The latest article in our Clinical Practice series reviews a systematic approach to diagnosis and management of supraventricular tachycardias. Adenosine, which blocks the AV node, is of diagnostic value but should not be used in cases of irregular wide-complex tachycardias, since it may lead to clinical instability.
Patients with symptomatic tachycardias require immediate medical attention. Although it is commonly believed that a precise diagnosis of the tachycardia is necessary before therapy is initiated, immediate treatment can usually be tailored to the characteristics of the ventricular response.
• What is the most common type of supraventricular tachycardia?
Sinus tachycardia, by far the most common supraventricular tachycardia, is not a pathologic arrhythmia (with the rare exception of inappropriate sinus tachycardia) but rather an appropriate cardiac response to a physiological event. Sinus tachycardia is gradual in onset and recession. The heart rate is regular and classically does not exceed 220 beats per minute minus the patient’s age. In sinus tachycardia, P waves precede the QRS complex. Atrial fibrillation is the most common pathologic supraventricular tachycardia, affecting more than 3 million people in the United States and many more worldwide. Atrial fibrillation is caused by multiple electrical wavelets appearing in the atria simultaneously, resembling the waves that would be produced if one dropped several pebbles in a bucket of water at the same time.
• What are the characteristics of atrioventricular reciprocating tachycardia?
Atrioventricular reciprocating tachycardia is caused by cardiac musculature that bypasses the normal insulation afforded by the tricuspid and mitral valves between the atria and the ventricles. These bypass tracts may conduct in an antegrade direction only, in a retrograde direction only, or in both directions. A delta wave, an initial slurring of the QRS complex, is present on the surface ECG in most cases of antegrade bypass tracts and indicates partial depolarization of the ventricular tissue resulting from rapid conduction of the electrical impulse from the atrium to the ventricle over the bypass tract. Delta waves are absent in cases in which there is no antegrade conduction and in some persons with left atrial free-wall bypass tracts (since the brisk atrioventricular node conduction can depolarize the ventricle through the His-Purkinje system before the atrial impulse arrives at the bypass tract). Patients who have both tachycardia and a delta wave have the Wolff-Parkinson-White syndrome.
Morning Report Questions
Q: Which supraventricular arrhythmias are characterized by sudden versus gradual onset and recession?
A: Sudden onset and recession are characteristic of acute atrial fibrillation and atrial flutter, atrioventricular nodal reentrant tachycardia, atrioventricular reciprocating tachycardia, and atrial tachycardia. Gradual onset and recession occur with sinus tachycardia, chronic atrial fibrillation and atrial flutter, multifocal atrial tachycardia, and atrial premature contractions.
Q: What is the differential of a wide-complex tachycardia?
A: In contrast to narrow-complex tachycardias, which can be generated only by impulses that depolarize the ventricle through the His-Purkinje system (and thus are, by definition, supraventricular tachycardias), wide-complex tachycardias can be ventricular or supraventricular in origin (or artifactual). Wide-complex tachycardias are caused by ventricular arrhythmia (ventricular tachycardia, ventricular fibrillation, and torsades de pointes or polymorphic ventricular tachycardia) or supraventricular tachycardia with aberrant conduction resulting from one of the following conditions: disease in the His-Purkinje system, such as left or right bundle-branch block; a bypass tract (i.e., the Wolff-Parkinson-White syndrome), with depolarization of the ventricle from the bypass tract; or a ventricular paced rhythm from a pacemaker.