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).
shaneparkk says
Can you explain the R on T phenomenon leading to V fib pathophys. How does a shock given during the T wave or replorization lead to v fib?
Jeff with admin. says
The T-Wave represents repolarization of the ventricles. The apex of the T-Wave is referred to as the absolute refractory period. The last half of the T-Wave is referred to as the relative refractory period. This last half of the T-wave is considered the vulnerable period when depolarization can cause problems.
When an unsynchronized shock (depolarization) occurs during this vulnerable period on the last half of the T-Wave, it causes depolarization of cardiac cells that are at different stages of the action potential. Some are depolarized and others are at different levels of repolarization. Since some are depolarized, this acts as a block. Some are completely repolarized, allowing the impulse (from the shock) to travel down the cardiac branches, then up again to the previously depolarized cells, and round and round.
Basically, you have cardiac cells that are now NOT working as a synchronized unit. There is random depolarization and repolarization occurring throughout the heart, thus completely eliminating the hearts ability to pump. This unorganized (random depolarization and repolarization) electrical activity is called ventricular fibrillation.
I hope this makes sense.
Kind regards,
Jeff
Hoo Cheung says
Thanks, Jeff. This is the best physiological explanation of the R on T phenomenon and effects .
Mark J Cooper says
Jeff, this is a great explanation. Thank you.
ACLS says
Hi Mark,
You’re very welcome. Stay safe!
Kind regards, Jeff
rengie says
Why can’t you just stick with the AHA algorithm? You consider expert consultation if your medications fail to convert a stable tachyarrythmia. True, the Cardiologist may order a sychronized cardioversion if your adenosine, beta blockers and calcium channel blockers fail, but just leave it to them.
Jeff with admin. says
I do try to stick to the American Heart Association guidelines as possible.
Kind regards,
Jeff
laurie 1 says
I was told today that any shockable rhythm that has pulse you must sync the shcok. If ther is no pulse than use unsync shock. Is this correct.
Jeff with admin. says
This is correct. The only instance where you would perform unsynchronized shock on tachycardia with a pulse would be if the machine will not synch with the rhythm. Example: polymorphic VT with a pulse.
Kind regards,
Jeff
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Jake says
If an unsuccessful synced shock moved a pt into VF would you immediately start compressions or would you defib as the rhythm change was witnessed?
Jeff with admin. says
Since the change was witnessed and you have a defibrillator connected, the next appropriate step would be to give the patient one high energy unsynchronized shock.
Kind regards,
Jeff
Rachael says
The last box that has a red outline says ” if your patient is stable use synchronized cardioversion” which you mainly used with tachycardia, there are two types of tachycardia, stable ( no signs and symptoms and treat with adenosine) vs unstable ( with signs and would use synchronized )
with unstable tachycardia you use synchronized, so saying using it when you are stable is not correct
Rachael says
Thank you the help though, best source found so far
Jeff with admin. says
Here is why the statement can be correct:
In cases where a patient has stable atrial fibrillation or stable atrial flutter, they may need to have synchronized cardioversion to eliminate the fibrillation or flutter. In this case a patient would be stable and still be receiving synchronized cardioversion.
Kind regards,
Jeff
Mahesh Jadhav says
You have mention the Jules in one question but not the type of defibrillator; biphsic/monophasic?
Jeff with admin. says
Assumed for this site that all references to defibrillators are referring to biphasic defibrillators.
Biphasic is becoming the standard of care.
Kind regards,
Jeff
san says
I read there are certain cases of V tach where you would use Synchronized cardiover. Is it true and when would we use it?
Jeff with admin. says
It is true. You would use synchronized cardioversion for symptomatic ventricular tachycardia with a pulse.
Unsynchronized cardioversion/defibrillation would be used for pulseless ventricular tachycardia or for symptomatic ventricular tachycardia with a pulse that has a rhythm that will not sync with the cardioversion machine.
Kind regards,
Jeff
Yan says
Jeff
This is the best and simplest explaination.
Appreciate your job very much.
Yan
Dr.Punitha says
Jeff, Can low energy cardio version work for pulseless VT ? Or should we go for defibrillation only.
Jeff with admin. says
Low energy cardioversion will not be effective for pulseless VT/VF and may in fact make further shocks less effective. Start with at least 120 and increase the shocks in a step-wise fashion. You should increase at least 50 joules with each successive shock. Here is what AHA recommends 120-200-300-360. I think that the literature supports AHA’s position.
Kind regards,
Jeff
Michael says
You are doing a very big job here thanks,
Can you pls tell me in a very brief what is happening in VF and VT as well as their recognition.
Jeff with admin. says
This page will help you understand VF
This page will help you understand VT
Kind regards,
Jeff
Tori says
Do you have to have the 3 lead ekg leads attached as well as the pads to do sychronized cardioversion?
Jeff with admin. says
Yes. To perform synchronized cardioversion, you must have the 3 lead EKG leads attached as well as the 2 cardioversion pads. The 3 leads read the ECG and help the machine synchronize with the rhythm.
For unsynchronized, the 3 leads are not necessary.
Kind regards, Jeff
Dr Praveen says
Thank you for the explaination
Rashminder Singh says
thanx for such a clear explanation of the differences
mojgan says
thank you very much.after several years i could solve my problem in this field:-)