Supraventricular Arrhythmias

Abstract

Supraventricular arrhythmias can be divided into those that arise above the atrioventricular (AV) node (atrial arrhythmias) and those involving the AV junction and usually the AV node (supraventricular tachycardias (SVTs) or, more accurately, junctional tachycardias). (Many of these tachycardias involve the ventricle in the reentrant ciruit, so cannot be accurately termed – supraventricular'.) Diagnosis can be aided by slowing conduction in the AV node by vagal manoeuvres or adenosine. Vagal manoeuvres – carotid sinus massage (5 seconds' firm pressure on each) can be tried, but the most successful manoeuvre is probably the Valsalva manoeuvre, in which the patient is placed in a supine position and asked to breathe out hard with a closed glottis for 15 seconds. Termination of the SVT occurs in the relaxation phase. Other vagotonic manoeuvres can also be tried. Adenosine is a powerful blocker of the AV node. It must be injected as a rapid bolus in incremental doses from 3–12 mg until an effect is seen. It slows the ventricular response of atrial tachycardias, facilitating analysis of the atrial ECG, and terminates tachycardias involving the AV node. It is particularly helpful when the diagnosis is in doubt because the QRS complex is broad. Ventricular tachycardia is unaffected by adenosine. Supraventricular arrhythmias with bundle branch block are either slowed (atrial) or terminated (most junctional tachycardias).