Mitral valve prolapse is a common cardiac disease that predisposes patients to higher risk for serious complications. Mitral valve repair has provided excellent midterm and long-term results and is deemed gold standard therapy for patients with severe regurgitation.1
Mitral valve repair through conventional sternotomy has been applied for several decades, and numerous innovative methods have been proposed to reduce its complexity. However, the increasing popularity of less invasive procedures has affected mitral valve surgery during the past 20 years. Despite obvious potential benefits of minimally invasive mitral valve surgery such as lower morbidity, postoperative pain, blood loss, hospital length of stay, and time to return to normal activity,2,3 acceptance of minimally invasive and on-the-top robotic mitral valve repair has been limited because of concern about its complexity, quality of repair, and cost as well as its increased cross-clamp, cardiopulmonary bypass, and procedure time.4–6
Chordal replacement has been used for both anterior and posterior leaflet repair, with excellent long-term results. Although this technique offers potentially greater physiological repair with preserved leaflet mobility in comparison with other techniques, the complexity of measuring the length of neochordae still increases the procedure time in minimally invasive mitral valve repair.
This study reports the initial clinical experience with a new device (Neochordae Loop Maker) that enables surgeons to make neochordae loops before commencing the cardiopulmonary bypass and might lessen the complexity and the procedure time especially in minimally invasive and robotic mitral valve repair.
The premeasured Neochordae Loop Maker serves as a tangible model for visualizing the three-dimensional geometry of an individual patient’s left ventricular structure. Different parts of this device represent the papillary muscle’s head and the free margin of the anterior and posterior mitral valve leaflets. Anterior/posterior, lateral/medial, and base-to-apex view of preoperative transthoracic echocardiography (TTE) define the exact position of each papillary muscle relating to the free margin of leaflets in each patient and are used for setting up the Neochordae Loop Maker. Therefore, surgeons prepare neochordae loops with the exact lengths required for each patient before starting the surgery. The main parts of the device include two semilunar blades, three setup screws, and a pledget clamp (Fig. 1A).
The semilunar blade models the free margin of the anterior and posterior mitral valve leaflets. The concave margin of the blade represents the free margin of the anterior leaflet, and its convex margin represents the free margin of the posterior leaflet (Fig. 1B). Several grooves are embedded on both margins representing the attachment sites of the neochordae loops on the free margins of the mitral valve leaflets. The lateral one-fourth portion of the concave and convex margins is considered the free margin of A1 and P1 scallops, respectively. The medial one-fourth portion of the concave and convex margins is considered the free margin of A3 and P3 scallops, respectively, and the middle halves of these margins are considered the free margin of A2 and P2 scallops. These removable blades (Fig. 1C) were developed in three standard sizes (28, 32, and 36) based on the size of the most useful Carpentier rings (direct measurements and published data).7 Blades number 28, 32, and 36 are suitable for mitral annuluses of 30 mm or less, 30 to 34 mm, and 34 mm or greater (based on echocardiography findings), respectively.
The pledget part of the neochordae loops is attached to the head of the papillary muscle. Therefore, the position of the pledget in the Neochordae Loop Maker represents the place of the papillary muscle’s head. A clamp is designed to secure the pledget firmly through the creation of the loops. The position of the clamp can be changed on the basis of the position of each papillary muscle in an individual patient. Accordingly, surgeons can first make the loops required for attachment to the anterolateral papillary muscle and then change the position of the clamp to create the loops necessary for attachment to the posteromedial papillary muscle.
Three setup screws are designed to change the position of the clamp in medial/lateral, anterior/ posterior, and up/down dimensions. The center of the semilunar blade is assumed to be the reference point (zero point), and the position of the clamp is adjusted toward it (point R in Fig. 1B).
The three main views of TTE, that is, two-chamber, four-chamber, and apical long-axis views, are used to determine the three-dimensional geometry of the left ventricular structure in an individual patient. Although transesophageal echocardiography is usually used for evaluating mitral valve regurgitation, left ventricular foreshortening in this technique would reduce the accuracy of our required measurements. We therefore applied TTE, which has demonstrated less foreshortening effect and more accurate results in left ventricular distance measurements. The intercept between the coaptation depth line and the annulus line (Fig. 2) is considered the zero point in TTE images, and it corresponds to the center of the semilunar blades (point R in Fig. 1B) in the Neochordae Loop Maker.
