Disorders of the heart rhythm (cardiac arrhythmias)
Cardiac arrhythmias are disorders of the heart rhythm. They can give rise to palpitations, breathlessness and loss of consciousness. The most serious forms can cause sudden cardiac death. They can be fast (tachyarrhythmias) or slow (bradyarrhythmias).
• AV Nodal Reentrant Tachycardia (AVNRT): An extra pathway lies in or near the AV node, which causes the impulses to move in a circle and re-enter areas it already passed through.
• Accessory pathway: These pathways connect the atrium and ventricles and 'short-circuit' electrical conduction.
• Atrial fibrillation (AF): extra impulses originating from the pulmonary veins and the atrium make the atria beat very rapidly.
• Atrial flutter: Extra impulses originating from different areas of the atrium cause the atria to beat, or 'flutter', rapidly.
• Ventricular tachycardia: If sustained, this is a life-threatening heart rhythm originating from the ventricles. It can lead to failure of the heart to pump and can present with breathlessness and loss of consciousness.
Slow heart rates can be due to conditions affecting the main pacemaker (sinoatrial node) or the communication between it and the main pumping chambers (ventricles).
Second-degree heart block: This refers to the disorder when some of the impulses from the atria are not passed through to the ventricles.
Third-degree, or complete, heart block: This refers to when no impulse from the atria are passed through to the ventricles. The heart rate slows down to around 20-40 per minute.
Sick sinus syndrome: This condition is where the sinoatrial node is damaged. . The heart can go slow or fast.
Each arrhythmia has a specific treatment. Any underlying cause (such as ischaemic heart disease, or high blood pressure) may also be important in controlling certain arrhythmias. The following are the sort of treatments which may be considered.
Medication: There are many medications available for rhtyhm abnormalities, but none should be used unless the arrhythmia has been identified.
Catheter ablation treatment: This is generally effective for fast heart rhythms (supraventricular tachycardias, atrial fibrillation and ventricular tachycardias). Each ablation consists of a different technique, or operation. Each technique also involves a different success rate and risks.
Cardioversion: This is useful as an emergency treatment for most fast heart rhythm abnormalities (tachyarrhythmias). It can also be undertaken as a non-urgent treatment in patients with atrial fibrillation (AF).
Pacemakers: These are used to treat slow heart rates (bradyarrhythmias).
Implantable cardioverter defibrillators (ICDs): These are used to treat life-threatening, fast heart rates (tachyarrhythmias), such as ventricular tachycardia and ventricular fibrillation.