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Cardiac Inherited Diseases Service
Public Service, Cardiology, Paediatrics
Cardiac Arrhythmias
The heart rate is controlled by a complex electrical system within the heart muscle which drives it to go faster when you exert yourself and slower when you rest. A number of conditions can affect the heart rate or rhythm. Heart rate simply refers to how fast the heart is beating. Heart rhythm refers to the electrical source that is driving the heart rate and whether or not it is regular or irregular.
Some common terms
- Sinus rhythm is the normal rhythm
- Arrhythmia means abnormal rhythm
- Fibrillation means irregular rhythm or quivering of one part of the heart
- Bradycardia means slow heart rate
- Tachycardia means fast heart rate
- Paroxysmal means the arrhythmia comes and goes
Tachycardia
The most common of these in inherited heart disease is ventricular tachycardia. The usual presenting symptom is sudden collapse with loss of consciousness, particularly during or after exercise and also at night, when there may also be a seizure (fit). These can usually be prevented with regular medication such as a beta blocker. Sometimes a defibrillator pacemaker is needed.
Bradycardia
The most common form of this is called heart block. This is because messages from the electrical generator of the heart don't get through efficiently to the rest of the heart and hence it goes very slowly or can pause. Symptoms of the heart going too slowly include feeling tired, breathless or fainting.
Tests
Tests to diagnose what sort of arrhythmia is present include:
- an electrocardiogram (ECG). This trace of the heart's electrical activity gives the diagnosis of the source of the arrhythmia. This is often normal at rest and more extensive testing is needed to try and catch the arrhythmia especially if it is intermittent.
- an Ambulatory ECG. This can be performed with a Holter monitor which monitors the heart for rhythm abnormalities during normal activity for an uninterrupted 24-hour period. During the test, electrodes attached to the chest are connected to a portable recorder - about the size of a paperback book - that's attached to a belt or hung from a shoulder strap.
Treatment
Most treatments for tachycardias consist of medication to stop the abnormal rhythm or make it slower if and when it occurs.
If bradycardia is diagnosed, a pacemaker may be fitted. This requires a small operation where a battery powered device is placed under the skin with wires that lead to the heart and provide it with electrical stimulation to prevent it from going too slowly.
