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Implantable Medical Devices: Evaluation of an ICD Shock

Roberts, James R. MD

doi: 10.1097/01.EEM.0000338053.45484.42

Part 2 in a Series



Author Credentials and Financial Disclosure: James R. Roberts, MD, is the Chairman of the Department of Emergency Medicine and the Director of the Division of Toxicology at Mercy Health Systems, and a Professor of Emergency Medicine and Toxicology at the Drexel University College of Medicine, both in Philadelphia.

All faculty and staff in a position to control the content of this CME activity have disclosed that they have no financial relationships with, or financial interests in, any commercial companies pertaining to this educational activity.

Learning Objectives: After reading this article, the physician should be able to:

  1. Describe the function of an implantable cardioverter-defibrillator (ICD).
  2. Discuss the concept of electrical storm.
  3. Outline the approach to therapy of a patient with an actively discharging ICD.

Release Date: September 2008

Although the implantable cardioverter-defibrillator (ICD) can be a lifesaving device, it is not free of quirks. One of those is delivering a shock when one isn't required, and emergency clinicians must know how to troubleshoot this and other clinical issues. Most patients who are shocked will come to the ED immediately, even though they have been told that a single shock without sequelae can be evaluated in a physician's office within 24 hours. This month, I focus on the patient who comes to the ED with recent or current ICD-delivered shock, or as I call it, shock and awe.

Evaluation and Management of Patients after Implantable Cardioverter-Defibrillator Shock

Gehi AK, et al



This article is an overview of the ED approach to a patient who has just received a shock from his ICD. It summarizes journal articles, position papers, and scientific statements and guidelines published over the past 15 years. The device most frequently reviewed was the ICD/defibrillator, which is capable of arrhythmia detection, antitachycardic pacing, basic pacemaker function, and low- and high-energy cardioversion/ defibrillation. Low-energy cardioversion delivers 5 joules to the apex of the right ventricle for ventricular tachycardia, and high-energy defibrillation is 30–40 joules delivered in the same area. The programming of the ICD allows it to function with various modes depending on the situation.





The authors note that inappropriate discharge for SVT or atrial fibrillation occurs at some time in about 20 percent to 25 percent of patients receiving an ICD, the device's most problematic failure. More rarely, inappropriate ICD shocks are caused by lead failure, electromagnetic inter ference, and other technical defects.

The improved absolute survival rates may be obscured or downplayed in some patients by a detriment to quality of life. As would be expected, many patients who have an ICD feel less healthy, have emotional and physical issues, and have an overall lower level of psychological well-being. This is most prominent in patients who have received prior shocks. The psychological downsides of an ICD, particularly post-shock, include anxiety, panic disorder, or overt agoraphobia. Explaining the benefits of an ICD shock, along with reassurance and psychological intervention, are crucial to improving the quality of life in any patient with an ICD. Psychiatric medications may be necessary, but they are not the total answer.

Probably the most effective way to decrease psychological problems with an ICD is to decrease inappropriate discharges. This is best accomplished by continuing to monitor the device and reprogramming it once an inappropriate ICD shock has been identified. Because antitachycardic pacing is effective in almost 95 percent of cases of spontaneous slow VT (160–180 beats/min), some devices will attempt overdrive pacing up to three times before delivering even a low-energy shock. Rapid VT can be successfully terminated less often with antitachycardic pacing, but it's still often effective. Obviously, overdrive pacing is preferred to shock, and patient acceptance of the device is greatly enhanced if they are not delivered an electrical shock. That shock, however, is designed to save a life if it is appropriately used.

Sophisticated programming allows the ICD to distinguish between sinus tachycardia and VT, allow the device to observe the rhythm for a short period of time, and undertake other sophisticated diagnostic analysis and interventions. The ICD can usually distinguish VT from AF because of the stability of the QRS complexes. Even the morphology of the QRS complex can be evaluated. Some devices have atrial sensing capabilities to increase discrimination of VT from SVT. The device can be programmed to wait for 16 to 24 beats of VT before responding, reducing shocks for short runs of VT that spontaneously convert. Non-life threatening arrhythmias are essentially ignored by sophisticated ICDs.

Some patients are empirically placed on prophylactic antiarrhythmics, but most have medication added once the ICD fires. More than half of ICD patients are eventually prescribed such medications. Drugs to control inappropriate shocks due to ICD misinterpretation of atrial dysrhythmias (AF, SVT, sinus tachycardia) are commonly used. A variety of cardiac medications can reduce ICD shocks by decreasing the overall frequency of VT or produce a slower ventricular response, rendering more episodes amenable to overdrive pacing while avoiding a shock. Sotalol (Betapace) is a beta blocker that has reasonable efficacy in this situation. A recent new class of antiarrhythmics, including azimilide, shows some promise to reduce ICD discharges. The most effective regimen so far, however, appears to be a combination of a beta blocker and amiodarone. This combination decreases the inappropriate shock rate to about 10 percent versus 20 percent. Both drugs do have their limitations and side effects, however. Interestingly, the lipid-lowering statins also may have an antiarrhythmic effect to reduce the occurrence of ICD shocks.

