The number of patients with cardiac implantable electronic devices (CIEDs) presenting for surgery is increasing.
Electromagnetic interference (EMI) is frequently encountered in the theatre environment and can interfere with the function of CIEDs.
Bipolar diathermy should be used in preference to monopolar diathermy to reduce the risk of EMI.
The degree of dependency on the implanted device and the potential consequences of pacing inhibition should be established.
The defibrillator function of an implantable cardioverter defibrillator should be deactivated immediately before surgery where EMI is likely.
Pacemakers effectively treat a broad range of cardiac arrhythmias by generating an electrical impulse to re-establish regular myocardial contraction. The implantation rate of pacemakers in the UK continues to increase.1 The design and capability of these devices have become increasingly complex and can encompass treatment modalities for patients with heart failure by provision of cardiac resynchronization therapy (CRT) and defibrillator functions to treat tachyarrhythmias.
This article comprises two parts. The first part will review the relationship between the underlying cardiac pathophysiology and the physics of recording, pacing, and defibrillation. The implications of electromagnetic interference (EMI) will then be introduced. The second part will focus on the safe perioperative management of a patient with a CIED who presents for unrelated surgery; procedure-specific considerations will be discussed.
Within the UK in 2010, 58% of permanent pacemakers (PPMs) were inserted for symptomatic bradycardia caused by atrioventricular (AV) block.2 AV block is classified according to the extent of the delay (first-degree block, P–R interval >0.2 s), or interruption (intermittent—second degree, or complete—third degree) to electrical conduction between the atria and ventricles. The pathophysiology of AV block is varied and includes ischaemic, degenerative, and infiltrative processes or may be iatrogenic after AV nodal ablation.
The second most frequent indication for PPM insertion (23.6% in 2010) is sick sinus syndrome. This describes sinus node dysfunction with intermittent loss of P-waves or sinus arrest causing episodes of symptomatic bradycardia.
Biventricular pacemakers are specific types of pacing devices indicated for symptomatic patients with moderate-to-severe cardiac failure with a left ventricular ejection fraction of <35% and a widened QRS interval.3 Biventricular pacing optimizes the timing of right and left ventricular contraction which is otherwise uncoordinated with sole right ventricular pacing; hence, the term CRT. The latest published implantation rate of these devices is 145 per million of the UK population.1
Implantable cardioverter defibrillators
Implantable cardioverter defibrillators (ICDs) sense and analyse myocardial electrical activity and are capable of pacing and shock therapy when necessary. Most ICDs are implanted (in accordance with NICE guidance), for secondary prevention in patients who have survived a cardiac arrest or other significant haemodynamic compromise after ventricular arrhythmias.3 ICD implantation is indicated in selected patients after myocardial infarction [usually with scar-related ventricular tachycardia (VT) risk] or those with significant left ventricular dysfunction. Other patient groups at high risk of sudden death due to ventricular arrhythmias include those with familial cardiac conditions such as long QT syndrome, Brugada syndrome, cardiomyopathies, and selected patients with congenital heart disease. There are specialized ICDs available which permit CRT for patients with indications for biventricular PPMs at risk of arrhythmias. These devices, predominantly inserted for primary prevention, are referred to as CRT-Ds (‘D’ denotes defibrillator).
Implantable loop recorders
These leadless cardiac monitoring devices function solely as a diagnostic tool. They are indicated for patients with recurrent unexplained syncope and/or palpitations and as a long-term monitoring device for some patients with atrial fibrillation (AF). Implantable loop recorders (ILRs) have self-contained electrodes capable of recording an ECG and can be automatically or patient triggered (via an external activator) when arrhythmias or symptoms arise.
Physics and nomenclature of CIEDs
A PPM system comprises a pulse generator (which contains a battery and electronic circuitry) and one or more pacing leads. The pulse generator consists of a silicon chip and electronic sensing and output circuitry which analyses the cardiac rhythm and paces as programmed. Pacing configuration may entail current delivery to a single cardiac chamber or to multiple chambers. Unipolar leads have a single electrode at the pacing tip which acts as the current emitting cathode; the PPM box serving as the anode. With more commonly encountered bipolar leads, the anode lies on the lead itself just proximal to the cathode tip; reducing the susceptibility of the device to EMI.
