Implantable cardioverter-defibrillators

Published on 07/02/2015 by admin

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Last modified 22/04/2025

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Implantable cardioverter-defibrillators

Efrain Israel Cubillo, IV, MD

Overview

Approximately 300,000 Americans die each year from sudden cardiac arrest, many of whom were taking antiarrhythmic drugs, but drugs alone were insufficient to prevent ventricular tachycardia and fibrillation. The implantable cardioverter-defibrillator (ICD) has revolutionized the treatment of patients at risk for experiencing sudden cardiac death due to these ventricular tachyarrhythmias. The superiority of the ICD device over antiarrhythmic therapy has been confirmed in several randomized trials. Expanding clinical indications for the implantation of these devices arose with the publication of the MADIT (Multi-center Autonomic Defibrillator Implantation Trial), the results of which have been validated by the MUSTT (Multicenter UnSustained Tachycardia Trial). Both studies demonstrated a survival benefit of ICDs over antiarrhythmic medication and placebo in patients with nonsustained ventricular tachycardia. The number of ICD implants continues to increase, with the United States leading the world in both total number and rate per population (434 new implants per 1 million people). In 2009 alone, based on industry statistics, 133,262 ICDs were implanted in the United States. ICD technology has progressed exponentially since its introduction by Michel Mirowski and colleagues in the early 1980s. Early devices were true “shock boxes,” capable of detecting a tachycardia and delivering a shock without the ability to pace.

The ICD system

The ICD system comprises a microprocessor/pulse generator, a battery, and a conducting lead system. The lead system is required for sensing, pacing, and the delivery of therapy. Earlier systems required that the pulse generators be placed abdominally because of their large size. Defibrillation was delivered via two epicardial patches positioned anteriorly and posteriorly. Occasionally, a transvenous spring electrode in the superior vena cava was utilized with an epicardial patch. Sensing was achieved through separate epicardial screw-in electrodes. Initial lead placement required a sternotomy, lateral thoracotomy, or a subxiphoid incision, making early implants quite cumbersome. ICD implantation has evolved quite rapidly due to advancements in lead technology, generator technology, and the development of biphasic defibrillation electric impulses, which lowered the energy requirements necessary for successful defibrillation. The creation of a bipolar lead combining pacing and sensing capabilities with a high-voltage electrode coil allowed for nonthoracotomy system implants, which reduced surgical morbidity and mortality rates. The leads were positioned transvenously via the subclavian vein and fixed to the inside of the right ventricle. However, the leads still had to be tunneled subcutaneously to the abdomen, as the generators remained fairly large. In current practice, generators are fairly small—the smallest commercially available devices today are approximately 7 cm × 5 cm × 1 cm and weigh well under 100 g—allowing for subcutaneous pectoral implantation and simplification of the implantation process. The ICD generator houses the batteries, high-voltage capacitors, and microprocessors necessary to process sensed intrinsic cardiac electrical activity. In essence, the generator is a minicomputer within a hermetically sealed titanium box, which is capable of storing an electric charge that can be delivered, “shocking” the atria and ventricles back to a sinus rhythm. Typically, ICDs deliver no more than 6 shocks per event, although some can deliver as many as 18. Within an event, each successive therapy must be at equal or greater energy than the previous attempt. Once a shock is delivered, no further antitachycardia pacing can take place.

Typical ICDs contain lithium silver vanadium oxide cells that store between 2 and 7 volts. The high voltages necessary for defibrillation are generated with the aid of high-voltage capacitors that are able to generate 700 to 800 volts of defibrillation energy in under 20 sec.

Current devices allow extensive programmability for tiered antitachycardia pacing, tiered high-voltage therapies, bradycardia pacing, supraventricular tachycardia discrimination algorithms, and detailed diagnostics of tachycardic and bradycardic episodes. They also allow physicians to conduct completely noninvasive programmed stimulation. The most recent iterations provide dedicated dual-chamber and antitachycardia pacing as well as options for atrial defibrillation. Diagnostic functions, including stored electrocardiograms, allow for verification of shock appropriateness. Device battery longevity has also increased; early devices lasted 2 years or less, whereas current devices are expected to last 6 years or longer.

