Stable and Unstable Tachycardia

Tachycardia is a faster than normal heart rhythm (greater than 100 beats per minute for an adult) that can quickly deteriorate to cardiac arrest if left untreated.

“When looking at the ECG, tachycardia can be classified as narrow complex with a QRS less than 0.12 seconds or wide complex when the QRS exceeds 0.12 seconds.”

A narrow complex rhythm, sinus tachycardia (ST), is not considered an arrhythmia. Originating above the ventricles of the heart, supraventricular tachycardia (SVT) may have a wide or narrow QRS complex. A wide complex rhythm, VT, can deteriorate to VF and cardiac arrest, and therefore, must be treated immediately.

Tachycardia Algorithm

For the tachycardic patient:

  1. Identify and treat the cause of the dysrhythmia.

  2. Monitor cardiac rhythm, blood pressure and oxygenation.

  3. Determine if the patient is stable or unstable. Unstable tachycardia = hypotension, chest pain, symptoms of shock and possible decreased mentation.

  4. For unstable tachycardia, perform immediate synchronized cardioversion:

  5. If the QRS is narrow and regular, cardiovert with 50-100 Joules.

  6. If the QRS is narrow and irregular, cardiovert with 120-200 Joules.

  7. If the QRS is wide and regular, cardiovert with 100 Joules.

  8. If the QRS is wide and irregular, turn off the synchronization and defibrillate immediately.

  9. For stable tachycardia and a prolonged/wide QRS complex (>0.12 seconds), go to Step 7.

  10. For stable tachycardia with a normal/narrow QRS complex (≤0.12 seconds), consider performing vagal maneuvers.

  11. Establish an IV or IO to administer medications.

  12. Consider giving adenosine 6 mg IV bolus; give a second double dose (12 mg) if needed. Adenosine must be given rapidly. Consider using stop-cock technique with 10 cc flush on one attachment and adenosine syringe on second attachment.

  13. If adenosine does not terminate the tachycardia, consider procainamide 20-50 mg/minute IV (maximum dose = 17 mg/kg IV). Start a maintenance infusion of procainamide at 1-4 mg/minutes. Instead of procainamide, you may consider giving amiodarone 150 mg IV over 10 minutes with second dose for any recurrent VT. Start a maintenance infusion of amiodarone at 1 mg/min IV.