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).
Boles says
In stable VT would we use synchronised or unsynchronized mode ?
Jeff with admin. says
For the purposes of advanced cardiac life support, you would not perform any type of cardioversion or defibrillation for a stable ventricular tachycardia. Other interventions would be performed. If a stable ventricular tachycardia with a pulse becomes unstable VT with a pulse you would use synchronized cardioversion.
In the case where someone is receiving an elective cardioversion for stable ventricular tachycardia, synchronized cardioversion him would be used.
Kind regards,
Jeff
pakiza says
Synchronised cardioversion means DC cardioverion?
Jeff with admin. says
Cardioversion is defined as a “synchronized DC discharge. Within the framework of ACLS, this is typically stated as “synchronized cardioversion” or even more simply as “cardioversion”.
You will see these two terms “cardioversion” and “defibrillation.”
Cardioversion is synchronized. Defibrillation is unsynchronized.
Kind regards,
Jeff
subbiah EMS says
if the patient has pulse VT and the patient is stable what should i do?
Jeff with admin. says
There are a lot of variables with this scenario that are not known. These things would need to be known prior to treatment.
Generally speaking, you would need to consult a cardiologist to treat the stable ventricular tachycardia.
This would probably require an admission to the intensive care unit and the use of antiarrhythmics to control the ventricular tachycardia it until cardiac consultation is completed.
There are a number of different treatments that can be used for stable tachycardia these include calcium channel blocker’s, beta blockers, and antiarrhythmics. The patient history and cause would help determine which medication would be appropriate.
Kind regards,
Jeff
V says
Amio or lido
Shauna pitchford says
Hi I’m a UK based als instructor. Got asked today if sync-cardioverted a VT with a pulse, and then it turned into VF, do you immediately start cpr for 2 mins as the myocardium is stunned from 100j,or do you immediately give an unsynchronised shock as the pt is already attached to the defibrillator?
Thanks,
Shauna
Jeff with admin. says
If they are already attached to the defibrillator the you would switch off SYNC and provide a single shock at 200j or higher.
After the shock, you would immediately began CPR for five cycles.
The earlier that defibrillation occurs the greater the chance that it will convert into a organized rhythm.
Kind regards,
Jeff
Autumn says
Thank you so much for this site, it helped tremendously. I am left with one question though. Your information states to increase the J when defibrillating VT for VF with a biphasic. My defibrillator today was biphasic, but I was told by my instructor that we only shock with 200J for VT/VF. Do you know why this is? I wasn’t able to get an answer. Thanks.
Jeff with admin. says
It may be that the defibrillator you are using only has a setting for 200 J. There are some defibrillators that only use a single dose setting.
I do not know of any other reason besides this one why you would only use a 200 J setting. The American Heart Association guidelines clearly state begin defibrillation at 120 J and increase in a stepwise fashion.
120-200-300-360.
Kind regards,
Jeff
Casey says
What is the difference in PEA and pulse less V-tach? I thought that pulse less V-tach would fall under PEA and that you would not defibrillated it.
Jeff with admin. says
Watch the video at the bottom of the following page for the answer to your question: PEA Video
Lawrenzo says
PEA to my understanding was a wave form showing on the monitor but the PT has no electrical capture
Jeff with admin. says
PEA is Electrical capture and conduction that does not produce a palpable pulse. The electrical current travels through the heart but fails to produce muscular contraction strong enough to generate a palpable pulse.
Kind regards,
Jeff
Lily says
Hi, does synchronise cardioversion can be used for unstable patient with polymorphic ventricular tachycardia?
Jeff with admin. says
No, you most likely would not be able to perform synchronize cardioversion for polymorphic ventricular tachycardia. Polymorphic ventricular tachycardia and usually requires the use of unsynchronized high energy shocks.
Kind regards, Jeff
William says
Hi. I wish to know the dose for unsynchromized shock for pulse less Vt /polymorphic VT/ VF. ? 360J or 200 J. Thanks
Jeff with admin. says
According to the American Heart Association ACLS guidelines, the initial shock does can range from 120–200J. Any subsequent shocks can be incrementally increased as followed 300 then 360.
Remember, the American Heart Association guidelines are just guidelines. If a provider, based on their own discretion and clinical judgment, wants to go straight to 360J they can do this.
The cardiologists that I have spoken with prefer to go straight to the highest dose and deliver a shock. They don’t like to mess around with lower dosing.
Kind regards,
Jeff
Marta says
You may also want to consider whether you are defibrillating with a monophasic or a biphasic defibrillator. A monophasic defibrillator will require more energy (360J), while a biphasic will require less (200J), which is still the maximum amount of J for a biphasic.
chintharsam says
hi Jeff, I see that you have mentioned,
“The most common indications for synchronized cardioversion are unstable atrial fibrillation, atrial flutter, atrial tachycardia, and supraventricular tachycardias”, and below that, it says, “For cases where electrical shock is needed, if the patient is stable and you can see a QRS-t complex use (LOW ENERGY) synchronized cardioversion.”
I am a little bit confused… how a patient can be stable if he/ she has unstable atrial fib, atrial flutter, SVT….?
I am sorry if this is a dumb question.
Jeff with admin. says
A patient could not be unstable and stable at the same time. However, patient can be symptomatic but stable. May times people have elective synchronized cardioversion before they get to the point of being unstable. Many times this is the reason for cardioversion. It is to prevent a symptomatic stable condition from becoming unstable. Kind regards, Jeff
Blonde4fun says
This year was my 2nd time to take a recertification for ACLS using your wonderful program. Did even better than the last time. I enjoy the explanations and videos that make learning not only fun, but make things more memorable. For this reason, I am going to subscribe year round. Thanks Jeff for your labor of love in making this site informative and fun!
