Introduction to Cardioversion, by Dr. Mjaye Mazwi.
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Hello, I am Mjaye Mazwi.
I am a clinical fellow in cardiology here at Children's Hospital Boston.
I'm going to talk about cardioversion.
I'm going to discuss cardioversion, and then show you the algorithm that we use here at
Children's Hospital Boston.
I want to emphasize that you might have to modify the algorithm based upon the equipment
that you have available or the circumstances at your hospital.
We are going to first of all start out by discussing the physiology of cardioversion.
We are going to move on to the indications for cardioversion.
I am going to orient you to some of the equipment that we use when we cardiovert patients, and
then finally run an actually simulated cardioversion to display the steps occurring in a simulated
clinical setting.
Introduction.
Cardioversion involves the application of an electrical shock to to the myocardium that
is synchronized with the cardiac cycle.
The way that cardioversion differs from defibrillation is that defibrillation is an asynchronous
shock meaning it can occur any point in the cardiac cycle.
Cardioversion is a shock that's timed to occur at a specific point in the cardiac cycle.
The specific point is ventricular depolarization.
So you are timing your shock to coincide with the QRS complex, specifically the R wave on
your EKG.
The goal when you do this in a clinical scenario is to cause a sustained diffuse depolarization
of cardiac myocytes that's typically followed by a slightly longer refractory period that
aids in the resetting of any reentrant arrhythmias and the restoration of sinus rhythm.
Indications.
The indications for performing cardioversion include supraventricular tachycardia, atrial
fibrillation and atrial flutter that are not responsive to chemical conversion, or in patients
that are hemodynamically unstable, and ventricular tachycardia with a pulse.
Please note that pulseless ventricular tachycardia requires defibrillation, which involves an
asynchronous shock.
Contraindications.
This procedure is contraindicated in patients who have indicated that they do not wish to
be resuscitated.
For example, a patient with a Do-Not-Resuscitate order.
Equipment.
Orienting you to some of the equipment that we use when we are cardioverting patients.
The basic function arises from the box.
There is considerable variation between manufacturers in where these basic functions lie.
So, in whatever environment you practice, it behooves you to spend a little bit of time
learning how your machine is laid out and where these functions lie so that you don't
waste precious time trying to understand the machine when you're called upon to use it.
The box interacts with the patient by means of paddles or pads.
This is an example of a paddle, which typically is actually attached to the machine.
This is an example of a pad, which is very much like an EKG lead in that it's got a sticky
surface that can be attached to the patient.
Paddles and pads come in two sizes.
Some machines have three sizes.
Most machines have two.
Our machine has two sizes.
There is an infant, pediatric size and an adult size.
The infant or pediatric size has a diameter of 4 and 1/2 centimeters, whereas the adult
size has a diameter of 12 to 13 centimeters.
I want to show you the size difference with the pediatric and the adult pads as well.
The way that we distinguish which size to use is based upon the patient's weight.
Patients that are 10 kilograms and below, we use the pediatric sized equipment for.
Patients that weigh more than 10 kilograms, we use adult sized equipment for.
Patient Assessment.
This is not always the case, but, as a general rule, rhythms that we cardiovert tend to be
relatively more hemodynamically stable than pulseless VT or ventricular fibrillation.
And, as a result of this, it actually makes a lot of sense to make sure that, in addition
to getting your resources together to deliver a shock as early as is necessary, you pay
attention to the evaluation of the patient to decide on where that shock occurs, whether
it's in the emergency department, the ICU, and under what circumstances.
The assessment of the patient to determine the effects that the arrhythmia has on the
patient should involve a neurological and hemodynamic assessment.
You're doing the neurological assessment to try to assess for, essentially, decompensated
shock.
In this case, it would be cardiogenic shock as a result of inadequate cardiac output as
a result of the tachyarrhythmia.
In pediatrics, that's looking for age-appropriate behaviors and interactivity.
Usually these rhythms occur in situations that are very unusual for the patient, and
quite stressful.
And so a baby with a hemodynamically stable tachycardia would look pink, be crying, be
agitated, possibly not feel too well, but would have a palpable pulse.
It's much more important to assess central pulses than peripheral pulses when we're looking
for hemodynamic stability, and our capillary refill.
Adjuncts to that hands-on patient assessment include looking at our pleth and looking at
our saturation and assessing a blood pressure by blood pressure cuff.
So, the questions that you need to answer when you've decided that a patient has come
in in a cardiovertable rhythm are: what the rhythm is, and whether this is a rhythm that
is shockable, and what the patient's hemodynamic and neurological status are.
If a patient presents and is hemodynamically stable for instance, with a reentrant supraventricular
tachycardia, then clinically, the appropriate next step would be to attempt vagal maneuvers
and medical therapy before considering cardioversion.
In a hemodynamically unstable patient with SVT, you bypass those earlier steps and proceed
directly to cardioversion.
Similarly, in a hemodynamically stable patient with atrial fibrillation, comes to an emergency
room or an ICU with a ventricular rate that is able to sustain the circulation, considerations
should be given to all kinds of ancillary pieces of management of the patient.
So, for instance, the need for a period of anticoagulation before cardioversion, sedation,
and possibly even anesthesia, because these are painful procedures.
All of these considerations are not things you should dwell on in a hemodynamically unstable
patient.
Hemodynamically unstable patients, you proceed straight to the shock, with your success being
contingent often on how quickly you can deliver that shock.
Procedure Placement of Pads.
For an adult-sized patient, place the pads over the midsternum, at the base of the heart,
and the mid axillary line over the apex of the heart.
If you have a pediatric-sized patient and/or the pads come into contact with each other
when placing both pads anteriorly, you should use the anterior-posterior pad placement,
where one pad is placed anteriorly in the mid-sternal position, and the other pad is
placed posteriorly, in the interscapular position.
