A pacemaker system consists of a small battery operated device (pulse generator) and either one or two leads. The device treats arrhythmias by sending low energy electrical impulses to prompt the heart to beat at a normal rate. Pacemakers are typically used to manage bradyarrhythmias but may also be recommended in other situations such as tachyarrhythmias, atrial fibrillation (AF) and long QT syndrome.

A pacemaker mimics the sinus node by pacing and sensing. Pacing occurs when electrical impulses are transmitted to the heart via the leads when there is an abnormal rhythm (see figure below). The sensing aspect monitors the heart’s natural electrical activity so that pacing is only delivered when required.

The underlying rhythm disturbance and origin of the dysrhythmia determines lead location and settings. Pacemakers may be single chamber (right atrial or ventricular lead) or dual chamber (right atrium and ventricle). Pacing the right atrium alone is rare and requires intact atrioventricular conduction. 

CRT delivers electrical impulses simultaneously to the left and right ventricles, hence the term biventricular pacing. This three lead system is used in those with HF who have poorly co-ordinated contraction of the left and right ventricles.

CRT aims to improve cardiac output by re-synchronising ventricular contraction. Leads are placed in the right atrium and right ventricle, and a third lead inserted through the coronary sinus to the posterior surface of the left ventricle.

Biventricular pacing may improve systolic function, reduce symptoms of breathlessness and fatigue, and decrease hospitalisation and mortality. [#saxon-la-bristow-mr-boehmer-j-et-al.-2006]

Figure 1: Pacemaker insertion

Two types of CRT devices are used:

• CRT-P (CRT with pacemaker function)
• CRT-D (CRT with pacemaker and ICD function)

Not all patients with HF are amenable to CRT.

Indications for this therapy include:

• NYHA III-IV symptoms despite optimal medical therapy
• Dilated HF with an ejection fraction <35%
• QRS duration ≥120ms
• Sinus rhythm (in some circumstances AF)
• Expectation of life >12 months

ICDs deliver an electric shock to restore a normal heart rhythm in the event of a life-threatening rhythm disturbance such as ventricular tachycardia or ventricular fibrillation. These devices may be inserted for the purpose of primary prevention in those at high risk of sudden cardiac death. For others who have survived potentially lethal arrhythmias or cardiac arrest, an ICD may be inserted for the purpose of secondary prevention.

Some ICDs also have a pacing function as part of the device. The right atrial lead and right ventricular lead are inserted in the same manner as a pacemaker and provide sensing, pacing and defibrillation function.

ICD indications for those at risk of sudden cardiac death include:

• NYHA II- III and LVEF ≤35%
• Survived cardiac arrest resulting from ventricular fibrillation or ventricular tachycardia not due to transient or reversible cause
• Spontaneous sustained ventricular tachycardia in association with structural CHD
• LVEF ≤30% measured at least 1 month after an acute MI, or 3 months after coronary artery revascularisation surgery

Defibrillators are programmed to meet individual needs. The type of electrical impulse delivered can range from mild (e.g., antitachycardia pacing) to extremely strong (defibrillation). See table below which summarises therapy provided by different implantable cardiac devices.

*CRT-D= Cardiac rescynchronization therapy with defibrillator function

Devices are usually implanted under conscious sedation as a hospital day case or overnight stay. Duration of the surgery varies depending on the technical complexity and the type of device and number of leads being implanted.

Electrode leads are inserted into the subclavian vein at the shoulder or the base of the neck and then guided to the appropriate heart chamber. The leads are then connected to the pulse generator which is fitted into the 'pocket' between the skin and pectoral muscle. (see figure 1)

Post-implantation care

All clinicians should monitor wounds during the post-implantation period and patients should seek medical advice if there is any concern of local infection.

In the immediate post-implantation period, advise patients to:

• Limit shoulder activity on the side of the device to below the level of the shoulder, to allow fixation of leads within the endocardium
• Avoid heavy lifting

Restrictions are usually for six weeks but may vary depending on the treating cardiologist.

Review of device function

Following implantation, regular device interrogations are undertaken to check settings and functions as well as providing a history of the device activity. Monitoring may be done remotely with device information transmitted via the internet. Batteries normally last between 6-10 years before requiring replacement.

New advances in device technology are continually being developed. Today’s devices are capable of complex and intuitive functions such as impedance measures to assess fluid status, remote storage and transmission, and many other functions.

Psychological adjustment

Ensure that patients are receiving adequate education and support before and after implantation. Living with an implantable device can be emotionally challenging and may provoke ongoing anxiety or depression. Patients may be concerned about receiving a shock, changes in body image, losing control, relationships, and uncertainty about the future.

