What is the management for a patient with tachycardia and a heart rate of 120 beats per minute (bpm)?

Management of Tachycardia with Heart Rate of 120 bpm

For a patient with tachycardia and heart rate of 120 beats per minute, initial assessment should focus on hemodynamic stability and identifying the underlying rhythm, with treatment directed at the cause rather than simply normalizing the heart rate. 1

Initial Evaluation

• Assess for signs of increased work of breathing (tachypnea, intercostal retractions, suprasternal retractions) and check oxygen saturation via pulse oximetry 1
• Provide supplementary oxygen if oxygenation is inadequate or patient shows signs of respiratory distress 1
• Attach cardiac monitor, evaluate blood pressure, and establish IV access 1
• Obtain a 12-lead ECG to define the rhythm (if available and patient is stable) 1
• Evaluate for potential reversible causes of tachycardia 1

Assessment of Stability and Rhythm Classification

• Determine if the patient is hemodynamically stable or unstable 1
• Assess for signs of instability: acute altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or other signs of shock 1
• Classify the tachycardia based on QRS duration:
  • Narrow complex (<120 ms): Most likely supraventricular in origin 1
  • Wide complex (≥120 ms): Could be ventricular tachycardia or supraventricular tachycardia with aberrancy 1

Management Algorithm

For Hemodynamically Unstable Patients (regardless of QRS width)

• Proceed to immediate synchronized cardioversion 1
• Recommended initial energy doses:
  • For atrial fibrillation: 120-200 J biphasic 1
  • For atrial flutter and other SVTs: 50-100 J initially, increasing in stepwise fashion if unsuccessful 1
  • For monomorphic VT: 100 J initially, with stepwise increase if needed 1

For Hemodynamically Stable Patients

If Heart Rate is 120 bpm:

• At this heart rate (120 bpm), it is unlikely that symptoms of instability are primarily caused by the tachycardia unless there is impaired ventricular function 1
• Identify the specific rhythm:

1. If Sinus Tachycardia (most common):

   • No specific drug treatment required 1
   • Therapy should be directed toward identifying and treating the underlying cause (fever, anemia, hypotension/shock, etc.) 1
   • Be cautious about "normalizing" heart rate when cardiac function is poor, as cardiac output may be dependent on the rapid rate 1

2. If Narrow Complex SVT (AVNRT, AVRT, atrial tachycardia):

   • Try vagal maneuvers 1
   • If unsuccessful, administer adenosine:
     • First dose: 6 mg rapid IV push followed by saline flush 1
     • Second dose: 12 mg if required 1
   • For persistent SVT, consider beta-blockers or calcium channel blockers 1, 2

3. If Atrial Fibrillation or Flutter:

   • Rate control with beta-blockers or calcium channel blockers 1
   • Consider anticoagulation based on stroke risk 1

4. If Wide Complex Tachycardia:

   • Treat as ventricular tachycardia unless proven otherwise 1
   • For stable monomorphic VT:
     • Procainamide: 20-50 mg/min until arrhythmia suppressed (maximum dose 17 mg/kg) 1, 3
     • Alternatively, amiodarone: 150 mg over 10 minutes 1

Important Considerations

• With heart rates <150 beats per minute (like 120 bpm in this case), the tachycardia is more likely secondary to an underlying condition rather than the primary cause of any instability 1
• Avoid verapamil or diltiazem in wide-complex tachycardias of uncertain origin, as they may cause hemodynamic collapse if the rhythm is ventricular tachycardia 1
• All patients treated for SVT should be referred for heart rhythm specialist opinion for long-term management 2
• Correct any underlying disorders that may precipitate tachyarrhythmias (e.g., hypokalaemia, hypomagnesaemia, myocardial ischemia) 4

Common Pitfalls to Avoid

• Treating the heart rate without identifying the underlying rhythm and cause 1
• Assuming all wide-complex tachycardias are ventricular in origin (some are supraventricular with aberrancy) 5, 6
• Failing to recognize that at a heart rate of 120 bpm, symptoms are often due to the underlying condition rather than the tachycardia itself 1
• Normalizing heart rate in compensatory tachycardias where cardiac output depends on the rapid rate 1