What is Synchronized Cardioversion?

Synchronized cardioversion is a treatment technique that uses a sensor to deliver a shock that is synchronized with a peak in the QRS complex.

Defibrillators can deliver two types of shocks – synchronized and unsynchronized. Unsynchronized shocks refer to a shock that is delivered immediately after the healthcare professional pushes the shock button. This means that the shock is not delivered precisely in the cardiac cycle; in other words, unsynchronized shocks are more random.

However, when a healthcare provider uses synchronized cardioversion, after pushing the shock button, that shock may not be delivered immediately. Instead, the shock delivery will be synced with the peak of the R wave in the patient’s QRS complex.

Synchronization avoids the delivery of a shock during cardiac repolarization, which is represented on the surface ECG as the T wave. This is a period of vulnerability in which a shock can precipitate VFib.

Synchronized cardioversion uses a lower energy level than normal defibrillation. These low-energy shocks must always be delivered as synchronized shocks to avoid precipitating VFib.

When is Synchronized Cardioversion Used?

Synchronized cardioversion is recommended in some ACLS algorithms, such as unstable tachycardia, particularly when a persistent tachyarrhythmia is causing the following to occur:

  • Hypotension
  • Acutely altered mental state
  • Signs of shock
  • Ischemic chest discomfort
  • Acute heart failure

Synchronized Cardioversion Technique

Synchronized cardioversion is the recommended treatment for patients who have a symptomatic, unstable reentry SVT or V-tach with pulses. Synchronized cardioversion is also routinely used to treat unstable atrial flutter and unstable atrial fibrillation.

Cardioversion may not be effective when treating junctional tachycardia or ectopic or multifocal atrial tachycardia, as these rhythms have an automatic focus arising from cells that are spontaneously depolarizing at a rapid rate. In these scenarios, the delivery of a shock typically cannot stop these rhythms. In fact, it may actually increase the rate of the tachyarrhythmia.

When performing synchronized cardioversion, the shocks are administered through either adhesive electrodes or handheld paddles. Healthcare providers must place the defibrillator/monitor in synchronized mode, which is designed to deliver energy just after the R wave of the QRS complex.

Synchronized Cardioversion Steps

ACLS providers should be aware that they may have to modify these steps for the specific device they’ll be using.

  1. Sedate conscious patients unless they are unstable or rapidly deteriorating.
  2. Turn on the monophasic or biphasic defibrillator.
  3. Attach the monitor leads to the patient. Remember lead placement with this – white to right, red to ribs, what’s left over to the left shoulder. You should also ensure that the patient’s rhythm is displayed properly. Then position the adhesive electrode or conductor pads on the patient.
  4. Engage the synchronization mode by pressing the sync control button.
  5. Look for markers on the R wave which indicate the sync mode.
  6. Adjust the monitor, if necessary, until the sync markers occur with each R wave.
  7. Choose the appropriate energy level and deliver monophasic synchronized shocks in the following sequence:
    a. If treating unstable atrial fibrillation, the initial dose is 200 J.
    b. If treating unstable monomorphic V-tach, the initial dose is 100 J.
    c. If treating another unstable SVT or atrial flutter, the initial dose is 50 to 100 J.
    d. If treating unstable polymorphic V-tach, you should treat it as VFib and deliver a high-energy shock.
  8. Make an announcement to the team members that you’re charging the defibrillator and tell everyone to stand clear.
  9. Press the charge button.
  10. Make sure the patient is clear once more after the defibrillator is charged.
  11. Press the shock button.
  12. Check the monitor. If tachycardia continues to persist, you should increase the energy level according to the Electrical Cardioversion Algorithm.
  13. Activate the sync mode. This should be done after each synchronized shock. Be aware that many defibrillators will default back to the unsynchronized mode after delivery of a synchronized shock. This default allows for an immediate shock if your cardioversion efforts produce VFib in the patient.

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