Ever wondered what the difference between synchronized and unsynchronized cardioversion is?
Synchronized cardioversion is a LOW ENERGY SHOCK that uses a sensor to deliver electricity that is synchronized with the peak of the QRS complex (the highest point of the R-wave). When the “sync” option is engaged on a defibrillator and the shock button pushed, there will be a delay in the shock. During this delay, the machine reads and synchronizes with the patients ECG rhythm. This occurs so that the shock can be delivered with or just after the peak of the R-wave in the patients QRS complex.
Synchronization avoids the delivery of a LOW ENERGY shock during cardiac repolarization (t-wave). If the shock occurs on the t-wave (during repolarization), there is a high likelihood that the shock can precipitate VF (Ventricular Fibrillation).
The most common indications for synchronized cardioversion are unstable atrial fibrillation, atrial flutter, atrial tachycardia, and supraventricular tachycardias. If medications fail in the stable patient with the before mentioned arrhythmias, synchronized cardioversion will most likely be indicated.
Unsynchronized cardioversion (defibrillation) is a HIGH ENERGY shock which is delivered as soon as the shock button is pushed on a defibrillator. This means that the shock may fall randomly anywhere within the cardiac cycle (QRS complex). Unsynchronized cardioversion (defibrillation) is used when there is no coordinated intrinsic electrical activity in the heart (pulseless VT/VF) or the defibrillator fails to synchronize in an unstable patient.
For cases where electrical shock is needed, if the patient is unstable, and you can see a QRS-t complex use (LOW ENERGY) synchronized cardioversion. If the patient is pulseless, or if the patient is unstable and the defibrillator will not synchronize, use (HIGH ENERGY) unsynchronized cardioversion (defibrillation).
Marie says
We should use synchronized cardioversion for VT with a pulse and on the other hand unsynchronized one for VT without a pulse. Since the underlying electrical physiology is more or less the same, the reason we treat them differently is what? Is it because VT with a pulse has comparatively slower rate, and the rest of the ventricle is more homogeneous, so the ventricle muscle can still manage to pump and for the VT without a pulse vice versa?
Jeff with admin. says
It is true that with pulseless VT, the very rapid rate makes it more difficult for the defibrillator to sync with the rhythm. There are two other reasons why synchronized cardioversion if favored for treating tachycardia with a pulse. 1. Using synchronized cardioversion prevents the risk of inducing ventricular fibrillation that can occur when using defibrillation (unsynchronized cardioversion). 2. Clinical experience and research has proved that synchronized cardioversion works better with tachycardia with a pulse and defibrillation works better with pulseless VT.
Kind regards,
Jeff
Simon Walsh says
Hi, this conversation came up in teaching. To what research and clinical experience are you referring? Do you have any links for this? Thanks.
Jeff with admin. says
Here is one of the primary source documents: Ventricular Tachycardia Rate and Morphology Determine Energy and Current Requirements for Transthoracic Cardioversion. You can also find a list of references at the bottom of this document that may guide your own research. Kind regards, Jeff
Niranjan Bhatia says
Thanks for the valuable information, you’ve made easy to understand.
leena pawar says
thanks for valuable informatin. if i may ask how to identify the risk of R on T phenomenon in a patient who is on demand pacing mode in the immediate post operative period ?
Jeff with admin. says
The risk of R on T phenomenon in a patient with demand pacing in the immediate post operative period would be the same for anyone with demand pacing. R on T is less likely to occur with demand pacing since the pacemaker is only providing a electrical impulse when no impulse is sensed by the pacemaker.
I hope that this answers your question.
This article may also give you some insights.
Kind regards,
Jeff
Ibtissam says
I had a very interesting night shift last night. Patient came in with stable conscious VT (on background of ischaemic heart disease) with multiple shocks from his implanted defibrillator. Amiodarone infusion was ineffective over some hours. Patient then deteriorated and became unstable.
It took us a while and several shocks (internal and external) before we used lignocaine with success.
Is there a guideline for managing the conscious stable VT patient if it is resistant to initial therapy. What drug is first line? procainamide or lignocaine or others? thanks.
Jeff with admin. says
The tachycardia algorithm would be the primary guideline for managing stable VT, but expert consultation would be important. There is no drug that would be considered “first line” and there is no guideline for this. One double blind study found no significant difference between antiarrhythmics. This case sounds like significant cardiovascular compromise/heart failure, and there is no easy answer when treating seriously diseased hearts.
Kind regards,
Jeff
Chang, Chih-Lun says
May I chose the synchroniezd on bradycardia( 30bpm, QT prolong) patient, sometime showed run multiple VPCs. So I use the TCP for keep the heart rate > 80bpm. Thank you!
Jeff with admin. says
If the VT is not persistent, you would not treat with synchronized cardioversion. Treat the cause of the bradycardia and you will most likely correct the irritability that is causing the PVC’s. Atropine followed by TCP if the atropine is ineffective would be the proper treatment of choice.
Kind regards,
Jeff
Ramon says
Could you explain why a patient would sometimes go into VFib after a synchornized cardioversion? Does it always meant that the shock was delivered on the later half of the T-wave (R on T phenomenon)? Synchronized cardioversion is suppose to deliver the shock on the QRS complexes or just after the QRS right?