ICD placement

Transvenous placement is performed by cardiologists to place ICDs, usually in the left or right infraclavicular area, with the leads tunneled transvenously while the patient receives intravenous sedation using monitored anesthesia care. A deeper level of anesthesia, which most would consider general anesthesia, is provided to the patient for the discomfort that occurs when the unit is tested (i.e., discharged) and an electric shock is delivered to the patient. Defibrillation can lead to prolonged periods of asystole that can result in significant myocardial and cerebral ischemia. Enough time should be allowed between tests to ensure reperfusion and restoration of hemodynamic stability. The anesthesia provider must monitor the duration and frequency of testing and ischemic periods. Vasoactive drugs are often used to stabilize these patients during and immediately after the testing period. Minimum monitoring includes standard American Society of Anesthesiologists monitors and continuous arterial pressure measurement, usually through an arterial cannula placed by the cardiologist.

Function of pacemakers with an ICD

Single-chamber and dual-chamber pacemakers can function in the presence of an ICD as long as the pacing electrodes are bipolar. An ICD with a built-in capability for pacing will begin pacing when the RR interval is greater than previously set limits. Beginning about 1993, most ICDs incorporated backup VVI pacing to protect the patient from the common occurrence of postshock bradycardia. In July 1997, the U.S. Food and Drug Administration approved devices with sophisticated dual-chamber pacing modes and rate-responsive behavior for patients with ICDs who needed permanent pacing (about 20% of patients with ICDs). If a patient with an ICD requires temporary pacing, bipolar leads, the lowest possible amplitude for capture, and the slowest rate associated with adequate hemodynamic status should be used. It is possible for a pacing spike followed by a QRS complex to be interpreted as ventricular tachycardia, causing discharge of the unit. Inactivation of the ICD may be required during temporary pacing if interference occurs. Cardioverter units for atrial fibrillation are presently under investigation. The perioperative management of these devices is unknown, but they will most likely behave similar to ICDs.

Indications for cardiodefibrillator implantation

The American College of Cardiology (ACC) and American Heart Association (AHA), in collaboration with the American Association for Thoracic Surgery and the Society of Thoracic Surgeons, have developed an extensive set of guidelines for cardiodefibrillator implantation. These guidelines represent a consensus statement that is largely evidence based and that summarizes the available clinical evidence as of the time of its initial publication in May 2008 and further revision in October 2012. The latest update emphasizes the role that left bundle branch block with a QRS complex of 150 ms or greater has in sudden death and now considers this to be an indication for implantation of a cardiodefibrillator if the patient’s status is New York Heart Association classification II or higher.

Electromagnetic interference and ICDs

The ability of ICDs to function is dependent on their ability to sense intrinsic cardiac electrical activity. Hermetic shielding, filtering, interference rejection circuits, and bipolar sensing have safeguarded ICDs (and pacemakers) against the effects of common electromagnetic sources. However, exposure to electromagnetic interference (EMI) may still result in oversensing, asynchronous pacing, ventricular inhibition, and spurious ICD discharges. EMI may also lead to loss of output, increased pacing thresholds, and decreased R-wave amplitude. Common sources of EMI include cellular phones, electronic article surveillance (antitheft) devices, and metal detectors. Occupational sources of EMI include high-voltage power lines, electrical transformers, and arc welding. Interference of concern to anesthesia providers can occur during procedures, such as magnetic resonance imaging, or from electrocautery, spinal cord stimulators, transcutaneous electrical nerve stimulator units, radiofrequency catheter ablation, therapeutic diathermy, and lithotripsy.

Inappropriate ICD shocks

One of the risks associated with an ICD is that of inappropriate ICD shocks, which can occur from EMI, as mentioned previously, or from inaccurate detection of other arrhythmias. An inappropriate ICD shock is one that is not precipitated by accurate detection of a malignant ventricular arrhythmia, ventricular tachycardia, or ventricular fibrillation. Typically, inappropriate ICD shocks result when atrial arrhythmias, such as atrial fibrillation, atrial tachycardia, or atrial flutter, accelerate the ventricular rate beyond the set limit for delivery of ICD shock therapy. Analysis of the MADIT II trial data revealed that 11.5% of the patients with an ICD received inappropriate ICD shocks and that 31.2% of all ICD shocks were deemed inappropriate. Inappropriate ICD shocks due to arrhythmias were attributed to atrial fibrillation (44%), supraventricular tachycardia (36%), and abnormal sensing (20%). Patients with inappropriate shocks had greater all-cause mortality rate (hazard ratio 2.29, P = 0.025).

