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Defibrillator vs Cardioversion

Defibrillator vs Cardioversion

Should you be an individual who knows anyone who has an issue with their heart, such as irregular heart rhythms or arrhythmias, you may be interested in knowing the differences between cardioversion and defibrillation. The procedures differ in what they are used for, and in the way they treat the patient. It is important that you are aware of the differences and how to act in an emergency situation. Being aware of this knowledge means that you can better assist anyone who may be in need of treatment for any heart rhythm-related issue. This article details all the necessary information that you could need, giving you a full breakdown of the differences between cardioversion and defibrillation.

What is Pulseless Ventricular Tachycardia?

Pulseless ventricular tachycardia is a life-threatening cardiac arrhythmia in which synchronized ventricular contractions are replaced by very fast but inadequate contractions, causing organ perfusion problems and heart failure. Ventricular tachycardia without a pulse is a medical emergency.

Cardioversion and Defibrillator Differences

There are a number of differences between defibrillation and cardioversion. They are used to treat different types of issues, making it crucial that you know which technique to employ when a patient has an emergency in your vicinity. Using the wrong technique could have some extremely dire effects on the chest of the patient, and can even cause the heart to go into cardiac arrest.

A defibrillation is a form of treatment that is used for patients who are facing life-threatening arrhythmias where the patient in question does not have a pulse. Forms of defibrillation include both ventricular fibrillation and pulseless ventricular tachycardia.

On the other hand, cardioversion relates to any procedure with the aim of converting an arrhythmia back to a sinus rhythm. When a patient has an unstable heart rhythm or has already tried chemical cardioversion, then electrical cardioversion is used in order to ensure their safety. Scenarios in which cardioversion is used are generally associated with pulmonary edema, hypotension, chest pain, or syncope. The technique is used less frequently in situations such as atrial fibrillation in order to revert the heart rhythm back to a sinus rhythm.

Both of these treatment processes aim to deliver electrical energy to the heart in order to stun it momentarily. This allows for a normal sinus rhythm to kick in due to the heart’s regular pacemaker known as the sinoatrial node.

Defibrillators, Cardioversion and Pacemaker

Defibrillators and cardioversion are therapeutic interventions designed to address abnormal heart rhythms, while a pacemaker is an implanted device that regulates these rhythms. A defibrillator, often found in Automated External Defibrillators (AEDs), delivers unsynchronized electric shocks to the heart to treat life-threatening arrhythmias like ventricular fibrillation. Synchronized cardioversion, a subset of defibrillation, delivers shocks that are timed or “synchronized” with the heart’s electrical activity to treat other specific arrhythmias like atrial fibrillation or atrial flutter. On the other hand, a pacemaker continuously monitors the heart and, when it detects an irregular or slow rhythm, sends electrical impulses to prompt the heart to beat at a normal rate. In some advanced devices, a pacemaker can be combined with a defibrillator, termed an Implantable Cardioverter Defibrillator (ICD). An ICD both regulates the heart’s rhythm and can deliver shocks if a life-threatening arrhythmia is detected. However, standard defibrillators or cardioversion procedures do not “use” a pacemaker, but they can exist in combination with specialized devices.

Longevity with Pacemaker

How long can you live with a pacemaker? The longevity of an individual with a pacemaker varies depending on several factors, including the reason for the pacemaker, the individual’s overall health, and how well they follow medical advice and attend regular check-ups. A pacemaker itself, as a device, typically has a battery life ranging from 6 to 15 years, depending on its type and usage. When the battery nears its end, the pacemaker will need to be replaced in a relatively straightforward procedure.

Regarding the lifespan of the individual, many people live full, active lives with pacemakers. In many cases, the pacemaker can rectify the heart rhythm abnormality, leading to symptom improvement and an enhanced quality of life. It’s crucial to understand that the pacemaker is addressing the electrical issues of the heart and not other aspects like the heart’s pumping function or any underlying heart diseases. Regular follow-ups with a cardiologist, adherence to medications, and addressing other associated health conditions will play significant roles in determining an individual’s lifespan and quality of life with a pacemaker.


Prévost and Batelli, two physiologists, conducted shock tests on the hearts of dogs at the end of the 18th century. They used electrical shocks on the dogs and found that small shocks placed their hearts in VF, which could be reversed with a larger shock. It was first used on a 14-year-old boy who was undergoing cardiothoracic surgery for congenital heart failure by Claude Beck, a cardiothoracic surgeon. The open heart was covered with electrodes. In Russia, closed-chest defibrillation was not adopted until the 1950s. Bernard Lown, however, did not design the modern monophasic defibrillator until 1959. This is based on capacitors being charged and then paddles producing a shock over a few milliseconds. The biphasic waveform was discovered in the 1980s. This resulted in a shock that was just as powerful as monophasic shocks at lower energy levels.