Procedure: Selecting Cardioversion Settings.
Looking at the basic functionality now of the box itself, to successfully cardiovert
a patient, you have to have the ability to select a particular electrical energy in the
form of joules on your machine.
Machines have a dial.
Typically it looks very much like the one on this machine, that allows you to switch
the machine on and then select a particular voltage based upon the patient's requirements.
With cardioversion, the initial shock is delivered at an energy level of 0.5-1 J/kg.
If that shock is unsuccessful, all subsequent shocks are delivered at 2 J/kg.
People tend to fall into specific reproducible behaviors and this is something I would encourage.
For instance, I usually use 1 J/kg as the first shock because it's easy to calculate,
and it's reproducible from one patient to the next.
It's important not to continue to progressively augment your voltage as higher shocks increase
the chances of skin burns occurring and increase the chances of myocardial damage and post-shock
tachyarrhythmias.
In addition to selecting your voltage, you have a button up here on the machine that
is a sync button.
Cardioversion requires that you synchronize your shock to the patient's native rhythm
in order to deliver that shock on the R wave.
Once you have selected a voltage, and for purposes of demonstration - very briefly - I'm
going to select a voltage of 20, you press the sync button so that the machine synchronizes
to the QRS complex.
On this machine, the synchronized activity is demonstrated by these little white dots
that appear above the QRS complex.
It's extremely important when you're going to cardiovert a patient that you actually
look at what the machine is synchronizing with.
Patients with a tall, prominent T wave quite often will have the machine inadvertently
synchronize the shock to the T-wave.
That is something that you very much want to avoid.
That is called R-on-T, or alternatively, delivering a shock during the relative refractory period
of the ventricle.
And the danger that you run when you do that is you run a significant risk of inducing
ventricular fibrillation, which is considerably more difficult arrhythmia to treat.
Once your machine is on, you've pressed your sync button and you've ascertained that the
machine is synchronized with the R wave on the QRS complex, the next button that you
need to know is the charge button.
The charged button is pressed and the machine then charges and indicates to you either by
an audio cue, by a visual cue, that it's ready to deliver the voltage.
On this machine, this little button, the shock button, lights up when we are ready to deliver
a charge.
The shock button is the final button that we'll talk about.
The shock button discharges the electrical shock and hopefully cardioverts the patient
by delivering a reversion shock converting from an arrhythmia back to sinus rhythm.
Before delivering the shock, it is the responsibility of whoever is going to press that button to
ensure that he or she and all other assistants at the resuscitation are clear of the patient.
The algorithm that we use here at Children's involves the person delivering the shock saying,
"I'm clear, you're clear, we're all clear."
And that gives you time to ask the question but also look around to make sure no one is
in contact with the patient so that you do not inadvertently shock one of your assistants.
Once you have ascertained that everyone is clear of the patient, you deliver the shock
by depressing this button.
It's important to note that in cardioversions, there is typically a lag between the depression
of the button and the delivery of the shock, and that's because the machine makes sure
that it's synchronized before shock is delivered.
So do not press immediately and release pressure on the button, press and hold the button down
when you cardiovert a patient to deliver the shock.
Procedure Complications.
The complications that you may observe include conversion into another type of arrhythmia,
dissemination of a formed thrombus to the small vessels in the brain, causing a stroke,
or the lungs, causing a pulmonary embolism.
Injury to heart muscle, skin burns from the electrodes.
Please note that you may or may not observe any of these complications during or following
this procedure.
I encourage you to monitor your patient closely for signs or symptoms of complications and
to be prepared to manage them, which includes having the necessary equipment available to
treat the complications, should any arise.
Procedure Documentation.
Following cardioversion, you should document the following information in the patient's
medical record: the indication for the procedure, the date and time of the procedure, the number
of synchronous shocks, and the voltage required to restore normal cardiac rhythm.
The name, dosage, and route of administration of any medications given during cardioversion.
The vital signs before, during, and after procedure.
Patient comfort with the procedure.
Any adverse outcomes.
Demonstration.
During our simulation, I'll leave the pads in front of the patient, over the approximate
area of the right ventricular apex, and the second pad in the anterior axillary line where
the approximate posterior base of the left ventricle is.
The mannequin is only able to sense the electrical activity when the pads are placed in very
specific positions, as you can see.
In the simulation, we have a 10-kilogram infant that has presented to our ICU who we will
demonstrate our algorithm in.
So, we start off with a hemodynamically stable patient, and we have an acute change in the
rhythm.
We look at our monitor, and we have a narrow complex tachycardia at a very high rate.
We quickly assess the patient's hemodynamics.
The patient is not responsive.
The patient's pulse is progressively getting weaker and weaker, and the patient's cap refill
is poor.
Our first step with the synchronized cardioversion is to press sync.
Watch our monitor and make sure that the synchronization spikes, those little white dots, are occurring
over the R wave of our QRS complex.
Select our voltage.
And our initial voltage is going to be 1 joule per kilogram, which I've dialed in.
When I'm happy that the machine is synced, I charge.
I'm clear, you're clear, we're all clear.
I deliver my shock.
Our first shock was unsuccessful, so I immediately go to 2 joules per kilogram.
I once again ensure that I am synchronized with the R wave of the QRS complex.
I charge the machine.
Clear.
I'm clear, you're clear, we're all clear.
Deliver a shock.
And we have a restoration of what appears to be sinus rhythm.
I reassess the patient's perfusion.
I can feel strong pulses.
We cycle the blood pressure and make sure that this is a perfusing rhythm.
That concludes our video on Introduction to Cardioversion.
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