Cardiac arrhythmias

A cardiac arrhythmia is when the heart beats abnormally. Arrhythmias occur when the electrical impulses in the heart don’t function properly. There are two types of arrhythmias:

  • Rapid heart rhythms
  • Slow heart rhythms

Helpful terms that can boost your understanding of arrhythmias include:

  • Atrioventricular (AV) node is part of the electrical conduction system of the heart, which transmits signals that cause the heart to beat. The AV node coordinates the top of the heart.
  • Atria refers to the right and left atrium, which are the two upper chambers of the heart. These play an important role in pumping blood.
  • The left and right ventricles are large chambers in the heart that collect and expel blood received from the atria.
  • The sinoatrial node, or sino node, is a group of cells in the right atrium of the heart that can produce electrical impulses that cause the heart to contract.

Rapid heart rhythms

Supraventricular tachycardia (SVT)

SVT is the occasional rapid beating of the heart not related to exercise, high fever or stress. For many people, this means that the heart will beat as many as 300 times per minute, before returning to normal. SVT is a series of very rapid heartbeats that begin in the heart’s upper chambers. SVT may occur when an extra pathway of electrical conducting tissue exists in the atria, the AV node or between the atria and ventricles.

Wolff-Parkinson-White (WPW) syndrome

In WPW, an abnormal “bridge” of tissue connects the atria and ventricles. This extra pathway, called an accessory pathway, makes it possible for electrical impulses to travel from the atria to the ventricles without going through the AV node.

Because it is prone to conduct impulses rapidly, an accessory pathway also may allow extremely rapid, and potentially serious, rhythms to occur.

Ventricular tachycardia (VT)

With VT, abnormal electrical pathways exist in the ventricles. If an electrical signal enters such a pathway, it may start traveling in a circular pattern. This may cause the ventricles to contract with each cycle, and may result in a rapid heartbeat.

VT may not stop by itself and may require medication or an implantable device to automatically terminate the rhythm. In some cases, it can deteriorate into ventricular fibrillation (see below) and cardiac arrest.

Ventricular fibrillation

Ventricular fibrillation is the most serious arrhythmia, potentially resulting in cardiac arrest unless it’s quickly treated. It takes place when multiple sites in the ventricles fire impulses very rapidly and in an uncoordinated fashion. As a result, the ventricles quiver and cease to pump blood effectively, therefore stopping the circulation of blood. Death follows within a few minutes, unless a normal rhythm is restored with emergency treatment.

Slow heart rhythms

Sick sinus syndrome

In this condition, the sinus node fails to perform its role as the heart’s natural pacemaker. It may not send electrical signals often enough, may skip some signals or may send too many signals all at once.

As a result, the heart may beat too slowly (a condition known as sinus bradycardia), pause for too long (sinus pause) or may alternate between being too slow and too fast (bradycardia-tachycardia syndrome). Pacemakers and other treatments can be utilized to ensure the heart beats normally.

Heart block

In heart block, there is an interruption of the pathway on which electrical impulses travel to the ventricles. Heart block may result in a very slow, unreliable heartbeat. This might require the placement of a pacemaker.

Ways to test for arrhythmias

How doctors diagnose arrhythmias

If your doctor suspects you have an arrhythmia, he or she may order one or more diagnostic tests to confirm its presence and determine whether it is causing symptoms.

There are a number of diagnostic tools that your doctor can use. The electrocardiogram (ECG or EKG) is a simple test that records the electrical activity of your heart. Holter monitoring is a continuous recording of the ECG, usually for 24 hours, while the patient goes about his or her usual daily activities.

If a Holter monitor doesn’t reveal anything, then your doctor may ask you to wear a device called an event recorder. This device can be worn over a period of days or weeks, and is used to record abnormal heart rhythms that occur infrequently. Implantable event recorders now are available for patients with very infrequent yet severe symptoms. The exercise ECG test (which involves a patient running or walking on a treadmill) allows doctors to record the ECG during the stress of exercise.

Electrophysiology (EP) study

EP studies are often recommended in people who have experienced life-threatening arrhythmias. Other likely candidates include people with persistent symptoms whose suspected arrhythmias could not be detected by other means.