Cardioversion is the restoration of normal sinus rhythm and frequency in the presence of a serious cardiac arrhythmia. In the vast majority of cases, cardioversion is intended to resolve atrial fibrillation with a frequency greater than 100 Hz and a noticeable loss of performance. In principle, cardioversion can be performed with medication or by delivering a shock of electricity – similar to that of a defibrillator.
What is cardioversion?
Cardioversion is the restoration of normal sinus rhythm and rate in the presence of a serious cardiac arrhythmia. Cardioversion is the qualitative and quantitative conversion of the heart rhythm in the presence of a persistent (persistent) dysrhythmia to a normal sinus rhythm with a frequency within the normal range of approximately 60 to 80 Hz without physical exercise. In principle, cardioversion can be performed by medication or by electric shock, because it offers the higher success rate in most cases and relapse into arrhythmia is less frequent. If successful, electrocardioversion (ECV) restores (normal) sinus rhythm immediately after the shock. Persistent arrhythmias in the form of atrial fibrillation are relatively common in men over 60 years of age. Atrial fibrillation with frequencies above 100 Hz is usually not immediately life-threatening, but it should not be confused with so-called ventricular fibrillation, which is immediately life-threatening. If there are no identifiable organic causes for the arrhythmia or atrial fibrillation, such as valvular heart disease or heart failure (weakness of the heart muscle), the chances of success of cardioversion are particularly high.
Function, effect, and goals
The sole purpose of cardioversion is to restore normal sinus rhythm to the heart in the presence of persistent arrhythmia. The arrhythmia may be in the form of atrial fibrillation, atrial flutter, or arrhythmia of the heart chambers (ventricles) associated with an increase in frequency (tachycardia). Atrial fibrillation is an arrhythmic and disordered beating of the atria with a relatively high frequency of over 100 to sometimes 150 Hz. If the ejection volume of the atria is impaired by the disordered contractions, there is a noticeable loss of performance, so that restoration of sinus rhythm brings about a noticeable improvement in the patient’s condition. Electrocardioversion, performed under short anesthesia, has the advantage of a higher and more sustained success rate over attempting to convert the heart rhythm with medication, depending on the type of arrhythmia. ECV is comparable to the effect of a defibrillator because electrocardioversion also uses direct current. The main difference is that ECV uses lower currents (50 – 100 joules) and the timing of the electric shock is controlled by the ECG. The shock is delivered at a time when the heart muscle cells are still working synchronously. The procedure increases the chances of success in converting the heart to a sustained sinus rhythm and minimizes the risk of ventricular fibrillation. If the arrhythmia has been present for more than 48 hours prior to conversion, it is important to determine whether blood clots (thrombi) have formed in the atria, which could cause an embolism or stroke by spreading into the bloodstream. A possible atrial thrombus can be detected by transesophageal echocardiography (TEE). To do this, the head of the ultrasound machine is inserted into the esophagus in a probe. The echoes are sent to a monitor. TEE also provides information about the functioning of the heart valves and the condition of the heart muscles (myocardium). Of particular interest is whether there is any thickening (hypertrophy) that may lead to insufficiency in the longer term. It is recommended to take anticoagulants before and after cardioversion – also in case of drug-induced cardioversion. In both cases, the restored sinus rhythm should be supported by medication for a longer period of time. In most cases, antihypertensive drugs are also needed because, for example, atrial fibrillation is often triggered by hypertension that has existed for a long period of time.In the presence of defined arrhythmias, so-called catheter ablation may be considered as an alternative to electrical or drug conversion, in which one or more catheters are advanced through veins in the groin into the left atrium and targeted cells in the left atrium responsible for the arrhythmia are destroyed or their conductivity is corrected.
Risks, side effects, and hazards
The major risks of cardioversion, whether performed electrically or with drugs, are, on the one hand, that further arrhythmias may develop or that atrial thrombi that have formed during the course of the arrhythmia may dislodge from the atrium after conversion and be carried into the bloodstream. At a crucial point, they can occlude vessels and cause embolism. If the thrombi occlude a cerebral vessel, a stroke occurs with corresponding symptoms and deficits. This risk is kept extremely low by the previously performed TEE. In the case of drug conversion, there is an additional risk of harmful side effects of the drugs, which can be quite serious for certain groups of patients with previous damage such as insufficiency of the myocardium or heart valves and must be seriously considered. In the case of electrical cardioversion, there is an additional minor anesthetic risk due to the short-term anesthesia required. There may also be a temporary reddening of the skin at the points of contact between the electrodes and the skin. Burns at the contact points occur extremely rarely. More common are harmless muscle ache-like symptoms in the area of the chest muscles, which disappear after a few days. Because of the prophylactic use of anticoagulants to prevent stroke and embolism, severe bleeding may occur in rare cases of internal or external injuries.
