The accompanying video describes a procedure for percutaneous placement of the WATCHMAN Left Atrial Appendage (LAA) Device. The WATCHMAN is a nitinol device designed to be permanently implanted at, or slightly distal to, the opening of the left atrial appendage (LAA) to trap blood clots before they exit the LAA, preventing thromboembolic stroke.
Atrial fibrillation (AF) is the most common cardiac arrhythmia, affecting an estimated 6 million people in the United States 1. Since AF affects primarily elderly people, its prevalence increases parallel with age. As such, it is expected that 15.9 million Americans will be affected by the year 2050 2. Ischemic stroke occurs in 5% of non-anticoagulated AF patients each year. Current treatments for AF include rate control, rhythm control and prevention of stroke 3.
The American College of Cardiology, American Heart Association, and European Society of Cardiology currently recommended rate control as the first course of therapy for AF 3. Rate control is achieved by administration of pharmacological agents, such as β-blockers, that lower the heart rate until it reaches a less symptomatic state 3. Rhythm control aims to return the heart to its normal sinus rhythm and is typically achieved through administration of antiarrhythmic drugs such as amiodarone, electrical cardioversion or ablation therapy. Rhythm control methods, however, have not been demonstrated to be superior to rate-control methods 4-6. In fact, certain antiarrhythmic drugs have been shown to be associated with higher hospitalization rates, serious adverse effects 3, or even increases in mortality in patients with structural heart defects 7. Thus, treatment with antiarrhythmics is more often used when rate-control drugs are ineffective or contraindicated. Rate-control and antiarrhythmic agents relieve the symptoms of AF, including palpitations, shortness of breath, and fatigue 8, but don’t reliably prevent thromboembolic events 6.
Treatment with the anticoagulant drug warfarin significantly reduces the rate of stroke or embolism 9,10. However, because of problems associated with its use, fewer than 50% of patients are treated with it. The therapeutic dose is affected by drug, dietary, and metabolic interactions, and thus requires detailed monitoring. In addition, warfarin has the potential to cause severe, sometimes lethal, bleeding 2. As an alternative, aspirin is commonly prescribed. While aspirin is typically well tolerated, it is far less effective at preventing stroke 10. Other alternatives to warfarin, such as dabigatran 11 or rivaroxaban 12 demonstrate non-inferiority to warfarin with respect to thromboembolic events (in fact, dabigatran given as a high dose of 150 mg twice a day has shown superiority). While these drugs have the advantage of eliminating dietary concerns and eliminating the need for regular blood monitoring, major bleeding and associated complications, while somewhat less so than with warfarin, remain an issue 13-15.
Since 90% of AF-associated strokes result from emboli that arise from the left atrial appendage (LAA) 2, one alternative approach to warfarin therapy has been to exclude the LAA using an implanted device to trap blood clots before they exit. Here, we demonstrate a procedure for implanting the WATCHMAN Left Atrial Appendage Closure Device. A transseptal cannula is inserted through the femoral vein, and under fluoroscopic guidance, inter-atrial septum is crossed. Once access to the left atrium has been achieved, a guidewire is placed in the upper pulmonary vein and the WATCHMAN Access Sheath and dilator are advanced over the wire into the left atrium. The guidewire is removed, and the access sheath is carefully advanced into the distal portion of the LAA over a pigtail catheter. The WATCHMAN Delivery System is prepped, inserted into the access sheath, and slowly advanced. The WATCHMAN device is then deployed into the LAA. The device release criteria are confirmed via fluoroscopy and transesophageal echocardiography (TEE) and the device is released.
1. The WATCHMAN Device
A fabric cap, constructed out of fabric polyethyl terephthalate (PET) serves as a 160-micron filter and prevents harmful emboli from exiting during the healing process.
2. TEE-Based Determination of WATCHMAN Device Size
3. Pre-Implantation Preparation
4. Implantation of the WATCHMAN Device
5. Partial Implant Recapture
6. Full Implant Recapture
7. Post-Procedure
8. Outcome/Representative Results
The PROTECT-AF clinical trial was performed to compare the safety and effectiveness of the implantation of the WATCHMAN device to that of warfarin treatment. 707 eligible patients were randomly assigned in a 2:1 ratio to either percutaneous closure of the LAA with subsequent discontinuation of warfarin (intervention; n=463) or to warfarin treatment (control; n=244).
As seen in Figure 5, the primary efficacy event rate (assessed by a primary composite endpoint of stroke, cardiovascular death, and systemic embolism) was compared in patients undergoing LAA closure with the WATCHMAN device (intervention group) and patients undergoing warfarin therapy (control group). The primary efficacy event rate was 3.0 per 100 patient-years (95% credible interval [CrI] 1.9-4.5) in the intervention group and 4.9 per 100 patient-years (2.8-7.1) in the control group. The ischemic stroke rate was 2.2 (1.2-3.5) in the intervention group and 1.6 (0.6-3.0) in the control group. The cardiovascular/unexplained death rate was 0.7 (0.2-1.5) in the intervention group and 2.7 (1.2-4.4) in the control group. The hemorrhagic stroke rate was 0.1 (0.0-0.5) in the intervention group and 1.6 (0.6-3.1) in the control group. The systemic embolism rate was 0.3 (0.0-0.8) in the intervention group and 0 in the control group. Taken together, this reflects a 38% decrease in cardiovascular adverse events demonstrating that LAA closure is not inferior to warfarin therapy.
Video 1. http://www.atritech.net/animation.html
Figure 1. The WATCHMAN Device. The WATCHMAN device is a nitinol cage with a polytetrafluoroethylene membrane on the surface, and fixation anchors around the perimeter
Figure 2. Transseptal Access System. The WATCHMAN introduction sheath is available with double and single curve for different anatomical situations.
Figure 3. WATCHMAN Delivery system. The WATCHMAN device is constrained within the delivery system, which is compatible with all 5 device sizes.
Figure 4. LAA Typing. (Left) The WindSock Type LAA is an anatomy in which one dominant lobe of sufficient length is the primary structure. (Center) The ChickenWing Type LAA is an anatomy whose main feature is a sharp bend in the dominant lobe of the LAA anatomy at some distance from the perceived LAA ostium. (Right) The Broccoli Type LAA is an anatomy whose main feature is an LAA that has limited overall length with more complex internal characteristics.
Figure 5. Kaplan-Meier curves of incidence of study endpoints in intervention and control groups. RR=rate ratio. Incidence probabilities for the intention-to-treat analyses are shown with time calculated as the days since randomization for the primary efficacy endpoint (A), the primary safety endpoint (b), all stroke (C), and all-cause mortality (D). Click here for larger figure.
Maximum LAA Ostium (mm) | Device Size (mm) (uncompressed diameter) |
17-19 | 21 |
20-22 | 24 |
23-25 | 27 |
26-28 | 30 |
29-31 | 33 |
Table 1. Determining proper device selection. The device sizing is based on the maximum LAA diameter. The maximum LAA ostium size should be >17mm or <31mm to accommodate available device sizes. The available/useable LAA length should be equal to or greater than the ostium.
The procedure for percutaneous implantation of the WATCHMAN left atrial appendage closure device described here, has been shown in clinical trials to be feasible 16, non-inferior to warfarin therapy 2, and safe 17. Though in all studies there was a higher rate of complications in the group receiving the implant 2,16,17, data from the PROTECT AF trial and CAP registry study, which assessed safety, suggests that the complications associated with implantation of the WATCHMAN can be largely attributed to operator inexperience. The frequency of safety event rates was initially high, but decreased over time 17.
The method presented here highlights several critical steps in preventing procedural complications. During the pilot study, three safety events occurred as a result of device failure. In two subjects the device embolized, and in one subject the wire fractured during the implantation procedure. Though these events occurred in first generation devices, and have not occurred in the second-generation device, the WATCHMAN system should always be thoroughly examined before use 16.
The most common complications associated with the procedure are pericardial effusions needing intervention and air embolism. Analysis of imaging data suggests that the serious pericardial effusions in the PROTECT AF trial were caused by operator error during transseptal puncture, by the manipulation of the WATCHMAN device or by manipulation within the LAA with the sheath to reach an optimal implantation procedure. By using a pigtail catheter the risk for perforation of the LAA by the tip of the sheath can be strongly reduced. One pericardial effusion most likely resulted from a vigorous “tug test” performed to check stability of the device in the LAA. For this reason, it is critical to use TEE and fluoroscopy throughout the procedure to monitor the implantation process. When checking for stability, contrast should be injected into the LAA to visualize the chamber, or the process should be continually monitored with TEE. With observation, no further tug-related effusions have been observed. Procedure-related stroke occurred in 3 cases as a result of air embolism from the large 12F transseptal access sheath. Therefore, it is critical to be diligent in properly flushing the sheath ensure that air is not trapped within the sheath 17. Also, fasting prior to the procedure can lead to dehydration resulting in a low left atrial pressure during the implantation procedure, which can cause air embolism. Therefore, prior to deploying the device, saline should be infused to increase the patient’s left atrial pressure to about 10 mmHg.
Despite the higher rate of safety-events with LAA occlusion compared to warfarin treatment, the overall outcome with regard to morbidity/mortality with LAA occlusion was improved 17. Closure of the left atrial appendage is therefore a promising effective alternative to continual warfarin therapy in patients with non-valvular atrial fibrillation.
The authors have nothing to disclose.
The authors thank Ms. Maggie Wallner (Atritech Inc./ Boston Scientific) for critical review of the article. The authors want to thank Mr. Mahesh Deshpanade (Boston Scientific) for his administrative support and organizing copyright permissions.
The video was supported by an unrestricted grant of Boston Scientific.