Arrhythmias
Abnormal heart rhythms; Bradycardia; Tachycardia; Fibrillation
An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm. The heart can beat too fast (tachycardia), too slow (bradycardia), or irregularly.
An arrhythmia can be harmless, a sign of other heart problems, or an immediate danger to your health.
The interior of the heart is composed of valves, chambers, and associated vessels.
The external structures of the heart include the ventricles, atria, arteries and veins. Arteries carry blood away from the heart while veins carry blood into the heart. The vessels colored blue indicate the transport of blood with relatively low content of oxygen and high content of carbon dioxide. The vessels colored red indicate the transport of blood with relatively high content of oxygen and low content of carbon dioxide.
An electrocardiogram (ECG) test measures the electrical activity of the heart. A normal resting heart rate is 60 to 100 beats per minute.
Bradycardia heart rhythms are characterized by a slowness of the heartbeat, usually at a rate under 60 beats per minute (normal resting rate is 60 to 100 beats per minute).
Ventricular tachycardia is a rapid resting heart rate initiated within the ventricles, typically at 160 to 240 beats per minute (normal resting rate is 60 to 100 beats per minute).
This picture shows an ECG (electrocardiogram, EKG) of a person with an abnormal rhythm (arrhythmia) called an atrioventricular (AV) block. P waves show that the top of the heart received electrical activity. Each P wave is usually followed by the tall (QRS) waves. QRS waves reflect the electrical activity that causes the heart to contract. When a P wave is present and not followed by a QRS wave (and heart contraction), there is an atrioventricular block, and a very slow pulse (bradycardia).
The intrinsic conduction system sets the basic rhythm of the beating heart by generating impulses which stimulate the heart to contract.
The atria, and their respective ventricles, are electrically insulated from each other by a fibrous tissue known as the atrioventricular (AV) junction. Impulses are transferred via a special bridge, called the His-Purkinje system (HPS). Some individuals, however, have additional bridges called accessory pathways. Irregular heartbeats resulting from impulses passing through accessory pathways are called supraventricular. Supraventricular tachycardias (SVT) may be atrial or AV junctional. In atrial tachycardia, the impulse arises from the superior portion of either atrium. This condition may arise when the tissues of the atria or pericardium, the membrane covering the heart, are affected by a chronic or acute inflammation, dilation or enlargement of an atrium, or formation of reparative tissue called fibrosis. Re-entry tachycardias result from congenital accessory pathways, and can be manifested at any age. AV nodal re-entry (AVNR) is the most common AV junctional tachycardia. The re-entry circuit is localized in the AV node, a small node involved in the conduction system of the heart. AV nodal re-entry results from differences in conducting fibers leading to divergence in impulses. Wolff-Parkinson-White syndrome is one of the most frequently encountered accessory pathway syndromes. The incidence is approximately 150 cases per year per 100,000 individuals. Electrical impulses bypass the AV node and travel along the bundle of Kent accessory pathway instead. This results in ventricular pre-excitation, because the impulse reaches the ventricle prematurely. Very rapid heartbeats, a complication of Wolff-Parkinson-White, can result in severe hypotension and syncope, or loss of consciousness.
Causes
Normally, your heart works as a pump that brings blood to the lungs and the rest of the body.
To help this happen, your heart has an electrical system that makes sure it contracts (squeezes) in an orderly way.
- The electrical impulse that signals your heart to contract begins in an area of the heart called the sinoatrial node (also called the sinus node or SA node). This is your heart's natural pacemaker.
- The signal leaves the SA node and travels through the heart along a set electrical pathway.
- Different nerve messages signal your heart to beat slower or faster.
Arrhythmias are caused by problems with the heart's electrical conduction system.
- Abnormal extra signals may occur.
- Electrical signals may be blocked or slowed.
- Electrical signals travel in new or different pathways through the heart.
