Rhythm and Conduction Disorders

Abstract

Supraventricular tachyarrhythmia (SVT) is a global term for abnormal rhythms generated in one or more of the following structures: the sinus node, the atrial myocardium, the AV node, or the bundle of His, down to its bifurcation. Thus, the designation, “supraventricular” departs from the anatomical landmarks, since the bundle of His is in the upper portion of the IVS; in fact, with one of these rhythms, that is, antidromic AV reentrant tachycardia (AVRT), part of the aberrant circuit is in the ventricular myocardium itself. The acronym “SVT” may stand for supraventricular tachycardia or tachyarrhythmia. Arbitrarily, the former term generally does not cover atrial flutter (AF) and flutter. During SVT, the HR is usually ≥100 bpm, but can be lower in case of coexisting AV block; the term, “tachycardia,” is still justified in these cases, as it applies to the atrial rate. SVT is quite frequent, although the exact incidence remains unclear, partly due to the large number of asymptomatic cases (demonstrated by Holter); however, the incidence of SVT increases with age and with the presence of structural heart disease. SVT may cause symptoms ranging from the sensation of “extra” or of “skipped” heart beats, to palpitations and even syncope. Additionally, in patients with underlying structural heart disease, it may exacerbate angina pectoris, HF, and/or hemodynamic instability. Occasionally, SVT may degenerate into ventricular tachyarrhythmia, with hemodynamic instability or sudden death, a particular concern in patients with professions impacting public safety (e.g., pilots). SVT may be difficult to differentiate from ventricular tachycardia, a condition with a different treatment and a significantly worse prognosis; moreover, the first-line treatments for SVT are generally contraindicated in VT. Additional concerns with SVT include the toxic (including proarrhythmic) effect of chronic AAD treatment and possible bleeding under antithrombotic therapy; the possibility of tachycardia-related CMP, in chronic cases; abolishment of the atrial kick, either due to AV discordance or to absent P waves (AF), precipitating HF in predisposed individuals; the risk of thromboembolism with AF and flutter (leading causes of stroke); and finally, the considerable amount of anxiety SVT generates.