Assessing intracardiac thrombus prior to cardioversion: A story yet to be told

Abstract

Direct current cardioversion was invented by Bernard Lown in 1962,and has been used for over half a century to restore sinus rhythm in patients with atrial fibrillation. Unfortunately, electrical cardioversion without anticoagulation has an inherent risk of thromboembolism that ranges from 5% to 7%, usually within the first week after the procedure. Patients undergoing electric cardioversion are therefore treated with therapeutic doses of anticoagulation for 3 weeks before the procedure and, for those without a reason to take chronic anticoagulation, for at least 4 weeks after. 1 The rationale for 3 weeks of therapeutic anticoagulation (that is maintaining an international normalized ratio [INR] > 2 for 3 consecutive weeks) prior to cardioversion is based on a number of lines of evidence. First of all, in nonrandomized studies, the incidence of thromboembolism in patients who have been properly treated with warfarin is a small fraction of what it is in patients who are not so treated. 2 In addition, Goldman et al. proposed that within 14 days there is sufficient fibroblastic infiltration to cause firm adherence of the thrombus to the atrial endocardium, thus reducing the likelihood of dislodgment. 3 Four weeks of anticoagulation following cardioversion is supported by Doppler echocardiographic studies showing restoration of the transmitral atrial (A) wave. 4The Assessment of Cardioversion Using Transesophageal Echocardiography (ACUTE) study showed that transesophageal echocardiography (TEE)-guided cardioversion with short-term anticoagulation was a safe and an effective alternative to warfarin pretreatment. 5 Since then, TEE has provided a reliable and expedient tool for detection of left atrial appendage thrombus before cardioversion. A major breakthrough in the management of atrial fibrillation and its associated thromboembolic risk was the advent of novel oral anticoagulant (NOAC) drugs, each showing noninferiority, and in some cases superiority, to warfarin in rates of all-cause stroke and systemic embolism. Though none of the NOAC trials had detection of left atrial thrombus as a primary endpoint, subgroup analyses of these trials revealed a low thromboembolic risk that was comparable to warfarin in patients treated with a NOAC for ≥3 weeks prior to cardioversion. In a subgroup analysis of patients in the RELY trial (Randomized Evaluation of Long Term Anticoagulant Therapy), the rate of detection of left atrial thrombus among patients undergoing TEE cardioversion was in the range of 1.2-1.8% and 2.9% for patients on dabigatran and warfarin, respectively. 6 In the ARISTOTLE trial (Apixaban for the Prevention of Stroke in Subjects with Atrial Fibrillation), none of the 86 patients who underwent TEE cardioversion had an LA thrombus. 7 The efficacy and safety of NOACs prior to cardioversion was further evaluated in three large prospective randomized trials: X-VeRT (eXplore the efficacy and safety of once-daily oral riVaroxaban for the prevention of caRdiovascular events in patients with non-valvular aTrial fibri...