Reentrant Arrhythmias

Tachyarrhythmias are produced by one of the three mechanisms; reentry, enhanced automaticity, or triggered activity. Reentry is the most common mechanism of arrhythmia, and it is responsible for the majority of supraventricular as well as ventricular tachycardias. Reentrant arrhythmias are distinct electrophysiology maladies of the heart caused by the presence of circuits in the normal myocardium. Reentrant arrhythmias occur when a cardiac impulse fails to stop and re-excites the tissues that have recovered from the refractory period. The impulse travels in a circus around a physiologic or anatomic obstacle, forming a reentry circuit in the myocardium.  The common reentrant arrhythmias include atrial fibrillation, atrial flutter, atrioventricular nodal reentrant tachycardia, atrioventricular reciprocating tachycardia, other pathway-mediated tachycardia, and ventricular tachycardia. In atrial fibrillation, multiple reentry circuits are found in the left atrium and pulmonary veins, while typical atrial flutter is characterized by a macro reentry circuit in the right atrium. Atrioventricular nodal reentry tachycardia (AVNRT) is the most common reentrant supraventricular tachycardia and utilizes the atrioventricular (AV) node as its reentry circuit. The atrioventricular reciprocating tachycardia and other pathway-mediated tachycardia involve the atrioventricular node, accessory pathway, and/or the surrounding atrial and ventricular myocardium. The reentry circuit in ventricular tachycardia is complex and formed by the scar in the myocardium. Some ventricular arrhythmias may involve bundle branches as a part of the reentry circuit. The clinical symptoms and signs of different reentry arrhythmias are variable, and the clinical course and outcomes depend on the cardiac status. Atrioventricular nodal reentrant tachycardia is the most benign reentrant arrhythmia, while scar-related ventricular tachycardia is a life-threatening tachyarrhythmia. Atrial fibrillation and atrial flutter are associated with thromboembolic complications, while pathway-mediated tachycardia has a risk of sudden cardiac death. The recent advancements in electrophysiologic mapping techniques have improved the understanding of reentrant arrhythmias, while ablation has emerged as an effective treatment option for most of these arrhythmias. Understanding the pathophysiology and basic mechanism of reentrant arrhythmias is essential before devising a patient management plan. This chapter will discuss the etiology, epidemiology, and pathophysiology of reentrant tachycardia and review the management of patients with reentrant arrhythmias.