Dofetilide

Patients with implanted cardiac devices constitute a growing segment of primary healthcare practice. While these devices are remarkably safe, the potential for electromagnetic interference (EMI), environmental interactions, and metabolic disruptions exists. Collaboration with the patient's cardiology provider is important for monitoring the device's sensing and capture thresholds, as well as for regular interrogation of the device to identify evidence of EMI. Frequent monitoring of antiarrhythmic drug and electrolyte levels to detect and correct metabolic abnormalities early can reduce EMI and environmental interactions. Education regarding sources of EMI that can potentially alter normal functioning of the device is an essential component of the providerpatient relationship.

Implanted Cardiac Device Treatment

According to the American Heart Association (AHA), more than 170,000 pacemakers' and 30,000 implantable cardioverter-defibrillators (ICDs)2 are implanted in the United States each year (see Figure: "Cardiac Pacemaker Procedures: United States between 1979-2000"). The results of the Multicenter Automatic Defibrillator Implementation Trials (MADIT I and II), which found ICD treatment superior to drug therapy alone for the treatment of ventricular arrhythmias, were released. Since then, the number of implantations of ICDs has quadrupled.3,4 In fact, ICDs with biventricular pacing capability are now being implanted for New York Heart Association Class III and IV heart failures, as well as to improve quality of life and survival in persons on waiting lists for heart transplantation.3 A recent study pooled data from three trials of 1,080 patients. It found that cardiac resynchronization (biventricular pacemaker-based therapy) decreased the risk of death from progressive heart failure (often sudden death from lethal arrhythmias) or cardiac transplantation compared to the control group by 59%.5

Despite the widespread use and remarkable safety features of these implanted cardiac devices, many instances of EMI and environmental interactions (including adverse metabolic and medication-device effects) have been reported in persons with ICDs and pacemakers.6-9 These interactions result in inappropriate ICD discharges, rhythm sensing problems, and occasionally, inhibition of. cardiac pacing. Inappropriate ICD discharges, as well as inhibition of cardiac pacing, are of concern because they can (a) potentially cause psychological distress, anxiety, and physical discomfort, (b) shorten generator life, (c) potentiate the proarrhythmic effects of cardiac defibrillation, and (d) lead to cardiac arrhythmia and arrest. Given the growing number of people with ICDs, EMI and environmental interactions are important adverse effects that healthcare providers need to recognize to counsel patients. Providers should also know the potential sources of EMI and environmental interactions to educate patients on avoiding certain risks and procedures if interference is suspected.

Electromagnetic Interference and ICDs

Electromagnetic interference is defined as "highly-regular electrical potentials of low amplitude and high frequency."6 Experts feel that sources of EMI must be in close proximity (within 6 inches) to the patients' devices in order to interfere with cardiac device functioning. Sources carrying the highest probability levels of interference with cardiac devices include: arc welding equipment, electronic muscle stimulators, radio transmitters, concert speakers, large motor-generator systems, electric drills, and hand-held metal detectors.2

The incidence of inappropriate ICD discharges was estimated as less than 1% per patient per year in a 2001 study of 341 ICD patients who were followed retrospectively over a 3-year period.6 Interrogation of the ICDs revealed instances where defibrillation (device activation) occurred in the absence of either ventricular tachycardia (VT) or ventricular fibrillation (VF). After excluding other sources of interactions, such as muscle contractions, lead fracture, and dislocation of the connector, it was concluded that EMI was the sole source of electrical interference. The ICD erroneously identified the EMI as a life-threatening arrhythmia and delivered a shock.

The overall number of EMI occurrences is likely underestimated; nonsustained episodes of EMI may have occurred unbeknownst to the patient or terminated spontaneously before the device(s) responded. In addition to documented EMI effects, unusual environmental interactions with ICDs have occurred, such as during showering, while seated at a slot machine, and while using an electric razor. Several of the ICD episodes clearly involved EMI, while the origin of others is less clear.

