Arrhythmias can be divided into 2 main categories.
Rapid arrhythmias
Slow arrhythmias
Below we provide a brief overview of the most common arrhythmias that may require electrophysiological examination, but not every arrhythmia mentioned will require electrophysiological examination.
Tachyarrhythmias
Tachyarrhythmias (tachycardia) can originate in the atria, atrioventricular node, or ventricles. Because the ventricles are the primary bearers of the heart’s pumping function, rapid abnormal rhythms that occur in the ventricles often have more serious consequences.
Supraventricular tachycardia (SVT)
SVT is a group of tachyarrhythmias that originate in the upper chambers of the heart, often due to abnormal conduction pathways between the atria, atrioventricular node, or atria and ventricles.
Atrioventricular node regurgitation tachycardia (AVNRT) is the most common type of supraventricular tachycardia and is primarily caused by the presence of an additional conduction pathway in or near the AV node. Once an impulse enters this abnormal pathway, it may cause a circular conduction pattern in which the heart contracts with each revolution of the impulse, resulting in a rapid and regular heart beat.
Pre-excitation syndrome (WPW)
This abnormal rhythm occurs mainly because of an abnormal “bridge” between the atria and the ventricles, called an additional bypass, which allows the electrical impulses to bypass the atrioventricular node and go straight from the atria to the ventricles.
In patients with pre-excitation syndrome, the impulse travels through the AV node to the ventricle and can then travel backwards through the bypass to the atrium, triggering another contraction, which can lead to tachyarrhythmias if the impulse continues to travel along this loop.
Atrial fibrillation
Atrial fibrillation occurs when impulses are delivered uncoordinated from multiple parts of the atria, triggering very rapid and ineffective contractions. The atrioventricular node acts as a “relay station” between the atria and ventricles, allowing only some of these impulses to travel down to the ventricles, resulting in an irregular, unstable, and abnormally fast heart rhythm. Atrial fibrillation can occur occasionally or persist (chronic atrial fibrillation).
Ventricular tachycardia (VT)
This arrhythmia occurs due to the presence of an abnormal current pathway in the ventricles, usually at the site of myocardial infarction or other heart disease damage. If impulses enter the abnormal pathway, cyclic excitation may be induced, resulting in tachycardia.
Ventricular tachycardia usually does not stop on its own, and worse, it sometimes progresses to ventricular fibrillation and cardiac arrest.
Ventricular fibrillation
Ventricular fibrillation occurs when multiple parts of the heart give off impulses in a rapid and uncoordinated manner. At this point, the ventricles begin to twitch and fail to pump effectively, thus causing a cessation of blood flow. If emergency treatment is not given to restore the rhythm, the patient often dies within minutes.
Slow arrhythmia (bradycardia)
Bradycardia includes 2 basic types.
Sick sinus node syndrome (SSS)
In this condition, the sinus node loses its normal pacing function. It may give out insufficient electrical signals, miss some electrical signals, or suddenly give out too many electrical signals. As a result, the heart may beat too slowly (sinus bradycardia), pause for a long time (sinus arrest), or beat fast and slow (bradycardia-tachycardia syndrome).
Heart block
The path of impulse propagation to the ventricles is interrupted and can be partial or complete. In the case of a complete block, all impulses from the sinus node cannot travel down to the ventricles, which are then controlled by “potential pacing points”, which are less frequent and less reliable than the sinoatrial node. As a result, conduction block often leads to a slow and unstable heartbeat.