PHOENIX, ARIZONA. There is considerable evidence that the left atrial appendage (LAA) is an important source of blood clots (thrombi) in atrial fibrillation (AF) patients with underlying heart disease. Clot formation may occur when the rate of blood flow in and out of the LAA is significantly reduced. The most common cause of reduced blood flow is an inadequate left ventricular ejection fraction. Thus, LAA clot formation is rare among lone afibbers unless they have undergone a catheter ablation targeting the area around the opening of the LAA.
The LAA is a remnant of the original embryonic left atrium formed during the third week of gestation. The LAA lies within the pericardium in close contact with the free wall of the left ventricle. Thus, blood flow in and out of the LAA depends, to a significant degree, on a properly functioning left ventricle. The LAA empties into the left atrium through an orifice located between the left upper pulmonary vein and the left ventricle. The diameter of the opening varies between 10 and 40 mm, the overall volume of the LAA varies between 0.77 and 19.27 cubic centimeters (mL), and its length can vary between 16 and 51 mm.
Prevention of clot formation and the associated risk of ischemic stroke and TIA (transient ischemic attack) are usually attempted through the use of oral anticoagulants such as warfarin. However, a significant proportion of AF patients cannot tolerate anticoagulants because of high risk for hemorrhagic stroke and major bleeding. For these patients, there are two options – remove the LAA or close it off. Removal is a fairly simple matter if the patient is undergoing a maze or mini-maze procedure, but is not an option in the case of catheter ablation. Thus several techniques and devices have been developed to effectively isolate the LAA from the left atrium.
One such device is the WATCHMAN which is a nitinol (nickel-titanium alloy) cage covered with a polyethylene membrane and having barbs for anchoring it to the inside of the LAA. The device is inserted with a special catheter entering the left atrium through the femoral vein – a procedure similar to that used in pulmonary vein ablation procedures. The first trial of the device involved 66 patients with AF and one or more risk factors for ischemic stroke; it was performed at the Mayo Clinic. After 45 days, 93% of participants had achieved satisfactory sealing of the LAA. Unfortunately, there have been reports of the device working itself loose and there are also concerns about leaving a foreign, metallic object in the heart for an extended period of time.
The newly developed LARIAT device overcomes these concerns as it is made from Teflon-coated polyester, which is non-metallic and non-absorbable. The LARIAT device is essentially a noose which is permanently tightened around the LAA where it empties into the left atrium, thus preventing any blood flow in and out of the LAA. Early trials showed that 95 to 98% of patients undergoing the LARIAT procedure retained complete closure 3 to 12 months after. The procedure is a two-stage process involving access to both the inside of the heart with a catheter (endocardial access) and access to the outside of the heart (epicardial access) via a small incision at the bottom of the rib cage. It is usually carried out by a team of two physicians (by an EP for the endocardial phase and by an EP or cardiologist for the epicardial phase). Here is an excellent video of the procedure.
Cardiologists at the Good Samaritan Medical Center now report their experience with a group of 27 AF patients who were at high risk for stroke. Anticoagulation was not an option since all the patients were also at high risk for major bleeding. Most of the patients (52%) had permanent AF, while 41% had paroxysmal, and 7% had persistent AF. Average age was 75 years, 74% were male, 96% had hypertension, 67% had congestive heart failure, and 37% had suffered a pervious stroke or TIA.
The trial participants had the LARIAT device installed while under general anesthesia and constant monitoring with TEE (transesophageal echocardiography). At the 45-day follow-up, complete closure was confirmed in 22 of 22 patients in whom the procedure was completed and who had TEE data. Three cases of procedure-related pericarditis (inflammation of heart lining) and one procedure-related stroke were noted. The authors conclude that percutaneous LAA exclusion with the LARIAT device can be achieved successfully with an acceptable rate of procedural complications.Stone, D, et al. Early results with the LARIAT device for left atrial appendage exclusion in patients with atrial fibrillation at high risk for stroke and anticoagulation. Catheterization and Cardiovascular Interventions, June 13, 2013 [Epub ahead of print]