With defibrillation, first responders use a direct current pulse to correct a life-threatening cardiac arrhythmia, which can result in a fatal heart attack if not counteracted in time. De-fibrillation is achieved exclusively by successfully administering a shock. The synonym for defibrillation is de-fibrillation.
What is defibrillation?
With defibrillation, first responders use a direct current pulse to correct a life-threatening cardiac arrhythmia that can result in a fatal heart attack if not counteracted in time. The direct current pulse is applied to the patient by means of a shock. The defibrillator acts as a shock generator for defibrillation and cardioversion. It is a controlled delivery of electrical shocks to the heart muscle. The European Resuscitation Council (ERC) defines the absence of the original arrhythmia five seconds after shock delivery as successful defibrillation. Defibrillation is performed in the presence of resuscitation for cardiac arrhythmias such as ventricular fibrillation, ventricular flutter and pulseless ventricular tachycardia (life-threatening arrhythmia originating in the heart chambers). In the meantime, so-called AED defibrillators are increasingly being used. These devices take over the ECG diagnostics and guide through the measures for cardiopulmonary resuscitation by means of visual and acoustic signals.
Function, effect, and goals
Contraction, the contracting of the heart muscle, occurs through the depolarization (discharge) of muscle fibers, whereas repolarization is an electrical phenomenon in which the original state of charge of the heart is restored. Cardiac arrhythmias, and thus sometimes life-threatening conditions that can lead to fatal heart attacks, occur whenever the heart muscle cells no longer work together in a coordinated manner and the blood supply to the body is not guaranteed. The heart remains active but does not show an orderly pumping function. Clinically, the first signs of a life-threatening circulatory arrest appear. If such a situation is present in the patient, the physicians use an ECG to check the underlying heart rhythm. Based on this data, cardiologists decide whether or not a defibrillatable rhythm is present. To treat a patient with life-saving defibrillation, first responders place one lead over the apex of the heart and a second over the base of the heart. The electrodes are placed using adhesive electrodes or what are known as paddles. Paddles are large-area plate electrodes that take less time to apply than adhesive electrodes. The paddles are applied on the right, parasternal below the clavicle (collarbone) and on the left at the level of the fifth intercostal space (space between two adjacent ribs) in the anterior axillary line. In the event of ventricular tachycardia (ventricular fibrillation), the paddles are exchanged in their position in a so-called cross-check in order to exclude possible disturbances in the ECG, which can feign a defibrillable rhythm although, for example, an asystole (lack of contraction of the heart muscle) is present. An ideal situation is when cardiac rhythm massage is interrupted exclusively for a very short period of time, less than five seconds, prior to shock administration. However, in the case of using so-called manual defibrillators, this is only possible with a well-rehearsed and practiced team. The physicians then try to depolarize as large a mass of heart muscle cells as possible; they are set “to zero.” This life-saving measure completely interrupts the excitation states previously circulating in the ventricle (one of the two lower chambers of the heart), and the heart now has a chance to allow excitation to resume its natural course (conduction system). If defibrillation is successful, the sinus node (the primary pacemaker center of the heart) resumes control of the work of the heart muscle. However, shock administration alone is not sufficient. The physicians must then continue with manual resuscitation so as not to “lose” the patient. There is no time to palpate the pulse or look at the ECG monitor; all measures must be taken very quickly. The myocardium (heart muscle that forms most of the heart wall) needs some time to recover from the stress of this life-threatening situation.Electrical cardioversion is not a regular emergency procedure and is usually ECG-guided, triggering the direct current impulse into the non-vulnerable phase (period during the cardiac cycle when an extraordinary impulse does not trigger ventricular fibrillation or flutter) of the cardiac action. It is used in atrial fibrillation and (supra)ventricular tachycardia. An optimal situation exists when a resting ECG is recorded in addition to ECG lead II, which is obtained via the device paddles on the sternum (breastbone) and appex (apex of the heart). Cardioversion is performed using R-wave synchronous electrical shocks, a significant difference from non-synchronous defibrillation. Synchronous delivery of the electrical shocks means that although the user initiates the current delivery, the device delays it until the R-wave can be closed again. By using this method, physicians avoid having the current delivery follow the excitation propagation during the refractory phase (relaxation phase). If current were delivered during this phase, there would be a risk of ventricular fibrillation and cardiovascular arrest. Electrical cardioversion operates at a lower joule strength (50 – 100) than defibrillation. Cardioversion requires patients to be given a benzodiazepine (midazolam) and a hypnotic (etomidate).
Risks, side effects, and hazards
In the case of contraindications and adverse environmental conditions, defibrillation brings dangers. A contraindication is when the patient has a body temperature of less than 27 degrees Celsius, or severe hypothermia. Other contraindications are digitalis intoxication (poisoning by digitalis), existing thrombi with risk of embolism, hyperthyroidism (pathological hyperfunction of the thyroid gland) and altered heart morphology. Environmental conditions are unfavorable and therefore risky if the ground is wet or there is metallic contact between the patient and the first aider. Defibrillation must also be avoided in the event of an explosion hazard. If the patient has expressed his or her opposition to any resuscitation measures by means of a living will, the medical professionals must refrain from defibrillation. During both defibrillation and cardioversion, no one is allowed to touch the patient or the bed, as the electric shock is transmitted to these persons and puts them in danger of death. Because of the risk of burns, the patient must not wear metallic objects such as rings or belts. Even a dental prosthesis is not without danger, as it can interrupt the spasm triggered during resuscitation or, if loosened, embarrass breathing. Because of the risk of aspiration, the patient must be fasting during cardioversion. During electrical cardioversion, the patient is anticoagulated (given a drug to inhibit blood clotting) for three weeks before and three weeks after the procedure. Possible complications may include pulmonary embolism from the release of thrombi, additional arrhythmias, anaphylaxis (allergic reaction to the drug administration), and skin reactions around the electrodes.
