The most common mechanism of tachyarrhythmias is reentry. Examples include atrial flutter, supraventricular tachycardias (SVTs) due to atrioventricular (AV) nodal reentry or reentrant circuits involving an accessory pathway, and ventricular tachycardia (VT) associated with ischemic cardiomyopathy after myocardial infarction.

In narrow QRS complex tachycardias, activation of the ventricles occurs via the His-Purkinje system, and the relationship of the QRS complex and P waves can be important in establishing the type of SVT.

Vagal maneuvers and adenosine can terminate supraventricular arrhythmias resulting from reentry involving the atrioventricular or sinus node, or it can allow the demonstration of atrial flutter waves, atrial tachycardia, or atrial fibrillation (AF).

The diagnosis of wide complex tachycardia (WCT) often can be established on the basis of clinical presentation, physical examination, electrocardiogram findings, and provocative maneuvers.

It is important that intravenous verapamil not be used to treat WCT—hemodynamic collapse and death have been reported, regardless of the cause of the WCT.

AF, the most common sustained arrhythmia, can occur in the absence of structural heart disease, but more commonly occurs with older age, hypertension, diabetes mellitus, and structural heart disease, including coronary and valvular disease, and congestive heart failure.

AF is associated with higher risk for thromboembolic complications, including stroke.

Addressing and treating risk for stroke, controlling ventricular rate and atrial rhythm are key components of treatment for AF.

In general, implantable cardioverter-defibrillator (ICD) implantation is justified for patients with nonischemic or ischemic cardiomyopathy, left ventricular ejection fraction (LVEF) ≤35%, and NYHA FC II or greater heart failure symptoms.