Introduction: Supraventricular Arrhythmias

Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia encountered in clinical practice. It is estimated that AF affects over 3 million adults in the United States, with prevalence increasing with age.1 Overall AF prevalence is around 1-2% in adults under 60 years old but rises to nearly 10% in those over 80 years. AF is characterized by rapid and disorganized electrical activation of the atria, leading to ineffective atrial contraction. This results in an irregularly irregular ventricular response as impulses conduct variably through the AV node. Hemodynamic consequences include loss of atrial kick, irregular ventricular filling, and potential for tachycardia-mediated cardiomyopathy. AF may be classified as first detected, paroxysmal, persistent, or permanent based on duration of arrhythmogenic episodes.

Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is a generic term that refers to any abnormally rapid heart rhythm that originates above the bundle of His in the conduction system. It is characterized by a sudden onset and termination of a regular, narrow QRS complex tachycardia. The heart rate during SVT is typically between 150-250 beats per minute. SVT is caused by either abnormal automaticity, triggered activity, or reentry. The most common mechanisms of SVT are atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT) involving an accessory pathway. Other less common forms include atrial tachycardia, sinus node reentrant tachycardia, and intra-atrial reentrant tachycardia.Both utilize a reentrant circuit that allows rapid activation of the atria and ventricles. AVNRT involves reentry within the AV node, while AVRT involves an accessory pathway that connects the atria and ventricles outside of the AV node. This chapter will focus specifically on AV nodal reentrant tachycardia.