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).
Edwyn says
Hai. May I know what is the reason we can’t deliver cardioversion at t wave, as in how cardioversion at repolarization can induced VT. had been thinking of it for quite sometime.
With thx.
Jeff with admin. says
There is some physiology involved here so I will try not to make it too technical.
During repolarization, there is a period that is called the absolute refractory period and another period called the relative refractory period.
During the relative refractory period, the heart isn’t quite ready to respond to a full depolarization, but a stimulus that’s strong enough can cause a depolarization. (kind of like when you have flushed a toilet and it is refilling, but there is not enough water to flush the toilet again.)
When an electrical discharge (defibrillation) occurs during the relative refractory period, part of the cells in the ventricle will be able to depolarize and part of the cells will not be able to depolarize. This creates a chaotic and disorganized state in the heart we call ventricular fibrillation.
This is why you do not want to deliver the shock on the T-wave.
(Technical: During the relative refractory period, some cell’s gated sodium ion channels are open and some cell’s gated sodium ion channels are closed. In other words, sodium ions are starting to come back into the cardiac cells to prepare for another depolarization, but the process is not complete. If a shock occurs when the repolarization process has started but is not complete, this can through the cardiac cells out of their synchronized state into a disordered and chaotic state (VF)
Kind regards,
Jeff
Mr. Jack says
Thanks for your good explanation. It makes me understand clearly. The kind of example you made is so visible.
Mr. Jack says
Dear Mr.
May i make a question regarding the point that:
Can we give chest compression during giving 2 times of ventilation?
Some say that ” we need to pause chest compression during 2 ventilation, but others comment , it is unnecessary to pause chest compression during 2 times of ventilation. i can’t find any accurate records regarding this point.
i hope you can help me.
Jeff with admin. says
If a patient does not have an (ET) endotracheal tube in place and ventilations are being provided with a bag valve mask, you need to stop chest compressions while ventilations are being given. The compression to ventilation ratio for this is 30:2
If a patient has an endotracheal tube in place, ventilations can be provided without stopping chest compressions. One ventilation should be provided every 6 seconds without stopping chest compression
Kind regards,
Jeff
Elaine McKinney says
Love your site. I now understand how to treat A-Fib and Atria flutter Thanks
Brian Chamberlain says
During cardiac arrest you have given epi q 5 min / amio 300 and 150 and shocked 4 times with persistent V fib . What should the5 th shock and any other subsequent shocks energy be used there after? I have been told continue with max joules 360. Is that correct?
Jeff with admin. says
By this time you would have reached the highest setting on the defibrillator regardless of the type a defibrillator. You would just want to use the highest setting and continue to use the highest setting for any further defibrillation. Kind regards, Jeff
Marco says
If i have a patient with pulseless monomorphic ventricular tachycardia, can i use synchronized cardiversion (i.e. 100J)?
Jeff with admin. says
Defibrillation/ unsynchronized cardioversion is always used for any type of pulseless ventricular tachycardia whether it is monomorphic or polymorphic.
Kind regards,
Jeff
Mallory says
You can’t. There is no pulse to sync. It is PULSELESS v-tach. Thats how I remember. Good Luck!
Jeff with admin. says
The defibrillator does not sync with the pulse. When synchronized synchrnozied cardioversion is used, the defibrillator attmpts to sync with the electrical impulse that is being generated by the heart.
The reason why unsynchronized cardioversion is used with pulseless VT is that there is a higher conversion success rate than with synchronized cardioversion.
Kind regards,
Jeff
Ryan says
It says that synchronized cardioversion should be performed using lower energy shocks. If someone in SVT for example didn’t respond to medications or lower energy synchronized cardioversion (50j to 200j) would you then proceed to shock at higher doses (300j to 360j synchronized) or would you you continue to shock at sync 200j?
Also if they didn’t respond to synchronized shocks would you ever deliver unsynchronized shocks to the patient in SVT I read somewhere that this can be done
Jeff with admin. says
1st question:
The shock dose for synchronized cardioversion can be increased in a stepwise fashion and can go higher than the 200 J recommendation.
That being said, the success rate for conversion from SVT is very high with lower dosing and a higher than normal shock dose would be out of the norm.
2nd question:
Whether the shock is given synchronized or unsynchronized should not change the outcome of the shock. The outcome for unsynchronized would not be somehow improved because it was unsynchronized.
Also, if unsynchronized cardioversion is utilized on a patient with SVT there is a strong likelihood that this could induce ventricular fibrillation. In most cases, unsynchronized cardioversion would not be recommended for the treatment of SVT.
