How to Manage Cardiac Pacemakers and Implantable Defibrillators in the Intensive Care Unit



How to Manage Cardiac Pacemakers and Implantable Defibrillators in the Intensive Care Unit


Melanie Maytin

Usha B. Tedrow



Introduction

Cardiac device technology has made great advancements since the introduction of the first implantable pacemaker in 1958. Since then, the number of cardiac device implants continues to increase annually as a result of the aging of the general population, expanding indications for device therapy, and ongoing innovation in the technology of cardiac pacing and defibrillation. As a result, many patients presenting to the intensive care unit (ICU) with noncardiac illness may have implanted cardiac devices. This chapter aims to briefly review basic cardiac device function and programming with emphasis on device malfunction and troubleshooting. A discussion of the indications for permanent pacing, defibrillator or resynchronization therapy is outside the scope of this text; for additional information regarding these topics, the reader is referred to the American College of Cardiology/American Heart Association/Heart Rhythm Society 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities [1].


General Device Management


Normal Device Function and Special Considerations

Identification of the type of device is critical in interpretation of its function. Although the patients would ideally be able to provide information regarding the type of device that has been implanted (pacemaker, implantable cardioverter defibrillator (ICD), cardiac resynchronization device, etc.) or carry a device identification card with them at all times, this is frequently not the case in hospitalized patients. Substantial device information can be gleaned from a chest radiograph, including the lead configuration, the type of device, abnormalities in lead position or integrity, and even the device manufacturer (Fig. 44.1A–C). Identification of the device manufacturer is essential if formal device interrogation or reprogramming is planned as each device company uses different software and programmers to communicate with their respective devices (Fig. 44.2). The overwhelming majority of devices implanted are manufactured by one of three companies, and patient device information and technical support are available 24 hours a day (Table 44.1).

The device system consists of a pulse generator or battery, logic circuits, and pacing or defibrillator lead(s). All implantable cardiac devices have programmable pacemaker functions. These devices can both sense intrinsic electrical depolarization and excite myocardial tissue through an artificial electrical stimulus delivered near the lead tip. Electrical stimuli can be delivered in many ways depending on how the device is programmed. Pacing nomenclature is standardized to easily communicate information regarding the device and the pacing mode (Table 44.2). Pacing algorithms are best understood as a function of timing cycles. A pacemaker operates like a timer with programmable intervals to coordinate all sensed and paced events. Nontracking modes of pacing (AAI, VVI, DDI) deliver electrical impulses at set intervals (lower rate limit) unless a sensed electrophysiologic cardiac event occurs in the appropriate chamber before the end of the programmed interval (in which case the timer resets, Fig. 44.3). Dual-chamber devices programmed to a tracking mode can provide pacing at the programmed lower rate or track-sensed intrinsic conduction up to a programmed upper rate limit. There is no sensing in asynchronous pacing modes (AOO, VOO, DOO) and electrical stimuli are produced at programmed intervals unaffected by intrinsic conduction.


Magnets

The placement of a magnet over a device affects pacemakers and defibrillators differently. Application of a magnet to a pacemaker will cause the reed switch to close and result in asynchronous pacing. The pacing rate is company-specific with a different rate once battery depletion has occurred. Thus, placement of a magnet over the device can assist with the determination of battery status and device identification. If exposure to electromagnetic interference (EMI) is anticipated, positioning a magnet over the device can prevent inappropriate pacing inhibition. On removal of the magnet, the pacing mode will revert to the originally programmed settings, and, in general, formal device interrogation is not required. In contrast, application of a magnet to a defibrillator will disable all antitachycardia therapies but will not affect the pacing mode. Therefore, magnets can be used to prevent inappropriate therapies due to supraventricular tachycardia (SVT), lead fracture, or EMI. On removal of the magnet, defibrillator therapies will be restored, and, in general, formal device interrogation is not required.


Electromagnetic Interference

In hospitals, many potential sources of EMI exist. Sources of electromagnetic energy that could possibly interfere with device function include magnetic resonance imaging (MRI), electrocautery, defibrillation, radiation therapy, neurostimulators, TENS units, radiofrequency ablation, electroconvulsive therapy, video capsule endoscopy, extracorporeal shock wave lithotripsy and therapeutic diathermy [2,3]. EMI exposure most commonly results in inappropriate inhibition or triggering of pacing stimuli, inappropriate ICD tachyarrhythmia

detection and therapy and reversion to an asynchronous pacing mode (noise-reversion mode).






