The heart’s rhythm is set by the sinus node, a small cluster of cells in the right atrium. Its electrical impulses travel across the atria to the ventricles and trigger every heartbeat. At rest, an adult’s heart usually beats 60 to 100 times a minute. Doctors speak of an arrhythmia when it beats too fast, too slowly or irregularly.
Many arrhythmias are harmless. Most people know occasional extra beats, felt as a flutter or a brief pause, for example after coffee, alcohol, stress or a short night. Others need treatment because they reduce the heart’s pumping capacity or can have serious consequences. What matters is whether the heart is otherwise healthy and which symptoms occur: a racing heart, dizziness, shortness of breath, reduced stamina or a brief faint.
The most common persistent arrhythmia is atrial fibrillation. The atria beat in a disorganised way, and the pulse becomes irregular and often fast; some people notice nothing at all. Because clots can form in the fibrillating atria, it increases the risk of stroke. It becomes more common with age and is promoted by high blood pressure, excess weight, diabetes, sleep apnoea and alcohol.
If the heart beats too slowly on a permanent basis, for example because electrical conduction weakens over the years, stamina suffers: tiredness, dizziness and fainting can result, and a pacemaker is then often an option. More serious are fast arrhythmias that originate in the ventricles. They usually occur in a previously damaged heart and can turn into ventricular fibrillation, a cardiac arrest. Chest compressions and a defibrillator are then needed immediately.