Dear Editor-in-Chief,

The work presented by Fowler et al1 aimed to describe patients' outcomes after undergoing implantation of the WATCHMAN device as an alternative to receiving anticoagulants to prevent stroke due to nonvalvular atrial fibrillation. In order to provide a balanced opinion on the implications of the procedure, we would like to shed some light on the device-related thrombosis after percutaneous left atrial appendage (LAA) closure. Fowler and colleagues'1 conclusion that the WATCHMAN device can replace anticoagulation should be interpreted with caution. Contrary to the evidence presented by Fowler et al,1 Wiebe et al2 demonstrated that in patients who underwent WATCHMAN device implantation, thrombus formation on the device, ischemic strokes, and transient ischemic attacks continued to occur at a rate of 1.4% per year. In 2 significant studies, Kubo et al3 and Fauchier et al4 established that the incidence of device-related thrombus secondary to LAA device implantation ranged between 3% and 7.2%. Therefore, the respective patients required treatment with low-molecular-weight heparin to prevent thrombus formation and vitamin K antagonists to prevent ischemic stroke secondary to atrial fibrillation. Murarka et al,5 in another study, echoed Wiebe and colleagues'2 conclusion where they underscored the importance of not withholding oral anticoagulation after WATCHMAN device implantation to prevent device-induced thrombus formation.

Historically, in patients at high risk for bleeding and atrial fibrillation, administering anticoagulation was associated with an increased risk of hemorrhage. In the same vein, the need for anticoagulation with warfarin for 45 days and antiplatelets (clopidogrel and acetylsalicylic acid) for 4.5 months after device implantation present similar concerns in these patients. Wiebe et al2 noted that major bleeding due to anticoagulation requiring hospitalization occurred at a rate of 2.1% annually, including intracranial hemorrhages, pharyngeal bleeding after transesophageal echocardiography, and gastrointestinal bleeding.

Device embolism is an established complication of LAA closure with the WATCHMAN device occurring in 4% of patients. A systematic review by Aminian et al6 noted that device embolism could occur in 65% of cases anytime during the procedure and in 30% of the cases, 7 months after the procedure. The embolized devices often required retrieval with percutaneous or surgical methods. The retrieval process was associated with an increased risk of internal bleeding, valvular damage, and cardiogenic shock from left ventricular outflow tract obstruction.6 As most patients are asymptomatic, the embolized device may cause significant damage before it is detected and leave the patient vulnerable to LAA thrombus from underlying atrial fibrillation.

Fowler et al1 also cited the use of transesophageal echocardiogram and transthoracic echocardiogram to gather their data. Whereas transesophageal echocardiogram is the criterion-standard modality for detecting the left atrial thrombus, small thrombus on the device may not be detected. Moreover, the authors did not report whose and where echocardiographic data were analyzed, questioning the accuracy and consistency of reported results.

Finally, in addition to evaluating risk for bleeding and stroke to support WATCHMAN device eligibility, other characteristics should be assessed as a predictor for device success, namely, the morphology of the LAA and patient body mass index.5 For example, the "anterior chicken wing" morphology described in the literature was an independent predictor of major adverse cardiac and cerebrovascular events. As the WATCHMAN device needs to be placed deep in the anterior lobe of the appendage, certain maneuvers of extreme counterclockwise torque and increased manipulation required in patients with anterior chicken wing morphology increased the incidence of complications (odds ratio, 3.7; confidence interval [CI], 1.24-11.06; P = .01).5 This implies that such patients would continue to require oral anticoagulation for thrombus prevention.

Given these findings, we would like to reiterate that the suggestion to use the WATCHMAN device for patients with high bleeding risk or as a universal alternative to anticoagulation should be interpreted with caution.

Mohamed Toufic El Hussein, PhD, RN, NP

Calgary, Alberta, Canada. [email protected]

Payal Fichadiya, NP, MN, BN, BSc

Calgary, Alberta, Canada

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