DC (direct current) Cardioversion is a corrective procedure where an electrical shock is delivered to the heart to convert, or change, an abnormal heart rhythm, usually atrial fibrillation (AF) or atrial flutter back to normal "sinus" rhythm.
What is atrial fibrillation?
Each normal heartbeat starts in an area of the heart known as the sinus node, located in the upper right chamber of the heart (right atrium). The sinus node sends organized electrical signals through the heart resulting in a perfectly timed, rhythmic heartbeat. In contrast, patients with atrial fibrillation have a chaotic electrical signal, causing the atria to fibrillate (or "quiver"). This typically results in a fast and irregular heartbeat. While some patients have no symptoms, others may experience shortness of breath, lightheadedness and fatigue. Depending on your specific medical history and symptoms, a DC (direct current) cardioversion may be recommended to try and return your heart to normal sinus rhythm.
How is DC Cardioversion performed?
In DC cardioversion, once you have received adequate sedation, a synchronized (perfectly timed) electrical shock is delivered through the chest wall to the heart via self-adhesive pads applied to the skin of the chest. The goal of the procedure is to disrupt the abnormal electrical circuit(s) in the heart and thereby to reset the heart to normal rhythm. This split second interruption of the abnormal beat allows the heart's electrical system to regain control and restore a normal heartbeat. Electrical cardioversion is performed in a hospital setting where oxygen levels, blood pressure and heart rhythm are closely monitored.
Normal sinus rhythm can be restored more than 90 percent of the time. However, atrial fibrillation may recur soon afterwards or over time, in which case it may be appropriate to consider a repeat DC cardioversion (often after adjusting medications). Occasionally, for patients with frequent recurrences of atrial fibrillation, it may be appropriate to consider a catheter ablation procedure.
Blood clots and anticoagulation
Since the upper chambers of the heart are fibrillating (quivering) rather than squeezing in atrial fibrillation, there is a risk that blood clots may form in the heart which could in turn dislodge and travel elsewhere (embolism), potentially causing a stroke or other complication. This risk may increase with age, high blood pressure, diabetes, coronary/vascular disease and in patients with reduced heart function. To help prevent blood clots and reduce the potential for stroke, most patients with atrial fibrillation require blood thinning medication called anticoagulants (such as warfarin, dabigatran, rivaroxaban, apixaban or edoxaban).
Since a pre-existing clot in the heart could be dislodged by a DC cardioversion procedure, anticoagulants are usually recommended for at least 3 weeks prior, and continued for at least 4 weeks following a DC cardioversion. Patients at risk of recurrence of atrial fibrillation, particularly those >65 years of age, usually benefit from longterm anticoagulation, even if the DC cardioversion is successful.
Occasionally, if patients need urgent DC cardioversion before 3 weeks of full anticoagulation have been completed, a transoesophageal echocardiogram (TOE) may be undertaken, prior to DC cardioversion to image the atrium and ensure there is no visible blood clot. During TOE, your throat is numbed with local anaesthetic spray, then a thin scope is swallowed and gently passed down your gullet to a position just behind the heart where detailed views are obtained.