Abstract
As the indications for these devices has widened, the prevalence of permanent pacemakers (PPMs) and ICDs has increased. The complexity of these devices makes them susceptible to perioperative interference and inadvertent reprogramming, placing patients at greater risk of perioperative morbidity. Management guidelines are largely based on case series and expert consensus rather than prospective, randomized studies.
Rhythm Management Devices
As the indications for these devices has widened, the prevalence of permanent pacemakers (PPMs) and ICDs has increased. The complexity of these devices makes them susceptible to perioperative interference and inadvertent reprogramming, placing patients at greater risk of perioperative morbidity. Management guidelines are largely based on case series and expert consensus rather than prospective, randomized studies.
Permanent Pacemakers
Over 1,000,000 PPMs are implanted every year worldwide. PPM systems comprise a generator (electrical circuits and a battery) and one or more leads, designed to sense cardiac electrical activity and deliver a stimulus. In unipolar lead systems the generator serves as an electrode for completing the electrical circuit. Unipolar pacing systems, which produce noticeable pacing spikes on the standard ECG, are more susceptible to interference (e.g. skeletal muscle contraction) than bipolar systems. The indications for PPMs are summarized in Box 18.1. Indications for pacing in children, adolescents and patients with congenital heart disease (CHD; not shown) are broadly similar.
- Acquired atrioventricular (A-V) block (in adults)
Third-degree A-V block with symptomatic bradycardia or documented asystole, neuromuscular disorders, following A-V node ablation
- Chronic bifascicular and trifascicular block
Intermittent second-degree (Mobitz type II) A-V block, intermittent third-degree A-V block
- A-V block following acute MI
Persistent second-degree A-V block; transient third-degree A-V block; need not be symptomatic
- Sinus node dysfunction
Documented symptomatic bradycardia; frequent sinus pauses
- Prevention of tachycardia
Sustained, pause-dependent VT in which efficacy of pacing has been documented
- Carotid sinus hypersensitivity
Recurrent syncope due to carotid sinus stimulation
- Heart failure
Cardiac resynchronization therapy – symptomatic heart failure (NYHA class >2) with impaired ventricular function with widened QRS complex.
- Specific conditions
Hypertrophic cardiomyopathy; idiopathic dilated cardiomyopathy; cardiac transplantation – persistent bradycardia
Device classification provides a concise and consistent means of describing device function. The generic PPM code is shown in Table 18.1.
Table 18.1 The NASPE/BPEG five-position generic pacemaker code
| Position | I | II | III | IV | V |
|---|---|---|---|---|---|
| Category | Chamber(s) paced | Chamber(s) sensed | Response to sensing | Rate modulation | Antitachycardia functions |
| Code letters | O A V D | O A V D | O T I D | O R | O P S D |
NASPE, North American Society of Pacing and Electrophysiology; BPEG, British Pacing and Electrophysiology Group. O = None, A = atrium, V = ventricle, D = dual (A+V), T = triggered, I = inhibited, R = rate modulation, P = antitachycardia, S = shock
VVI systems, which have largely superseded VOO systems, are appropriate for chronic AF with slow ventricular rate. Dual-chamber devices (DDD), which are capable of sensing and pacing both the atrium and the ventricle, are more haemodynamically efficient than ventricle pacing alone. Rate-adaptive (DDDR) devices, which allow the HR to increase during exercise, are more physiological. Some PPMs have the ability to switch mode. Switching from DDD to VVIR or DDIR mode may be useful in patients with paroxysmal AF.
Temporary Pacing
In patients with symptomatic bradycardia that is unresponsive to chronotropes (e.g. isoproterenol), emergency transvenous (internal jugular or femoral) VVI or VVO pacing can be used as a bridge to recovery or definitive treatment. A balloon-tipped floatation catheter is inserted through a haemostatic sheath and advanced into the RV, ‘blind’ or under fluoroscopic guidance.
In the setting of cardiac surgery, wires attached to the epicardial surfaces of the RA and RV are used for temporary pacing. Fixed-rate pacing (VOO, AOO, DOO) should be converted to demand mode (VVI, AAI, DDD) at the end of surgery. The anaesthetist must be familiar with both single- and dual-chamber pacing systems. Dealing with common pacing problems requires bedside monitoring of the ECG together with the CVP and arterial waveforms.
Implantable Defibrillators
ICDs have the ability to detect abnormal cardiac rhythms and deliver either antitachycardia pacing or a DC shock. The devices are used for the primary and secondary prevention of ‘sudden cardiac death’. The indications for ICD therapy are shown in Box 18.2.
Box 18.2 Indications for ICD therapy
Primary prevention of sudden cardiac death
Coronary artery disease
Non-ischaemic dilated cardiomyopathy
Long-QT syndrome
Hypertrophic cardiomyopathy
Arrhythmogenic RV dysplasia/cardiomyopathy
Non-compaction of the LV
Primary electrical disease (idiopathic VF, short-QT and Brugada syndromes and catecholaminergic polymorphic VT)
Idiopathic VT
Advanced heart failure and cardiac transplantation
Secondary prevention of sudden cardiac death
Sustained VT
Coronary artery disease
Non-ischaemic dilated cardiomyopathy
Hypertrophic cardiomyopathy
Arrhythmogenic RV cardiomyopathy
Genetic arrhythmia syndromes
Syncope with inducible sustained VT
Device Implantation
Most PPM and ICD implants are performed in the cardiac catheter laboratory, on a day-case basis under local anaesthesia with conscious sedation. The subclavian, cephalic or axillary veins are commonly used for lead insertion. The device is usually sited in the pre-pectoral region or in the sub-pectoral space.
In 2016, the FDA approved the first ‘leadless’ PPM (MicraTM, Medtronic – VVIR) for clinical use. This small cylindrical device (6.7 × 25.9 mm, 1.75 g) is delivered percutaneously under local anaesthesia and attached to the RV apex by Nitinol tines. Concerns about lost telemetry and poor battery life have prompted the manufacturer of a similar device (NanoStimTM, St Jude) to halt implantation.
ICD implantation is typically more complex because of the nature of the devices (larger devices and thicker leads) and the types of patients encountered. Device testing requires the deliberate induction of VF and measurement of the minimally effective defibrillation threshold (DFT). Newer, entirely subcutaneous systems (e.g. EMBLEM S-ICD, Boston Scientific) require a large axillary incision to accommodate the generator. Patients undergoing S-ICD implantation tend to be young and typically opt for general anaesthesia (Figure 18.1). The complications of device implantation are shown in Box 18.3.
Figure 18.1 The subcutaneous ICD system (Boston Scientific).