Figure 44.1. Information regarding implantable cardiac devices can be gained from chest radiograph. A: Dual-chamber pacemaker with leads in the RA and RV. B: Single-chamber, dual-coil defibrillator with high-voltage conductors in the RV and SVC–RA junction. C: Cardiac resynchronization device with leads in the RA, RV, and CS. These devices may or may not have defibrillator function. RA, right atrium; RV, right ventricle; SVC, superior vena cava; CS, coronary sinus.






Figure 44.2. Many cardiac devices are marked with a radiopaque code that specifically identifies the manufacturer and model of the device. A: Medtronic ICD with magnified view of radiopaque code (inset). The manufacturer is identified by the Medtronic logo at the extreme left of the code and the model by the three letter code that represents the engineering series number. B: Boston Scientific ICD with magnified view of radiopaque code (inset). The manufacturer and model are identified by the radiopaque codes “GDT” and “104”, respectively.








Table 44.1 Device Manufacturers’ Contact Information

















Medtronic 1.800.MEDTRONIC
Boston Scientific 1.800.CARDIAC
St. Jude Medical 1.800.PACEICD
Biotronik 1.800.547.0394
Sorin Group 1.800.352.6466

Inappropriate inhibition of ventricular pacing can be catastrophic in the pacemaker-dependent patient; similarly atrial oversensing with inappropriate ventricular tracking could result in a myriad of symptoms including heart failure exacerbation, hypotension, or angina. Improper ICD tachyarrhythmia detection due to EMI could potentially be arrhythmia-inducing as a result of unsynchronized inappropriate shock delivery during the vulnerable period of repolarization. Noise-reversion mode is an algorithm that reverts transiently to asynchronous pacing in response to rapid frequency signals. The algorithm is designed to protect against inappropriate inhibition of pacing when high-frequency signals are sensed. Although this algorithm is present in all pacemakers regardless of manufacturer, this is not the case for ICDs. Less frequently, EMI can result in reprogramming of the device parameters or permanent circuitry or lead damage. When EMI exposure is unavoidable, certain measures can be taken to minimize the potential risk. For example, pacemaker or defibrillator patients requiring surgery with electrocautery should have a magnet placed over the device during the operation. Other forms of EMI (e.g. MRI, radiation therapy) carry substantial risk and may prompt the revision or removal of the entire cardiac device system prior to planned exposure. Care should be taken to avoid sources of EMI in device patients or, if exposure to EMI cannot be avoided, at a minimum, measures should be taken to minimize potential harm with consideration of device interrogation following exposure.


Mode Switch

Mode switch is a programmable pacing algorithm that automatically changes the pacing mode to a nontracking mode in response to a sensed atrial arrhythmia. The purpose of this algorithm is to prevent inappropriately fast ventricular tracking at the upper rate limit in response to a rapid atrial tachyarrhythmia. Once the device has mode switched, it will remain in a nontracking mode until the atrial rate has fallen below the mode switch threshold for a specific number of intervals. This algorithm is very useful for patients with paroxysmal atrial arrhythmias (e.g. SVT, atrial fibrillation or atrial flutter). The atrial rate at which mode switch occurs is programmable in most devices and the feature can even be programmed “off.”








Table 44.2 Pacing Designation
































NASPE/BPEG Generic (NBG) Code
Position I II III IV V
Category Chamber(s) pace Chamber(s) sensed Response to sensing Programmability, rate modulation Antitachy-arrhythmia function(s)
Letters used O-None
A-Atrium
V-Ventricle
D-Dual (A + V)
O-None
A-Atrium
V-Ventricle
D-Dual (A + V)
O-None
T-Triggered
I-Inhibited
D-Dual (T + I)
O-None
P-Simple Programmable
M-Multiprogrammable
C-Communicating
R-Rate modulation
O-None
P-Pacing (antitachy-arrhythmia)
S-Shock
D-Dual (P + S)
Manufacturer’s designation only S-Single (A or V) S-Single (A or V)      


