Three-dimensional imaging provides information about the shape of the ostium prior to deployment, and beautiful images of a device in position at the end of the procedure, but due to unreliability of the 3D imaging planes with any 2D measurements and often obstruction of the device landing zone by the limbus of the LSPV, it is not recommended that 3D imaging be used to guide decision making about device size or positioning during the procedure. A 3D imaging platform, however, is very useful as it allows for 2D biplane imaging which is helpful in guiding sheath position, and manipulation of the imaging planes for “hard to image” LAA angles, particularly 135° view in some patients. Keep in mind that prolonged use of 2D biplane or 3D imaging during a case can cause overheating of the TEE imaging head in the esophagus, and can lead to deterioration in image quality due to esophageal edema as the case progresses. Turning down the power output settings to TI 0–0.1 and MI 0.3–0.4 reduces the amount of heat at the imaging head without significant deterioration of the procedural imaging.

Successful LAA device closure requires careful measurement of the dimensions where the device will be seated, often referred to as the “landing zone”. For the WATCHMAN LAA occluder device , the landing zone is located between the LCx medially and 1–2 cm inside the limbus laterally. The measurements are taken in four views to determine the widest measurement (most often the 135° view or anteroposterior view), whether the landing zone is round vs. elliptical, and to determine whether there is appropriate depth to accept a delivery system once the size of the device has been determined. The four views are taken at 0, 45, 90 and 135°, and the measurements recorded in millimetres. Examples of measurements obtained in these views are illustrated in Fig. 6.5. Some views may be difficult to achieve with omniplane manipulation of the imaging window, and thus 2D biplane imaging can assist in this regard. For example, imaging at 135° can prove to be difficult in some patients, so getting the best 45° view and bisecting this image with biplane imaging (and sometimes a degree of elevation or subtraction) can better achieve this view.

The WATCHMAN device size selection is based on the largest measurement at the landing zone allowing for 20 % compression. The device sizes are 21, 24, 27, 30 and 33 mm. Each device sizing has the maximum landing zone dimension recommended for that size device, and relies on equal depth for successful positioning and deployment of the device. For example, a maximum LAA landing zone dimension of 19 mm will not be adequately compressed with a 21 mm device, and thus a 24 mm device is chosen. This however, requires at least 24 mm of coaxial depth. Sometimes a compromise is reached such that if there is insufficient depth to deploy a particular sized device, a decision must be made to deploy a smaller device more distally to successfully occlude the LAA distal to the landing zone. Alternatively, choosing a different device may be necessary if there is insufficient depth, such as the Amplatzer Cardiac Plug (ACP) device , which is less reliant on depth for successful device deployment. The Lariat system is another option but has the limitation of LAA size to be captured by the wire loop and requires instrumentation of the pericardium.

In contrast, measurements for the ACP device are made differently. As the ACP device has two components (distal lobe and proximal disc) the measurements need to be made in different positions to the WATCHMAN device. The lobe is deployed approximately 10 mm into the LAA (from the LCx landmark). Measurement for device sizing, which is based on lobe size (16–30 mm), should be made inside the LAA approximately 10 mm distal to the LCx in the long axis view, with matching measurement in the short axis view at the same depth. For disc sizing, the distance between the LCx margin and the LSPV limbus should be made in the long axis view (Fig. 6.6). As the disc will be 4–6 mm bigger than the device measurement as determined by the lobe size, measurement of the ostium will determine whether the device size chosen by lobe measurement will be compatible with a suitable ACP device.

The trans-septal puncture position is probably the most crucial step which will influence the ease of device positioning and deployment. As the LAA is anterior and lateral, the trans-septal puncture position is best achieved at the most posterior location on the fossa ovalis. This usually provides the most coaxial sheath position for accessing the LAA. The craniocaudal position is not quite so critical for LAA access or coaxial alignment, but a mid-to-low fossa position is usually best for puncture with good “run off” into the atrium for the trans-septal puncture needle.

It is best to start with a bicaval view (craniocaudal or superior–inferior view) with the thin membrane of the fossa and the superior vena cava (SVC) on view with the sheath in the SVC. This is best achieved with an imaging plane of 90–110°. The sheath is then drawn down the SVC until it reaches the fossa. It is important to keep the tip of the sheath on view at all times during draw down of the sheath. Once the sheath reaches a suitable position on the fossa (mid to low), the imaging plane should then be focussed on the anteroposterior aspect of the fossa, which is best achieved at the 45° view. This view normally has the aortic valve in short axis, and is usually the plane used to identify any patent foramen ovale or secundum ASD. In this view, the fossa membrane is in an anterior–posterior orientation. For best LAA instrumentation, the most posterior position on the fossa membrane is favourable (Figs. 6.7 and 6.8). Some anterior angulation on the sheath is important so that when the needle punctures across the septum it does not course posteriorly to the back of the left atrium. Improper positioning of this puncture position can have serious consequences such as perforation or tamponade, so care must be taken to guide the needle across the septum safely, keeping the antero-posterior plane on view with care to keep the tip of the needle on view at all times. If the septum is too mobile such that other important structures are at risk of perforation due to excessive tenting of the fossa membrane, advise your proceduralist to pull back the needle to the tip of the sheath and suggest diathermy to cross the septum. This will provide a safer option for trans-septal puncture and reduce the risk of perforation. It is common at this juncture of the procedure for the proceduralist to challenge the advised position of the puncture as determined by the TEE, as it often is at an unusual angle to the usual landmarks which are more familiar to the proceduralist for routine trans-septal puncture for other procedures! It is important that there is communication and trust about the position of the needle as determined by TEE given the posterior position of the needle and the surrounding structures at risk of perforation. Once the needle is across the septum, saline contrast bubbles can be seen in the LA. It is important to notify the proceduralist if air can be seen entering into the LA from the needle or introducer.