Jeff with admin. says
VF is always a risk when performing cardioversion. VF after a shock does not always mean that the shock was delivered on the T-wave.
The shock is supposed to be delivered just after the peak of the R-wave in the patients QRS complex.
Kind regards,
Jeff
Carter Newton says
Excellent work and dialogue, thanks. I am not convinced that a “blind defibrillation” risking a shock during the T wave is that dangerous. I know with a patient wired up in the EP lab, it is real, but with an external defibrillation not seeing an ECG (dont have an automated device with a machine read) is there really a risk that outweighs the risk of a delay. I have searched for literature on this but so far am empty handed. Your thoughts would be helpful.
Thanks
Jeff with admin. says
First- Animal research demonstrates a clear risk for delivering electricity during repolarization. Second- all modern manual defibrillators have the capability to synchronize and view the rhythm. The situation that this person is describing could not happen. I guess the closest thing that would simulate the described situation is performing a cardiac thump in an out-of-hospital situation.
Kind regards,
Jeff
angie says
What if the patient suddenly had undetermined BP and no pulse but rhythm is unknown (since the pt is not hooked on the cardiac monitor) is it right to perform CPR first prior to defibrillation? thanks in advance.
Jeff with admin. says
You would start CPR and continue with CPR until you can determine what the rhythm is.
Kind regards,
Jeff
GlendaHMCS says
What is the speed for pacing?
Jeff with admin. says
The desired rate is usually 60 /min., but you would also titrate up as needed to improve the patients perfusion status.
Kind regards,
Jeff
ignacy baumberg says
It is said, that t-wave shock may precipitate the VF – ok… But in VT with pulse and without there is no difference in ECG curve sometimes – does the leak of pulse excludes the risk of t-wave shock causing VF?
Jeff with admin. says
VT with a pulse should be treated using synchronized cardioversion. This prevents the shock from being delivered on the T-wave. If the t-wave is not distinguishable, the machine will not sync. In this case, you would use unsynchronized cardioversion (defibrillation).
Kind regards,
Jeff
ignacy baumberg says
It is said, that t-wave shock may precipitate the VF – ok… But in VT with pulse and without there is no difference in ECG curve sometimes – does the leak of pulse excludes the risk of t-wave shock causing VF?
Jeff with admin. says
VT with a pulse should be treated using synchronized cardioversion. This prevents the shock from being delivered on the T-wave. If the t-wave is not distinguishable, the machine will not sync. In this case, you would use unsynchronized cardioversion (defibrillation).
Kind regards,
Jeff
James Taylor says
Have you heard of any changes to the increased energy level during a cardiac arrest defibrillation? Is is true that you give your first shock at 120 then increase with each shock?
Jeff with admin. says
At this time AHA recommends starting at 120 J and incrementally increasing the shock dose. (120 – 200 -300 – 360)
There are many cardiologists that go straight to 360, but this is not the standard of care set forth in the AHA ACLS guidelines at this time.
Kind regards,
Jeff
grisuna says
is there fixed amount of joule or voltage of energy per gram tissue of myocardium that is needed for defibrilation?
Jeff with admin. says
I am not aware of a fixed about of energy that is needed for defibrillation. This is why there is an incremental increase in the shock dose if conversion fails. 120 then 200 then 300 then 360.
Kind regards,
Jeff
Kenneth says
In which tachydysrhythmias would synchronized cardioversion not be appropriate? other than VT without a pulse and sinus tach? and not considering inability to sync
Jeff with admin. says
Synchronized cardioversion is used in all cases for unstable tachycardia with a pulse. This is assuming that the defibrillator will sync with the patients rhythm.
Kind regards,
Jeff
David says
Last night at con-ed we discussed synchronized cardioversion and shock dosage. There was a question that arose with regards to the dosage when a patient goes into Pulseless Vfib/Vt following multiple cardioversion attempts and increase in dosage. So if I cardiovert at 300j and the pt then develops a pulseless rhythm, would my first defibrillation be at 200j , 300j, or 360j? The debate is between a change in protocol (and starting from the beginning) vs. Continued increase in joules for a response….
Jeff with admin. says
If you cardiovert at 300 J and then the patient develops a pulseless rhythm, you should increase the shock dose from 300J to 360J in this situation.
The more shocks that take place, the less susceptible the heart is to the dose of electricity. This is why you always increase the dose in a stepwise fashion.
I hope this answers your question.
Kind regards,
Jeff
Cruiz says
How to treat patient with recurrent svt/vt ? If you have give patient with antiarythmia drug. I have patient with atrial fibrillation and become VT, I have to treat following Acls algorithm and patient back again to Atrial fibrillation, this condition not in long time, just in 30 minute patient have to VT again. I have give patient with amiodaron injection. In my patient there’s history of hypertension and stroke non hemoragic, GCS E4M4V1. Thanks
Jeff with admin. says
This type of scenario would require expert consultation with a cardiologist. I have seen similar situations where the physician would use either an amiodarone drip or a lidocaine drip to help control arrhythmias. Some type of continuous IV calcium channel blocker may be in order. If VF reoccurs, you will use ACLS protocol for VF. Kind regards, Jeff