersons. The first implantable defibrillator was inserted in 1980 for a patient with recurrent VF. Subsequently the device has been used to manage recurrent arrhythmias primarily for prevention of sudden death in persons with coronary heart disease.Figure: Single-lead shock-only ICDs have been replaced by numerous ICD-pacemaker combinations. ICD/pacing technology is advancing rapidly. While intuitively lifesaving, the number need to treat to save one life from VT/VF in end-stage CHF is 15.An ICD has a pulse generator and one or more leads for pacing and cardioversion and defibrillation. It has a computer to store information concerning prior cardiac rhythms and prior function of the ICD. The electrode is placed in the apex of the right ventricle via the superior vena cava. The ICD reads the QRS complex and interprets its rate, but occasionally an elevated T wave is mistaken for a QRS complex. Technical advances have allowed the device to eliminate sensing high T waves as a ventricular impulse, and have eliminated muscle activity that used to trigger the device. The ICD essentially detects bradycardia, tachycardia (hopefully only VT), ventricular fibrillation, and asystole, and subsequently treats the disturbances with antibradycardic pacing or overdrive pacing first. A shock is delivered if the malignant tachycardic rhythm persists. Short nonsustained bursts of VT are ignored per programming. A continuing problem is that the device is oversensitive to a supraventricular tachycardia, such as atrial fibrillation, which is interpreted as VT. The discrimination between SVT and VT has greatly improved. The device now further analyzes the rhythm before delivering shocks, decreasing the number of false alarms and unnecessary shocking of atrial fibrillation or another atrial tachycardia. The ICD delivers bursts of rapid pacing in an attempt to terminate the tachycardia in a painless manner, a method that would not be readily sensed by the patient. This is successful in an amazing 90 percent of cases of VT. The magnitude of the shock is between 5 joules and 30 joules. The 30-joule shock is usually a defibrillating dose. All currently used models also have single- or dual-chambered pacing ability, can store electrocardiograms for the sensed rhythm, and allow analysis or interrogation of the device for historical purposes. It's easy to find out what happened, but not all shocks are appropriate. Early excitement that every shock the device delivered was a life saved has not been documented. The ICD is used for primary prevention of sudden death in high-risk patients without a history of VT/VF and as secondary prevention for those who have had an episode of VT/VF. Multiple studies have demonstrated a higher survival rate and greater decrease in mortality of the ICD versus pharmacological intervention. The prevention drugs generally studied were beta blockers and amiodarone. The overall reduction in total mortality, however, is not as high as one might suspect, generally being in the 20 percent to 30 percent range over five to six years. The ICD is, however, the only other option for patients maxed out on drug therapy, except for ablation intervention. Additional antiarrhythmics may be needed after resuscitation, for stabilization, to decrease the frequency of shocks, or to terminate an acute dysrhythmia. Frequently quoted trials are the Multicenter Automatic Defibrillator Implantation trials (MADIT I and II) and the Antiarrhythmics Vs. Implantable Defibrillator trial (AVID), which were initial attempts designed to identify the role of the ICD. Inducible VT and a low injection fraction, high risks for sudden death, were the criteria for enrollment. Interested clinicians should read these trials in detail because they are frequently referenced. Many patients in these trials already suffered a myocardial infarction, or had severe ischemic end-stage heart disease. A few trials have looked at the ICD in patients with nonischemic dilated cardiomyopathy or other unusual causes of sudden death, such as prolonged QT interval, Brugada syndrome, and hypertrophic cardiomyopathy. The ICD can be safely used in pregnancy, but MRI is contraindicated. The device is turned off during surgery (electrical cautery can interfere) and lithotripsy. Microwaves are safe, but cell phones should be kept away from the ICD, and interrogation should be done with a land phone. Having an ICD creates an altered mental state in all patients; some are reassured, others are terrified to the point that the ICD is removed (overall removal rate is about 5%). It is important to note that patient's physiological response to an ICD is variable, but depression and anxiety are common. Getting shocked is similar to external defibrillation/cardioversion, and a shock is not subtle. As one might suspect, there may be increased anxiety, particularly after a patient has already experienced a shock. Some ask to have it removed and opt to take their chances. Periodic evaluation of the device and interrogation of prior discharge events are key to proper functioning. Comment: Most patients who experience a shock will immediately come to the hospital. I doubt if there are many patients who can sit at home after such an event, although patients are told that a single shock without sequelae can be evaluated in a physician's office during a routine visit. Those who have multiple shocks within a 24- to 48-hour period are advised to contact their physician within 24 hours. I believe that's also a fantasy. Such multi-shocked patients will certainly come to the ED, and I am sure almost all of them come after their first shock. Fortunately, the device can be interrogated by the company representative or cardiologist to determine if the shock was appropriate. Pacing and sensing shocking thresholds also can be evaluated. An interrogation is a very cool intervention. A magnet can be placed over the ICD to inactivate it, and this would be the intervention if you can be assured that the ICD is responding to an SVT or is otherwise delivering an inappropriate shock in the ED. Cardiology consultation is usually required for an electrical discharge, although sometimes these cases are handled over the phone in reliable patients and by a brave cardiologist. Currently I discuss every case with the cardiologist, and I have yet to send someone home without at least an interrogation of the device in the ED or prolonged monitoring. An ICD battery is replaced every three to five years, but the defibrillator leads usually last the lifetime of the patient. Finally, the ICD is not expected to reduce death from heart failure per se or from noncardiac causes (stroke, cancer, infection), and the absolute reduction in all case mortality is around seven percent, meaning that about 15 patients need to be treated to prevent one death. This is not the optimal answer for all patients, and some ask to have it removed. There is little in the medical literature to guide the emergency clinician who evaluates patients who present to the ED with a history of ICD discharge. Next month's column will discuss how to approach the patient whose device is currently discharging in the ED, but I will take a stab at a protocol for patients who enter the ED with merely historical information. Despite recommendations that patients with a single discharge, an immediate return to baseline, and no associated symptoms (seizure, syncope) can have the device interrogated in the office in one to two days, I doubt this happens frequently. Many decisions are hoisted onto emergency physicians. I believe it's reasonable to treat these patients as if they have just had a cardiac-induced syncopal episode (albeit thwarted by the ICD). To me, that's VT/VF until proven otherwise. I don't take a nonchalant approach to VT/VF, and I think a shock warrants consideration and often an investigation for ischemia, MI, worsening CHF, and drug course, one needs to up patients for particularly low The of prolonged should be considered as should disease if the patient is on amiodarone. A approach routine an and particularly and if the patient is on a It also reasonable to find out what actually One can do this in the absence of the ICD, but it can be readily interrogation of the ICD. cool is can in or out an arrhythmia with a in the patient. Interrogation is on a few in hospital by the company Patients carry a or the of device and the number to for It reasonable at least to to a cardiologist about the although the literature not and actually the need for immediate consultation or routine I have a number of patients who have home after interrogation and four to six of and frequently the device has This often can be by or drug therapy. the ICD discharges in your intervention such as a beta amiodarone, or may be I would be to off the ICD with a magnet because that would the of the device. Next I will discuss the ED treatment of a patient who has recurrent arrhythmias and when the ICD frequently discharges in the ED. of Implantable Cardioverter-Defibrillator About of are to the ICD About are to the About of are not The most is inappropriate shock in about to of patients. 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