The PPM box generates an electrical current between the anode and cathode which is transmitted to the myocardium via a lead to achieve a wave of depolarization. Successful pacing-induced depolarization is referred to as ‘electrical capture’. The stimulation threshold is defined as the minimum electrical stimulus that consistently exceeds the excitation threshold of the myocardial cells to produce cardiac depolarization. Depending on the number of leads and the programming of the device, the box responds to sensing of intrinsic electrical activity in single or multiple chambers by either inhibiting or triggering pacing in one or more chambers.
The Generic Pacemaker Code describes the PPM function; positions 1–3 refer to the chamber paced, the chamber sensed, and the response to sensing, respectively (Table 1).4 For example, VVI would denote a ventricular paced and sensed PPM with an inhibiting response to sensing. The commonly encountered DDD mode can have essentially four responses according to the detected intrinsic cardiac rhythm:
Atrial sensing and ventricular sensing
If both atrial and ventricular activity are detected within the appropriate pre-programmed time interval (which depends on the desired heart rate), then there will be inhibition of any pacing activity.
Atrial pacing and ventricular sensing
Atrial pacing leads to intrinsic ventricular activity within the programmed time interval which is sensed by the ventricular lead and therefore inhibits pacing (e.g. sick sinus syndrome with a normal P–R interval).
Atrial sensing and ventricular pacing
Sensed intrinsic atrial activity triggers ventricular pacing when spontaneous ventricular depolarization is not sensed within a programmed time interval (e.g. with complete AV block and normal sino-atrial node function).
Atrial pacing and ventricular pacing
In this scenario, there is pacing of both the atrium and ventricle if intrinsic electrical activity is undetected within the specified pre-set time interval (e.g. with complete heart block and inadequate intrinsic atrial rate).
The fourth position of the generic PPM code refers to rate-responsive pacing whereby the pacemaker can alter the paced heart rate in response to motion or sensed physiological conditions. Most commonly, an accelerometer detects activity during exertion and increases the paced rate to optimize cardiac output. Other sensing mechanisms may detect an increase in physiological parameters, including minute ventilation or myocardial contractility, adjusting heart rate accordingly.
The Generic Pacemaker Code (adapted from Bernstein and colleagues4 with permission from John Wiley & Sons Ltd)
Position I: pacing chamber(s)
Position II: sensing chamber(s)
Position III: response(s) to sensing
Position IV: programmability
O = None
O = None
O = None
O = None
A = Atrium
A = Atrium
I = Inhibited
R = Rate modulation
V = Ventricle
V = Ventricle
T = Triggered
D = Dual (A+V)
D = Dual (A+V)
D = Dual (A+V)
Implantable cardioverter defibrillators
Conventional ICDs are analogous to pacemaker devices but with a larger generator which houses electronic circuitry, batteries, and a capacitor. Defibrillation requires ∼750 V (to deliver an output of 30–45 J); achieved by charging the capacitor and then dissipating this energy. The device continuously senses and analyses native electrical activity (the R–R interval) to detect VT or ventricular fibrillation. It incorporates anti-tachycardia pacing (ATP) capabilities whereby a programmed burst of overdrive pacing is used to attempt to terminate VT. In the case of VF, or if ATP fails, a capacitor within the ICD will charge and then release a shock which passes between the defibrillator coils. These coils are either both located on the ventricular lead or alternatively the box acts as one coil with a single ventricular lead coil. Shock delivery is painful and utilizes more battery life or capacity (measured in ampere-hours) than ATP. An ICD has the anti-bradycardia capabilities of a pacemaker and is able to pace in the event of ‘post-shock’ bradyarrhythmias.
Sensing and the implications of EMI
Sensitivity of a PPM describes the minimum intrinsic atrial or ventricular electrical activity measured in millivolts that is sensed by the device. This is set as a margin around the amplitude of a sensed signal and depends on origin (atrial or ventricular) and lead type (unipolar or bipolar). If incorrectly set, the device may ‘under-sense’ and fail to detect intrinsic atrial or ventricular activity. Consequently, ‘over-pacing’ can occur whereby the pulse generator fires, despite intrinsic activity with the potential risk of triggering malignant tachyarrhythmias. An alternative scenario of ‘over-sensing’ is when the device inappropriately registers myocardial activity when none exists, leading to failure to pace in the context of no intrinsic electrical activity. The most frequent PPM interaction with EMI is over-sensing.5 EMI is particularly important to consider in a patient who is PPM-dependent since over-sensing may result in inappropriate inhibition and significant haemodynamic compromise. In the case of ICDs, EMI may be falsely interpreted as a shockable rhythm and as such, there is a risk of intraoperative shock delivery. Disabling the defibrillator function of a device before exposure to EMI is therefore advised.
