What does a pacemaker do in supraventricular tachycardia (SVT)?

Role of Pacemakers in Supraventricular Tachycardia (SVT)

Pacemakers can effectively terminate SVT through programmed stimulation and rapid overdrive pacing techniques when drugs fail to control the arrhythmia or produce intolerable side effects. 1

Mechanisms of Action in SVT

Pacemakers can manage SVT through several mechanisms:

1. Termination of Reentrant Rhythms:

   • Pacemakers can interrupt reentrant SVTs using:
     • Programmed stimulation (single or multiple extrastimuli)
     • Short bursts of rapid pacing 1
   • These antitachycardia pacing (ATP) techniques work by disrupting the reentry circuit

2. Prevention of Recurrences:

   • Atrial synchronous ventricular pacing may prevent recurrences of reentrant SVT 1
   • Continuous pacing can be used to prevent pause-dependent arrhythmias 1

3. Automatic Detection and Response:

   • Modern antitachycardia devices can automatically detect SVT and activate a pacing sequence
   • Some respond to external instructions (e.g., application of a magnet) 1

Efficacy and Safety Considerations

• Efficacy: Approximately 30-60% of atrial tachyarrhythmias can be terminated with atrial ATP in patients with pacemakers 1

• Safety Precautions:

  • Important: All pacing for SVT termination should be done in the atrium because of the risk of ventricular pacing-induced proarrhythmia 1
  • Patients should undergo extensive testing before implantation to ensure the device safely terminates arrhythmias without:
    • Accelerating the tachycardia
    • Inducing ventricular fibrillation 1

• Contraindications:

  • Pacemakers are not indicated for SVT in patients with accessory pathways having capacity for rapid anterograde conduction 1
  • Should not be used for tachycardias that are accelerated or converted to fibrillation by pacing 1

Clinical Indications for Pacemakers in SVT

According to ACC/AHA guidelines, pacemakers for SVT are indicated in:

• Class I (Definite indication):

  • Symptomatic recurrent SVT when drugs fail to control the arrhythmia or produce intolerable side effects 1
  • Atrioventricular reentrant or AV node reentrant SVT not responsive to medical therapy 1

• Class IIa (Reasonable indication):

  • Permanent pacing is reasonable for symptomatic recurrent SVT that is reproducibly terminated by pacing when catheter ablation and/or drugs fail 1

• Class II (May be considered):

  • Recurrent SVT as an alternative to drug therapy 1

Modern Pacemaker Technology for SVT

• Dual-chamber pacemakers and ICDs may incorporate suites of atrial therapies that are automatically applied upon detection of atrial tachyarrhythmias 1

• Programming considerations:

  • Programmability is essential for successful long-term efficacy due to changing requirements for effective termination 2
  • ATP algorithms should not be activated until the atrial lead is chronically stable to prevent accidental dislodgement into the ventricle 1

Practical Considerations

• Pacemaker therapy for SVT has been shown to significantly improve quality of life by avoiding prolonged episodes of tachycardia and repetitive hospital admissions 3

• In patients with drug-resistant SVT, pacemakers can reduce hospital admissions from one per patient-month to one per 137 patient-months 3

• Some patients may require combination therapy with antiarrhythmic drugs and conservative antitachycardia pacing modes to avoid pacing-induced atrial fibrillation 3

• The decision to use a pacemaker to control tachycardias should be made only after careful observation and electrophysiologic study by experienced specialists 1

While catheter ablation is now recommended as first-line therapy for many forms of SVT, pacemaker therapy remains an important option for patients who are not candidates for ablation or in whom ablation has failed.