With drug therapy also comes the chance that the threshold for defibrillation will be increased, making an ICD shock less likely to terminate VF successfully. Amiodarone can increase the defibrillation threshold, but this seems variable, and it can be corrected by reprogramming the device. Amiodarone also has pulmonary and thyroid toxicity, and sotalol has been associated with Torsades de pointes. These authors suggest that all patients first be treated with a beta blocker unless contraindicated. If the ICD has already discharged, sotalol and amiodarone are suggested as a first option combination.

The occurrence of three or more episodes of sustained VT requiring a shock within a 24-hour period has been termed electrical storm. This often produces repetitive shocks, and this distressing event can occur in up to 20 percent of patients with an ICD. The ICD discharge can be appropriate or inappropriate, and electrical storm for appropriate discharges indicates serious life-threatening dysrhythmias. There are limited data on how to manage this phenomenon acutely. Some obvious precipitants, such as electrolyte imbalance, drug overdose, worsening CHF, and myocardial ischemia, may be treated. The first antiarrhythmic choice for electrical storm appears to be amiodarone. In addition, sympathetic blockade with beta blockers can be added. Sedation is also important in controlling electrical storm to decrease sympathetic outflow and the tachycardia associated with it. Ablation therapy also is an option if drug therapy fails, but this cannot be accomplished rapidly.

These authors reiterate the prior adage that a single ICD shock is not necessarily a requirement for an ED or office visit. The authors note that “occasional shocks are to be expected.” Evaluation within one week seems to be the suggested norm for a single shock without associated symptoms. Syncope, shortness of breath, palpitations, or chest pain prior to the shock should prompt an ED visit. Following a shock in a now-asymptomatic patient requires evaluating ICD-stored EKGs via device interrogation to determine the exact event.

The authors note that multiple shocks for sinus tachycardia can be made worse by anxiety, pain, or fever. The ICD can be disabled by placing a magnet over the chest wall pocket. This would be counterproductive in the presence of VT.

Comment: The ability of the ICD to detect and treat cardiac dysrhythmias is mind-boggling. These devices appear to be better than some physicians at differentiating AF from VT, and are even smart enough to wait to observe patients further before shocking them again. Instituting antitachycardic pacing rather than delivering a shock at the first sign of VT also is an amazing ability. Low-energy shocks are used first, reserving high-energy shocks for non-responders. Despite the admonition by our cardiology colleagues that a single shock without associated symptoms is “no big deal,” very few patients can sit at home and follow their doctor's advice that an occasional shock is nothing to worry about. When a patient rolls into the ED, usually by ambulance in a terrified or agitated state, the emergency physician must be prepared not to act promptly. Once the shock and awe subsides, the clinician can then try to figure out what happened and what to do next.



I recently treated one patient with electrical storm who experienced an amazing 51 shocks for bona fide VT, all delivered over a few hours. It was not a pleasant experience for me and certainly not for the patient. Imagine getting a 30 joules shock every few minutes, often sensing the VT and knowing that the jolt will come soon after. I cannot overemphasize that need for rapid and appropriate sedation and analgesia under such circumstances. The authors of this paper suggest propofol, stating that it has some “antiarrhythmic properties” (news to me, but interesting). Most emergency physicians would likely opt first for a benzodiazepine and fentanyl, an effective combination that is familiar to physicians for a variety of ED procedures, including cardioversion. Most patients with electrical storm cannot wait for a cardiologist in the ED, so some ED game plan needs to be in place.

After sedation and analgesia, the cause of the discharge should be determined. It's easy if the underlying problem is VT. Those patients should be treated with IV amiodarone (in a dose equal enough to be effective), beta blockers, and possibly lidocaine. The exact dose and sequence has yet to be determined, but don't forget beta blockers as an early intervention. It seems most reasonable to first administer amiodarone (150 mg IV) and then metoprolol (Lopressor in 2–3 mg aliquots). This approach slows the heart rate, treats the underlying VT, and hopefully also negates the next shock.