Older generation ICDs and those implanted in the upper abdomen are more likely to be affected by EMI than the newer generation ICDs. Better identification of 50 to 60 cycle (Hz) interference has improved differentiation of ventricular arrhythmias and rapid patient movement from EMI, which lessens the occurrence of inappropriate ICD discharges. Similarly, industry advances in pacemaker lead technology, such as bipolar sensing and pacer leads dedicated to defibrillation instead of integrated bipolar sensing circuits have also reduced EMI.6

EMI Effects on Pacemakers

Dual-chamber pacemakers are programmed to be more sensitive to electrical stimuli than single-chamber pacemakers, and therefore have the highest incidence of EMI. Dual-chamber pacers are also more likely to revert to asynchronous, fixed-rate pacing from EMI exposure. Pacemaker-dependent persons (those with an intrinsic heart rate of less than 30 BPM) are most likely to experience signs and symptoms attributable to EMI, or from the reversion to asynchronous, fixed-rate pacing (see Table: "Signs and Symptoms of Patients with a Dysfunctional Pacemaker"). Electronic-article surveillance systems (EAS) (the wand-type of surveillance often used at airports) affect pacemakers more than ICDs, due to the stronger protective-device shielding used in ICDs. A 2000 study reported that the interaction between pacemakers and EAS occurred in 20% of dual-chamber pacers and 10% of single-chamber pacers.7

Metabolic Effects

The minimal output energy required from the pacemaker or ICD pulse generator to depolarize myocardial tissue is called the capture threshold. The capture threshold is quite sensitive and may be altered by sleep, illness, and certain medications. Metabolic and electrolyte disturbances have variable effects, raising or lowering the capture threshold of pacemakers and the newer, pacing-capable ICDs (see Table: "Metabolic Effects on Pacemakers"). The usual effect of a metabolic or an electrolyte disturbance is to raise the capture threshold of myocardial tissue, thereby requiring the generator to expend more energy in order to stimulate a myocardial contraction. This will result in shortened generator life if the effect is prolonged or occurs regularly.

Antiarrhythmic Drug Effects on Pacemakers and ICDs

Antiarrhythmic drugs are intended to suppress and control rhythm and/or heart rate disturbances, however, they can also increase myocardial capture and pacing thresholds as an unintended consequence. The class IA drugs (quinidine sulfate, quinidine gluconate, procainamide hydrochloride, and disopyramide phosphate) decrease sodium influx and can increase the pacing threshold when given in high doses. The class IB drugs (lidocaine and mexiletine) impede the fast sodium channels, thereby increasing the defibrillation threshold. This results in more ICD-expended energy in order to terminate potentially lethal arrhythmias. The class IC drugs (flecainide acetate and propafenone) increase both the capture threshold and the QRS duration, (i.e. ventricular depolarization). These effects can have important implications in patients with ICDs, which are designed to analyze the width of the QRS complex to distinguish between narrow-complex and wide-complex tachycardias. The class III agents, sotalol and dofetilide (Tikosyn), lower the defibrillation threshold and are used as adjunct therapies in patients with an ICD. The class III agent amiodarone is a common potential cause of pacer noncapture, in addition to increased defibrillation thresholds. When given in high doses, amiodarone can markedly increase defibrillation thresholds, resulting in ICD failure to defibrillate and death from sustained ventricular tachycardia.8

Guidelines for Providing Care

Patients who have a pacemaker or an ICD should always be encouraged to carry the manufacturer's identification card with them at all times. In addition, the following information must be documented in the permanent medical record: (a) the manufacturer of the device, (b) the model number, (c) the serial number, (d) implant date, (e) mode of operation, (f) programmed parameters (output, rate, sensitivity), (g) upper and lower rate limits for rateresponsive devices, (h) type of lead fixation (active or passive), (i) unipolar or bipolar lead system, (j) ICD capability (shock, pacing, both), and (k) type of delivery system for ICD shocks (epicardial patches, subcutaneous patches, or transvenous system).2,9