PPMs are usually implanted subcutaneously below the left clavicle with trans-venous access commonly via the left cephalic, subclavian, or axillary veins. In paediatric patients, the PPM may be implanted in other locations including the abdominal wall. The atrial lead is generally positioned in the right atrial appendage and the ventricular lead in the right ventricular apex. Biventricular systems require the additional positioning of a lead to stimulate the wall of the left ventricle; this is usually achieved by passing a lead into the coronary sinus via the right atrium (Fig. 1). A retrospective study reported a 7.5% complication rate, most commonly from lead displacement (4.8%), pneumothorax (3.7%), or infection (1.5%).6 Recently developed leadless PPMs have a small sensing and pacing device entirely contained within the right ventricle with no leads (Fig. 2).
Chest radiograph demonstrating a leadless pacemaker system (arrowed) within the right ventricle.
ICDs are implanted similarly to pacemakers with trans-venous leads which sense and deliver shock therapy as required. A less invasive, subcutaneous ICD has been developed (S-ICD), primarily for patients with difficult venous access or complex cardiac anatomy. A lead is placed subcutaneously in the midline, connecting to a pulse generator sited in the left axilla (Fig. 3). The device analyses and treats ventricular arrhythmias by delivering an 80 J biphasic shock without the need for endovascular lead placement and the potential associated complications. The anticipated battery longevity is shorter than conventional ICDs; pacing capabilities are limited to post-shock pacing only.
Chest radiograph demonstrating a subcutaneous pacemaker system. P, pulse generator; S, subcutaneous lead with shock coil.
Preoperative assessment of patients with CIEDs
History and examination
The presence of a CIED indicates a high likelihood of coexisting significant cardiac disease and warrants conduct of a thorough history and examination. Direct inquiry of any symptoms suggesting device malfunction should be made, including dizziness, syncope, or indicators of deteriorating cardiac function. Prescribed anti-arrhythmic agents should be continued in the perioperative period. Electrolyte abnormalities (including hypomagnesaemia), acid–base disturbances, or blood gas abnormalities should be corrected since they may influence the stimulation and/or defibrillation thresholds.
A recent ECG should be examined and may demonstrate pacing activity; sole atrial pacing is seen as a single stimulus (spike) followed by a p-wave and then the patient's own QRS complex (Fig. 4). Ventricular pacing results in a spike followed by a broad QRS complex (Fig. 5). Dual-chamber pacing shows features of both atrial and ventricular pacing. Spikes preceding all p-waves, QRS complexes or both would indicate potential PPM dependency.
Sole ventricular pacing—pacing spikes (arrowed) are followed by broad QRS complexes.
Important information regarding the nature and function of a CIED can be determined from a chest radiograph. This includes device-specific identifiers and the number and configuration of leads together with other findings including the presence of cardiac failure. An ICD can be distinguished from a pacemaker by the presence of one or two thick, linear, radiopaque shock coils on the right ventricular lead (Fig. 6). Radiographic appearances may also suggest potential malfunction of the device such as lead fracture or migration (Fig. 7).
A chest radiograph demonstrating a CRT-D device—note the widened shock coils (S) located on the right ventricular (RV) lead, in contrast to the right atrial (RA) lead and the narrow left ventricular (LV) pacing lead.
Chest radiograph demonstrating right ventricular lead migration (arrowed) outside of the heart.
Device analysis and interpretation of the preoperative check
The patient should carry a European Pacemaker Patient Identification Card which provides detailed information including the pacemaker centre details, the date and indication of implantation, and the manufacturer, model, and serial number of the device (Fig. 8 and Supplementary Fig. S1). Guidelines vary, although it is generally considered acceptable for a PPM to have been checked within 12 months and an ICD within 6 months. Conventional in-person interrogation involves external placement of a programming head onto the implant for recognition; a ‘cardiac dashboard’ displayed on the attached programmer provides a summary of CIED performance during the follow-up interval. Most modern ICDs and some PPMs have the ability to communicate wirelessly; permitting device interrogation in the patient's home with data transmitted automatically to secure websites.
Example of a European Pacemaker Patient Identification Card for a patient with a CRT device programmed to VVI-R (‘D2, C8, E3’ indicates a patient with heart failure and chronic AF who required a PPM due to AV-block caused by nodal ablation—see Supplementary Fig. S1).
