Pacemakers and cardiac devices

Cardiac implantable electronic devices (CIEDs) are increasingly common with an estimated 1.5 million devices implanted each year. Since the first pacemaker was implanted by Ake Senning in 1958 for treatment of complete heart block, CIEDs have evolved beyond treatment of bradycardias to include resynchronisation therapies for heart failure, defibrillators to prevent sudden arrhythmic death, and monitoring devices for various arrhythmias.

The past decade has seen significant evolution in device design, implantation techniques, and pacing-algorithms in order to achieve more physiological pacing and avoid long-term complications.

General physicians and non-cardiology specialists are highly likely to encounter pacemakers and other CIEDs. As the prevalence and variety of devices increases, an appreciation of CIED behaviours and limitations will be valuable, particularly in older patient cohorts. In this review, we will overview current standards of care for device implantation in addition to highlighting key areas of discovery and changing practice over the past decade.

Indications

The simplest indications for long-term pacing are symptomatic bradycardia or high-degree atrioventricular block (even in the absence of symptoms). (Table 1)

 

Table 1. CIEDs and common indications for use

Device type	Lead positions	Pacemaker code	Key clinical indications
Single-chamber pacemaker	One lead in RV	VVI	Symptomatic bradycardia (high degree AV block, sinus node dysfunction) Prolonged asymptomatic pauses or high degree AV block Tachycardia-bradycardia syndrome Reflex asystolic syncope Cardiac syncope in presence of bundle branch block with other features suggestive of conduction failure
Dual-chamber pacemaker	Two leads, in RA and RV	DDD
Implantable cardioverter defibrillator (ICD)	One lead in RV	VVI	Secondary prevention of VF or haemodynamically unstable VT Primary prevention in patients at high risk of VF/VT arrest (eg. LVEF
	Two leads, in RA and RV	DDD
Biventricular pacemaker (CRT-P)	Two leads, in RV and LV	VVI	Drug-refractory symptomatic heart failure with LVEF 120ms Patients with reduced EF with other indication for pacemaker and likely to have high pacing burden
	Three leads, in RA, RV and LV	DDD
Biventricular ICD (CRT-D)	Two leads, in RV and LV	VVI	Indication for CRTP and ICD
	Three leads, in RA, RV and LV	DDD
Subcutaneous ICD	Single subcutaneous ICD lead	No permanent pacing capabilities	Indication for ICD in patients with no requirement for pacing or antitachycardia therapies (particularly young patients and those at risk of transvenous system infections)
His-bundle pacing and left bundle branch pacing	One lead, His-bundle, para-Hisian region or left bundle branch	VVI	Indication for pacing with anticipated high burden of ventricular pacing and potential pacemaker induced-cardiomyopathy
	Two leads, in RA and His-bundle, para-Hisian region or left bundle branch	DDD
Leadless pacemaker	One lead, in RV	VVI	Indication for single chamber pacing and access issues   precluding standard transvenous device
Implantable loop recorder	Subcutaneous device	No pacing capabilities	Long-term monitoring for syncope of unknown cause or possible   atrial fibrillation causing cryptogenic stroke

 

Abbreviations: AV = atrioventricular, RA = right atria, RV = right ventricle, VF = ventricular fibrillation, VT = ventricular tachycardia, LVEF = left ventricular ejection fraction, DDD = dual pacing, dual sensing, dual response, VVI = ventricular pacing, ventricular sensing, inhibition, CRT = cardiac resynchronisation therapy

 

Cardiac resynchronisation therapy (CRT) involves implanting an extra lead that paces the left ventricle and is a proven treatment in patients with heart failure who have interventricular dyssynchrony as demonstrated by a broad QRS complex on electrocardiogram (usually a left bundle branch block (LBBB)).

Patients who develop dyssynchrony due to a high burden of right ventricular pacing are at risk of heart failure and pacemaker induced cardiomyopathy (PICM) (up to 20% of individuals who receive over 40% right ventricular pacing) and may also benefit from CRT.

Finally, implantable cardioverter-defibrillator devices (ICDs) improve survival in patients with a history of cardiac arrest secondary to a ventricular tachycardia/fibrillation.^1-2 Primary prevention ICDs, which represent the majority of new implants, are inserted in those at high risk of ventricular arrhythmias, including those with heart failure and reduced ejection fraction (

 

Figure 1. Single chamber implantable cardioverter defibrillator

Implantation techniques

The basic procedural technique for implantation of CIEDs has remained largely unchanged over the past two decades. A small incision is made under conscious sedation and local anaesthesia and a pocket fashioned in the left or right pectoral region usually above the pectoralis muscle group but sometimes beneath.

Transvenous access to the right heart is obtained percutaneously via the axillary or subclavian veins using anatomical landmarks and fluoroscopic guidance or through direct ‘cut-down’ to the cephalic vein. Pacing leads are fixed to the right-ventricular apex or septum, and right atrium (usually in the appendage).

