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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 bystander 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

      • Must also be used with caution in patients with reactive airways disease because it ...

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