Kind regards,
Jeff
Hanani says
This is so helpful. Thank you so much.❤️
HHS4717 says
Great explanations and an understood read.
David says
I received a question recently asking me why we shouldn’t synchronize cardiovert pulse less v-tach like we do when treating v-tach with a pulse. Any ideas. Is it just because it involves an additional step which may lead to a delayed shock?
Jeff with admin. says
Synchronized cardioversion for wide complex tachycardia with a pulse is 50-100 J. Shock dose for VF and pulseless VT is 120-200 J. The higher dose is recommended for the pulseless state with both VF and VT. I believe that this is the main reason for defibrillation when VT is pulseless.
Kind regards,
Jeff
Soma says
Is there a different etiology for monomorphic and polymorphic ventricular tachycardia
They claim all ischemic vT is polymorphic and those from hyperkakemis or scar tissue initiated VT is monomrphic?
Jeff with admin. says
The etiology can be quite varied for both monomorphic and polymorphic VT. There are many cases of monomorphic and polymorphic ventricular tachycardia that are caused by ischemia.
The main thing to remember is monomorphic ventricular tachycardia originates from a single focus within the ventricles.
Polymorphic ventricular tachycardia originates from multiple foci within the ventricles.
Kind regards,
Jeff
SUILUJ says
Hi!
Greetings!
I would like to ask if you have an idea why disposable electrodes in an AED are not advisable to be re-gel?
Thank you
Jeff with admin. says
Most of these AEDs are placed in areas to be used by non-healthcare providers. The patches/electrodes are meant to be used one time only for ease of use in public areas.
There is also a hygiene issue and the disposable electrodes eliminates the issue.
Kind regards,
Jeff
happy7 says
Thankyou for your site, and the information you share with us. You are so nice to explain things to us to make it so simple. I have used your site multiple times and shared it with others.
zeina says
in A Fib, the rythm is irregular, therefore how can the shock be synchronized on the QRS that came before?
zeina
Jeff with admin. says
The computer in the defibrillator senses the qrs and can deliver simultaneously. The rhythm does not need to be regular. Kind Regards, Jeff
Jlj says
Hi ?
Confused! I thought synchronize cardioversion can only use for arrhythmia s with regular rhythm or same pattern of beat.
Jeff with admin. says
This is incorrect, the arrhythmia does not have to be regular. For instance atrial fibrillation often has an irregular rhythm, and the machine can sense the QRS and delivery the shock at the correct moment.
Kind regards,
Jeff
Ankit data says
Is there any limit to the number of shocks which can be given for pulse less VT or VF patients. I mean if a patient has VF which is refractory to high energy shocks even if amiodarone or epinephrine is administered .
Jeff with admin. says
There is no set limit. However, at some point, you have to seriously consider whether further efforts are futile. Also, pulseless VT and VF will ultimately degrade into asystole or PEA which are not shockable rhythms. When a heart is dying, things don’t persist for long.
Kind regards,
Jeff
hasan says
You can start amiodarone drip after 2 shocks as per ACLS (Up to Date)
doctabiz says
amiodarone drip is to be started in immediate post cardiac arrest management (after ROSC) if needed.
doctabiz says
amiodarone iv push (not drip) might be given after 3 shocks, not 2.
Roxanne says
I have discrepancy at my hospital. Here’s the issues:
1. Do you need the limb leads to cardio vert?
2. There was a comment that the lif pack 12 cannot identify a wide qrs to sync to. However, when I’m doing it I notice the identifying triangles that it is synced.
Any clarity would be appreciated
Roxanne
Jeff with admin. says
Typically, defibrillators require only three leads for synchronized cardioversion. Some of the older models had thee leads for monitoring and two patches for the administration of shocks.
Most new defibrillators only require the two patches that are used for both monitoring and cardioversion.
If you see the regular red triangles then the machine is synced with the patients heart.
The wide QRS complex should not inhibit the machine’s ability to synchronize. There are times when polymorphic ventricular tachycardia and or sporadic irregularities in the QRS complex can limit the defibrillators ability to synchronize.
Kind regards,
Jeff
Indra Dasanayaka says
What wil happen if i give unsynchronzed shock to VT with pulse but haemodynamically unstable tatient..?why cant we give same shock to both pulseless VT and VT with pulse because both of them are having same ECG pattern ..
Jeff with admin. says
If the shock is delivered at the peak of repolarization (on the T-wave) it can induce VF therefore you synchronize so that the shock will be timed to be delivered on or near the R-wave and teduce the likelihood of having to deal with VF.
Kind regards,
Jeff