Fixing of the leads is achieved either actively using an extendable helical screw at the lead tip or passively by ‘hooking’ tines into cardiac trabecula. Sensing and threshold parameters for each lead are tested and subsequently secured to the pectoralis muscle prior to attachment of the device generator which is placed within the created pocket, with subsequent closure of the wound in layers.

Pre-procedural intravenous antibiotic prophylaxis with an anti-staphylococcal agent (such as flucloxacillin or vancomycin) with good surgical practice reduces rates of infection.³ Post-procedural antibiotics have not been shown to reduce infection rates. Recent trials have demonstrated the safety and efficacy of an absorbable, antibiotic-eluting device envelope in reducing CIED infections.⁴ This envelope is recommended in high risk patients, which include those with end-stage renal failure, those undergoing generator replacement or having additional leads inserted.

Post-procedure, a chest radiograph is performed to confirm satisfactory lead position and exclude pneumothorax.

 

Figure 2. Single chamber pacemaker

Patients are generally discharged home the following morning, although many centres now practise same-day discharge for uncomplicated pacemaker implantations⁵. Patients are advised on movement restrictions of the affected arm to limit potential lead dislodgement and wound dehiscence for first few weeks post-implantation.

Most studies report complication rates of around 3-10%,⁶ which includes risk of infection (pocket or lead-related), pneumothorax requiring drainage, cardiac perforation, haematoma that may require re-intervention, and lead dislodgement or failure requiring revision. Mortality rates remain low at 0.1-1.3%.⁶

Patient- and procedure-related risk factors can have significant effect on complication rates including low body-mass index, use of anticoagulants, more complex devices and low-volume centres.⁷ Increased age has not consistently been demonstrated to be an independent risk factor.

Peri-procedural anticoagulation

Avoidance of post-procedural haematoma is an essential consideration at time of implantation, particularly to reduce rates of re-intervention and device infection. Although several procedural strategies are used to prevent haematomas, careful planning of peri-procedural anticoagulation is a key modifiable risk factor. Patients presenting for pacemaker implantation are frequently on anticoagulation and antiplatelet agents, for indications including post-myocardial infarction, mechanical valve and atrial fibrillation with high thromboembolic risk.

Antiplatelet agents have conventionally been continued peri-procedurally without significant differences in bleeding risk. There are recent randomised controlled trials showing that it is safe to continue Vitamin-K antagonists or direct oral anticoagulants (DOACs) when there is high risk of thromboembolic events, whereas stopping oral agents and bridging with heparins is rarely appropriate.^8-9

Follow-up

The patient is initially reviewed 4-6 weeks post implant and thereafter every 6-12 months (some of these reviews may be performed remotely with patient device data sent electronically to a secure platform). Pacing clinics are often supported by specialist cardiac technicians. At each visit, device function is tested, pacing algorithms are optimised, symptoms are monitored, and the patient is surveyed for complications. Sometimes, episodes of asymptomatic atrial high rate episodes are identified in pacing checks. These often prompt cardiologist involvement to ascertain if these events are atrial fibrillation and whether the patient requires further management, in particular initiation of anticoagulation to reduce risk of thrombo-embolic stroke.

Remote monitoring is offered by some centres but is currently not the standard of care. Using wireless and automated technology, device diagnostics can be transmitted to treating teams on a day-to-day basis as a complement to routine in-office care. This model of care has been demonstrated to reduce costs, healthcare utilisation, time to clinical decision making and inappropriate shocks from ICDs¹⁰. Multiple professional society guidelines now recommend that remote monitoring is offered to all patients and the utilisation of generated data to assist patient care is likely to expand in the near future.

MRI compatibility

Most new CIED implants are performed with MRI-conditional leads and generators, and are certified for use with standard lower-tesla magnetic resonance scanners. For older devices, each implanted lead and current generator needs to be checked for MRI certification individually. A recent study in which MRIs were performed in patients with CIEDs that were classified as not MRI-conditional reported no long-term clinically significant adverse events, although it was necessary to re-programme the devices peri-procedurally.¹¹

Advances in bradycardia pacing

Current generation devices can last over 10 years without requiring a generator replacement. A large body of evidence now supports programming the pacemaker to minimise right ventricular pacing to reduce the risk of development of atrial fibrillation and PICM.¹²

Once established, PICM can be effectively treated by upgrading the device with a left ventricular lead and cardiac resynchronisation therapy. There is growing interest in conduction system pacing (His bundle or left bundle branch) to promote physiological pacing. Evidence-based indications for conduction system pacing are evolving but it may be used in patients who are at risk of developing PICM¹³ or in those in whom it is difficult to achieve a good left ventricular lead position.