ICD magnets

As with pacemakers, ICDs can be altered by magnets. Antitachycardia therapy in some Guidant/CPI devices can be permanently disabled by magnet placement for 30 sec. The application of a magnet overlying the ICD pulse generator forms a magnetic field that trips a reed switch in the ICD generator circuit, resulting in a suspension of tachycardia detection and therapy delivery. The magnet response of an ICD varies from manufacturer to manufacturer. In Medtronic devices, the application of a magnet temporarily disables tachycardia detection and therapy with no effect on bradycardia pacing. Removal of the magnet will resume arrhythmia detection. When activated, newer Medtronic devices (Gem II DR, patient alert function) will elicit a continuous beep lasting for 15 sec if a magnet is placed directly over the ICD. A magnet applied over Guidant/CPI defibrillators also inhibits tachycardia therapy with no effect on bradycardic pacing. These devices also generate beeping tones, which, if they change to a continuous tone, indicate that the device is off and will not deliver antitachycardia therapy; the device can be turned on by reapplying the magnet for 30 sec. Tones will now change from continuous to beeping synchronous with R waves, signifying that the device is on again. To ensure correct magnet placement on their devices, Medtronic plans to market a “smart magnet” that maintains communication with the device and reports on the device’s status during the magnet session. Newer generation Guidant ICDs (Prism II) have a built-in electrocautery feature that can be activated by use of the Guidant programmer. This will suspend tachyarrhythmia therapies and pace in the DOO (dual pacing, no sensing, no inhibition) mode. Regular functioning of the ICD is restored by turning this feature off. Interrogating the device by a trained technician or by calling the manufacturer remain the most reliable ways to determine response to a magnet.

Preoperative evaluation

All ICDs should have the antitachycardia therapy disabled before induction of anesthesia and commencement of the procedure if electrocautery is to be used. As with pacing devices, monopolar electrosurgical cautery has been reported to “confuse” an ICD into delivering inappropriate therapy. Also, many ICDs have no noise reversion behavior, so electrosurgical cautery-induced ventricular oversensing might cause nonpacing in a patient who depends on an ICD for pacing.

Intraoperative management

No special monitoring or anesthetic technique is required for the patient with an ICD. However, the Heart Rhythm Society and American Society of Anesthesiologists have developed guidelines and recommendations for how the patient with an ICD coming to the operating room for an elective procedure (Box 152-1) or an emergent procedure (Box 152-2) should be managed. Electrocardiographic monitoring and the ability to deliver prompt external cardioversion or defibrillation must be present if the ICD is being disabled, are recommended whether or not the device is used for pacing, and are recommended whether or not the patient is pacemaker dependent (Box 152-3). Should external defibrillation become necessary, device manufacturers recommend using the lowest possible energy, placing the paddles perpendicular to the path of the implanted leads, and keeping the paddles away from the implanted generator, the same as with a standard pacemaker device. The guidelines outline when and how the ICD must be reinterrogated and reenabled postoperatively (Box 152-4).

Box 152-1

General Principles of ICD Management

The perioperative management of ICDs must be individualized to the patient, the type of ICD, and the procedure being performed.

An ICD team is defined as the physicians and physician extenders who monitor the ICD function of the patient.

The anesthesia team should communicate the type of procedure and likely risk of EMI with the ICD team.

The ICD team should communicate with the anesthesia team to deliver a prescription for the perioperative management of patients with ICDs:

1. Manufacturer and model

2. Indication for device

3. Battery longevity documented as >3 months

4. Are any of the leads <3 months old?

5. What is the response of this device to magnet placement?

6. Will ICD detection resume automatically with removal of the magnet?

Note: Inactivation of ICD detection is not a universal requirement for all procedures.

EMI, Electromagnetic interference; ICD, implantable cardioverter-defibrillator.

Modified from Crossley GH, Poole JE, Rozner MA, et al. The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA) Expert Consensus Statement on the perioperative management of patients with implantable defibrillators, pacemakers and arrhythmia monitors: Facilities and patient management. Heart Rhythm. 2011;8:1114-1154.

Box 152-2

Approach to Emergent/Urgent Procedures

Identify the type of device:

Evaluate the medical record

Examine the patient registration card

Telephone the company to clarify device type

Examine the chest radiograph

Determine if the patient is pacing:

Obtain a 12-lead electrocardiogram or rhythm strip documentation

If there are pacemaker spikes in front of all or most P waves or QRS complexes, assume pacemaker dependency *

Whether or not the patient is pacemaker dependent, place magnet ^† over ICD to suspend tachyarrhythmia detection, use short electrosurgical bursts^‡

Monitor patient with plethysmography or arterial line

Place transcutaneous pacing and defibrillation pads anterior/posterior

Evaluate the ICD before leaving a cardiac-monitored environment

*Pacemaker (PM) dependency is defined as absence of a life-sustaining rhythm without the pacing system.

