Last update: April 2020

  Direct Current (D.C.) is used for electroshock treatment of arrhythmias (electrical cardioversion).

 
D.C. is less harmfull to the myocardium when compared to alternative current (A.C.).

  In cardiac arrhythmia patients with hemodynamic deterioration or unconsciousness, electroshock therapy becomes an EMERGENCY. There is no need for sedatization in such an instance.

  In arrhythmic patients with full conscioussness and stable hemodynamics, sedatization is necessary to alleviate the pain of electroshock.



What are the differences between cardioversion and defibrillation?

  Cardioversion is used for regular tachyarrhythmias and also for atrial fibrillation.

  In cardioversion, electrical current is discharged at the same time with patient's QRS (R wave). This is called
synchronization.

  If you apply defibrillation to a regular tachyarrhythmia and if the electrical energy is discharged at the vulnerable period of T wave, then the arrhythmia may degenerate into ventricular fibrillation (VF).

 
Defibrillation is used only for the treatment of VF.



What is synchronization?

  During a normal cardiac cycle, there is a vulnerable period of 20-30 msec on the T wave. If an electrical stimulus arises at this time (R on T) it may convert the regular tachyarrhythmia into VF.

  When performing cardioversion, the purpose is to prevent givin electroshock during vulnerable period on T wave.

  To achieve this, the QRS complex (R wave) is targeted (
synchronized). The purpose is to give electroshock just at the peak of R wave.

  Instead of P or U waves, R wave is chosen as a target since the QRS complex with its larger amplitude is easily discernible.

  For the electroshock equipment (
cardioverter / defibrillator) to make correct timing (synchronization), two conditions must be satisfied:

1- the cardioverter must already be following the patient's rhythm (
through electrodes connected to the patient)

2- the person to give electroshock should prepare the equipment for this purpose (
the synchronization button must be activated: SYNCH ON position) .

  If the patient is in VF and you are going to perform
defibrillation then:

1- there is no need to connect the electrodes to the patient.

2- the synchronization button need not be ACTİVATED.



In what types of arrhythmias do we use electrical CARDIOVERSION?

  Arrhythmias with a mechanism of reentry benefit from cardioversion.

  Arrhythmias due to increased automaticity do not benefit from cardioversion.



Electrical cardioversion is chosen for the treatment of

  Atrial fibrillation

  Atrial flutter

  AVNRT

  Ventricular tachycardia (VT)



How should we place the paddle electrodes on chest wall during cardioversion?

  Sternal paddle should be placed on right side of the upper sternum, just under the clavicle.

  Apical paddle should be placed on the left side of left nipple and the middle of the paddle should be on midaxillary line.

  If not succeeded, the patient should be turned on one side and
anteroposterior paddle placement must be done.

  For anteroposterior placement, one paddle must be near the sternum and the other one should be under left scapula.



Which factors determine the success of electrical cardioversion?

  Size of the paddles

  Placement of the paddles.

  Transthoracic impedance.

  Applied current.

 
Presence of gel between the skin and the paddles: Gel eases the passage of electric current from the paddle to the skin and increases the success of cardioversion. However, the gel should be present only between the paddle and the underlying skin. If there is more than enough gel on the chest wall then short circuit may occur and instead of travelling through the heart, the electrical current may now prefer to travel through the low resistance skin.

  Shaving of the chest wall will decrease the transthoracic impedance and thus will increase the success of cardioversion.

  The time between the delivery of shocks.



Cardioversion and pregnancy

  It has been reported that 50 to 300 Joules (J) of energy delivered during pregnancy have negligible effects on fetus.



Selection of biphasic or monophasic energy

  At equal amounts of delivered energy biphasic shock is more effective than monophasic shock.

  200 J biphasic shock is at least as effective as 360 J monophasic shock.



Recommended starting levels of energy for cardioversion

  100 J -200 J for Atrial fibrillation.

 
50 J - 100 J for Atrial flutter.

 
200 J for Polymorphic ventricular tachycardia.

 
100 J for Monomorphic ventricular tachycardia. Sometimes even 5 J - 10 J may suffice.

  If you are uncertain on whether the arrhythmia is SVT or VT, then start cardioversion with
5 J - 10 J. Starting with low energy levels (such as 5 J - 10 J) may be useful for the diagnosis of the arrhythmia. SVT is not expected to respond to low energy levels (5 J - 10 J). If 5 to 10 J is enough for successful conversion to sinus rhthym, it is generally thought that the previous rhythm is of ventricular origin.

