What to give in a patient with Supraventricular Tachycardia (SVT) whose heart rate is dropping to bradycardia?

Management of SVT with Bradycardia

In a patient with SVT whose heart rate is dropping to low 50s, atropine is the first-line treatment to address the bradycardia, with a recommended dose of 0.5 mg IV up to a maximum of 3 mg, titrating according to heart rate response. 1

Initial Assessment and Management

When dealing with a patient who has had SVT but is now developing bradycardia (HR in low 50s), follow this approach:

1. Assess hemodynamic stability:

   • If patient shows signs of cardiac failure, hypotension, or altered mental status with bradycardia < 40 bpm, immediate intervention is required
   • Monitor vital signs continuously

2. First-line treatment:

   • Atropine: Start with 0.5 mg IV, can be repeated up to a total dose of 3 mg
   • Titrate dose according to heart rate response
   • Goal: Increase heart rate to physiologically appropriate level (>60 bpm)

3. Monitoring for complications:

   • Watch for excessive tachycardia after atropine administration
   • Monitor for signs of myocardial ischemia
   • Continuous cardiac monitoring is essential

Management Algorithm

For bradycardia after SVT:

1. If bradycardia < 40 bpm OR symptomatic (hypotension, altered mental status, cardiac failure):

   • Administer atropine 0.5 mg IV
   • Reassess after 3-5 minutes
   • If inadequate response, repeat atropine 0.5 mg IV every 3-5 minutes up to maximum 3 mg

2. If bradycardia persists despite atropine:

   • Prepare for temporary cardiac pacing, especially if:
     • Pauses longer than three seconds
     • Mobitz type II heart block
     • Type II heart block with anterior myocardial infarction
     • Previous asystole 1

3. If bradycardia is transient and patient is stable:

   • Observe with continuous monitoring
   • Prepare for intervention if clinical deterioration occurs

Cautions and Considerations

• Avoid AV nodal blocking agents that may have caused or worsened the bradycardia:

  • Calcium channel blockers (verapamil, diltiazem)
  • Beta-blockers
  • Digoxin 1

• Avoid combination of AV nodal blocking agents with longer duration of action, as profound bradycardia can develop if given serially 1

• For patients with pre-excited atrial fibrillation or flutter:

  • AV nodal blocking agents are contraindicated as they may accelerate ventricular response 1

• For inferior myocardial infarction patients:

  • Transient bradycardias are common and may require more aggressive management 1

Special Considerations

• If the patient has pauses longer than three seconds or high-grade AV block, temporary cardiac pacing may be necessary regardless of atropine response 1

• For patients with SVT who developed bradycardia after treatment with AV nodal blocking agents, the effects of adenosine are short-lived (half-life of seconds), but calcium channel blockers and beta-blockers have longer durations of action 1

• Electrophysiology consultation should be considered for definitive management once the acute bradycardia is resolved

By following this algorithm, you can effectively manage a patient with SVT whose heart rate has dropped to the low 50s, prioritizing treatments that address the immediate bradycardia while preparing for escalation of care if needed.