Some common causes of abnormal heartbeats are:
- Abnormal levels of potassium, magnesium, or other substances in the body
- Heart attack, or a damaged heart muscle from a past heart attack
- Heart disease that is present at birth (congenital)
- Heart failure or an enlarged heart
- Overactive thyroid gland
Arrhythmias may also be caused by some substances or drugs, including:
- Alcohol or stimulant drugs
- Certain medicines
- Cigarette smoking (nicotine)
Some of the more common abnormal heart rhythms are:
- Atrial fibrillation or flutter
- Atrioventricular nodal reentry tachycardia (AVNRT)
- Heart block or atrioventricular block
- Multifocal atrial tachycardia
- Paroxysmal supraventricular tachycardia
- Sick sinus syndrome
- Ventricular fibrillation or ventricular tachycardia
- Wolff-Parkinson-White syndrome
Symptoms
When you have an arrhythmia, your heartbeat may be:
- Too slow (bradycardia)
- Too quick (tachycardia)
- Irregular, uneven, possibly with extra or skipped beats
An arrhythmia may be present all of the time or it may come and go. You may or may not feel symptoms when the arrhythmia is present. Or, you may only notice symptoms when you are more active.
Symptoms can be very mild, or they may be severe or even life threatening.
Common symptoms that may occur when the arrhythmia is present could include:
- Chest pain
- Fainting
- Lightheadedness, dizziness
- Paleness
- Palpitations (feeling your heart beat fast or irregularly)
- Shortness of breath
- Sweating
Exams and Tests
The health care provider will listen to your heart with a stethoscope and feel your pulse. Your blood pressure may be low or normal or even high as a result of being uncomfortable.
An electrocardiogram (ECG) will be the first test done.
Heart monitoring devices are often used to identify the rhythm problem, such as a:
- Holter monitor (where you wear a device that records and stores your heart rhythm for 24 or more hours)
- Event monitor or loop recorder (worn for 2 weeks or longer, where you record your heart rhythm when you feel an abnormal rhythm)
- Other long-term monitoring options
An echocardiogram is sometimes ordered to examine the size or structure of your heart.
In selected cases, coronary angiography may be performed to see how blood flows through the arteries in your heart.
A special test, called an electrophysiology study (EPS), is sometimes done to take a closer look at the heart's electrical system.
Treatment
When an arrhythmia is serious, you may need urgent treatment to restore a normal rhythm. This may include:
- Electrical therapy (defibrillation or cardioversion)
- Implanting a short-term heart pacemaker
- Medicines given through a vein or by mouth
Sometimes, better treatment for your angina or heart failure will lower your chance of having an arrhythmia.
Medicines called anti-arrhythmic drugs may be used:
- To prevent an arrhythmia from happening again
- To keep your heart rate from becoming too fast or too slow
Some of these medicines can have side effects. Take them as prescribed by your provider. Do not stop taking the medicine or change the dose without first talking to your provider.
Other treatments to prevent or treat abnormal heart rhythms include:
- Cardiac ablation, used to target areas in your heart that may be causing your heart rhythm problems
- An implantable cardioverter defibrillator, placed in people who are at high risk of sudden cardiac death
- Permanent pacemaker, a device that senses when your heart is beating too slowly. It sends a signal to your heart that makes your heart beat at the correct pace.
Outlook (Prognosis)
The outcome depends on several factors:
- The kind of arrhythmia you have.
- Whether you have coronary artery disease, heart failure, or valvular heart disease.
When to Contact a Medical Professional
Contact your provider if:
- You develop any of the symptoms of a possible arrhythmia.
- You have been diagnosed with an arrhythmia and your symptoms worsen or do not improve with treatment.
Prevention
Taking steps to prevent coronary artery disease may reduce your chance of developing an arrhythmia.
References
Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: Executive summary: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. Heart Rhythm. 2018;15(10):e190-e252. PMID: 29097320
Nattel S, Tomaselli GF. Mechanisms of cardiac arrhythmias. In: Libby P, Bonow RO, Mann DL, Tomaselli GF, Bhatt DL, Solomon SD, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12th ed. Philadelphia, PA: Elsevier; 2022:chap 62.
Olgin JE. Approach to the patient with suspected arrhythmia. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 49.
Tracy CM, Epstein AE, Darbar D, et al. 2012 ACCF/AHA/HRS focused update of the 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2012;60(14):1297-1313. PMID: 22975230
Version Info
Last reviewed on: 5/27/2024
Reviewed by: Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
