Synchronized and Unsynchronized Cardioversion
Synchronized vs. Unsynchronized Cardioversion
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 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 stable 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 EVERGY) unsynchronized cardioversion (defibrillation).
Do AEDs in airports, large buildings etc. provide nonsync shocks as well?
Thanks.
There are many different types of AED’s out there. Some deliver just unsynchronized shocks while others deliver both synchronized and unsynchronized shocks. AED’s meant to be used by the general public will primarily use an unsynchronized shocks for VT and VF.
Hi. I am trying to understand whether synchronising with pulseless VT to deliver a shock is possible and if so, why isn’t it best practice? Surely there is still a risk in defibrillation of administering the shock during repolarisation, thus inducing VF? And also, wouldn’t the chances of converting the pulseless VT to a sustainable rhythm be increased if we synchronised shocks?
Thanks for your help, and sorry if the answer is obvious – I am just a student afterall!
When using synchronized shocks, the defibrillator must synchronize with the rhythm of the heart before it can deliver a shock. Due to the random nature of pulseless VT and the incredibly fast rate it has been shown that the defibrillator/monitor is not able to synchronize in a reasonable amount of time.
This is why the recommendation for the unsynchronized shock. If you perform an unsynchronized shock and hit the rhythm at the wrong time, the most likely rhythm you will see is VF. In this case after a round of CPR and a rhythm check, you will shock again. —-Jeff
And how about the random nature of AF/Atrial Flutter?
In AF/A-flutter, the patient will still have normal QRS complexes for the debrillator to synchronize to.
See for instance:
Turner I, Turner S, Grace AA., Timing of defibrillation shocks for resuscitation of rapid ventricular tachycardia: does it make a difference?, Resuscitation. 2009 Feb;80(2):183-8. Epub 2008 Dec 16.
In fact, it appears to be true that as perfusion disappears conduction through the Purkinje system slows, contractions become weaker, ischemia progresses and the electrical conduction becomes more regular and of lower slope. Polymorphic VT would typically be non-shockable in an emergency basis, this is reflected in ACLS by delaying defibrillation until the VT degrades into a non-perfusing VT/VF.
Sync cardioversion detection is very rapid, normal testing with modern systems now require only one or two cardiac cycles to consistently detect and sync to VT. As the Turner and Turner paper discuss, doing a proper sync in VT also makes a tremendous difference in shock success. It is both important and feasible in current emergency equipment.
truly simple and fantastic. It gives the exact answer to my question, makes me understand and of, course, it makes me happy. Thank you!!