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Cardiothoracic Services

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Pacemaker and ICD Clinic

An Implantable Cardioverter Defibrillator (ICD) is a small device which can treat people with dangerously abnormal heart rhythms.

It sends electrical pulses to regulate abnormal heart rhythms, specifically those that can be dangerous and cause a cardiac arrest.

Patients are referred for an ICD or a Cardiac Resynchronisation Therapy Defibrillator or Pacemaker (CRTD/P) after a consultation with their medical team.

Patients may also see a Complex Device Nurse Specialist before the procedure, who will be able to answer any questions.

Please visit the links below for information about the procedure.


After a patient has had a device implanted, we offer follow-up appointments with a Cardiac Physiologist or Complex Device Nurse Specialist.

We check the device is working well and that the wound is well-healed, assess ongoing symptoms and medication and perform tests.The patient may also see a Consultant Cardiologist if necessary.

Types of devices

Implantable Loop Recorder (ILR)

ILRs are miniaturised ECG recorders implanted underneath the skin which do not have leads connected to the heart.

These devices record the heart rhythm continuously and can detect intermittent arrhythmias that cannot be diagnosed by ECG or Holter monitors.

Patients with occasional palpitations, dizzy spells or loss of consciousness may benefit from an ILR.

The device can be monitored remotely, allowing us to see any changes that have occurred in the heart rhythm or battery status.

Patients can also use an 'activator' to allow us to see their heart rhythm when they have symptoms.

Permanent Pacemaker (PPM)

A pacemaker is a small electrical device comprising a generator (battery) implanted under the skin in the chest, with one or two leads passed via a vein into the heart to sense and pace the atrium or ventricle.

'Leadless' pacemakers comprise a tiny generator directly attached to the ventricle to stimulate it.

Pacemakers treat abnormal heart rhythms that can cause the heart either to beat too slowly or miss beats.

They can improve symptoms such as dizziness and shortness of breath and improve life expectancy in patients with conduction block.

Implantable Cardioverter Defibrillator (ICD)

ICDs can detect and treat life-threatening fast heart rhythms such as ventricular tachycardia or ventricular fibrillation.

These devices can terminate a dangerous ventricular arrhythmia by rapid pacing (antitachycardia pacing) or by delivering an electrical shock to restore normality (cardioversion or defibrillation).

Most can also provide a pacemaker function to treat slow heart rhythms.

There are two main types of ICDs:

  • transvenous ICDs comprise a generator in the chest and lead or leads that are implanted in a similar way to pacemakers
  • subcutaneous ICDs have a generator that is implanted under the skin in the side of the chest, with a lead buried under the skin in the middle of the chest.

ICDs can improve life expectancy in patients who have already suffered a dangerous heart rhythm (secondary prevention) and in those who are at risk of a dangerous arrhythmia but have not yet experienced it (primary prevention).

Cardiac Resynchronisation Therapy (CRT)

A CRT device can improve the coordination of the heart's contractions making it beat more efficiently.

It comprises a pulse generator connected to leads threaded along veins to the heart, and paces the main pumping chambers of the heart from both sides, stimulating both ventricles at the same time.

This can improve heart function and reduce the symptoms of heart failure.

Remote monitoring

Devices can monitor their own function (battery status, lead integrity) as well as record arrhythmias etc.

Some devices can be monitored remotely by the CRM Department without the active participation of the patient.

We can see information and alerts but cannot make any changes to device remotely.

Examples of automatic alerts are:

  • abnormal rhythms (fast or slow heart rate, atrial fibrillation)
  • battery depletion
  • malfunctions of the device or leads.

When a patient has a device with this option, we provide full instructions for how to send transmissions.

Symptomatic patients may also be able to use an 'activator' to record information from their device for download on to the hospital's computer. They should use the activator whenever they have symptoms, so that we can see what is happening to their heart rhythm when they feel unwell.

They should also call the department to tell us what symptoms led them to use the activator.

We expect patients we are monitoring to share important information with us (e.g. up-to-date contact numbers and travel plans), and tell us about any clinical events, symptoms, hospitalisation or changes in medication.

Ongoing support

Complex Device Specialist Nurses

Our Specialist Nurses provide support, education and technical help to patients before and after the implantation of an ICD and/or CRT. Patients can contact them with any questions or concerns.

We encourage shared decision-making with patients and their families, ensuring they fully understand the procedure and how an implantable device will affect their lives.


Find us and contact us

Cardiac Rhythm Management


Appointments / general enquiries: 01865 220981

Complex Device Specialist Nurses

Tel: 01865 221667

Clinic locations and opening hours

Please see Cardiac Physiology - Find us and contact us

John Radcliffe Hospital 8.00am - 5.00pm

Horton General Hospital 8.30am - 5.00pm

Last reviewed:24 November 2023