The key features that should be identified when interpreting a CIED check before a surgical procedure are summarized in Table 2. The format of CIED checks varies between devices and manufacturers. The check will not provide comprehensive information about the patient's underlying cardiac condition but will provide some insight into clinical issues that may be relevant in the perioperative period.
Pacing percentages—sensing (S), pacing (P), and chamber (A and V) will be given for all four combinations, i.e. ASVS, ASVP, APVS, APVP. A high percentage of pacing will indicate a higher degree of pacemaker dependency
Pacing threshold—the report should confirm an adequate safety margin with the output on the lead (pacing amplitude) programmed to at least double the pacing threshold (in volts) to ensure capture
Lead impedance—resistance to current flow (measured in ohms) and trends. Abnormal lead impedance may suggest lead crush or fracture (excessively high impedance) or an insulation defect (excessively low impedance)
Sensed P/R amplitude (mV)—confirmation of appropriate sensing parameters
Battery life—presented as a graph, figure, or battery life in years
ICD features—therapy since last interrogation will be displayed in the form of ATP or shock therapy. Some devices will indicate the total number of therapies that the device has delivered
‘Current EGM (endocardial electrogram)’—will display the current signals from the atrial and ventricular channels allowing the underlying rate and rhythm to be seen. Some devices will indicate any episodes of AF
‘Alerts’—most devices will provide a summary box that highlights any clinical or device functionality issues
Although advances in technology have limited the repeated need to check the defibrillator function of ICDs, a patient may recently have been sedated for a defibrillator safety margin test. This test involves inducing VF under controlled conditions (providing there is no contraindication such as cavity thrombi) to ensure that the device senses, detects, and terminates the arrhythmia reliably and with adequate energy delivery.
Device re-programming considerations
Reprogramming of a CIED before surgery should be considered in the following circumstances:
Significant pacemaker dependency
If the patient is highly pacemaker-dependent, and the procedure involves potential EMI, a cardiac physiologist should be consulted as temporary reprogramming of the device to an asynchronous (non-sensing) mode (A00, V00, or D00 depending on the set configuration) may be required.
Advanced CIED functions
Any device with a rate response function using minute ventilation as the mechanism of regulating pacing should have this programmed off during surgery since mechanical ventilation may stimulate excessive pacing rates. Sleep/rest mode is another example of an advanced function whereby the programmed base rate is gradually reduced during a specified sleep phase. This should be deactivated if late surgery is planned.
The defibrillator function should be deactivated immediately before any surgery where EMI is deemed likely. If this is not possible, the application of a magnet should be considered.
A magnetically activated switch is incorporated into CIEDs to enable alteration of the pacing or defibrillator modes. Application of a magnet to a PPM varies according to the model and settings of the device. Usually, it delivers an asynchronous mode at a rate specific to the manufacturer; however, it may initiate a diagnostics function and then revert to its programmed mode of pacing. It is important to appreciate that an asynchronous mode may be suboptimal in a patient with an underlying native rhythm and rarely may induce malignant arrhythmias.5 The device should revert to programmed baseline settings upon removal of the magnet.7
It is possible to deactivate the defibrillator function of an ICD in an emergency by placing and securing (with surgical tape) a medical grade magnet on the device for the duration of surgery. This is the case with all commonly encountered ICDs, provided that this magnet function has not been disabled. Some manufacturers (including Medtronic and Boston Scientific) have incorporated audible tones emitted from the ICD to indicate when a magnet has been applied and defibrillator functions have been deactivated. Removal of the magnet at the end of surgery should promptly reactivate the defibrillator function.7
Implantable loop recorders
These devices do not deliver any treatment and they present no risk to the patient when EMI is encountered. Since noise created by diathermy may fill up the memory banks of the device and overwrite existing data, it is prudent to contact the cardiac physiology department to allow them an opportunity to download any relevant clinical data before planned surgery.
Anaesthesia should be tailored to the patient's cardiac state, existing comorbidities, and the intended surgical intervention. Hypoxia, hypercapnia, acidosis, and electrolyte abnormalities (especially of potassium and magnesium) should be avoided since they may precipitate arrhythmias and/or interfere with pacemaker capture. If re-programming of the device is required, this may be done by a cardiac physiologist in the anaesthetic room immediately before induction. If an asynchronous mode is deemed necessary, reliable capture at an appropriate rate with haemodynamic stability should be confirmed.
