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Overall key points
- Arrhythmias occur as a result of a disturbance in the normal sinus rhythm.
- Atrial fibrillation is the most common sustained arrhythmia, affecting 1 per cent of the population.
- A patient's clinical history is the most important aid for making the diagnosis.
- The cornerstone of arrhythmia diagnosis is the 12-lead ECG.
- Atrial fibrillation may be asymptomatic and may be detected during routine review.
Part 1: What is a cardiac arrhythmia?
Arrhythmia describes an abnormal heart rhythm. It is due to disturbance of normal sinus rhythm, i.e. the electrical impulses produced by the sinoatrial node in the wall of the right atrium. Normal heart rate is 60-100 beats per minute (bpm). Tachycardia describes a rate >100bpm and bradycardia a rate <60bpm.
Arrhythmia may present as palpitations. When heart rate becomes so fast or slow that the heart becomes less efficient and cardiac output drops, there may be additional symptoms (see box). Arrhythmias are a cause of sudden death in the under-40s and are among the top 10 reasons for hospital admission.1
Palpitations may be normal, occurring when cardiac output increases in response to stress, exercise or emotion; in this case they have normal sinus rhythm. Ectopic beats are common, rarely sinister, and may arise from the atria or ventricles. The ECG above shows normal sinus rhythm with frequent ventricular ectopics (broad, slurred complexes). The rhythm is best assessed in the …