Elective electrical cardioversion for atrial fibrillation/flutter
Elective electrical cardioversion for atrial fibrillation/flutter is often done in conditions in which the atrial booster function is needed as in hypertrophic cardiomyopathy. Sometimes it is performed after balloon mitral valvotomy as well. In situations in which it is likely to recur, antiarrhythmic therapy may be continued after the procedure. Sometimes when the arrhythmia does not respond initially, or recurs, a repeat attempt after treatment with amiodarone may be considered. It may be kept in mind that amiodarone may increase the defibrillation threshold.
Adequate anticoagulation is a must prior to elective electrical cardioversion in atrial arrhythmias which have lasted more than 48 hours. Some resort to cardioversion after exclusion of left atrial appendage clot by transesophageal echocardiogram. Usual duration of anticoagulation is for about 4 weeks, which is initiated with heparin and followed up with warfarin. Anticoagulation has to be continued for 4 weeks to 6 months after the procedure as well as there is a chance for atrial stunning which may predispose to clot formation.
The procedure can be done as an outpatient procedure, but usually in the setting of an intensive care setting with standby anaesthesia cover. Person should be fasting overnight and skin should be free of any ointments or other applications. Intravenous short acting sedation is given prior to the procedure to allay the pain and anxiety of the shock. Intravenous access, continuous monitoring and emergency crash cart should be at hand. It is ideal to use adhesive pads for cardioversion rather than paddles as the latter can be used for immediate transcutaneous pacing in case of post shock bradycardia. Anteroposterior placement is also easy in case of patches rather than paddles and it improves the success rate of cardioversion.
Lower energy levels may be enough for atrial flutter which is due to a macro re-entry while higher energies are often needed for atrial fibrillation. The principle of cardioversion is to simultaneously depolarise a critical amount of myocardium so that when the spontaneous electrical activity restarts, it is the dominant pacemaker, usually the sinus node which takes over. When there is a large and scarred atrium as in uncorrected mitral valvular lesions or congenital heart disease, the chance of recurrence is high. Electrolyte imbalances and digoxin toxicity should be excluded as these may lead to more severe arrhythmias after cardioversion.
Atrial electrical stunning is the phenomenon of delayed atrial electrical activity after a cardioversion, which is rare. Atrial mechanical stunning is more commonly seen, as a delay in recovery of the contractile function of the atrium even after successful restoration of sinus rhythm. This is one of the reasons for continuing anticoagulation after a successful cardioversion. Elective cardioversion is usually done with therapeutic INR range of 2 – 3.
Even though the persons undergoing elective electrical cardioversion of atrial fibrillation can be sent home after observing for a few hours, they are asked not to drive a vehicle or make important decisions on the same day because of residual sedation.