Cardiac arrhythmias

How the heart’s rhythm works and what an arrhythmia is

The heart has its own electrical system. The impulse starts in the sinus node, a group of cells in the right atrium, spreads through the atria, passes through the atrioventricular node (a “gate” that delays the impulse slightly) and then spreads through the ventricles via the conduction network. At rest the heart normally beats about 60–100 times a minute with a regular rhythm; during exertion, emotion, fever or after coffee the rate rises naturally.

An arrhythmia is any disturbance of this rhythm: the impulse starts in the wrong place, spreads wrongly or conducts too slowly. Several main groups are distinguished:

• Tachycardia: a very fast rhythm. It can start in the atria (supraventricular tachycardia, atrial fibrillation, atrial flutter) or in the ventricles (ventricular tachycardia, which is more dangerous).
• Bradycardia: a very slow rhythm, from weakening of the sinus node or blocked conduction at the atrioventricular node (atrioventricular block).
• Irregular rhythm, such as atrial fibrillation, the most common arrhythmia in adults.
• Extrasystoles: premature beats, very common and usually harmless.

In this grouping, what matters to the patient is not the name but three questions: are there symptoms, is there heart disease and is there a risk of complications (stroke, fainting, sudden death). The answers decide whether reassurance alone, follow-up, medicines or a procedure is needed.

Symptoms

Some arrhythmias cause no symptoms and are found by chance on an ECG. When there are symptoms, they include:

• palpitations: a sensation of strong, fast, irregular beats or “skips”;
• fatigue, dizziness and reduced ability to exert yourself;
• dyspnea (difficulty breathing) and chest discomfort;
• fainting (syncope) or near-fainting, a symptom that needs special attention, especially when it occurs during exertion or without warning.

Not every palpitation is an arrhythmia and not every arrhythmia causes palpitations. Stress, anxiety, coffee and lack of sleep can cause strong sensations of the heartbeat in a healthy heart. Even so, new or worsening symptoms should be assessed before being put down to anxiety.

Causes and contributing factors

• heart disease: coronary artery disease and a previous heart attack, heart failure, valve disease, cardiomyopathies, myocarditis;
• uncontrolled high blood pressure, which loads the atria and the ventricle;
• thyroid disorders, especially hyperthyroidism;
• changes in potassium, magnesium and other electrolytes, for example after vomiting, diarrhea or with diuretics;
• some medicines (including some antiarrhythmics and decongestants), alcohol, excess caffeine, energy drinks, smoking and stimulant drugs;
• sleep apnea, obesity, diabetes, lung disease and anemia;
• inherited cardiomyopathies and arrhythmias (appearing in families with sudden death at a young age);
• age, because the electrical system “wears” and the sinus node may weaken.

In many cases no single cause is found: several factors act together. Correcting those that can be changed (blood pressure, apnea, alcohol, weight, thyroid) is part of treatment.

When to see a doctor

Book a cardiology consultation if you have recurrent palpitations, unexplained dizziness, reduced exercise capacity or if your doctor has found an irregular pulse or a changed ECG. Note when episodes occur, how long they last, what you were doing and whether the pulse was regular or not.

Seek assessment without delay (and emergency care if severe) for fainting, chest pain with fast beats or new dyspnea. A family history of sudden death before age 50 or of inherited heart disease is very important information to tell the cardiologist.

How the diagnosis is made

An arrhythmia is diagnosed only when it is captured on a recording. The doctor starts with the history (how an episode starts and ends, whether there has been fainting) and an examination, then chooses among the following:

• ECG: records the rhythm at the moment of the test; useful when the arrhythmia is present or leaves traces (for example hypertrophy, an old heart attack, conduction changes).
• Holter ECG (24–48 hours or longer): when episodes come and go. For very rare episodes, longer or implantable recorders are used, which the doctor recommends in certain cases.
• Echocardiography: assesses the structure and function of the heart, the valves and the size of the atria.
• Blood tests: TSH, electrolytes (potassium, magnesium), blood count, kidney function, as needed.
• In selected cases: an exercise test or imaging, cardiac magnetic resonance imaging and an electrophysiology study; these are done at specialized centers and may be recommended to you when indicated.

A normal ECG or Holter does not exclude an arrhythmia that did not occur during the recording. That is why describing symptoms accurately and keeping a diary of episodes helps a great deal. See also ECG or Holter: what is the difference.

How they are treated

Treatment depends on the type of arrhythmia, the symptoms and the condition of the heart. The aims are to ease symptoms and prevent complications.

• Correcting the cause: checking the thyroid, electrolytes and blood pressure, treating sleep apnea, reviewing medicines, cutting down on caffeine, alcohol and smoking.
• Vagal maneuvers for some supraventricular tachycardias (for example holding the breath with gentle straining as instructed by the doctor) can stop an episode.
• Medicines to control rate or rhythm: beta-blockers, calcium channel blockers or antiarrhythmics. Every antiarrhythmic has side effects and special rules; it is taken only as directed.
• Cardioversion: restoring normal rhythm with a controlled electric shock under brief anesthesia, or with medicines. In atrial fibrillation it requires planning for anticoagulation.
• Catheter ablation: a catheter destroys, with heat or cold, the small area that causes the arrhythmia. For some supraventricular arrhythmias it can cure permanently; it is done at specialized centers.
• Pacemaker for severe bradycardia or conduction block, and an implantable defibrillator (ICD) for patients at high risk of dangerous ventricular arrhythmias.

Atrial fibrillation and the risk of stroke

In atrial fibrillation blood can form clots in the atrium that travel to the brain. That is why stroke risk is always assessed and, when indicated, anticoagulants (blood thinners) are given. Aspirin does not replace an anticoagulant. The decision is based on risk, not on how often you feel palpitations. See the dedicated page on atrial fibrillation.

Do not start, stop or change rhythm medicines or anticoagulants without your doctor.

Sudden stopping of the heart: what you should know

The most severe arrhythmias, such as ventricular fibrillation, can cause the circulation to stop suddenly (cardiac arrest). The person loses consciousness and does not breathe normally. This is an absolute emergency: call 127, start chest compressions as instructed by the operator and use an automated external defibrillator (AED) as soon as one is available, because every minute without intervention lowers the chance of survival. It is precisely to prevent such events that dangerous arrhythmias are looked for and treated, and that families are assessed when there is a history of sudden death.