Tiffany says
Thank you so very much for this easy explanation. Just finished ACLS Part 1 and going do mock code tomorrow. I’ve been an LPN for 24 years and just graduated with my ASN and for the life of me couldn’t pull that out my brain. I’m someone who HAS to understand the mechanism of action of all things!!
Again,
Thank you,
Tiffany
ola hadi says
hi..my questions are:
what happened if you give synchronized shock to pt with VF?
What happened if you give non synchronized shock to pt with SVT?
Thanks..
Jeff with admin. says
You cannot give synchronized cardioversion to ventricular fibrillation. Synchronize cardioversion requires that the defibrillator synchronize with the QRS complex. Since there is no QRS complex with intricately fibrillation, there is no way to synchronize therefore, the different later will never be able to shock ventricular fibrillation when in synchronized mode.
If you give in unsynchronized defibrillation to a person with SVT, if the shock is delivered on the T wave, this will induce ventricular fibrillation. Therefore, you always provide synchronized cardioversion for the patient with an organized rhythm.
Kind regards,
Jeff
Satheesh.Chandran says
It iss a valuable information for me thank u very much sir
ercdamerc says
What are the electrical doses for shocking in different scenarios?
Jeff with admin. says
The electrical doses for synchronized cardioversion are covered on this page: Tachycardia Algorithm
The electrical doses for defibrillation are covered on this page: Cardiac Arrest Algorithm
Kind regards,
Jeff
Judith says
Hi Jeff
Thanks for a really clear explanation.
In response to an earlier comment you’ve stated:
“January 19, 2015 at 9:13 am
First- Animal research demonstrates a clear risk for delivering electricity during repolarization. …. ”
And I get that shock delivery on the t-wave (ventricular repolarisation) can lead to ventricular fibrillation.
So why doesn’t synchronised cardioversion precipitate Atrial Fibrillation?
My thinking is a synchronised shock is delivered at or with the r-wave and at this time the atrial muscle is repolarising.
So why doesn’t shock delivery in atrial repolaristaion start atrial fib, much the same way that shock delivery in ventricular repolarisation can start ventricular fib?
Cheers
Judith
Jeff with admin. says
DC cardioversion can precipitate V tach, but I have not heard of it precipitating atrial fibrillation the logic of your question make sense though however I don’t know if it bears itself out in the research. I am not aware of any research regarding this being a problem or even a consideration. Kind regards, Jeff
leilarocks says
“The most common indications for synchronized cardioversion are unstable atrial fibrillation, atrial flutter, atrial tachycardia, and supraventricular tachycardias. ”
This has always confused me as to why we synch with the QRS complex… it seemed like if all of these indicative rhythms have issues with the atria, that it would make more sense to shock at the p wave than the QRS as the p represents the atrial depolarization and I had thought that would be what you would want to change. I always wondered why shocking during ventricular depolarization would affect the atrial muscle and change its rhythm.
But its like a lightbulb came on, that maybe the best time to give synchronized energy would be during the REPOLARIZATION stage as opposed to during the depolarization….
Ive just always associated the QRS with the ventricles, of course, but had forgotten about that hidden wave and the repolarization.
S0- is it maybe that we synch our shock with the QRS because that is also the time when the atria are repolarizing (wave is hidden in the QRS complex)? So we actually are going for the effect on the atria, but because that atrial repolarization wave is hidden we just do the QRS?
It was Judith’s question that made me wonder about this and think further about the reason that we synch with the QRS (I had just succumbed to commit it to memory even though I didnt understand it)…. further to her question and why that wouldnt precipitate atrial fibrillation, could it be that “yes, giving a shock during the repolarization phase (whether atrial or ventricular) will create a change in rhythm”, but the SA node is a stronger pacemaker (the primary pacemaker), so it is more prone to be able to convert back into its normal rhythm than if a ventricular pacemaker receives the energy.
Am I on the right track Jeff? I am still quite weak in my cardiac knowledge base and still have a ton to learn, but this just came to me today.
(Also- its quite possible this is just common knowledge for everyone else and I’m just super slow on the uptake, haha).
Jeff with admin. says
Synchronization avoids the delivery of a LOW ENERGY shock during cardiac repolarization (t-wave)of the ventricles. If the shock occurs on the t-wave (during repolarization of the ventricles), there is a high likelihood that the shock can precipitate VF.
Once the shock occurs and the ventricles are reset, the SA node hopefully with pick up the ventricles with the normal electrical conduction that the SA node generates.
Please let me know if you have any other questions and if this makes sense.
Kind regards,
Jeff
Alexandra says
In atrial fibrillation/flutter there are no QRS complex, how does the cardioversion work?
Thanks.
Jeff with admin. says
There are QRS complexes with atrial fibrillation and atrial flutter. The QRS complex is the electrical impulse that occurs with ventricular contraction. This impulse (QRS complex) is present in both atrial fibrillation and atrial flutter.
Here is a review of afib and aflutter:
Atrial Fibrillation
Atrial Flutter
Kind regards,
Jeff
pramod sonone says
ecg s/o r on t phenomenon with vt dc cardioversion followed by electrical artifacts plz give suggestion
Jeff with admin. says
I don’t understand your question. Can you please clarify by rewording this?
Kind regards,
Jeff