Looking back at the history of artificial mechanical valves, there has been a development process, initially there were the first generation of cage ball valves and cage disc valves, then there were the second generation of single-leaf tilting disc valves and finally there were the third generation of bileaflet mechanical prosthetic heart valves. In 1960, the cage ball mechanical valve was the initial prosthetic that was used for heart valve replacements worldwide. In 1963, researchers in China also developed the domestic cage ball valve and applied it in the clinic. In 1969, the second generation of single-leaf tilting disc valves was developed abroad, and in 1978, the domestic single-leaf tilting disc valves were developed and eventually were widely used, with good clinical effects. Since its invention in 1980, the bileaflet mechanical prosthetic heart valve has eliminated the use of the previous two kinds of valves because the bleaflet mechanical prosthetic heart value has an excellent performance and has become the mainstream product that is used today. Barbetseas J et al. and McLintock C et al. reported that the main causes of bileaflet mechanical prosthetic heart valve replacement include postoperative valve restenosis (53.3%~62.5%), prosthetic valve dysfunction (18. 6%~20.4%) and prosthetic valve perivalvular leakage (5. 3%~9.2%)[5–7]. Fuwai Hospital and Guangyuan First People's Hospital have completed 24,710 valve replacements and 3,264 second-time valve replacements within a time frame of longer than ten years. Only two patients with unilateral leaflet shedding were found, accounting for 0.06% of the cases of second-time valve replacements. After completing the retrieval of medical data, only one report about leaflet shedding was found [4]. This shows that unilateral leaflet shedding after mechanical valve replacement is a rare complication. Therefore, we will summarize the two patients in this study, will combine the report by Nakamura T and will determine the possible causes and treatment strategies for leaflet shedding to obtain a reference for scholars and valve companies.
The clinical manifestations and diagnosis of the patients with unilateral leaflet shedding
Both patients had symptoms, such as recent chest tightness, shortness of breath, and decreased heart function, which suggested that the patients had acute heart failure. The patients’ preoperative ultrasounds had improved, and no valve leaflet shedding was detected. Therefore, it is difficult to find leaflet shedding and to make a diagnosis by using only cardiac color Doppler ultrasound. However, the patient with aortic valve failure underwent a preoperative CT examination of the entire aorta, and the detached valve leaflet was then found. This also proves that preoperative CT examination of the whole aorta is necessary for such patients. In the report by Nakamura et al., they found that preoperative coronary angiography could clearly show the activity of the valve leaflets, which provided us with options for which to make a diagnosis[4]. From the preoperative angiographic data of the patient with mitral valve disease, we found that from the different angiographic angles, only one valve lobe could clearly be seen (Fig. 4). Therefore, for patients with sudden heart failure who have undergone valve replacement but who have improvements in their cardiac ultrasound, we can further improve the use of whole aorta CT or coronary angiography to facilitate the differential diagnosis of diseases.
Causes of leaf shedding
Susin FM et al.'s in vitro model study showed that when the heart contracts, the forward blood flow rushes out from both sides and from the middle of the valve leaflets, and the side with a smaller opening has a higher forward blood flow velocity after the closing of the valve leaflet [8]. This shows that the different forward pressures on the valve leaves lead to different types of losses of the valve leaves. Toshinosuke Akutsu et al. found that the turbulence that is formed in the coronary sinus will counteract the opening and closing of the valve leaflets, which causes pressure on the valve leaflets and reduces their service life [9]. Therefore, the requirements for our industrial design are higher, and it is necessary to adjust the opening and closing angle of the valve leaves by combining the changes in the fluid dynamics and the differences in human anatomy, especially when perfecting the use and design of the valve in animal experiments and in vitro experiments. From the report by Nakamura et al., the valve leaflet leakage that was reported in this report had broken into two pieces that had sharp acute angles, and the patient had lower limb symptoms[4]. However, we found that the leaflets of the two patients in our report were all intact, which indicated that the reasons for unilateral leaflet shedding were different. The patient that was reported by Nakamura T could have developed leaflet shedding mainly due to material problems of the leaflets, and the leaflets eventually ruptured. However, the two patients in our report may developed leaflet shedding due to valvular design problems, which resulted in leaflet shedding.
Cardiac management strategy
It is necessary to improve cardiac ultrasound and whole-body CT so that when acute heart failure occurs in a patient, the physicians can determine whether there is valve failure. The research of Nobuyuki Kagiyama et al. and Michael C Scott et al. emphasized the importance of early intravenous drug therapy for acute heart failure[10–11]. For older patients with high surgical risk scores and who are not good candidates for surgery, diuretics can be used to treat their heart failure. Manantunes and Rajput FA said that patients with mechanical valve failure with a low surgical risk score should undergo a second-time valve replacement as soon as possible[12–13].
Treatment strategy of leaflet shedding
Mechanical valve leaflet shedding is a rare complication, and there is no current treatment for the valve leaflet that has shed. Due to the need to obtain the consent of patients and their families, we did not remove the detached valve leaflets in either of the patient and instead chose to monitor the patient with aortic valve detachment for 10 years. We also summarized these two patients in this report. During the 10-year follow-up, we found that the detached leaflets gradually migrated distally. The detached leaflets were initially located in the left common iliac artery, and at the last follow-up, the leaflets were stable in the left external iliac artery, as shown in Fig. 5. Therefore, we conclude that there are three risks. 1. During the 10-year follow-up, thrombosis can develop in patients with embolisms, which may lead to lower limb ischemia. Second, in the process of leaflet shedding, there is the possibility of the development of abrasions within blood vessel, leading to blood vessel rupture or acute thrombosis. Third, in the process of the detached leaflets migrating distally, there is the possibility that the valve leaflet can block blood vessels. Nakamura et al. reported cases in which the shedding leaflets (leaflet rupture) were surgically removed in time, but the author only reported the cases and did not report on the mid-term and long-term follow-up results. Therefore, the advantages and disadvantages of the two treatment schemes can be selected according to a case by case basis, without more evidence-based guidelines. For the patient with mitral valve diseases, we did not perform primary surgical removals of the shedding leaflets. The reasons for this are as follows: 1. The patient did not have obvious lower limb symptoms and did not develop any concerning symptoms. 2. Through the examination of CT and color Doppler ultrasound, there were no thrombi or hematomas, the valve leaflets were intact, and the blood flow velocity was not significantly affected. 3. The patients need to take oral warfarin anticoagulation chronically, and this treatment prevents thrombosis; and 4. The risk of simultaneous thoracotomy, iliac artery incision and exploration is high, which can increase the perioperative mortality of patients. At present, there is no report of a case of a peripheral vascular injury caused by leaflet shedding, but Tokuda T and others reported a case of an external iliac artery pseudoaneurysm (27 *29 mm) that was caused by stent shedding[14]. Therefore, due to the careful monitoring, the patients' symptoms and signs were identified, the findings were combined with the findings of auxiliary examinations, and the treatment plan was adjusted.
Limitations of the study
1. This study is a retrospective analysis, and it had a small sample size and no clear statistical significance; 2. This study used the follow-up data from different time periods and different centers, and there was systematic errors.