At each clinic visit, primary healthcare providers are obligated to inquire about symptoms indicative of arrhythmias, heart failure, and/or ischemia, as well as device complications such as the development of dizziness, syncope, palpitations, chest pain, and shortness of breath. The patient should be specifically queried about arm swelling and increased warmth on the side ipsilateral to implantation of the endovascular leads, and redness or swelling at the device site. Reported cardiac device infection rates vary between 2% and 8%.2 Treatment typically involves the removal of all implanted hardware, in addition to long-term antibiotic therapy. Patients should always be questioned about ICD discharges (shocks) that have occurred between visits, however it is not uncommon for ICDs to reach end-of-life without ever delivering a shock for a clinical event. The clinic staff should be aware that there is no danger to them if they come in contact with a defibrillator patient during an active ICD discharge. Touching the person will not harm them.

Unintended effects of antiarrhythmic drugs can deplete generator life and lead to device malfunctioning, such as firing for sinus tachycardia or atrial fibrillation with a rapid ventricular response. Electrolyte imbalances, including hyperkalemia or hypokalemia, alter the heart's electrical response and must be avoided. Primary care providers who manage patients with implanted cardiac devices who are also taking antiarrhythmic drugs, need to monitor drug and electrolyte levels on a regular basis (every 2 to 3 months). A chest radiograph is obtained postimplantation of either a pacemaker or ICD to document baseline location and condition. It should be repeated on an annual basis or whenever a lead fracture, patch crinkling, lead dislodgement, or migration is suspected.

Many patients with ICDs have questions and concerns about driving motor vehicles. The highest incidence of defibrillator shocks occurs within the first month following ICD implantation and typically declines over the ensuing year.2 Current North American Society for Pacing and Electrophysiology (NASPE) and AHA guidelines prohibit aircraft piloting and commercial driving after an ICD device has been implanted, but not a pacemaker. Noncommercial driving has traditionally been prohibited for 6 months or until medical management is optimized if the indication for the ICD was life-threatening, symptomatic, sustained VT, or sudden death. However, a 2001 investigation of 559 patients treated with amiodarone or ICD implantation for life-threatening ventricular tachyarrhythmias supports the observation that patients frequently ignore driving restrictions recommended by healthcare providers, and resume driving soon after the index episode of tachyarrhythmia.10 In this group of patients, the annual risk of a motor vehicle crash was 3.4%, which is lower than the annual probability of a motor vehicle crash for all U. S. drivers (7.1%).10 Furthermore, the annual probability that a crash is attributable to an arrhythmia is 0.4%. These data support permitting the early resumption of driving-typically within 3 months, or as soon as associated medical conditions allow. No noncommercial driving restrictions are recommended if the ICD was implanted prophylactically for asymptomatic, nonsustained VT, or VT/VF that was only inducible on an electrophysiology study. This is in accordance with the findings of the MADIT-II study.4

It is advisable to develop a collaborative relationship with the patient's cardiologist, who specializes in treating patients with cardiac rhythm devices. These medical professionals should be consulted for specific questions regarding interactions between medications and devices.9 Threshold testing, as well as further electrophysiology testing, are warranted to determine drug effects on pacing capabilities and potential proarrhythmic side effects.

Despite the ongoing technological improvements in cardiac devices, patients need explicit instructions about potential sources of EMI and how to avoid environmental interactions. These instructions should include education about potential adverse environmental effects of known and suspected sources of EMI (see Figure: "Patient Information Sheet").

Psychological and Social Effects

The psychological and social effects of an ICD and to a lesser degree, a pacemaker, have been documented in the U.S. and internationally.11'14 Implantable cardioverter-defibrillators are highly effective in preventing sudden cardiac death, and are well-accepted as life-saving devices. However, many patients still experience fear of being shocked, anger, high levels of anxiety, and depressive symptoms. Anxieties range from fear of death, loss of control, and body image change to concern about resuming hobbies, device malfunction, and driving an automobile. Additionally, some patients report difficulty sleeping due to fear and anxiety, an inability to concentrate, and problems with overprotective family members. Healthcare providers play an important role in helping patients and their families address these concerns, as well as in encouraging them to seek professional counseling. Many nurse practitioners are trained in mental health counseling, and can offer support groups and individual therapy to help patients focus on emotional issues and develop practical coping strategies.

