| Background:Functional tricuspid regurgitation (FTR) is a frequent problem among patients with valvular disease, especially in association with acquired left heart valve disease of rheumatic origin, pulmonary hypertension or congenital heart disease (pulmonary valve stenosis, Eisenmenger syndrome), primary isolated tricuspid regurgitation (TR) being very rare. Most series reported the number of patients with functional tricuspid regurgitation was very large.20%-30% of cases have been reported to have moderate-to-severe TR. Dreyfus et al observed that up to 48% of the patients with chronic severe mitral regurgitation had tricuspid regurgitation. The current prevalence of moderate-to-severe tricuspid regurgitation (TR) is estimated to be 1.6 million in the United States. Of these, only 8,000 patients undergo tricuspid valve (TV) surgeries annually, most of them in conjunction with left heart valve surgeries (LHVSs). It is even more frequent among patients in whom the TR is "ignored" at the time of LHVSs.Generally, the patients of tricuspid regurgitation associated with rheumatic mitral or aortic valve disease have characteristics such as longer duration, older, recurrent rheumatic fever. Not only those patients with pulmonary vascular resistance increased and pulmonary hypertension, secondary respiratory dysfunction, and accompanied by high-pressure venous system circulation and long-term congestion, liver, kidney and other major organs functions are obstacles; gastrointestinal tract system, the long-term congestion mucosa also leads to digestion and absorption of dysfunction in some patients and even determined to cachexia. Coexisting TR have poor functional status that increases their operative risk. Kuwaki reported that concomitant correction of TR with LHVS yielded in-hospital mortality of 8.9% and a 10-year survival of 78±3%.Although TR may decrease gradually after left-sided valve surgery owing to reduced right ventricular pressure or volume overload, TR does not always regress after adequate correction of the underlying lesions. It is stated in the guidelines that the timing of surgical intervention for TR remains controversial, as do the surgical techniques. At present, surgery on the tricuspid valve for significant TR should occur at the time of mitral valve surgery, as TR does not simply "go away" after mitral valve surgery. On long-term follow-up, the prevalence of residual TR may increase to as high as 31%. In order to correct heart failure, many patients had to undergo reoperation again, but this will increase the difficulty and the risk of surgery. Surgical repair or replacement, which is the only corrective therapy presently available, carries a high operative mortality in this high-risk patient population.With the advances in biomedical materials, the application of percutaneous approach is more widely in the treatment of heart valve disease. There has been considerable development in percutaneous technologies for the mitral valve. Percutaneous TV technology may be initially useful for patients with FTR who are at high risk for open-heart surgery. Once the other percutaneous technologies for mitral, aortic, or pulmonary valve become widely available, the need for percutaneous TV procedures will be even more apparent. Although many obstacles still exist, initial data from animal studies have shown encouraging results. In order to promote the technology in our country, we cooperated with the ShangHai Shape-Memory Alloys Material Limited Company to develop a new-type tricuspid valved stent and performed serial experiments to investigate the feasibility of transcatheter implantation of this valved stent in nature tricuspid valve annulus.Objective:To evaluate the feasibility, safety and efficacy of transcatheter implantation of the new-type self-expanding tricuspid valved stent into the nature tricuspid valve annulus of sheep.Methods:(1) Applied anatomy of percutaneous replacement of tricuspid valves:30 normal adult heart specimens (20 male and 10 female) and 20 fresh healthy sheep hearts were dissected. The long diameter, short diameter and the perimeter of tricuspid valves were measured. The distance from the tricuspid valves to the coronary sinus and supraventricular crest were also measured. (2) The optimal project position for demonstrating tricuspid annulus in angiography:Eight healthy sheep underwent right atrial angiography by using 6F pigtail catheters. Under fluoroscopic monitoring the contrast media (total 110 ml, flow rate 12 ml/s, pressure 800 PSI) was injected continuously while a serious exposures were performed from RAO 90°position to LAO 90°position (totally 180°rotation). The maximum diameter of the tricuspid annulus in every picture was measured and the results were compared with that obtained from sonography. (3) Development of the tricuspid valved stent and delivery system:A unidirectional semilunar valve of porcine pericardium was sutured to a valvular ring. Then the ring with pericardial valve was mounted on a double-edge nitinol stent to construct the