By stopping the heart racing, the heart's normal clock, the sinus node, then has a chance to set a normal rhythm again. During this treatment, the patient receives a mild anaesthetic, as the electric shock also causes a painful contraction of the muscles in the chest. In the case of ventricular fibrillation, however, this is usually not necessary, as the patient is usually unconscious and no longer has any sensation of pain.
Difference between Cardioversion und Defibrillation?
Cardioversion is an electrical shock treatment that is mostly used to stop an atrial arrhythmia. The shock is synchronised with the ECG (R-wave synchronised cardioversion) so that it is not delivered during a particularly sensitive phase of electrical excitation of the main chamber (the so-called vulnerable phase).
In defibrillation, on the other hand, there is no such coordination with the ECG because ventricular fibrillation, i.e. chaotic excitation of the heart, is present anyway. This is an emergency situation.
Planning a Cardioversion
Before cardioversion, an elective, i.e. planned therapy for atrial fibrillation, either an ultrasound examination of the oesophagus (transoesophageal echocardiography) should rule out clot formation in the atrium or blood thinners should be administered for three to four weeks to prevent clots. Overall, cardioversion is a very safe treatment method with few complications, especially if the safety measures mentioned above have been observed. In an emergency, i.e. in ventricular fibrillation, for example, the measures are of course not possible.