Management of intraoperative arrhythmias
There is a possibility of intraoperative arrhythmias, particularly in susceptible patients with ICDs when the defibrillator function has been temporarily disabled. Equipment should be immediately available for external defibrillation and/or temporary pacing. External defibrillator/pacing pads should be attached to patients with CIEDs before surgery, particularly when access to the chest wall might be difficult. Pads should be placed at least 10–15 cm away from the edge of the CIED to avoid the remote possibility of damage to the device or the theoretical risk of damage to the myocardium as a consequence of excess current flow. Arrhythmias should be treated conventionally following standard ALS procedures and using the usual recommended external defibrillation energy levels. Should external pacing become necessary, capture can usually be achieved at currents of ∼50–100 mA using external pads.
Patients should receive standard recommended monitoring; an appropriate ECG lead should be displayed that demonstrates any pacing spikes. The ECG should be monitored throughout surgery with particular attention paid to the effects of diathermy. Note that the monitored heart rate may be inaccurate due to double-counting of the pacing spike and the QRS complex. Monitoring must also include a plethysmographic pulse measurement and display. Invasive arterial pressure monitoring will provide additional beat-to-beat evidence of mechanical capture and may add valuable information in patients with cardiac failure. Where central venous access in the upper body is deemed necessary, sites should be chosen well away from the site of lead implantation. Caution should be taken to avoid passing guide wires into the heart precipitating arrhythmias or potentially (in recently implanted devices) lead dislodgement. Peripheral nerve stimulators are considered safe, providing that they are distant from the device and that the stimulus is not in a vector parallel to that of the pacemaker current.
Drug and fluid considerations
Succinylcholine should be used with caution since fasciculations may cause over-sensing and result in pacing inhibition;8 ICDs have robust sensing algorithms and inappropriate shock delivery is unlikely. Antibiotic prophylaxis should be carefully considered depending on the surgery. CIED infection, predominantly staphylococcal, is difficult to diagnose and treat with a mortality of up to 35%.9
Many patients with CIEDs will have impaired cardiac function and the potential for development of malignant arrhythmias. Monitoring and anaesthetic technique should reflect the need to ensure myocardial optimization in these patients. Whilst negative inotropic drugs should be avoided, positive inotropes may precipitate (catecholamine sensitive) tachyarrhythmias in susceptible patients.
Fluid balance is an important consideration since patients with a fixed ventricular rate will be unable to respond to hypovolaemia with an increase in heart rate; this may compromise end organ perfusion and oxygen delivery. Cardiac output monitoring is recommended for surgery with the potential for significant haemodynamic compromise.
Bipolar electrodes and engineered shielding protection have reduced the risk of EMI; however, sources of EMI around the patient should be avoided. If the device has been recently checked and the surgical site is remote, the likelihood of malfunction is minimal. Although mobile phones are generally considered safe, care should be taken to avoid direct placement of any phone onto the CIED since they remain a source of EMI and could potentially activate the ‘magnet mode’ of the device. Medical equipment which incorporates wireless technology, for example, some infusion pumps, monitoring devices, and ultrasound probes, should also be distanced from a CIED since these devices may provide a source of EMI. Diathermy should be avoided where possible; bipolar electrical diathermy is considered safer than monopolar. Should monopolar diathermy be required, it should be used in short 1–2 s bursts with 10 s pauses and (where possible) the use of the cutting rather than coagulation current. The pathway from the diathermy to the return electrode should not pass near the CIED and the current field should be at right angles to the pacing leads. Diathermy cables should be kept well away from the site of the implant.
The likely risk of EMI should be considered with reference to the site and type of procedure to be undertaken, and the diathermy required. Broadly speaking, over-sensing as a complication of EMI is unlikely for procedures where the application of diathermy and the return electrode are below the level of the umbilicus.5
Radiofrequency ablation involving the continuous application (several minutes) of radiofrequency energy via an emitting electrode to cause local heating and tissue coagulation is used in many kinds of surgery. The risk of prolonged current exposure leading to EMI with this technique means that it is especially important to disable the defibrillation function of ICDs. Direct contact between the ablation catheter and any CIED should be avoided and the radiofrequency current path should be as far away as possible from the CIED and lead.10
Tissue expanders in breast surgery
Tissue expanders that use magnets to orientate a needle to allow fluid filling to occur should be avoided. Their close proximity to a CIED may risk magnetic switch activation with conversion to asynchronous pacing, or failure of an ICD to detect a tachyarrhythmia.