  In children, the recommended energy level is about
1-2 J/kg .



Electrical cardioversion in patients with pre-existing permanent cardiac pacemakers

  The electrical current delivered during cardioversion/defibrillation may result in pacemaker dysfunction.

  Pacemaker function must be evaluated after electrical cardioversion/defibrillation.

  During the procedure, paddles of the defibrillator should be placed at least 15 cm away from the pacemaker battery.



Possible complication of cardioversion with synchronization

  Asystole lasting more than 5 seconds followed by bradycardia (0.7%)

  Bradycardic complications are more frequent in the
elderly and the women.

  The use of pericardioversion
antiarrhythmic drugs are NOT related to the development of bradycardia.

  It has been reported that more than 40% of the patients developing bradycardia after cardioversion will require implantation of a permanent cardiac pacemaker in the future.




Possible complication of electrical cardioversion without synchronization

  If synchronization is not done, the electrical current may coincide with the vulnerable period on T wave, initiating ventricular fibrillation

  The synchronization button must be "ON" during electrical cardioversion.

  Synchronization is not necessary during ventricular fibrillation since there are no regular QRSs to synchronize with.




What is Refractory Ventricular fibrillation (VF)?

  VF that does not convert with three or more single defibrillation attempts.



What is double external defibrillation (DED)?

  The application and administration of transthoracic electrical currents from two defibrillator devices to a single patient experiencing a single type of lethal dysrhythmia during cardiac arrest, known as refractory VF.

  Two biphasic defibrillators and two sets of defibrillator pads are needed.

  If the pads touch one another, there is a risk of damaging one or both defibrillators.

 
Further research is needed to better characterize and understand the use of DED for refractory VF.



How can double external defibrillation (DED) be applied?

  Both defibrillators may give electrical discharge at the same time or as close together as possible: Double Simultaneous Defibrillation.

  Alternatively, electrical discharges from both defibrillators are NOT delivered simultaneously, but close together: Double Sequential Defibrillation.

  In clinical practice, however, timing of DED shocks may be difficult.

  Optimum delay after first defibrillation needs further research.

  Even if an optimum delay is determined, then inconsistency in timing of manually triggered DED shocks may result from variations in human ability, switch debouncing, and device-to-device differences in timing from button press to the beginning of the high-voltage pulse, etc.




References

  Prehosp Emerg Care 2020 Feb 25:1-6. https://doi.org/10.1080/10903127.2020.1716283

  Resuscitation 2019;140:194-200.

  Am J Emerg Med 2018;36(9):1674-1679.

  Am J Emerg Med 2018;36(8):1474-1479.

  Ramzy M, Hughes PG. Double Defibrillation. [Updated 2019 Jun 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-

  Europace 2013;15:1432-1435. Ramzy M, Hughes PG. Double Defibrillation. [Updated 2019 Jun 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-

  Tex Heart Inst J 2011;38(2):111-121.

  Resuscitation 2010;81(8):956-961.

  Ann Saudi Med 2009;29:201-206.





Figure 1a. During cardioversion/defibrillation the
paddles should be placed as seen above.
Sternal
paddle should be placed on RIGHT SIDE of the UPPER STERNUM, just under the clavicle.
Apical
paddle should be placed on the left side of left nipple and the middle of the paddle should be on midaxillary line.
This way of
paddle placement is necessary to increase the amount of electric current passing through the heart.




Figure 1b. If the procedure is not successful with standard
paddle placement, the patient should be turned on one side and
ANTEROPOSTERIOR
paddle placement must be tried.
For anteroposterior placement, one
paddle must be near the sternum and the other one should be under left scapula.





Figure 2a. The above cross-sectional image is from a thorax computed tomographic examination of a man.
It shows the position of heart in the thorax. Think it as if we are looking to the heart from below.
Correct placement of the paddles should be as shown above.
While flowing from the negative lead (paddle) to the positive lead (paddle), the electric current prefers
the path with the lowest resistance.
A: Anterior, P: Posterior, L: Left, R: Right.



Figure 2b. If both paddles are placed anteriorly, the amount of electric current flowing through the heart will be less.
Paddle placement as seen in the above figure is not advised.
A: Anterior, P: Posterior, L: Left, R: Right.



Figure 2c. If both paddles are placed anteriorly on a woman with large breast tissue (as seen in the above image),
the electrical shock will be less effective.
Paddle placement as seen in the above figure is not advised.
A: Anterior, P: Posterior, L: Left, R: Right.