C. Transesophageal echocardiography to exclude a left atrial appendage thrombus followed by direct current cardioversion and aspirin alone for thromboembolism prophylaxis

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9. C. Transesophageal echocardiography to exclude a left atrial appendage thrombus followed by direct current cardioversion and aspirin alone for thromboembolism prophylaxis

When the duration of atrial fibrillation is thought to be more than 48 hours, transesophageal echocardiography is required to evaluate for left atrial appendage thrombus prior to direct current cardioversion. Alternatively, the patient can be fully anticoagulated (warfarin, dabigatran, rivaroxaban) for 3 to 4 weeks prior to cardioversion, which can then safely be done without transesophageal echocardiography with a low risk for thromboembolism.

The determination of anticoagulation after direct current cardioversion is based on an individual patient’s risk using the CHA₂DS₂-VASc score. This patient has a score of 0, and thus aspirin alone afterwards is considered adequate.

Another reasonable approach would be to simply rate-control the atrial fibrillation with nondihydropyridine calcium channel blockers (diltiazem, verapamil) and/or beta-blockers, then reevaluate symptoms. Direct current cardioversion could be performed at a later time; however, once the duration is beyond 48 hours, full anticoagulation needs to be initiated 3 to 4 weeks before and after the procedure regardless of the thromboembolic risk (CHA₂DS₂-VASc score).

10. C. AV nodal ablation and permanent pacemaker implantation

When high doses of AV blocking drugs are not successful in lowering ventricular rates in the setting of atrial fibrillation, AV nodal ablation can be utilized ― especially if antiarrhythmic drug therapy fails to maintain sinus rhythm.

Remember that all atrial action potentials must pass through the AV node to reach the ventricle. AV node ablation destroys this connection, stopping any atrial activity from reaching the ventricle. This results in the intrinsic pacemaker of the heart shifting from the atria to the ventricles. Unfortunately, the His-Purkinje system in the ventricles is only able to generate action potentials at a rate of 30 to 40 beats per minute, resulting in slow ventricular rates and severe bradycardia after the AV node is ablated. Thus, a permanent pacemaker must be implanted to prevent symptoms of bradycardia.

Pulmonary vein isolation (a.k.a. atrial fibrillation ablation) is less successful as the left atrium enlarges and with advanced age. Two beta-blockers simultaneously will not have any added benefit compared with the maximum dose of one beta-blocker alone. While amiodarone is good to restore/maintain sinus rhythm, it is not normally recommended as a heart rate controlling therapy.

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