The brief (1–2 s) electrical stimulus with electroconvulsive therapy (ECT) may cause pacemaker inhibition, although this is unlikely to be clinically significant. Subsequent seizure activity, however, may cause more prolonged over-sensing. Reprogramming to an asynchronous mode may be appropriate for selected patients before ECT, although this may also risk arrhythmias when intrinsic electrical activity exists. The defibrillator function of an ICD should be disabled since seizure activity may trigger an inappropriate shock either due to EMI or if there is a marked reactive sinus tachycardia that encroaches on the ICD tachycardia trigger rate. ECT often occurs in isolated sites which adds complexity to planning.
Transcutaneous electric nerve stimulation
Transcutaneous impulses may cause inappropriate sensing and subsequent inhibition of pacemaker function or inappropriate shock administration by an ICD; transcutaneous electric nerve stimulation is therefore considered contraindicated in patients with CIEDs.
Diagnostic imaging in general does not have a significant impact on CIED function. However, there are rare case reports of inappropriate sensing and electronic reset with the higher radiation doses utilized by new-generation multi-slice computerized tomography scanners. Magnetic resonance imaging (MRI) is usually contraindicated in patients with CIEDs. MRI-conditional PPMs and ICDs which can be used only in certain well-defined conditions are produced by some manufacturers. Stipulations include specific MRI systems, combined use of generator and leads designated MRI-compatible, the pacing system in place for longer than 6 weeks, and specific programming of the device outside the MRI safety zone.11 Programming will be set to an asynchronous or non-pacing mode by a cardiac physiologist depending on the device and the degree of dependency.12 Device design modifications include a reduction in ferromagnetic components, a sensor designed to resist the magnetic field, and robust well-insulated circuitry.
This is usually considered safe, although direct radiation of the CIED should be avoided and the device may need to be re-sited if it is located directly within the field of radiation.10 Device function should be verified frequently in the case of radiation-induced reversion to a backup safety mode (usually VVI, but manufacturer-specific).7
Extracorporeal shock wave lithotripsy
Shock waves are acoustic pressure waves created from electromagnetic, piezoelectric, electroconductive, or electrohydraulic sources. The wave form comprises a compressive and tensile phase which generates acoustic energy for stone disintegration (lithotripsy).13 Generally, the risk of CIED dysfunction is low but devices should be checked within 1 month of the procedure.7 There have been case reports of pacing suppression and backup safety mode reversion. The lithotripter should be kept at least 6 inches away from the CIED and the beam should not be focused near the CIED.10 Lithotripsy pulses should be timed with the ECG, and rate modulation should be deactivated.
Patients with CIEDs are ideally managed in a high dependency recovery environment with continuous monitoring and full resuscitation equipment immediately available. The defibrillator function of an ICD and any rate modulator pacing function which has been suspended needs reactivating by a cardiac physiologist after surgery. The device should be checked at the earliest opportunity if a magnet is used to deactivate a CIED intraoperatively. Any adverse incident relating to a CIED in the perioperative period should be addressed by a cardiac physiologist as soon as possible.
An increasing number of patients are presenting for surgery with varying forms of cardiac implantable electronic devices. It is important to consider the indications for insertion of the device, the degree of pacemaker dependency, the nature of the procedure being performed, and the likelihood of EMI. Careful preoperative and intraoperative preparation can help reduce complications and permit timely intervention if required.
National Institute for Health and Care Excellence. Implantable cardioverter defibrillators and cardiac resynchronisation therapy for arrhythmias and heart failure. NICE technology appraisal (TA314) 2014. Available from https://www.nice.org.uk/guidance/ta314 (accessed 25 November 2015)
. The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group. Pacing Clin Electrophysiol 2002; 25: 260–4
. 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: 1114–54
. Guidelines for the diagnosis, prevention and management of implantable cardiac electronic device infection. Report of a joint Working Party project on behalf of the British Society for Antimicrobial Chemotherapy (BSAC, host organization), British Heart Rhythm Society (BHRS), British Cardiovascular Society (BCS), British Heart Valve Society (BHVS) and British Society for Echocardiography (BSE). J Antimicrob Chemother 2015; 70: 325–59
American Society of Anesthesiologists. Practice advisory for the perioperative management of patients with cardiac implantable electronic devices: pacemakers and implantable cardioverter-defibrillators: an updated report by the American Society of Anesthesiologists Task Force on Perioperative Management of Patients with Cardiac Implantable Electronic Devices. Anesthesiology 2011; 114: 247–61