By Dr Ananya Mandal, MD
Defibrillators are the devices used to deliver shocks to the heart in cases of life threatening cardiac disorders. Electrodes that are connected to the machine are usually held in place over the chest of a patient while one or more shocks are delivered.
Defibrillators are used to re-establish a normal heart rhythm in cases of cardiac arrhythmia, ventricular fibrillation and pulseless ventricular tachycardia.
The chest of the patient is cleared of any clothing or jewellery and adhesive or metal electrodes are applied to the chest. These electrodes are connected to the defibrillator.
Adhesive gel electrodes are commonly used with the automated and semi-automated units used in ambulance or non-hospital settings due to their ease of application. These adhesive gel electrodes are available in solid-gel and wet-gel forms, with solid-gel electrodes the easier to use of the two, as there is no need to clean the patient’s skin after removing the electrodes.
These electrodes, however, may burn the skin, whereas wet-gel electrodes can spread the current more uniformly. The adhesive patches are also safer for healthcare personnel to use due to the very low risk of the operator coming into contact with the electrode. The operator can stand several feet away from the patient. Furthermore, the adhesive patches require no force of application, while approximately 25 lbs of force is required to apply the metal electrodes.
After application of the electrodes (metal or adhesive), the machine is charged and the shock is delivered. The electrodes are placed in one of two schemes:
The anterior-posterior scheme – This is preferred in cases of long-term electrode placement. One of the electrodes is placed over the lower part of the chest, in front of the heart, while the other is placed on the back, behind the heart and inbetween the scapula bones.
The anterior-apex scheme – This is useful in cases where the anterior-posterior scheme is unnecessary or not practicable. The first electrode is placed on the right, below the collar bone and the other is placed over the apex of the heart, on the left side just below and to the left of the chest muscle. This is useful in defibrillation and cardioversion.
Reviewed by Sally Robertson, BSc