Paroxysmal Supraventricular Tachycardia (PSVT)

Key Features

Essentials of Diagnosis

• Rapid, regular tachycardia most commonly seen in young adults

• QRS duration narrow (< 120 msec) except in the presence of bundle branch block or accessory pathway

• Often responsive to vagal maneuvers, atrioventricular (AV) nodal blockers, or adenosine

• Cardioversion rarely required

General Considerations

• Characterized by a sudden onset and offset and a regular ventricular response

• Episodes may last from a few seconds to several hours or longer

• Often occurs in patients without structural heart disease

• The most common mechanism is reentry, which may be initiated or terminated by a fortuitously timed atrial or ventricular premature beat

  • AV nodal reentrant tachycardia (AVNRT)

    • The reentrant circuit usually involves dual pathways (a slow and a fast pathway) within the AV node

    • Accounts for 60% of cases of PSVT

  • AV reciprocating tachycardia (AVRT)

    • Reentry is due to an accessory pathway between the atria and ventricles

    • Less commonly (30% of cases)

Clinical Findings

• Symptoms can be variable depending on the degree of heart rate elevation, resultant hypotension, or the presence of other comorbidities

• Symptoms may include

  • Palpitations

  • Diaphoresis

  • Dyspnea

  • Dizziness

  • Mild chest pain (even in the absence of associated coronary heart disease [CHD])

• Syncope is rare

Diagnosis

• 12-lead ECG

  • Should be obtained when feasible to help determine the tachycardia mechanism

  • The QRS duration will be narrow (< 120 ms), except in cases of PSVT with aberrant conduction (left bundle branch block, right bundle branch block, or antegrade conducting accessory pathway)

  • Heart rate

    • Regular

    • Usually 160–220 beats/min

    • May be > 250 beats/min

  • P wave

    • Usually differs in contour from sinus beats

    • Often simultaneous with or just after the QRS complex

Treatment

• In the absence of structural heart disease, serious effects are rare, and most episodes resolve spontaneously

• Particular effort should be made to terminate the episode quickly if cardiac failure, syncope, or anginal pain develops or if there is underlying cardiac or (particularly) coronary disease

• Effective therapy requires that conduction be interrupted at some point in the reentry circuit and the majority of these circuits involve the AV node

Mechanical measures

• The Valsalva maneuver

  • Performed with the patient semirecumbent (45 degrees), exerting around 40 mm Hg of intrathoracic pressure (by blowing through a 10 mL syringe) for at least 15 seconds

  • Moving the patient supine immediately following the strain maneuver and passively raising the patient's legs for an additional 15 seconds may increase effectiveness of the maneuver

• Carotid sinus massage

  • Often performed by clinicians but should be avoided if the patient has a carotid bruit

  • Firm but gentle pressure and massage are applied first over the right carotid sinus for 10–20 seconds and, if unsuccessful, then ...