Blood Stasis Secondary to Heart Failure Forms Warfarin-Resistant Left Atrial Thrombus

Anticoagulants such as warfarin are recommended for patients with atrial fibrillation (AF) to decrease stroke risk associated with thrombus formation in the left atrium (LA). In a subgroup of patients, however, warfarin is unable to prevent LA thrombus formation at therapeutic doses. This study characterized the clinical and echocardiographic features of patients having warfarin-resistant LA thrombus. Of the 1364 nonvalvular AF patients examined by transesophageal echocardiography, 431 received warfarin. A total of 10 patients (2.3% of warfarin-treated patients) exhibited LA thrombus formation even during warfarin treatment at a dose and duration sufficient for increasing the prothrombin time international normalized ratio (PT-INR) to the therapeutic range for >= 30 days. Categorical regression analysis revealed that decreased LA appendage (LAA) flow velocity, greater LA spontaneous echocardiographic contrast (LASEC), and lower left ventricular ejection fraction (LVEF) significantly contributed to residual LA thrombus (P < 0.05 for all). Receiver operating characteristic (ROC) curve analysis indicated that higher right ventricular systolic pressure, which suggests LA pressure (area under curve, 0.85), LV mass index (0.81), and LA dimension (0.68), as well as lower LAA flow velocity (0.92) and LVEF (0.91) predicted warfarin-resistant LA thrombus formation (all P < 0.05). These results suggest that blood stasis secondary to heart failure contributes to the formation of warfarin-resistant LA thrombus. We propose that therapies to increase LVEF should be administered together with warfarin for AF patients with heart failure to decrease stroke risk.