Cardiac arrhythmias arise when there is an abnormality in the heart's electrical activity. The electrocardiogram (ECG) is a gold standard tool used in the diagnosis and monitoring of arrhythmias. There is no "one" thing that results in the formation of arrhythmia, in fact, there are several factors that can lead to them. Some causes include changes in autonomic nerve activity, medication (not just prescriptions, but all sorts of drugs) side effects, stress, electrolyte changes, action potential changes, and anything else that changes the heart tissue. For example, "An excess of thyroid hormone can cause the heart to beat faster, and thyroid deficiency can slow your heart rate" (31).

When one of the factors above causes change to the heart tissue, electrical pathways in the heart can either be made or blocked. Common broad types of arrhythmias are bradyarrhythmias, tachyarrhythmias, or ectopic beats. Bradyarrhythmias are those that result in a slower than normal heartbeat, usually from a conduction delay. Tachyarrhythmias are those that result in a faster than normal beat and may be associated with an accessory conduction pathway. Lastly, ectopic beats are those that result in extra heartbeats. "Abnormal impulse formation can be caused by the expression of ectopic pacemaker sites within the heart. These are sites outside of the SA node that can spontaneously depolarize and thereby produce atrial and/or ventricular action potentials independent of SA nodal firing" (6).

Besides a block in cardiac conduction, arrhythmias can also result from altered changes in action potential direction and formation such as in Triggered Activity and Reentrant Circuits. "Triggered activity occurs when abnormal action potentials are triggered by a preceding action potential, and can result in either atrial or ventricular tachycardia. The abnormal impulses are seen as spontaneous (yet triggered) depolarizations that occur during either phase 3 or 4 of an action potential (6)." Triggered activity can be further split into early afterdepolarizations and delayed afterdepolarizations. (Click here to learn more about Triggered Activity!) Reentry Circuits form when certain conditions in the heart allow for a new electrical pathway to be formed, moving the action potentials in a "circular" motion, allowing the impulses to essentially get stuck in a revolving door. "Reentry can take place within a small local region [local reentry] within the heart or it can occur, for example, between the atria and ventricles (global reentry)" (6). (Click here to learn more about Reentrant Circuits!).

Though this may be tricky to understand, it is never a bad idea to get the physiological background to better understand the type of condition you may be looking at, and appreciate the true complexity of the human body and disease!