Cardioversion

Cardioversion refers to the process of restoring normal heart rhythm to an abnormally beating heart. This can be achieved thorough electrical cardioversion and through the use of medications.

Symptoms Indicative of an Abnormal Heart Rhythm

• Sudden collapse with no response
• Abnormal pulse: either very rapid, irregular or missing pulse
• Shortness of breath
• Palpitations or feeling of the heart racing
• Sensation of missed heart beats
• Syncope or transient reversible loss of consciousness

Electrical Cardioversion

This involves providing the heart with an electrical shock which will essentially stop the heart completely and reset the rhythm. When an external device is used, it is called an external defibrillator. An easy to use variation of this is usually available in public areas called an Automated External Defibrillator (AED). In certain patients with an abnormal heart rhythm, a device may be placed within the body to monitor the electrical activity and provide shocks, if needed, to maintain normal rhythm. These are called Implantable cardioverter-defibrillators (ICD).

External Defibrillators

These are found in all hospitals and used frequently in emergency rooms to fix abnormal heart rhythms (arrhythmias) which often occur suddenly and leading to cardiac arrest and failure of the heart to pump blood. The following types of rhythm can be corrected using a defibrillator

• Ventricular tachycardia (VT): A very fast heart rate arising from abnormal electrical activity in the ventricles (the two lower heart chambers)
• Ventricular fibrillation (VF): This is an irregular heart rhythm where abnormal electrical activity in the ventricles leads to a wriggling appearance of the ventricles
• Atrial fibrillation (AF): This is an abnormal rhythm arising from the atria (the upper two chambers of the heart), which leads to an irregular and fast heart rate. This is a very common condition in individuals over the age of 60 to 70 years and is not as dangerous as the ventricular arrhythmias described above.

Steps in using an External Defibrillator

• There are two patches or pads which are attached to the defibrillator. These are placed at defined locations on the body. Usually one goes on the left side of the chest and the other is below the right shoulder or on the back.
• In emergency situations, the individual may already be unconscious, but in an elective scenario, the patient is generally sedated and provided with local anesthesia.
• The defibrillator is switched on and the electrical rhythm is analysed. This resembles the rhythm recorded by an Electrocardiogram (ECG)
• A shock is then delivered, which stops the activity of the heart completely. When it restarts, it should have reverted to normal rhythm
• Occasionally multiple shocks may be needed to establish normal rhythm.

Implantable cardioverter-defibrillators

These are small devices that are surgically placed under the skin in the region of the chest or upper abdomen. There are electrodes which are threaded through the blood vessels in the chest to reach the heart. This detects the rhythm of the heart throughout the day. In the event of an abnormal heart rhythm, the ICD is capable of delivering a shock to the heart. These devices are used for individuals who are prone for recurrent life threatening arrhythmias.

It is important to remember to mention you have an ICD if scheduled for an MRI scan. Older ICDs have been an absolute contraindication for MRIs, but several newer ICDs are now in the market which can be adjusted to avoid complications.

Medications

There are several different classes of drugs which can be taken both orally and through injections in the veins which can help to control arrhythmias. These medications act by changing the movement of charged ions in the cells of the heart muscle and thereby can modify the electrical activity. This can take a few days before any effect is seen. These medicines are usually initiated while admitted in the hospital under cardiac supervision. In the case of AF, drugs can be taken to control the heart rate alone even if it is not possible to treat the abnormal rhythm.

Side Effects and Complications of Cardioversion

• Abnormally high voltage shock can cause skin burns
• The sudden jolt the heart can dislodge any clots if present inside and lead them to travel to other parts of the body with risk of stroke.
• Several drugs used for cardioversion may themselves cause arrhythmias, especially if an incorrect selection of drug or dose is made.

Rferences:

• Cardioversion: MedlinePlus Medical Encyclopedia [Internet]. [cited 2018 Aug 27]
• Cardioversion [Internet]. www.heart.org. [cited 2018 Aug 27] 
• Cardioversion | National Heart, Lung, and Blood Institute (NHLBI) [Internet]. [cited 2018 Aug 27].