• Clinical science

Paroxysmal supraventricular tachycardia (Supraventricular tachyarrhythmia)

Abstract

Paroxysmal supraventricular tachycardia (PSVT) is a type of arrhythmia arising from a defect in atrioventricular conduction, which causes the heart to sporadically beat faster. There are different forms of PSVT, including atrioventricular nodal reentrant tachycardia (AVNRT; about two-thirds of cases), atrioventricular reentrant (or reciprocating) tachycardia (AVRT), and atrial tachycardias. In AVNRT, extra electrical conduction pathways (accessory pathways) within the AV node lead to non-extinguishable, circulating electrical impulses (reentrant circuits). AVRT, on the contrary, is caused by circular depolarizations that travel through ectopic connections between the atria and ventricles. PSVT is characterized by tachycardia attacks that may cause dizziness, dyspnea, chest pain or syncope, and are usually self-limiting. Diagnostic steps for any type of PSVT include obtaining the patient history and a 12-lead ECG, which typically shows tachycardia and narrow QRS complexes. Because most tachycardia attacks subside before an ECG is conducted, continuous recording with a Holter monitor is often needed to confirm the diagnosis. In some cases, invasive electrophysiological studies may be indicated. Patients with a congenital condition known as Wolff-Parkinson-White (WPW) syndrome commonly exhibit AVRT because of the presence of an accessory pathway known as the bundle of Kent. This pathway bypasses the AV node and transmits the sinus impulse directly to the ventricles, resulting in a premature depolarization (pre-excitation) that appears as a delta wave on ECG. Management of PSVT should be tailored to the individual patient: hemodynamically unstable patients should undergo urgent cardioversion, whereas patients who are hemodynamically stable may benefit from vagal maneuvers, e.g., carotid massage. Pharmacologic therapy is indicated if the sinus rhythm cannot be restored by vagal maneuvers. The appropriate drug depends on the conduction pathway in the heart as revealed by ECG findings. Catheter ablation may be performed as a definitive treatment.

Epidemiology

  • Prevalence: ∼ 2.25 per 1000 people
  • Sex: > (2:1)
  • Age of onset

References:[1][2]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

References:[1][3][4]

Pathophysiology

AVNRT

  • The AV node contains two electrical pathways: one fast and one slow → the electrical impulse circles around the AV node within both pathways → continuous circuit that conducts impulses to the ventricles → tachycardia
  • Approx. 90% of cases are due to anterograde conduction across the slow-conducting pathway and retrograde in the fast pathway (although the reverse is possible)

AVRT

  • There are two types of atrioventricular reentrant tachycardia. The direction of the reciprocating impulse helps distinguish between the two:
    • Orthodromic AVRT: most common (90–95%) → narrow QRS complex
      • Antegrade conduction (atrium → ventricle) through AV node; retrograde conduction (ventricle → atrium) through accessory pathway
    • Antidromic AVRT: least common (5–10%) → delta wave
      • Antegrade conduction (atrium → ventricle) through accessory pathway; retrograde conduction (ventricle → atrium) through AV node

Do not confuse atrioventricular reentrant (or reciprocating) tachycardia (AVRT) with atrioventricular nodal reentrant tachycardia (AVNRT)! AVRT is caused by an accessory pathway between the atrium and ventricle, while in cases of AVNRT, there are two functional pathways present within the AV node!

References:[5][6]

Clinical features

References:[1][7]

Diagnostics

ECG

A 12-lead ECG should be performed in patients suspected of PSVT. If inconclusive, consider recording the heart's electrical activity for 24 to 48 hours with a Holter monitor or event recorder.

ECG findings in AVNRT

ECG findings in AVRT

  • Orthodromic AVRT:
  • Antidromic AVRT:
    • Shortened PR interval
    • Delta wave = slurred upstroke in QRS complex due to pre-excitation wide QRS complex
      • This feature of pre-excitation can not be observed during tachycardia or in a patient with "concealed pathway" (retrograde conduction)
      • Commonly found on ECG in WPW
      • Not visible during tachycardia or in patients with a concealed pathway (retrograde conduction)
        • Delta wave positive in lead V1 and negative in leads I, aVL (left-sided accessory pathway)
        • Delta wave negative in lead V1 and positive in leads I, aVL (right-sided accessory pathway)

Steps for identifying underlying causes

  • Laboratory tests
  • Imaging
  • Electrophysiological studies
    • A catheter is inserted into a large vein (typically the femoral) and guided to the heart
    • Wire electrodes are inserted that measure the heart's electrical activity
    • Intracardiac recordings help identify accessory pathways and reentry circuits
    • Generally conducted in combination with radiofrequency catheter ablation of accessory pathways

References:[5][1][7]

Differential diagnoses

References:[7][8]

The differential diagnoses listed here are not exhaustive.

Treatment

Hemodynamically unstable patient

  • Cardioversion: fastest and most effective treatment of supraventricular tachycardia

Hemodynamically stable patient

  • Goal: re-establish and maintain sinus rhythm
  • Most asymptomatic patients do not require medical intervention, so observation is sufficient

Acute Management of PSVT

AV nodal blocking agents (i.e., adenosine, verapamil, beta-blockers, digoxin, amiodarone) are contraindicated in patients with signs of preexcited tachycardia on ECG (e.g., antidromic AVRT; AF in WPW patient)!

Administration of adenosine and calcium channel blockers together may potentiate a bradycardic or hypotensive response!

Long-term management of PSVT

  • For the management of well-tolerated, infrequent episodes, the patient may be instructed to perform vagal maneuvers
  • Catheter radiofrequency ablation
    • First-line therapy (curative) in AVNRT, AVRT, or drug refractory AT
    • Indicated especially for:
      • Symptomatic patients with concomitant structural heart disease
      • Symptomatic patients who want to avoid long-term drug therapy (especially younger patients)
      • Asymptomatic patients with special lifestyle considerations (e.g., pilots)
  • Medical therapy (second line)

References:[1][9][10][11]