Line Management

The placement of central venous catheters in cardiac device patients warrants special consideration. Depending on the location and age of the device and the planned location of central venous access, a number of potential complications can occur. Reported complications associated with central venous catheters in cardiac device patients include lead damage from needle puncture [4], lead dislodgement, and inappropriate ICD therapies [5]. In addition, central venous stenosis as a consequence of prior cardiac device implantation may present a challenge to central venous catheter placement ipsilateral to the device [6]. Cardiac device infections and device-related endocarditis represent a particularly serious hazard of indwelling central venous catheters necessitating removal of the entire device system [7]. Central venous access should be performed contralateral to the device whenever possible.


Magnetic Resonance Imaging

The likelihood that patients with cardiac devices will require an MRI is high [8] but this imaging modality is not without risks in these patients. The potential hazards of magnetic resonance imaging in cardiac device patients include movement of the device, programming changes, asynchronous pacing, activation of tachyarrhythmia therapies, inhibition of pacing output, and induced lead currents that could lead to heating and cardiac stimulation [9], resulting in altered pacing and defibrillation thresholds, device damage, asystole, arrhythmias, or even death [10]. Although an implantable cardiac device remains a strong relative contraindication to MRI, certain centers have developed protocols for performing MRIs in cardiac device patients [11] and MRI-safe pacemakers are being developed. If an MRI is the only diagnostic imaging option in a cardiac device patient, imaging at 1.5 Tesla with appropriate programming and monitoring can likely be undertaken safely with careful assessment of the risk–benefit ratio on a case-by-case basis [11,12,13,14].







Figure 44.3. Timing of events in various pacing modes. AAI is an atrial nontracking mode of pacing that provides backup atrial pacing at the programmed lower rate limit. Similarly, VVI is a ventricular nontracking mode of pacing that provides backup ventricular pacing at the programmed lower rate limit. DDD is a dual-chamber mode of pacing that can both inhibit and trigger events in both the atrium and the ventricle. AS, atrial-sensed event; AP, atrial-paced event; VS, ventricular-sensed event; VP, ventricular-paced event; LR, lower rate limit.


External Defibrillation

In the event of a cardiac arrest or hemodynamically unstable arrhythmia in a patient with an implantable cardiac device, resuscitative efforts should proceed as per guidelines without deviation. Defibrillation or cardioversion can result in permanent damage to the cardiac device; to minimize these risks, the defibrillation pads should be placed at least 10 cm from the pulse generator [15]. Other potential risks of external defibrillation include device reprogramming [16] and myocardial damage at the interface with the lead resulting in an acute rise in threshold [17]. Following defibrillation or cardioversion, cardiac devices should be interrogated formally to insure proper function and programming. Again, the low potential risk of damage to the device should not impede usual and necessary resuscitative efforts for the patient.


Infection

Cardiac device-related infection encompasses a disease spectrum from pocket infection to device-related endocarditis. The clinical manifestations of cardiac device-related infection are protean and can range from pain at the implant site without cutaneous manifestations to minor erythema or swelling of the device pocket (Fig. 44.4A) to overt erosion of the system (Fig. 44.4B) to device-related endocarditis (Fig. 44.4C) [18,19]. In the absence of bacteremia, systemic manifestations and leukocytosis are rare. Cultures of the device leads yield the highest results and, Staphylococci are the primary pathogen identified [20]. A high index of suspicion is warranted in a patient with implanted pacemaker or ICD and signs and symptoms of infection. Cardiac device-related infection requires prompt removal of the entire device system for complete treatment unless significant comorbidities preclude extraction [7,18]. Although no specific vegetation size has been established as a contraindication to transvenous extraction, most experts agree that vegetations greater than 3 cm in size are better treated surgically [7]. Patients with device-related endocarditis require a minimum of six weeks of intravenous antibiotics and pose a particular problem with respect to the timing of re-implant in pacemaker-dependent patients.

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Sep 5, 2016 | Posted by in CRITICAL CARE | Comments Off on How to Manage Cardiac Pacemakers and Implantable Defibrillators in the Intensive Care Unit

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