Differences Between Monophasic and Biphasic Systems

  • The current in monophasic systems only flows in one direction, from one paddle to the next.
  • The current in biphasic systems moves towards the positive paddle, then reverses and returns several times.
  • Biphasic shocks are associated with fewer burns and less myocardial damage since they produce one cycle every 10 milliseconds.
  • The rate of first shock performance in cardiac arrests due to a shockable rhythm is only 60% with monophasic shocks, but it rises to 90% with biphasic shocks.
  • However, biphasic defibrillators’ effectiveness over monophasic defibrillators has not been reliably reported.

Types of Defibrillators

Automated External Defibrillators (AEDs) are the most commonly known types of defibrillators but you might wonder why is an AED needed. They are often the first choice of an organization due to them being extremely useful, as well as the fact that they do not require any special medical training to properly utilize. These types of defibrillators are often found in public venues such as offices, shopping centers, airports, and other similar public buildings. The work by analyzing the heart rhythm of the patient, and then charging and delivering an appropriate shock to their heart in order to correct the rhythm. Unfortunately, these devices cannot be overwritten, and in some cases, can take between 10 and 20 seconds to identify arrhythmias. However, the ease of use, as well as the speed of these devices, makes them a popular choice for many.

Types of Defibrillators

Semi-automated automated external defibrillators are another variation of an AED that is not as popular as regular AEDs; however, these are primarily utilized by used by paramedics due to their ability to pace. They are generally very similar to regular AEDs but they can be overridden when needed, and tend not to have an ECG display.

Other types of defibrillators include standard defibrillators with a monitor, which can be monophasic or biphasic, as well as transvenous or implanted defibrillators.

Risks Associated with Defibrillation

It’s extremely unlikely for a well-maintained, stable defibrillator to malfunction. The unit assesses and measures the victim’s heart rhythm. The device then provides you with a number of instructions that you should follow in order to save the life of the individual in trouble. By following the instructions provided to you, you ensure that you are not doing anything wrong, even if you have no prior medical training.

It’s more likely that you’ll sustain an injury while practicing CPR, as broken ribs are common, particularly among the elderly. You risk aggravating their injuries by pushing them into the protected airway location. These potential problems are the lesser of two evils as compared to what can happen if you don’t obey the chain of survival for treating a sudden cardiac arrest.

Energy Levels for Defibrillators

Different types of defibrillation use different levels of power in order to achieve the results that they are after.

Monophasic defibrillators generally adhere to the cardiopulmonary resuscitation (CPR) algorithm that suggests a single shock that is started and repeated at 360 Joules.

When it comes to biphasic defibrillators, the CPR algorithm suggests initial shocks that are between 150 and 200 Joules, followed by subsequent shocks that range between 150 and 360 Joules.


Cardioversion is used for decompensated rapid atrial fibrillation that is associated with a rapid ventricular response. Examples of this include hypotensive patients who do not respond to any medical therapy. It is also used to treat ventricular fibrillation with a pulse, as well as supraventricular tachycardia that includes atrial fibrillation without decompensation.

What is Cardioversion

The shock in cardioversion must be timed correctly so that it does not occur during the vulnerable cycle, an example of this is the T wave. 

Atrial Fibrillation

  • Cardioversion is a rhythm regulation technique.
  • Cardioversion is not always effective, with 50% of patients redeveloping atrial fibrillation after a year.
  • Cardioversion and medical therapies have equal efficacy (unless permanent atrial fibrillation).
  • Since cardioversion of atrial fibrillation is linked to an increased risk of thromboembolic disease (TED), anticoagulation is recommended for at least three weeks prior to and four weeks after the procedure.
  • While some centers use a transesophageal echocardiogram to look for thrombus during the operation, a few patients still develop TED despite negative results. 
  • When cardioverting, a more recent paper suggests using a transoesophageal echocardiogram.
  • In patients who have had a past failure to cardiovert or an early recurrence of atrial fibrillation, sotalol or amiodarone should be provided for at least four weeks prior to cardioversion.
  • Others recommend using drugs like sotalol and amiodarone to keep the sinus rhythm after cardioversion.

