Tachycardia, Paroxysmal Supraventricular

Key Features

Essentials of Diagnosis

• Rapid, regular tachycardia most commonly seen in young adults and characterized by abrupt onset and offset

• QRS duration narrow (< 120 ms) 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 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)

  • Defined as the reentrant circuit usually involving dual pathways (a slow and a fast pathway) within the AV node

  • Accounts for 60% of cases of paroxysmal supraventricular tachycardia (PSVT)

• Atrioventricular reciprocating tachycardia (AVRT)

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

  • Accounts for 30% of cases of PSVT

Clinical Findings

• Variable; depend on the degree of heart rate elevation, resultant hypotension or the presence of other comorbidities

• May include palpitations, diaphoresis, dyspnea, dizziness, and mild chest pain (even in the absence of associated coronary heart disease)

• Syncope is rare

• Diagnosis

• Obtaining a 12-lead ECG when feasible is important 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)

• The heart rate regular and is usually 160–220 beats/min but may be > 250 beats/min

• The P wave usually differs in contour from sinus beats and is 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

• Mechanical Measures

  • Valsalva maneuver

  • Lowering the head between the knees

  • Coughing

  • Splashing cold water on the face

  • Breath holding

• Pharmacotherapy

  • Intravenous adenosine

    • First-line agent due to its brief duration of action and minimal negative inotropic activity (Table 10–11)

    • Dosage: 6 mg bolus followed by 20 mL of fluid; can be given rapidly (in 1–2 seconds) because the half-life of adenosine is < 10 seconds

    • If this regimen is unsuccessful at terminating the arrhythmia, a second higher dose (12 mg) may be given

    • Minor side effects are common and include

      • Transient flushing

      • Chest discomfort

      • Nausea

      • Headache

    • May cause atrial fibrillation (in up to 12% of patients) or rarely ventricular arrhythmias and therefore administration should be performed with continuous cardiac monitoring and availability of an external defibrillator

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