The heart has its own 'pacemaker' to control the rate of the heartbeat and ensure effective and coordinated pumping. This pacemaker is called the sinus node and is at the top of the right atrium. The normal heart rate is about 70 beats a minute at rest, and is influenced by exercise and emotion.

The sinus node sends electrical signals directly to the atria, telling them to pump first. It then sends electrical signals to the ventricles through other nerve connections.

Who needs an artificial pacemaker?

An artificial heart pacemaker may be needed:

• if the sinus node or atria are damaged (sick sinus syndrome); or
• if electrical signals don't get through to the ventricles (heart block).

Patients with sick sinus syndrome may have both slow and fast heart rhythms, feel tired and short of breath, and occasionally faint. Heart block can be more serious, causing people to faint.

Artificial pacemakers are very successful in controlling sick sinus syndrome and heart block. Patients of any age can receive artificial pacemakers.

What is an artificial pacemaker?

The artificial pacemaker is an electrical system used to stimulate the heart. It has a pulse generator and a lead. The pulse generator is a tiny computer powered by a special battery, which is very reliable and lasts many years.

The lead connects the pulse generator to the heart and is made of a metal coil conductor covered by soft plastic insulating material. It is usually put into a vein below the collarbone and passes to the heart, where it may be attached to an atrium or ventricle by soft plastic hooks or a small metal corkscrew.

The heart-end of the lead has small electrodes made of metal. These are connected to the conductor and keep the heart beat regular by electrical stimulation. Sometimes the lead is attached to the outside of the heart.

Artificial pacemakers are strong enough to deal with normal daily activities, including most non-contact sports.

How does a pacemaker work? When the heart rate is slow, the pacemaker delivers up to five volts of electricity into the atrium or ventricle, which then contracts. The lead, together with the pulse generator, can also be used to 'sense' the heart's natural rhythm, and then inhibit the pacemaker to allow the heart's natural pacemaker to work. Patients cannot 'feel' this amount of electricity.

Pacemakers come in two types, single and dual chamber.

Single chamber systems 'pace' only one heart chamber, usually the ventricle. Dual systems need two pacing leads and are more sophisticated. They use information from the atria to set the ventricles' pumping rate. These systems are ideal for heart block, as they work in the same way as the normal heart.

Sick sinus syndrome often results in the heart rate not increasing with exercise. Special pacemakers can 'sense' vibrations or measure the way the patient breathes, enabling the pacemaker to work out the level of exercise being done and change the pace rate accordingly. Both single and dual chamber pacemakers have these special sensors, but not all patients are suited to dual chamber systems.

Pacemaker follow-up

After patients receive a pacemaker they attend a clinic or visit a doctor regularly for tests. Modern pacemakers can be fine-tuned painlessly from outside the body using a radio-wave programmer.

Pacemakers are checked every six months on average. When batteries begin to run down, the generator can be replaced easily under local anaesthetic.

People with pacemakers can do most normal activities, such as drive a car, bathe, swim, have sex or play non-contact sports. Pacemakers are protected from electrical interference, although patients should discuss any concerns with their doctor. There are no problems with microwave ovens, televisions and most electrical tools. Metal pulse generators will trigger airport security machines, but these machines will not damage the pacemaker. Most medicines will not affect the way pacemakers work.

Implantable Cardioverter Defibrillator (AICD)

Ventricular Tachycardia and Ventricular Fibrillation are abnormal, life threatening heart rhythms requiring immediate treatment. Management of these rhythm disturbances includes tablets, catheter ablation, heart surgery and/or an Implantable Cardioverter Defibrillator (ICD).

What is an ICD?

ICD is a sophisticated device, somewhat like a pacemaker but larger in size and with many more functions. This device has the following functions:

• identify a life threatening heart rhythm (ventricular tachycardia or ventricular fibrillation);
• it can pace the heart to a program rate to try and return the heart rate to normal;
• it can internally deliver an electrical shock to return the heart rhythm to normal;
• it supports the heart rhythm (like a pacemaker) if the heart rhythm is very slow.

Who is suitable?

People are thought to be suitable for an ICD if they have had:

• a life threatening heart rhythm that may happen again;
• successful out of hospital resuscitation
• evidence of life threatening rhythms through different tests - eg. a test that checks for abnormal rhythms in the heart (electrophysiology study);
• unsuccessful treatment, eg. tablets, surgery or by heat to desensitise the area in the heart (ablation).

The cardiologist will talk to the patient about the benefits of having this operation done. Currently over 250 ICD per year are being implanted in Australia.

What happens during the procedure?

The operation is done in the Cardiology Laboratory or an Operating Theatre. The patient is generally anaesthetised (put to sleep) or heavily sedated and does not suffer any discomfort during the procedure.

During the operation the cardiologist will test the settings so they meet that particular patient's needs. Antibiotics to stop infection are given before the operation. Leads or fine electrodes, capable of both pacing and delivering shock, are threaded into the right chamber of the heart. The ICD device is positioned in the chest wall under the collarbone or occasionally in the abdominal wall. Currently devices can be expected to last for up to 5 years or more.

After the ICD has been implanted the patient will spend a brief period of time in an area that has heart-monitoring facilities, ie. Coronary Care or Intensive Care Unit.

A test called an electrophysiology study may be conducted before going home. Information about wound care, follow up appointments and driving will be provided either by the cardiologist or by the cardiology registered nurse. How long a patient stays in hospital depends on the opinion of the cardiologist, but the stay generally is now between 2-4 days.

What kind of follow up is expected?

Regular checks are important to make sure the ICD is working correctly. Ongoing appointments to the cardiologist include checks to the ICD that usually take about an hour. Appointments are usually every 6 months, but may be more often depending on your condition.

What happens when the ICD delivers a shock?

Patients react differently but most say:

• its like a kick in the chest;
• some report brief chest discomfort which lasts a few seconds.

What will my quality of life be?

To have an ICD put in can be stressful, as can the illness that came before it. The cardiologist and staff at the hospital are there to help patients and families deal with all their concerns. Talking to medical carers and having an understanding about the ICD and how it works will ease many concerns.

As the general health of each patient is very different a set of questions listed below will guide you in asking your cardiologist all about adjusting to life with an ICD:

• Can I drive?
• What happens if the device does not work?
• Can I return to work?
• Can I trigger the device to shock inappropriately when I am exerting myself?
• Can I trigger the device to shock inappropriately if I get upset?
• My partner is scared and will not let me do anything?
• Are there any support groups?
• What sports can I play?
• Is the device sensitive to electric devices and magnets?
• Can I go overseas/interstate for a holiday?
• Who do I call if I think something is wrong?

Your cardiologist, nursing and paramedical staff involved in ICD implantation and follow up, are available to answer your queries and deal with any problems after discharge from the hospital.

This paper was prepared by Dr Harry Mond, Royal Melbourne Hospital, Dr Juti Vohra, Royal Melbourne Hospital, and Dr David Richards, Westmead Hospital, New South Wales.