Critical Care Trauma Centre


Arrhythmia is a term that is used to describe an abnormal electrical pattern within the heart. The heart is divided into two upper chambers (atria) and two lower chambers (ventricles) [Image 1]. Before the chambers can contract, they must receive an electrical signal, the same way that you must plug in an electrical appliance before the motor will work. The electrical signal is picked up by electrodes on the chest and displayed as a waveform call an Electrocardiogram or ECG (Image 2).

Normally, the electrical signal takes on a very predictable pattern. The upper chambers send the first electrical signal, followed by a signal from the lower chambers. The electrical signal begins in the right atrium in a special area called the "sinoatrial node". When the electrical pattern of the heart takes on a normal sequence, the sinoatrial node (or sinus node) produces the first wave. This wave is followed by a signal from the lower chambers. The term "normal rhythm" or "normal sinus rhythm" is used to describe the normal electrical waveform pattern. Normal sinus rhythms are regular. A normal heart rate is 60-100 beats per minute.

For many reasons, different areas of the heart can initiate the electrical message. Beats that start from a location other than the sinus node are called "ectopic beats" (outside the normal). They are easy to recognize because the ECG pattern looks different. An ectopic beat is also called an "arrhythmia". Sometimes, all of the beats begin from another location. This is called an an ectopic rhythm. They can be regular or irregular, and may be fast, slow or at a normal heart rate.

Most healthly people have occassional arrhythmias, therefore, they do not indicate a problem. When they happen frequently, they can cause problems with the blood pressure or the strength of the heart's contraction. A heart that is diseased is more likely to have arrhythmias. We only treat arrhythmias if they are affecting the blood pressure or strength of contractions. If we need to treat arrhythmias, amiodarone is a drug that is frequently used in the critical care environment. A drug that stops arrhythmias is called an "antiarrhythmic".

Occassionally, the lower chambers can begin firing very quickly, causing a life-threatening rhythm called ventricular tachycardia. The BP will usually drop with this type of rhythm. It can deteriorate to a caotic and ineffective quivering of the ventricles, called ventricular fibrillation. This is a type of Cardiac Arrest. The treatment for ventricular fibrillation is Defibrillation or "electrical shock".


Image 1 : Chambers of the Heart.

SA Node

Image 2: Electrical pathway (called conduction pathway) beginning with SA Node.

Image 3: Normal Sinus beat (normal ECG).

Image 4: An example of a serious arrhythmia.


Last Reviewed: October 23, 2014