tricuspid valved stent. The fresh pig pericardium was shaked in a 0.01% trypsin solution for 24 hours then cross-linked with a 0.6% glutaraldehyde solution for 48 hours at 4℃. The pericardium was removed toxicity of glutaraldehyde in 2%L-glutamic acid solution for 24 hours. The delivery system consisted of an external sheath, guide sheath, short pre-loaded sheath, a matched push cable. (4) The tricuspid valved stent implantation to tricuspid position in vitro. Through a 16 French sheath positioned in the right ventricle of isolated sheep heart via superior and inferior vena cava, the device was delivered into the tricuspid valve, respectively. When the right ventricle disk was deployed, it was applied to the tricuspid annulus by pulling back the external sheath. Then the waist and the right atrial disk were deployed in the annulus and right atrium, respectively, by pulling the sheath. Thus the whole device was deployed in the native tricuspid. Water was injected into the right ventricle to test the competence of the prosthetic heart valves. (5) Percutaneous establishment of tricuspid regurgitation:A special-designed grasping forceps was used to grasp chordae tendineae or the tricuspid valve leaflets through a catheter. Transcatheter creation of tricuspid regurgitation was performed on 7 healthy sheep. These sheep were followed up shortly after the procedure and at 6 months post-procedure with echocardiography. Additionally, all sheep were sacrificed for anatomic evaluation at six months. (6) Transcatheter tricuspid valved stent implantation. Transcatheter tricuspid valved stent implantation was performed on 10 healthy sheep. These sheep were followed up shortly after procedure with echocardiography evaluation and 64-slice CT imaging examination during the periodical follow up at 1 month and at 6 months post-implantation. Additionally, two sheep were sacrificed after the procedure for anatomic and histological evaluation one at 1 hour and the other at six month, respectively.Results:(1)The long diameter, short diameter and the perimeter of tricuspid valves of adult and sheep were (4.30±0.55)cm, (3.09±0.59)cm, (11.86±1.37)cm and (3.30±0.35)mm, (1.79±0.78)mm, (9.88±1.62)mm, respectively. The distance from the tricuspid valves to the coronary sinus and the supracristal was 1.12±0.21cm and 1.79±0.31cm, respectively. The distance from the tricuspid valves to the coronary sinus and the supracristal of sheep was (0.82±0.21)mm and (1.19±0.25)mm, respectively. (2) The best angiographic projections to visualize tricuspid annulus was the profile one at right anterior oblique 27°±3°.This projecting position was helpful for observing and measuring the diameter of tricuspid annulus. (3) We developed a valvular ring constructed from a 0.25-mm nitinol wire. Three identical semilunar valve leaflets, which were tailored with fresh porcine pericardium cross-linked with a 0.6% glutaraldehyde solution, were mounted and sutured to the valvular ring with 7-0 Prolene. The formed unidirectional semilunar valve was then assembled to a double-edge stent constructed from a 0.18-mm nitinol wire. We developed different size stents with the waist diameter of the stent ranging from 22 to 26 mm. (4) The prepared tricuspid valved stent could be stably positioned at the native valves. There was no stent migration when it was repeatedly pulled. The two disks sandwiched the native tricuspid valve with one disk lying in the right ventricle and the other one in the right atrium. The prosthetic heart valves showed satisfactory function without structure damage. (5) Creation of tricuspid regurgitation was successfully accomplished in all sheep. Necropsy confirmed that damage was done to the tricuspid valve apparatus in all animals (tearing of the anterior leaflet of the tricuspid valve in five animals and posterior leaflet of the tricuspid valve in two animals). At six-month follow up, there was no significant increase in the right ventricle dimension and ejection fraction measured by echocardiography. Autopsy examinations demonstrated the tearing of tricuspid valve leaflets. (6) Percutaneous valve implantation was successful in eight of 10 sheep. Two sheep died during the procedure due to migration of stent and fatal arrhythmia. The pressure of right heart did not significantly change after the procedure. Further echocardiography and imaging confirmed the stents were in desired position during the follow-up. The remaining six sheep with normal valvular and cardiac functionality survived for 6 months after implantation.Conclusions:The tricuspid stent with a valvular ring and pericardial valve can be implanted in tricuspid annulus percutaneously. The double-edge stent could substitute the native tricuspid valve chronically. This technique expands the potential therapeutic options for patients with functional tricuspid valve regurgitation having a high risk for open heart surgery. Additional studies with larger cohorts and longer follow-up are needed to evaluate its safety.
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