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Lesson

Synchronized Cardioversion in the Field

10 min Cardiac & ECG Skip to quiz

Objective: Use synchronized cardioversion when a fast rhythm with a pulse is why the patient is unstable. Confirm the sync markers on the R waves, then shock at the energy in your protocol.

Why this matters

If the patient has a pulse, a fast rhythm, and poor perfusion, prepare synchronized cardioversion. Do not give adenosine while the blood pressure is 60 systolic just because the shock feels harder. Unstable means poor perfusion from that rhythm. Your protocol owns the energy. For atrial fibrillation and atrial flutter, AHA 2025 prefers a higher first shock. The guideline example is 200 joules or more, not a low first setting. Do not shock sinus tachycardia that is compensating for another problem.

Key points
  • Sedate if they are awake and protocol allows it. This site does not publish a sedation dose. For atrial fibrillation and atrial flutter, AHA 2025 prefers a higher first shock, with 200 joules or more as the guideline example. Your protocol still chooses the number you deliver.
  • See the sync marks on the R waves before you charge. If it will not sync, you may be in VF (ventricular fibrillation), or the gain is wrong.
  • If they lose pulses, use unsynchronized defibrillation. Do not keep hunting for sync on a pulseless patient.

Clinical sequence

  1. If this is unstable tachycardia with a pulse and perfusion is failing, use electricity. Do not start with a medication infusion.
  2. Sedate if they are awake and protocol allows it. Place the pads so the shock goes through the heart. Turn SYNC on. Confirm the markers on the R waves.
  3. Shock at the protocol energy. If it fails and they lose the pulse, start CPR. If they still have a pulse, go to the next energy or the drug your protocol names.
  4. If the strip is wide and irregular, still do not give an AV-node blocker. If they arrest, treat it as VF or pVT (pulseless ventricular tachycardia).

Teaching points

  • Unstable signs: shock, severe altered mental status, ischemic pain, or acute heart failure. A heart rate of 150, by itself, is not a reason to shock.
  • Do not cardiovert sinus tachycardia that is compensating for another problem, such as fever, bleeding, or pulmonary embolism (PE). Treat the cause.
  • Pre-excited atrial fibrillation uses an extra pathway (Wolff-Parkinson-White). Do not give a drug that blocks the atrioventricular node. If the patient is unstable, cardiovert per protocol. Do not give adenosine.
  • After the shock, check the pulse and the rhythm. Then follow the pathway that matches what you find.

Common errors

  • Giving adenosine for unstable wide-complex tachycardia from habit.
  • Forgetting to turn SYNC on.
  • Cardioverting a talking patient with sinus tach from sepsis.

Practice

One-minute check

Partner gives three patients: (1) regular narrow rate 190, BP 50, sweating; (2) sinus at 130 with a fever and a GI bleed; (3) pulseless VT. For each, say sync, unsynchronized shock, or no shock.

Related: Stable vs unstable, SVT.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.

Check Your Understanding

Questions drawn only from this lesson. After you check, the key is highlighted. Education practice — not a certification exam.

1. Unstable regular narrow tachycardia with a pulse should get:
2. They become pulseless during setup. You should:
3. Sinus tach at 130 in a GI bleeder should get:
4. Energy for cardioversion comes from:
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