Defibrillator Settings For Cardioversion

When one asks “What is Synchronized Cardioversion,” they are inquiring about a specific medical procedure designed to restore normal heart rhythms in patients with certain types of arrhythmias. Synchronized Cardioversion involves delivering a timed electric shock to the heart, synchronized with the cardiac cycle, particularly targeting the R-wave’s peak. This precise timing distinguishes it from standard defibrillation, ensuring the shock does not inadvertently induce a more dangerous rhythm like ventricular fibrillation. The procedure is often employed when patients suffer from rhythms like atrial fibrillation or atrial flutter, especially when medications fail to bring about the desired effect or the arrhythmia is acutely life-threatening.

Start synchronized cardioversion with a biphasic defibrillator at 120 Joules (J) in patients with AF causing hemodynamic compromise, and raise to 200 J during subsequent shocks. Unstable atrial flutter or paroxysmal supraventricular tachycardia (PSVT) requires much less energy, so cardioversion can be started at 50 J biphasic (100 J monophasic) at first, then increased to 100 J if it fails. If the shock fails to stop the SVT, a 200 J (360 J monophasic) follow-up shock can be provided. 

Monomorphic VT with a pulse is handled with synchronized cardioversion, which starts with a 100 J biphasic (100 J monophasic) shock and gradually increases the energy to 200 J biphasic (360 J monophasic) shocks before sinus rhythm is achieved. An initial defibrillation shock of 120 J (200 J monophasic) is normally enough to stop ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). If the first shock fails, the energy can be increased to 200 J (360 J monophasic) for the next shock. Defibrillation with similar energy settings (120 to 200J biphasic) is used in the case of polymorphic VT with a pulse as it is in the case of pulseless VT.

Indications For Defibrillation

You may be wondering what the indications for defibrillation are. Knowing the indicators can make it much easier for you to identify when a patient is in need of defibrillation in order to save their life. By you being aware of these indicators, you can buy yourself some valuable time in diagnosing when an individual requires an energy shock to reset the electrical activity of the heart, and allow it to resume a regular rhythm. 

There are three primary indicators for defibrillation, and these are:

  • Pulseless ventricular tachycardia
  • Ventricular fibrillation
  • Cardiac arrest as a result of or causing ventricular fibrillation 

Is Unsynchronized Cardioversion the Same as Defibrillation?

Synchronized cardioversion is a low energy shock that uses a sensor to transmit electricity at the same time as the QRS complex’s peak (the highest point of the R-wave). When a defibrillator’s “sync” option is selected and the shock button is pressed, the shock may be delayed. The computer reads and synchronizes with the patient’s ECG rhythm during this time delay. This is achieved so that the shock can be administered at or near the height of the R-wave in the QRS complex of the patient.

During cardiac repolarization, synchronization prevents the transmission of a low energy shock (t-wave). If the shock happens on the t-wave (during repolarization), there is a fair risk that it can cause VF (Ventricular Fibrillation).

Unstable atrial fibrillation, atrial flutter, atrial tachycardia, and supraventricular tachycardias are the most common signs of coordinated cardioversion. If drugs fail to control the arrhythmias in a stable patient, coordinated cardioversion would almost certainly be needed.

Unsynchronized cardioversion (defibrillation) is a high-energy shock delivered as soon as the defibrillator’s shock button is pressed. This means that the shock can occur at any time during the cardiac cycle (QRS complex). If there is no coordinated intrinsic electrical activity in the heart (pulseless VT/VF) or the defibrillator fails to synchronize in an impaired patient, unsynchronized cardioversion (defibrillation) is used.

If the patient is stable and a QRS-t complex can be seen, use (low energy) synchronized cardioversion in cases where electrical shock is needed.

It is therefore safe to say that unsynchronized cardioversion and defibrillation are the same things. The term unsynchronized cardioversion is just a more accurate term used to describe the process of what defibrillation really is.

When Should You Do Synchronized Cardioversion?

A pulse that is too rapid (tachycardia) or erratic may be corrected with cardioversion (fibrillation). Cardioversion is often used to treat patients with atrial fibrillation or flutter. When the electrical signals that usually cause your heart to beat at a regular pace do not propagate correctly through the upper chambers of your heart, these conditions occur.

Cardioversion is typically performed in advance, but it can also be done in an emergency.

Electric shocks transmitted by electrodes connected to your chest when you’re sedated are typically used for cardioversion. Your doctor can see right away whether the operation has restored a natural heartbeat with electric cardioversion.

Electric cardioversion takes less time than medication-only cardioversion. You may not receive electric shocks to the heart if your doctor suggests cardioversion and drugs to restore the heart’s rhythm.

Cardioversion is not to be confused with defibrillation, which is an emergency treatment used when the heart slows or quivers ineffectively. Defibrillation shocks the heart with more intense shocks to adjust its rhythm.