If the patient is in rapid atrial fibrillation, IV beta blockers and calcium channel blockers, in standard regimens familiar to most emergency physicians, are indicated. Other ICD-triggering atrial arrhythmias are treated as necessary, including adenosine. If the ICD continues to fire in the presence of AF, placing a magnet over the device will inactivate it, and stop the inappropriate discharge. The key is to determine whether this is AF with aberrant conduction (wide QRS) or VT, not easy with a very fast rate (hint: try carotid massage). Theoretically, helpful adjuncts are diuretics for worsening CHF, acetaminophen for fever, IV nitrates for hypertension, and high-flow oxygen.

Once the initial electrical event has been addressed, interrogation of the device is important to gather historic information. All device companies have 24-hour assistance with this process, although some cardiologists can interrogate the device themselves. In my experience, the company rep is always called. Amazing information can be obtained by interrogation, and it seems reasonable to do it almost every time a true emergency exists. A leisurely stop by the ED for a checkup when the device discharged two days earlier, without symptoms, could probably await an office visit for interrogation.

Of course, one should always consider reversible causes such as electrolyte abnormalities. Drug toxicity presents a more puzzling scenario; hopefully the patient did not overdose on a tricyclic antidepressant or digoxin. It seems reasonable also to take a chest x-ray to look for lead fracture or displacement, but such findings are subtle and actually quite rare. Some antiarrhythmics are pro-arrhythmic by nature. Sticking with amiodarone and beta blockers for ventricular arrhythmias seems like a safer bet to me. If the patient is already maxed out on medication, there are few options left. Such patients are probably near the end of their lives, and have end-stage heart failure or intractable arrhythmias, and this is indeed a dire situation. Ablation procedures, cardiac assist devices, or some of the newer experimental drugs may be helpful, but this is a sad state of affairs for the patient.

Finally, the psychological impact of an ICD can probably only be appreciated by the recipient of the shock. I can only imagine what it is like to walk around with a bulge in your chest wall that can shock the daylights out of you at any time. That can't be good for your psyche or love life, and certainly doesn't prompt you to make reservations for an exotic cruise. So much for the golden years when you have an ICD.

The ICD is a remarkable device that can keep some patients productively alive for many years. The data are not as sanguine as the theories behind them. The number needed to implant with an ICD to save one life is about 15, probably attesting to the seriousness of end-stage CHF, which has a prognosis worse than many cancers, particularly in the presence of prior MI and cardiomyopathy.

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Interventions and Options for ICD Programming



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Suggested Initial ED Approach to ICD Electrical Storm

  • ▪ IV, oxygen, monitor, 12-lead EKG, vital signs (including temperature)
  • ▪ Immediate sedation/analgesia if active discharge
  • ▪ STAT electrolyte determination (including magnesium)1
  • ▪ Atrial arrhythmia (ST, AF, SVT): Diltiazem/metoprolol/adenosine2
  • ▪ Ventricular arrhythmia: Amiodarone/metoprolol3
  • ▪ Cardiology consultation
  • ▪ Address CHF, thyroid status, hypertension, hypotension, hypoxia
  • ▪ Evaluate for AMI, reversible ischemia
  • ▪ Post-therapy: Interrogation of device, admission
  • ▪ Consider diuretics, statins, BP control, nitrates
  • ▪ Evaluate for drug overdose/toxicity
  1. Value not known/more likely if patient is on diuretics.
  2. Place magnet over ICD if truly inappropriate discharges.
  3. Consider also lidocaine, magnesium, procainamide, others.
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Episode Lists Report



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Discharges/Shocks from an ICD

  • ▪ Monomorphic ventricular tachycardia
  • ▪ Polymorphic ventricular tachycardia
  • ▪ Torsades de pointes
  • ▪ Ventricular fibrillation
  • ▪ Atrial fibrillation
  • ▪ Atrial flutter
  • ▪ Atrial tachycardia
  • ▪ Supraventricular tachycardia
  • ▪ Junctional tachycardia
  • ▪ Sinus tachycardia
  • ▪ Multiple premature ventricular contractions
  • ▪ Oversensing T waves
  • ▪ Double counting of QRS complex
  • ▪ Oversensing due to lead failure or insulation break
  • ▪ Oversensing of diaphragmatic myopotentials
  • ▪ Electromagnetic interference

Adapted from JAMA 2006;296[23]:2839.

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CME Participation Instructions

To earn CME credit, you must read the article in Emergency Medicine News, and complete the quiz, answering at least 80 percent of the questions correctly. Mail the completed quiz with your check for $10 payable to Lippincott Continuing Medical Education Institute, Inc., 770 Township Line Road, Suite 300, Yardley, PA 19067. Only the first entry will be considered for credit, and must be received by Lippincott Continuing Medical Education Institute, Inc., by September 30, 2009. Acknowledgment will be sent to you within six to eight weeks of participation.

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