Why is a thrombus a contraindication to cardioversion (cardioversion, or electrical Cardioversion (CV))?

From the Guidelines

A thrombus is a contraindication to cardioversion because performing cardioversion when a thrombus is present can dislodge the clot, potentially causing a stroke or systemic embolism. During cardioversion, the heart's electrical rhythm is reset, causing the heart to contract forcefully. This sudden contraction can break off pieces of the thrombus, particularly if it's located in the left atrial appendage (common in atrial fibrillation), allowing them to travel through the bloodstream and block blood vessels in the brain or other organs.

Before cardioversion, patients typically require anticoagulation therapy for at least 3-4 weeks, or a transesophageal echocardiogram (TEE) to rule out thrombus presence, as recommended by the ACC/AHA/ESC guidelines 1. If a thrombus is detected, cardioversion should be postponed, and the patient should receive anticoagulation therapy (such as warfarin with INR 2-3, direct oral anticoagulants like apixaban, rivaroxaban, dabigatran, or edoxaban at appropriate doses) for at least 3-4 weeks before reassessing for cardioversion eligibility.

Some key points to consider include:

• The use of TEE to identify patients without LAA thrombus who do not require anticoagulation, although this approach has been found to be unreliable in some studies 1.
• The administration of anticoagulation therapy regardless of the method used to restore sinus rhythm, with a recommended INR of 2-3 for at least 3-4 weeks before and after cardioversion 1.
• The performance of immediate cardioversion in patients with acute AF accompanied by symptoms or signs of hemodynamic instability, without waiting for prior anticoagulation, but with concurrent administration of heparin or low-molecular-weight heparin 1.

This approach significantly reduces the risk of thromboembolism associated with the procedure, as supported by the guidelines and studies 1.

From the Research

Thrombus as a Contraindication to Cardioversion

• A thrombus is considered a contraindication to cardioversion due to the risk of thromboembolic complications, particularly stroke 2, 3.
• The presence of a thrombus in the left ventricle or atrium increases the risk of embolization during cardioversion, which can lead to serious complications 4, 2.
• Studies have shown that cardioversion in patients with left ventricular thrombus is not associated with increased thromboembolic risk if proper anticoagulation is used 4.
• However, the risk of thromboembolic complications after cardioversion is still a concern, and anticoagulation therapy is essential to prevent these complications 2, 3, 5.

Anticoagulation Therapy

• Anticoagulation therapy is crucial in preventing thromboembolic complications after cardioversion 2, 3, 5.
• The choice of anticoagulant depends on the patient's underlying condition, such as atrial fibrillation or venous thromboembolism 5.
• Direct oral anticoagulants are recommended as first-line agents for eligible patients, while vitamin K antagonists are recommended for patients with mechanical valves and valvular atrial fibrillation 5.
• The intensity of periprocedural anticoagulation and the timing of cardioversion are significant determinants of the risk of thromboembolism 2, 3.

Clinical Evaluation and Management

• The clinical evaluation of patients undergoing cardioversion should include an assessment of the risk of thromboembolic complications 2, 3.
• The use of transoesophageal echocardiography can be useful in clinical scenarios where early cardioversion is desirable, but it does not lessen the need for effective anticoagulation after cardioversion 2.
• Validated bleeding risk assessments, such as HAS-BLED, should be performed at each visit, and modifiable factors should be addressed 5.
• Major bleeding should be treated with vitamin K and 4-factor prothrombin complex concentrate for patients already being treated with a vitamin K antagonist 5.