Risk Associated with Cardioversion

Although experiencing any complications when it comes to cardioversion is very rare, there are still some present. You should be aware that your doctor should take all the necessary precautions in order to reduce the chance of any of these risks occurring; however, these are some of the complications that could occur:

  • Blood clots that have been dislodged. Blood clots can form in the hearts of people who have irregular heartbeats. These blood clots may travel to other parts of your body as a result of electric cardioversion. This can result in potentially fatal complications, such as a stroke or a blood clot that travels to your lungs. Until cardioversion, your doctor can prescribe blood-thinning medications or check for blood clots in your core.
  • A heart rhythm that is irregular. Some people who have cardioversion develop other heart rhythm issues during or after the operation, although this is uncommon. This is a relatively uncommon complication. If this occurs, it normally occurs within minutes of your operation. Should this happen, your doctor can prescribe you medication or administer additional shocks in order to sort the issue out.
  • Burns to the Skin. In very rare circumstances, individuals may notice that they have received some very minor burns on their skin where the electrodes were previously placed.

Cardioversion procedures can be administered during pregnancy; however, it is recommended that the heartbeat of the baby is monitored throughout the entire process in order to ensure that they do not have any negative reactions to the procedure being done.

How to Prepare for Cardioversion?

Cardioversion procedures are usually planned ahead of time. If your symptoms are serious, you can need cardioversion in a hospital emergency room.

Before your operation, you won’t be able to eat or drink anything for about eight hours. Before your procedure, your doctor can tell you whether or not you should take any of your regular medications. If you must take drugs prior to your operation, just drink enough water to allow you to swallow your pills.

A transesophageal echocardiogram can be performed prior to cardioversion to check for blood clots in your heart. Cardioversion can cause blood clots to break free, posing a life-threatening risk. Until cardioversion, your doctor assesses if you need a transesophageal echocardiogram.

If blood clots are discovered, the cardioversion operation can be postponed for three to four weeks. To minimize the risk of complications, you’ll take blood-thinning drugs during that period.

What to Expect During the Procedure?

You should be given drugs via an IV to put you to sleep during the operation so that the shocks won’t harm you. Other drugs can be administered through IV to aid in the restoration of your heart rhythm.

On your chest, a nurse or technician positions numerous large patches known as electrodes. Wires attach the electrodes to a cardioversion system (defibrillator). The machine tracks your pulse and sends shocks to your heart to bring it back to normal. If your heart beats too slowly after cardioversion, this machine can fix it.

After you have been sedated, the process of electric cardioversion usually only takes a few minutes to complete.

What to Expect After the Procedure?

Electric cardioversion is performed as an outpatient procedure, which means you can go home the same day. You should spend an hour or two in a recovery bed, where problems can be closely monitored.

You could most probably need someone to bring you home, and your decision-making abilities may be impaired for several hours after your treatment.

Even if no clots were detected in your heart prior to your operation, you need to take blood thinners for at least a few weeks afterward to prevent new clots from forming.

The Results of Electrical Cardioversion?

Cardioversion can easily restore a normal heartbeat in most people. It’s likely that additional procedures would be needed to maintain a regular heart rhythm.

Results of Electrical Cardioversion

Your doctor may advise you to make lifestyle changes to improve your heart health and prevent or treat arrhythmias-causing conditions like high blood pressure.

Choosing the Right Defibrillator for Your Needs

Your defibrillator may have been gathering dust for a while, but it must be ready to support you in an emergency. Depending on where it is placed, it may be exposed to extremely difficult conditions. If it’s aboard a ship, it’ll have to be able to endure the most severe conditions.

The most critical move is to find out which manufacturer makes the AED that better suits your or your organization’s needs. If you want the rescue to go smoothly, you may need to select the right defibrillator to deliver the shock. If you know you’ll be operating in a noisy atmosphere where you won’t be able to hear audio prompts clearly, an AED with visual prompts may be a better option to avoid any issues during the operation.

There are a variety of choices available to you, each with its own set of advantages and disadvantages. Some of these options include:

The Bottom Line

By being aware of the differences between cardioversion and defibrillation, you can ensure that the proper treatment is performed for the resuscitation of any individual who may be in need of assistance. Knowing how to assist a patient based on the symptoms that they are displaying gives you the best chance of properly assisting them in recovering from arrhythmia or other chest-related issues. By ensuring that you are able to administer the appropriate medical treatment to an individual, the chances of them experiencing any negative side effects are greatly reduced. The patient’s life is the most important thing at the end of the day, and it is imperative that everything is done to give them the best chance of survival.

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