Anesthesia for Cardioversion

Direct-current cardioversion is a common cardiological procedure, consisting of delivering an electric shock to the patient’s heart with the goal of restoring normal sinus rhythm. The common indication for the procedure is atrial fibrillation or flutter and less commonly other supraventricular arrhythmias or ventricular tachycardia. The shock is usually delivered by a pair of conductive pads applied to the patient’s skin on the anterior and posterior chest or, if the patient already has an implanted cardioverter-defibrillator (ICD), by discharge from the internal device. In either case, the electric shock is painful and provokes anxiety in conscious patients. An anesthetic is usually administered in conjunction with the cardioversion. The main challenge to the anesthesiologist involved with a cardioversion is that although the procedure is simple and short, the patient often has comorbid cardiac and pulmonary conditions that require careful titration of anesthetic depth and duration against circulatory and respiratory embarrassment. Transesophageal echocardiogram (TEE) is often obtained just before direct-current cardioversion to discern the presence of a left atrial (LA) thrombus, which may be dislodged by the shock or subsequent resumption of synchronized atrial contractions. Both procedures are performed under the same anesthetic at many institutions, significantly extending its length and the likelihood of hypotension, hypoventilation, or oxygen desaturation episodes.

Cardioversion became a method of restoring normal sinus rhythm in the early 1960s after Lown and colleagues published a report of successful treatment of patients with atrial fibrillation with a synchronized direct-current shock by a device they termed a cardioverter. Their innovation featured the synchronization of the discharge to the R-wave of the electrocardiogram (ECG) to avoid inducing ventricular fibrillation during the vulnerable portion of the cardiac cycle. In the years since, electric cardioversion has been accepted for use as a treatment of all cardiac arrhythmias except ventricular fibrillation, which requires asynchronous defibrillation. More recently, devices using biphasic current waveform have supplanted the older monophasic cardioverters, allowing greater success rates at lower energies. TEE has an excellent ability to visualize the left atrium and atrial appendage in detail to exclude the presence of atrial thrombus. Such information is valuable in patients with symptomatic arrhythmia or hemodynamic compromise but uncertain duration of atrial fibrillation and inadequate state of anticoagulation. For this reason, TEE extended the therapeutic reach of cardioversion to patients who would otherwise face a delay in treatment of several weeks to establish proper anticoagulation. The proportion of TEE-guided cardioversions is growing and now exceeds 30% in some large centers.

Over the last half century, the majority of intravenous sedative-hypnotic drugs, alone and in combination, have been used for procedural sedation and anesthesia in conjunction with direct-current cardioversion with or without TEE. Overall, anesthetic goals have remained the same—elimination of pain from the shock and blunting of recall of this unpleasant event. Early observations led to speculation whether electric shock might be tolerated by patients without anesthesia, but subsequent experience convinced physicians this was not the case. Considering the need in many patients for repeat cardioversions over their lifetime, the anxiety engendered by recalling a prior painful shock likely would act as a deterrent to obtaining the necessary treatment. Many patients with atrial dysrhythmias currently receive cardioversion on an outpatient basis, on a prearranged date after a 3- to 4-week period of anticoagulant therapy, and with emphasis on the briefest duration of preprocedure stay and prompt discharge thereafter. In this setting, sedative premedication is usually impractical, the use of all but the shortest-acting opiates is inadvisable, and neuromuscular blockade is contraindicated. Therefore the intravenous anesthetics suitable for the procedure are the short-acting barbiturate methohexital, etomidate, and, most commonly today, propofol. However, prospective studies supporting a decisive advantage for any of these agents during cardioversion are lacking.