Arrhythmia (Abnormal Heart Rhythm)

How the heart's rhythm works

The heartbeat starts in the sinus node, a cluster of cells in the right atrium (upper chamber) that fires 60 to 100 times a minute at rest. The signal spreads across the atria, passes through the atrioventricular (AV) node, then travels down specialized fibers to the ventricles (lower chambers), which contract and pump blood to the body. An arrhythmia occurs when this system misfires anywhere along the way.

Types of arrhythmia

Extra beats

• Premature atrial contractions and premature ventricular contractions (PVCs): early beats felt as a skip, flutter or thud. They are very common and usually harmless, though very frequent PVCs can weaken the heart over time.

Fast rhythms from the upper chambers (supraventricular)

• Atrial fibrillation: chaotic atrial activity causing an irregular, often fast pulse. It is the most common sustained arrhythmia and raises stroke risk about fivefold.
• Atrial flutter: a rapid, organized atrial circuit, with stroke risk similar to atrial fibrillation.
• Paroxysmal supraventricular tachycardia (PSVT): sudden episodes of a regular racing heartbeat, often 150 to 250 beats a minute, which start and stop abruptly.
• Wolff-Parkinson-White syndrome: an extra electrical pathway that can cause fast rhythms.
• Sinus tachycardia: a normal rhythm that is fast because of exercise, fever, anxiety, anemia or dehydration. It is a response, not usually a rhythm disorder.

Fast rhythms from the lower chambers (ventricular)

• Ventricular tachycardia: a fast rhythm starting in the ventricles. Paroxysmal episodes come and go suddenly. Sustained VT can cause fainting or cardiac arrest, especially with heart disease. See paroxysmal ventricular tachycardia.
• Ventricular fibrillation: chaotic ventricular activity with no effective pumping. It causes cardiac arrest and death within minutes without CPR and defibrillation.
• Torsades de pointes: a twisting polymorphic VT linked to a long QT interval.

Slow rhythms (bradyarrhythmias)

• Sinus bradycardia: a slow but normal rhythm. It is common and healthy in athletes and during sleep.
• Sick sinus syndrome: a worn-out sinus node causing slow rhythms, pauses, or alternating fast and slow rhythms.
• Heart block: signals delayed or blocked at the AV node. First-degree block is usually harmless. Second- and third-degree block can cause fainting and often need a pacemaker.

Symptoms

• palpitations: fluttering, pounding, racing or skipped beats
• dizziness or lightheadedness
• shortness of breath and reduced exercise tolerance
• chest discomfort
• fatigue
• fainting or near-fainting
• anxiety during episodes
• no symptoms at all, especially with atrial fibrillation in older adults

Causes and risk factors

• coronary artery disease and previous heart attack
• heart failure, cardiomyopathy and heart valve disease
• high blood pressure
• an overactive or underactive thyroid
• low or high potassium, low magnesium and low calcium
• obstructive sleep apnea, obesity and diabetes
• alcohol, especially binge drinking ("holiday heart")
• stimulants: caffeine in large amounts, nicotine, cocaine, amphetamines and some decongestants
• medicines that prolong the QT interval, and digoxin toxicity
• congenital heart disease and inherited conditions such as long QT and Brugada syndromes
• aging, which wears the conduction system

Diagnosis

• ECG: the basic test, ideally recorded during symptoms.
• Holter monitor: 24 to 48 hours of continuous recording.
• Event monitor or patch monitor: worn for 1 to 4 weeks to catch less frequent episodes.
• Implantable loop recorder: placed under the skin, records for up to about 3 years.
• Smartwatches and phone ECG devices: helpful for capturing episodes, especially atrial fibrillation, but findings need medical confirmation.
• Echocardiogram: checks heart structure and pumping.
• Exercise stress test: for arrhythmias triggered by exertion.
• Blood tests: thyroid function, electrolytes and blood count.
• Electrophysiology study: catheters map the heart's electrical system and can treat the arrhythmia with ablation during the same procedure.

Treatment

Treatment depends on the type, symptoms and risk.

No treatment or lifestyle changes

Many arrhythmias, such as occasional PVCs, need only reassurance and reducing triggers: cutting back on caffeine and alcohol, stopping smoking, treating sleep apnea, managing stress and weight.

Vagal maneuvers

For PSVT, bearing down as if straining (the modified Valsalva maneuver) or splashing ice water on the face can stop an episode.

Medicines

• Rate control: beta-blockers, calcium channel blockers (diltiazem, verapamil) and digoxin.
• Rhythm control: antiarrhythmics such as flecainide, sotalol, dronedarone and amiodarone, chosen by a cardiologist.
• Blood thinners: for atrial fibrillation and flutter when stroke risk is raised, usually with a direct oral anticoagulant.

Procedures and devices

• Electrical cardioversion: a timed shock under sedation to restore normal rhythm.
• Catheter ablation: destroys or isolates the tissue causing the arrhythmia. It can cure most PSVT, atrial flutter and WPW, and is increasingly used early for atrial fibrillation.
• Pacemaker: for symptomatic slow rhythms and heart block.
• Implantable cardioverter-defibrillator (ICD): for people at high risk of dangerous ventricular arrhythmias.
• Left atrial appendage closure: an alternative to long-term blood thinners for some people with atrial fibrillation.

Living with an arrhythmia

• learn to take your pulse and keep a symptom diary
• take blood thinners exactly as prescribed
• check new medicines and supplements with a pharmacist
• keep blood pressure, diabetes and weight under control
• ask family members to learn CPR if you are at risk of ventricular arrhythmias

Frequently asked questions

What is an arrhythmia?

An arrhythmia is an abnormal heart rhythm: too fast, too slow or irregular. It is caused by problems in the heart's electrical system. Some arrhythmias are harmless, while others increase the risk of stroke, heart failure or cardiac arrest.

What are the main types of arrhythmia?

The main types are extra beats (premature contractions), supraventricular tachycardias (including atrial fibrillation, atrial flutter and PSVT), ventricular arrhythmias (ventricular tachycardia and fibrillation), and bradyarrhythmias such as sick sinus syndrome and heart block.

What are paroxysmal ventricular arrhythmias?

These are abnormal rhythms starting in the ventricles that occur in sudden episodes, such as runs of ventricular tachycardia or frequent PVCs. Brief runs in a healthy heart are usually low risk. Sustained episodes, or episodes in people with heart disease, need urgent assessment by a cardiologist.

Are arrhythmias dangerous?

Many are not. Occasional extra beats and sinus bradycardia in fit people are usually harmless. Atrial fibrillation increases stroke risk and needs treatment. Ventricular tachycardia and ventricular fibrillation can be life-threatening. A doctor can tell which type you have with an ECG or monitor.

Can anxiety cause an arrhythmia?

Anxiety raises adrenaline, which speeds up the heart (sinus tachycardia) and can trigger extra beats in susceptible people. It rarely causes dangerous arrhythmias. Palpitations should still be checked with an ECG, because anxiety and a true arrhythmia can coexist.