(1)
Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, WA, USA
Background
Overview of Device-Related Complications
Patients with pacemakers or internal cardioverter-defibrillators (ICDs) are at risk for device malfunction on exposure to electromagnetic interference (EMI) from monopolar cautery, magnetic resonance imaging (MRI), or radiofrequency ablation and therapeutic radiation [1]. The most common and potentially life-threatening adverse effects of EMI are:
Inhibition of cardiac pacing leading to severe bradycardia or asystole
Inadvertent shocks if an ICD interprets the EMI as a heart rate higher than the therapy trigger rate
However, EMI may also lead to tachycardia from:
Noise reversion (when EMI makes the rhythm uninterpretable to the device, the device may automatically switch to asynchronous pacing and thereby create a rhythm that competes with the intrinsic rhythm).
Activation of the rate-response feature by EMI may cause the pacing rate to increase, which typically results in a paced tachycardia (see below).
EMI sensed as intrinsic atrial beats that lead to ventricular paced beats.
In addition, if the EMI becomes intense, such as if the cautery occurs within 8 cm of the device, the device may:
Transiently turn off and when it reboots, revert to default settings instead of the original programmed settings.
Burn the myocardium at the pacer lead tip if there is a break in the lead insulation.
If cautery is applied to the device, it may fry the electronics and render the device nonfunctional.
Basic Pacemaker and ICD Function
Pacemaker function is often summarized with a three- or four-letter code, with the letters designating the chambers that are paced, the chamber(s) where sensing is performed, and the device’s response to a sensed beat [2–4] (see Table 12.1). A fourth letter, “R,” is often added if a rate-adaptive or rate-responsive mechanism is operational. When the activity sensor within the device determines that the patient is active, the backup (demand) pacing rate increases. Sensor options include the following [5]:
Table 12.1
Pacemaker function codes
First letter | Second letter | Third letter |
|---|---|---|
Chamber(s) paced | Chamber(s) sensed | Response to sensing |
A = atrium | A = atrium | I = inhibited |
V = ventricle | V = ventricle | T = trigger |
D = dual (both chambers) | D = dual (both chambers)O = no sensing | D = dual (inhibit or trigger depending on the situation)O = nothing |
A piezoelectric crystal that detects either muscle pressure on the device or body movement: In the operating room (OR), shaking the patient can cause increases in heart rate.
Bioimpedance measurement within the chest to estimate minute ventilation: To make this measurement, the device emits a small current between the generator and the lead. This permits an impedance measurement that reflects tidal volume, and its frequency provides the respiratory rate. The respiratory rate module of most OR/ICU monitors has similar technology and can fool the pacer/implantable cardioverter-defibrillator (ICD) into thinking the patient is physically active. This results in an inappropriate paced tachycardia.
Bioimpedance measurement within the myocardium (an index of sympathetic nervous system activity): This measurement is made at the tip of the lead. No known interactions in the OR.
Most Common Pacing Modes
VVI: Senses and paces the ventricle (demand pacing).
DDD: Both atrium and ventricle are sensed and paced individually.
VVIR and DDDR: Same as VVI or DDD, but with rate-adaptive mechanism.
Implantable Cardioverter-Defibrillators [2, 3]
Respond to tachyarrhythmias (typically ventricular tachycardia and fibrillation) based on detection of defined, high ventricular rates.
Therapies include rapid pacing, low-energy synchronized shocks, or high-energy unsynchronized shocks.
All ICDs have pacing capability. The pacemaker component of an ICD is the same as a regular pacemaker, and the four-letter code still applies. In an ICD, the pacemaker settings vary from very basic (patient with no need for a pacemaker) to as complex as any patient with pacemaker requirement.
Cardiac Resynchronization Therapy
These devices pace both the right and left ventricles in order to produce a more coordinated left ventricular contraction [2, 3].
If defibrillation capability is present, it is referred to as CRT-D.
The four-letter pacing mode nomenclature can still be used to describe the pacemaker capability of the cardiac resynchronization therapy (CRT) or CRT-D device.
Preoperative Evaluation
Most experts recommend that a plan for device management for surgery be made by a qualified individual with the recommendation based on knowledge of the proposed surgery and the information gleaned from a recent interrogation of the device [1, 6, 7]. The typical recommendations will be one of the following:
1.
Nothing required (e.g., surgery on the leg where EMI detection by the device is virtually unheard of).
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