Supraventricular arrhythmias: an introduction

Supraventricular arrhythmias, an introduction. Abnormal heart rhythms occur when the electrical impulse does not originate at the sinus node and follow the normal path through the atria and ventricles. There are many causes of arrhythmias, including coronary heart disease, hypoxia and congenital heart disease. Broadly speaking, arrhythmias can be divided into two main types, supraventricular and ventricular, depending on their origin.

Supraventricular arrhythmias arise from a problem within the atria, the AV node, or the bundle of His. Examples include atrial fibrillation, atrial flutter, and supraventricular tachycardia. All these arrhythmias are characterised by the absence of normal P waves and are typically associated with fast heart rates. However, because they affect atrial rather than ventricular depolarisation, QRS complexes are usually normal. Atrial fibrillation is a common supraventricular arrhythmia in which multiple areas within the atrial muscle tissue generate impulses randomly and at a very fast rate. Some of these impulses will travel through the atrial ventricular node and depolarise the ventricles in the normal fashion.

On the ECG, P waves will be absent, although you may be able to see some small non-uniform wave forms called fibrillation waves. These represent the chaotic atrial activity. As the impulses are generated randomly within the atria, the overall heart rate is also irregular. QRS complexes appear normal.

One of the risks of atrial fibrillation is that the uncoordinated depolarisation and contraction within the atria can lead to pooling of blood and clot formation. If part of the clot then breaks off or embolises, it can potentially travel through the bloodstream to the brain and cause a stroke. Because of this, people with chronic atrial fibrillation may require long term anticoagulation therapy.