Information the patient needs to carry with them

Ensure that patients have information from the device company including a card outlining device details and settings as well as what to do in the event of symptoms or shock. Encourage patients to carry this card at all times and check that they should know who to contact in the event of concerns.

Driving

Driving regulations associated with ICDs vary in different states in Australia as well as in other countries and clinicians should access local resources for more detailed information.

General guidelines are as follows:

• Following a cardiac arrest, driving is not normally allowed after the insertion of a device until the patient has experienced an event free period of six months
• Devices implanted for primary prevention or CRT may be eligible to drive after one month
• Patients with ICDs cannot usually hold a commercial driving licence

Exercise

Patients with a device are safe to exercise. The exercise specialist should be aware of the reason for the device (i.e., atrial versus ventricular arrhythmias, primary prevention, CRT) and device settings should be recorded. Exercise programmes should be modified to ensure upper limb activity is restricted on the side of implantation in the initial post implantation period. The number of weeks for this will be guided by the treating cardiologist. For ICDs, exercise should be prescribed at an intensity to keep the heart rate at least 10-15 beats/min below the threshold for the delivery of therapies. Contact sports should be avoided to prevent blunt trauma injury and damage to the device.

Sexual intimacy

Heart rate increases during sex may equate to that achieved during other forms of exercise. Devices should be programmed to prevent shock during sex. However, if the patient receives a shock, his or her partner may also feel a tingling sensation. Medical advice should be sought to enable the device to be reprogrammed.

Electromagnetic interference (EMI)

Most devices used on a daily basis will not affect modern implantable devices. As a general rule, appliances or machinery that emits strong EMI should be kept 30-60 cm away from the implantable device.

Recommendations relating to the use of common appliances and situations are summarised below:

• Mobile phone should be held to the ear on the opposite side to the device and should not be carried in a pocket within 15cm of the device.
• Antitheft devices: Individuals with an implantable device can pass through doorways with antitheft devices (e.g., in libraries and department stores) at a normal pace but should not linger in the area.
• Airport security archways will not harm devices but the metal in the device will set off the security alarms. Individuals with a device should notify airport staff and show their Medical Device ID card. The wand used by the security staff may temporarily affect the device if held over it for a period over 30 seconds. Individuals should ask security staff to perform the search quickly or conduct a hand search.
• Medical and dental procedures require cardiologist approval for example:
  • Magnetic resonance imaging (MRI) is not usually performed in patients with implantable devices except when the device is MRI conditional, meaning that patients can safely undergo an unmonitored scan following a programming change to the device.
  • Diathermy, electrocautery and radiation treatment require consultation with the treating cardiologist as devices may be required to be turned off or may require protection during the procedure.
  • Transcutaneous electrical nerve stimulation (TENS) may affect the device and so should be used only in consultation with the treating cardiologist.

Appliances considered safe to use or be near with an implantable device, under normal circumstances:

• Electric blankets
• Electric razors
• Electric can openers
• CD/DVD players
• Blenders
• Hair dryers
• Heating pads
• Microwave ovens
• Stoves
• Pagers
• Personal computers
• Fax machines
• Remote controls
• TV or radio towers

Appliances to be kept 30-60cm from the implantable device

• Arc welders
• Magnetic wands
• Chain saws
• Lawn mowers
• Leaf blowers
• Stereo speakers
• CB radio antennas
• Slot/poker machines
• Drills (corded or cordless)

Appliances/ actions to avoid

• Bathroom scales that record body fat
• Operating a jack hammer
• Leaning over running motors and alternators such as the engine of a running car
• Using stun/laser guns

Patients should develop, with their doctor or nurse, a plan regarding action to take in the event of receiving an ICD shock. A friend or family member should know who to phone and when to seek medical attention. This information is usually provided by the electrophysiology staff in the cardiology department where the device is implanted. The plan may include contacting the relevant cardiology department for device interrogation. Further information is available from How to Respond to an Implantable Cardioverter-Defibrillator Shock.

For patients approaching end of life, disabling the defibrillating function of the ICD should be considered to avoid the trauma of fruitless repeated shocks. The discussion regarding defibrillation deactivation should include the patient, family and relevant members of the treating team.

Disabling the defibrillator is undertaken by a technician from the device company using regular monitoring equipment. If a defibrillator has not been disabled and repeatedly shocks, a magnet designed for this purpose is placed over the generator to disable the defibrillator. Defibrillator deactivation does not alter the pacing function which should continue for symptomatic relief.