A heart arrhythmia is any abnormality in the heart's rhythm — beating too fast, too slow, or irregularly. The heart's rhythm is controlled by its own electrical system, and an arrhythmia occurs when this system misfires. A normal resting heart rate is between 60 and 100 beats per minute, and it is entirely normal for the heart rate to rise with exercise or fall during rest or sleep.
Arrhythmias span an enormous range of severity. Many are harmless, causing nothing more than an occasional, brief sensation of a skipped or fluttering beat that requires no treatment at all. Others, such as atrial fibrillation, are common and generally not immediately dangerous, but carry a significant long-term risk — most importantly, an increased risk of stroke — that requires active, ongoing management even when the arrhythmia itself doesn't feel severe. And a small number of arrhythmias, such as ventricular fibrillation, are immediately life-threatening and require emergency treatment within minutes. Understanding which category a particular arrhythmia falls into is the single most important factor in how it should be approached.
Each heartbeat begins with an electrical impulse generated by the sinoatrial (SA) node, a small cluster of specialised cells in the right atrium (the heart's upper right chamber) that acts as the heart's natural pacemaker. This impulse spreads across both atria, causing them to contract, then passes through the atrioventricular (AV) node — a checkpoint that briefly delays the signal before sending it down into the ventricles (the heart's lower chambers) via a specialised conduction pathway, triggering them to contract in turn and pump blood out to the body.
An arrhythmia develops when this electrical signal is generated too fast, too slow, or in the wrong place, or when it fails to travel properly along its normal pathway. Depending on where in this system the problem occurs, and how the heart's chambers respond, the result can range from a barely noticeable irregular beat to a complete failure of the heart to pump blood effectively.
Atrial Fibrillation (AF)
The most common significant arrhythmia, in which the atria beat rapidly and chaotically instead of in a coordinated way. Usually not immediately dangerous to the rhythm itself, but significantly raises the long-term risk of stroke, which is why it requires active, ongoing management.
Bradycardia
A heart rate slower than normal (generally below 60 beats per minute), which can be a normal finding in fit, healthy individuals, or can indicate a problem with the heart's electrical system causing inadequate blood flow, particularly if accompanied by symptoms such as dizziness or fatigue.
Tachycardia
A heart rate faster than normal at rest (generally above 100 beats per minute), which can originate in the upper chambers (supraventricular tachycardia) or the lower chambers (ventricular tachycardia) — a distinction that matters significantly, since ventricular tachycardia is generally more dangerous.
Premature Contractions (PACs/PVCs)
Extra, early heartbeats originating in the atria (PACs) or ventricles (PVCs), often felt as a skipped beat or a flutter. Usually harmless and common in healthy people, though frequent premature contractions warrant assessment to rule out an underlying cause.
Ventricular Fibrillation (VF)
A chaotic, disorganised electrical activity in the ventricles that prevents the heart from pumping blood at all. The most dangerous arrhythmia, causing sudden cardiac arrest, and immediately life-threatening without emergency defibrillation within minutes.
Atrial fibrillation deserves particular attention because its main long-term danger isn't necessarily how it feels — it's a complication that can develop silently. When the atria fibrillate instead of contracting normally, blood can pool and stagnate within them, particularly in a small pouch called the left atrial appendage, creating conditions in which a blood clot can form. If part of this clot breaks free, it can travel to the brain and cause a stroke.
This is why the treatment of atrial fibrillation involves two largely separate questions: controlling the rhythm or rate itself, and separately assessing and managing stroke risk. Doctors use validated risk scoring tools, weighing factors such as age, sex, and coexisting conditions like high blood pressure, diabetes, heart failure, and prior stroke, to estimate an individual's annual stroke risk and decide whether blood-thinning medication (anticoagulation) is warranted. Critically, this decision is generally independent of how noticeable or bothersome the arrhythmia symptoms are — someone with few symptoms and a high calculated stroke risk still needs anticoagulation, while someone with very bothersome symptoms but low calculated risk may not.
This is the central reason atrial fibrillation, despite being common and not immediately life-threatening in the way ventricular fibrillation is, is not a condition to leave unmanaged simply because the palpitations themselves feel tolerable.
Ventricular fibrillation occurs when the heart's lower chambers quiver chaotically instead of contracting in a coordinated way, meaning no blood is pumped to the brain or the rest of the body. This causes sudden cardiac arrest — collapse and loss of consciousness within seconds, with no pulse and no normal breathing.
Survival depends almost entirely on how quickly effective treatment begins. Cardiopulmonary resuscitation (CPR) helps maintain some blood flow to vital organs, but the only treatment that can restore a normal rhythm is defibrillation — delivering an electric shock to the heart using an AED or a hospital defibrillator — and the chance of survival falls significantly with every minute this is delayed. This is why bystander CPR and public access to AEDs (increasingly available in public spaces in Singapore) genuinely save lives, and why any sudden, witnessed collapse with no pulse should prompt an immediate call to emergency services and CPR, without waiting to see if the person recovers on their own.
Many arrhythmias, including some episodes of atrial fibrillation, cause no noticeable symptoms at all. When symptoms do occur, they include:
