**4.1 The birth of water sac technique**

Patients with severe calcification in the ascending aorta are more likely to have stroke after anastomosis of ascending aorta and great saphenous vein in OPCABG. The most common reason is the loose or detached atherosclerotic plaque on the inner wall of ascending aorta, or detached thrombus due to clamp damage. Multivariable analysis revealed that the use of aortic wall clamp was the most important independent risk factor for postoperative stroke, resulting in a sixfold increase of postoperative stroke rate. It is suggested that the indicators of serious calcification of ascending aorta include carotid stenosis, hypertension, peripheral vascular disease or abdominal aortic aneurysm, male gender, renal insufficiency and left main artery disease in patients over 65 years old.

There are two main methods hitherto to solve the problem of proximal anastomosis in patients with calcification of ascending aorta, including using proximal anastomotic device and using non-touch ascending aorta of CABG. The former mainly includes the application of Enclose, Heartstring and other devices, while the latter mainly refers to the methods of CABG without ascending aorta operation, such as bilateral internal mammary artery and other forms of total arterial CABG.

The indications of non-touch technique of ascending aorta are limited to some extent, and the requirements to operation are relatively high. Moreover, collection of bilateral internal mammary artery will reduce the blood supply of sternum, affect the healing of sternum, and may cause complications such as loosening of sternum, delayed healing and infection of incision. Radial artery is also commonly used in total arterial CABG; however, when comparing with internal mammary artery, it is more prone to produce spasm and affect surgical effect.

There are some limitations in the use of proximal anastomotic devices. For example, when using Heartstring for proximal anastomosis, the internal umbrella cap may not fit tightly with the uneven calcified aortic inner wall, causing continuous bleeding at the anastomosis and affecting the operation. When using Enclose for proximal anastomosis, at least two holes are needed to be drilled in the ascending aorta, increasing the chance of atherosclerotic plaque falling off. Further, the needle tip may puncture the diaphragm with hemostatic effect and lead to uncontrollable bleeding. In addition, the cost of proximal anastomotic device is high and will increase the medical burden for patients in developing countries and remote areas.

Given the above situation, we have figured out the method of water sac blocking proximal anastomosis method in clinical practice. Its short-term and mediumterm effects were similar to those of patients without ascending aortic calcification who used side wall clamp, and no patients had complications such as stroke or proximal anastomotic stenosis. It is well demonstrated that OPCABG combined with water sac blocking anastomotic method can further reduce the incidence of postoperative stroke.