REFERENCES

1. American Heart Association: Statistics. Heart disease and stroke Statistics2004 update (charts). Accessed at: www.americanheart.org/presentc. jhtml?identifier= 1200026.

2. Wilbur SL, Marchlinski FE: Implantable cardioverter-defibrillator followup. What everyone needs to know. Cardio Rev 1999;7(4):176-90.

3. Shaffer R: ICD therapy: the patient's perspective. AJN 2002;102(2):46-50.

4. Moss AJ, Daubert J, Zareba W: MADIT-II: clinical implications. Card Electrophysiol Rev 2002;6(4):463-5.

5. Bradley D, Bradley E, Baughman K, et al.: Cardiac resynchronization and death from progressive heart failure. JAMA 2003;289(6):730-40.

6. Goldschlager N, Epstein A, Friedman P, et al.: Environmental and drug effects on patients with pacemakers and implantable cardioverter/defibrillators. Arch Int Med 2001;161:649-55.

7. Kolb C, Zrenner B, Schrnitt C: Incidence of electromagnetic interference in implantable cardioverter deflbrillators. PACE 2001;24:465-8.

8. Mugica J, Henry L, Podeur H: Study of interactions between permanent pacemakers and electronic antitheft surveillance systems. Pacing & Clin Electrophysiol 2000;23:333-7.

9. Brode S, Schwartzman D, Callans D, et al.: ICD-antiarrhythmic drug and ICD-pacemaker interactions. J Cardiovas Electrophysiol 1997;7:830-42.

10. Akiyama T, Powell J, Mitchell LB1 et al.: Resumption of driving after lifethreatening ventricular tachyarrhythmia. NEJM 2001;345(6):391-7.

11. American Heart Association: Pacemakers, 2004. Accessed at: www.amcricanheart.org/presenter.jhtml?identifier=24

12. Thomas S, Friedman E, Kelley F: Living with an implantable cardioverterdefibrillator: a review of the current literature related psychological factors. AACN Clin Is 2000;12(1):156-63.

13. Reid S, McKinley S, Nagy SH: Outcomes, problems and quality of life with the implantable cardioverter defibrillator. Aust J of Adv Nurs 1999;16(4):14-9.

14. Schuster P, Phillips S, Dillon D, et al.: The psychological and physiological experiences of patients with an implantable cardioverter defibrillator. Rehab Nurs 1998;23(1):30-7.

15. Sear SF, Todaro JF, Urizar G, et al: Assessing the psychosocial impact of the ICD: a national survey of implantable cardioverter defibrillator health care providers. PACE 2000; 23:939-945.

ACKNOWLEDGEMENTS

Special thanks to Sandra Kuszeweski, MSN, CRACNP, former electrophysiology nurse practitioner in the Division of Cardiology at The Johns Hopkins Hospital, Baltimore, MD; and Margaret Pluth, RN, MPA, Director of Clinical Services at the St. Paul Heart Clinic for lending us their expertise in reading and commenting on this manuscript.

Theresa P. Yeo, PhDc, MSN, MPH, CRNP

Nancy C. Berg, MA, CRNP

ABOUT THE AUTHORS

Ms.Yeo is an Assistant Professor of Nursing at The Johns Hopkins University School of Nursing, Baltimore, Maryland, and a doctoral candidate in environmental health science at the Bloomberg School of Public Health. She is a former electrophysiology nurse specialist, currently in clinical practice at the Johns Hopkins Oncology Center. Ms. Berg is a Nurse Practitioner and Electrophysiology Nurse Specialist, who manages clients with implanted cardiac devices at the St. Paul Heart Clinic in St. Paul, Minnesota.

Copyright Springhouse Corporation Dec 2004
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