**2. Left atrial appendage anatomy**

The embryonic origin of LAA is different to atria. It is originated from the embryonic remnant of left atrium (LA) during first trimester, with a multilobed structure positioned anteriorly in the atrioventricular sulcus close to the left circumflex artery, the left phrenic nerve, and the left pulmonary veins [4]. The appendage contains numerous trabeculae, with a complex and highly variable anatomy. The LAA typically consists of three major components:


### **3. Rationale for LAAO**

Thromboembolic events in AF are correlated to loss of atrial contraction, stasis of blood flow, and thrombus formation, particularly in the LAA. The LAA is notoriously labeled as "human most lethal attachment," as it has been demonstrated that thrombus in the LAA is the primary source for thromboemboli [2]. A review of studies in patients with nonrheumatic heart disease demonstrated that 90% of LA thrombi examined by transesophageal echocardiography (TEE), cardiac surgery, or autopsy, were located in the LAA [9]. Another study also showed that LA thrombus was evident in 15% of patients without OAC after 48 hours of AF, in which almost all thrombi were found in LAA. The LAA is particularly prone to thrombus formation in AF due to its inherent anatomy with extensive trabeculations, increased blood stasis and hypercoagulability, and endothelial damage [10].

The role of the LAA as a source for thromboemboli in AF patients provides the rationale for ligation, amputation, or occlusion of the LAA structure, especially if patients are indicated for stroke prevention strategy; on the other hand, they are either contraindicated or noncompliant to long-term OAC. In addition, some LAAO techniques may have an additional role in sinus rhythm maintenance through nonpulmonary vein triggers elimination, atrial mass decrease, and atrial electrical remodeling reversion [11, 12].

## **4. Techniques for LAAO**

Currently, there are two major different strategies in LAA exclusion from systemic circulation:

#### **4.1 Surgical approach**

The first reported resection of LAA in a human was by John Madden in 1949 [13]. In his report, he performed surgical excision of LAA structure during open *Left Atrial Appendage Occlusion: Current and Future DOI: http://dx.doi.org/10.5772/intechopen.105776*

heart surgery specifically aimed for stroke prevention in AF patients. This approach was not routinely done after this report was published. Nevertheless, LAA surgical closure is now class IIa indication in the 2020 American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for management of patients with valvular heart disease undergoing heart surgery [14] and has currently become widely performed. Similarly, in patients with AF undergoing cardiac surgery, surgical LAA closure is also a class IIb indication based on 2019 ACC/AHA/Heart Rhythm Society (HRS) guidelines [15].

The method of LAA exclusion is usually dictated by the concomitant cardiosurgical procedure.

#### **4.2 Percutaneous LAAO device**

To date, several LAAO devices have been approved to be used worldwide (**Figure 1**).

*4.2.1 Endocardial system*

a.the Watchman (Boston Scientific, Natick, MA)

This device has been approved by the Federal Drug Administration (FDA) in the year of 2015 as an alternative to warfarin OAC based upon data from the PREVAIL and PROTECT-AF trials. The device system comprises of a 14 Fr (outer diameter), frame with fixation barbs, and fabric cover [16].

b.the Amplatzer Cardiac Plug/ACP (St. Jude Medical, St. Paul, MN)

The Amulet is a second-generation self-expanded LAAO. The device system includes 14.4–16.5 Fr delivery sheath, lobe and stabilization hook, and fixed-size cover disk [16].


**Figure 1.** *LAAO devices (modified from [10, 16–18]).* c.LAmbreTM LAA Closure System (Lifetech Scientific Corporation)

LAmbre occluder is a Conformité Européenne (CE) recognized LAA closure device. It is a self-expanded device consisting of a 10.4–12.3 Fr sheath (delivery system), hook-embedded umbrella, and size adaptive cover [19]. In 2020, LAmbreTM LAA Closure System has obtained the approval by FDA for the commencement of an investigator-initiated clinical trial in the United States.