^†A magnet placed over an implantable cardioverter-defibrillator (ICD) (or cardiac resynchronization therapy-ICD [CRT-ICD]) will not result in asynchronous pacemaker function. This can only be accomplished by reprogramming of ICDs (or CRT-ICDs) capable of this feature (majority of newer devices implanted).

^‡Long electrosurgery application (>5 sec or frequent close-spaced bursts) may result in PM inhibition, causing hemodynamic risk in a PM-dependent patient. Long electrosurgery application in close proximity to the device generator may rarely result in power on reset or Safety Core programming.

Modified from Crossley GH, Poole JE, Rozner MA, et al. The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA) Expert Consensus Statement on the perioperative management of patients with implantable defibrillators, pacemakers and arrhythmia monitors: Facilities and patient management. Heart Rhythm. 2011;8:1114-1154.

Box 152-3

Problems That Can Occur During Procedures in Patients with ICDs

Bipolar electrosurgery does not cause EMI unless it is applied directly to an ICD.

EMI from monopolar electrosurgery is the most common problem incurred during surgical procedures.

ICDs with antitachycardia function may be inhibited or may falsely detect arrhythmias when exposed to EMI.

Pulse generator damage from electrosurgery can occur, but is uncommon.

Impedance-based rate-responsive systems may go to upper rate behavior with electrosurgery exposure.

Risk mitigation strategies can be effective.

Keeping the current path away from ICDs diminishes the potential for adverse interaction with the device.

Use bipolar electrosurgery whenever possible.

Minimize the length of monopolar electrosurgery bursts to ≤5 sec.

Radiofrequency ablation can cause all of the interactions that monopolar electrosurgery can cause but may have a more significant risk profile because of the prolonged exposure to current.

TENS units can result in EMI.

EMI, Electromagnetic interference; ICD, implantable cardioverter-defibrillator; PM, pacemaker; TENS, transcutaneous electrical nerve stimulation.

Modified from Crossley GH, Poole JE, Rozner MA, et al. The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA) Expert Consensus Statement on the perioperative management of patients with implantable defibrillators, pacemakers and arrhythmia monitors: Facilities and patient management. Heart Rhythm. 2011;8:1114-1154.

Box 152-4

Indications for the Interrogation of ICDs Prior to Patient Discharge or Transfer from a Cardiac Telemetry Environment

Patients with ICD reprogrammed prior to the procedure that left the device nonfunctional such as disabling tachycardia detection in an ICD

Patients with ICDs who underwent hemodynamically challenging surgeries such as cardiac surgery or significant vascular surgery (e.g., abdominal aortic aneurysm repair)*

Patients with ICDs who experienced significant intraoperative events including cardiac arrest requiring temporary pacing or cardiopulmonary resuscitation and those who required external electrical cardioversion *

Emergent operations in which the site of EMI exposure was above the umbilicus

Cardiothoracic operations

Patients with ICDs who underwent certain types of procedures that emit EMI with a greater probability of affecting device function

Patients with ICDs who have logistic limitations that would prevent reliable device evaluation within 1 month from their procedure *

*The general purpose of this interrogation is to ensure that reset did not occur. In these cases, a full evaluation, including threshold evaluations, is suggested.

EMI, Electromagnetic interference; ICD, implantable cardioverter-defibrillator.

Modified from Crossley GH, Poole JE, Rozner MA, et al. The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA) Expert Consensus Statement on the perioperative management of patients with implantable defibrillators, pacemakers and arrhythmia monitors: Facilities and patient management. Heart Rhythm. 2011;8:1114-1154.

Complications

Implantation of an ICD has an intraoperative and perioperative risk of approximately 1% to 3%, including a death rate of 1% or less, perforation and cardiac tamponade of 1% or less, and acute lead dysfunction. Postimplantation pocket infection is a major complication, which generally requires the removal of the complete system. It is reported to occur in 1% to 2% of patients. The most frequently identified organism in patients with a postimplantation pocket infection is Staphylococcus aureus. Infection risk seems to be a little higher at the time of battery or lead replacement than at the time of initial implantation. Lead dislodgement can occur shortly after implantation or at any time thereafter. In patients in whom the lead is completely dislodged, monitoring and timely removal of the lead is mandatory to avoid mechanically induced arrhythmias. Lead dysfunction from insulation breakage or insulation erosion is most frequently preceded by inappropriate ICD discharge caused by electrical noise on the rate electrocardiogram. It usually displays high, frequent, irregular signals with pseudo-RR intervals at the resolution boundary of the device. Some newer devices provide a counter for these specific signals to detect the problems early and avoid inappropriate discharges.

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