The proposed work seeks to further understand the effects of LAA occlusion on cardiac structure and function, and in homeostasis.

Numerous studies have implicated the left atrial appendage (LAA) as the source of the vast majority of left atrial thrombi in the setting of AF3.

The University of Pittsburgh Medical Center will be implanting a Left Atrial Appendage filter system (the WATCHMAN® Left Atrial Appendage Filter System, manufactured by Atritech, Inc.). We aim to follow these patients for six months post implant in order to assess their heart rhythm, function, and to do blood tests to evaluate for neurohormonal changes.

Atrial fibrillation (AF), a heart rhythm disorder, is a major health problem. As many as 3 million US persons are afflicted; this number is expected to rise significantly in coming decades because AF incidence is directly correlated with age1. AF is significantly associated with cardiovascular morbidity and mortality.

The University of Pittsburgh Medical Center will be implanting a Left Atrial Appendage filter system (the WATCHMAN® Left Atrial Appendage Filter System, manufactured by Atritech, Inc.). We aim to follow these patients for six months post implant in order to assess:

1. Blood tests to monitor biochemical markers of cardiac remodeling and indices of heart function. We will assess atrial natriuretic factor; brain natriuretic peptide; norepinephrine; matrix metalloproteinases 1, 2, 3, 8, 9, and 13; gelatinases 2 and 9; soluble tumor necrotic factor-II; angiotensin; aldosterone; ADH; rennin; interleukin-6; TNF-α; homocysteine; C-reactive protein; quantitative D-dimer; fibrin; fibrinogen; and fibrin split products. Biochemical markers of cardiac remodeling are being intensively studied globally, with novel markers discovered and published frequently. Serum will be banked for the duration of the study to allow for retrospective investigation of newly published markers.
2. Echocardiogram to evaluate myocardial function and atrial work.
3. 24 hour holter monitor to evaluate the subjects' heart rhythm for presence or absence of atrial fibrillation.

This study will be a non-blinded observational study with a control group. Subjects will be recruited from the patient pool of the Principal Investigator and Co-Investigators. All subjects in the intervention group will have had the WATCHMAN device implanted at UPMC. The control group in this trial will be comprised of age-matched controls from the control group in the WATCHMAN device trial, also from the patient pool of the Principal Investigator and Co-Investigators. Subjects will be approached by one of the Investigators.

The primary outcome of interest will be left atrial work, measured on a continuous scale. Analysis of covariance (ANCOVA) will be used to compare mean left atrial work scores at 12 months between the intervention and non-intervention patient groups adjusting for baseline values.

Inclusion Criteria:

• 18 years of age or older
• Ability to give informed consent.
• Patient will be enrolled in the WATCHMAN device trial at UPMC. 4 -Documented history of atrial fibrillation.

Exclusion Criteria:

• Inability to give informed consent