Leadless pacing

The pacing lead is prone to problems including lead failure secondary to insulation or conductor break, infection and venous thrombosis, and is considered the weakest link in the system. There are now leadless pacemakers, which are 26mm fully-contained generator and electrode systems, that can be deployed entirely in the right ventricle via the femoral vein.

 

Figure 3. Leadless pacemaker

Recent studies have demonstrated procedural safety with similar complication rates and procedure times to conventional devices¹⁴ while maintaining comparable generator longevity and programming possibilities. These devices are a useful alternative to single-chamber pacemakers in patients with venous access issues or previous pocket and lead complications.

Advances in implantable cardiac defibrillators

The scope of primary prevention defibrillators in treatment of cardiomyopathy with severely reduced ejection fraction was defined in the early 2000s.^1-2 A recent trial suggests that, while there is a reduction in sudden cardiac death, there is probably no overall survival benefit from implanting ICDs in many patients with non-ischaemic dilated cardiomyopathies.¹⁵

The presence of myocardial scar, characterised on cardiac magnetic resonance imaging (CMR) is a strong predictor of clinical response to ICD¹⁶. The role of using CMR to identify patients with non-ischaemic dilated cardiomyopathy who might benefit from an ICD is yet to be fully elucidated.

Programming ICDs with longer detection intervals before delivering any therapies (anti-tachycardia pacing or shocks), and also using a higher heart rate as a trigger, have resulted in fewer appropriate and inappropriate therapies which has translated into improved survival.¹⁷

Subcutaneous defibrillators

Entirely subcutaneous implantable cardioverter defibrillators (S-ICD) are emerging as an alternative to conventional transvenous ICDs for prevention of sudden cardiac death. S-ICD devices use a subcutaneous shock coil over the sternum with generator in the left lateral chest to remove the need for transvenous electrodes and the associated long-term complications such as lead-related endocarditis or subclavian lead crush. Initial studies have shown promising results as an alternative device for younger patients who do not require transvenous pacing, those with difficult venous or cardiac anatomy and those at high risk of infection.¹⁸ A large randomised controlled trial comparing S-ICD and standard ICD is currently in progress.

Advances in cardiac resynchronisation therapy

Treatment of drug-refractory heart failure with severely reduced ejection fraction through use of a biventricular pacemaker (also known as CRT), has developed into a mature treatment option with strong evidence to improve symptoms and left ventricular systolic function, reduce heart failure hospitalisations and overall mortality. The greatest benefit of CRT has been demonstrated in patients with sinus rhythm and left bundle branch block (LBBB) on ECG with QRS duration >150ms.¹⁸ There is weaker evidence of benefit for CRT in patients with permanent atrial fibrillation (usually requiring a staged atrio-ventricular node ablation) and non-LBBB morphology. CRT is also offered to patients at risk of PICM.

Following implantation, historically up to one third of patients failed to have significant clinical or echocardiographic improvement and are referred to as ‘CRT non-responders’. These patients may benefit from optimisation of the device settings and heart failure medications in specialist clinics.¹⁹

Successful delivery of left ventricular leads in ideal (posterior-lateral and non-apical) locations is possible in greater than 80% of cases through increased experience, wider availability of fit-for-purpose delivery systems and the introduction of quadripolar leads. Quadripolar leads, which have four unique pacing electrodes at their tip, allow a greater number of pacing vectors in order to improve synchronisation and reducing issues with high lead thresholds or phrenic nerve stimulation (which can cause uncomfortable twitching of the diaphragm).

In those patients in whom standard CRT cannot be effectively delivered, other potential options include His bundle and left bundle branch pacing, leadless left ventricular endocardial pacing, and surgical epicardial lead implantation.

Implantable loop recorders

Implantable loop recorders (ILR) are capable of providing continues cardiac monitoring for prolonged periods to investigate unexplained syncope and clinically-important arrhythmias such as atrial fibrillation post-stroke. Device size has reduced significantly and modern ILRs are the size of a small USB key. With decreased size, devices have also become simpler to implant and can now routinely be performed in outpatient settings such as clinic rooms, without need for sedation or significant observation period.

 

Figure 4. Implantable loop recorder

The future

Pacing now represents a mature technology with established, evidence-based techniques. Future advancements in traditional CIED indications will likely involve further incremental improvements to current device design, improved programming and better selection of the correct device for the correct patient. Conduction system pacing and leadless systems will continue to be refined in the next decade and may become more common implanting techniques, while remote monitoring will allow for a more convenient and dynamic approach to follow-up.

 

For more cardiology articles go to our cardiovascular section.

 

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Dr Dharshan Palasubramaniam (Cardiologist, Alfred Hospital, Melbourne, Australia)

Associate Professor Justin Mariani (Cardiologist and Head of Pacing, Alfred Hospital, Melbourne, Australia)

Dr Hitesh Patel (Cardiologist, Alfred Hospital, Melbourne, Australia)

[email protected]

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