This view is used to determine how much the pledget clamp should be moved in a medial and a lateral direction for the posteromedial and the anterolateral papillary muscle, respectively. To compute this distance, first, the annulus line is drawn (A-B line in Fig. 3A). Then, a perpendicular line is drawn from each papillary muscle to the annulus line, and these two intercepts are marked (points M and N for the posteromedial and anterolateral papillary muscles, respectively, in Fig. 3A). The distance between the zero point and each intercept determines the medial or the lateral movement of the pledget clamp for that papillary muscle (O-M and O-N lines in Fig. 3A). Figure 3B shows a schematic view for determining the medial/lateral distance. Figure 3C demonstrates the top view of the Neochordae Loop Maker. Moving the clamp to the lateral side of the zero point (equal to O-N distance) will place it in the position of the anterolateral papillary muscle, and moving it to the medial side of the zero point will situate it in the position of the posteromedial papillary muscle.
The side view of the anterolateral papillary muscle is best visible here. This view is used to compute the anterior distance of the anterolateral papillary muscle’s head from the zero point. Therefore, the annulus line (A-B line in Fig. 3D) is first drawn. Then, the perpendicular line is drawn from the papillary muscle to the annulus line, and their intercept is marked (point L in Fig. 3D). The distance between the zero point and this intercept (O-L line in Fig. 3D) defines how much the pledget clamp should be moved to the anterior side of the zero point in the device. Figure 3E shows a schematic view for computing this distance. Figure 3F illustrates the top view of the Neochordae Loop Maker. Moving the clamp toward the anterior side of the zero point will set it in the position of the anterolateral papillary muscle.
Apical Long-Axis View
The side view of the posteromedial papillary muscle is best visible here. Using the same technique as that in the anterolateral papillary muscle, the posterior distance of the posteromedial papillary muscle is extracted from this view (Figs. 4A, B). Figure 3F shows that moving the clamp toward the posterior side of the zero point (equal to O-L distance) will place it in the position of the posteromedial papillary muscle.
The up/down direction is defined as the perpendicular distance between the head of each papillary muscle and the annulus line (Fig. 5). Any TTE image that provides a more optimal longitudinal view provides a better estimate of this distance. Moreover, if the patient has unileaflet valve prolapse, the coaptation depth (Fig. 2) is measured first and is subsequently subtracted from this distance. This new measure provides a more accurate distance for unileaflet valve prolapse.
The length and the number of required neochordae loops depend on the position of the prolapsed scallops. For example, if the scallop A2 is prolapsed, the surgeon opts to attach two neochordae loops from the anterolateral papillary muscle to A2. The following steps should be taken:
- Put the appropriate size of the semilunar blade (based on echocardiography measurements) in the defined place of the Neochordae Loop Maker.
- Place the pledget in the clamp.
- Change the position of the clamp on the basis of the three previously estimated distances (lateral, anterior, and downward distances) for the anterolateral papillary muscle.
- Pass the needle of a 4-0 Gore-Tex suture through the pledget and turn it around the middle groove in the A2 part of the semilunar blade. Then, pass it again through the pledget. Now, the Gore-Tex suture can be tied in the usual manner without knot slippage. The second loop can be made in the same way on the groove next to the previous one.
- Mark each loop, using a pen, on the basis of its corresponding position on the Neochordae Loop Maker.
- Separate the made neochordae loops having just been created with their pledget from the Neochordae Loop Maker and pass another 4-0 Gore-Tex suture through each loop.
Figure 6 shows a neochordae with two loops. These steps could be done from any papillary muscle to any prolapsed scallop.
The Neochordae Loop Maker is sterilized before surgery. In the operating room and before initiating cardiopulmonary bypass, the device is set up, and the required loops are made in a couple of minutes. After left atriotomy, the needles of the neochordae are passed through the respective papillary muscle’s head and tied over a second pledget. The 4-0 Gore-Tex suture is then used to fix each premeasured loop to the respective prolapsed segment of the mitral leaflet, preferably to the atrial surface with the knot on the ventricular surface.
The first phase was aimed to estimate the accuracy of TTE measurements and the calibration of the Neochordae Loop Maker. Therefore, we designed a study to compare the length of normal chordae with the length of respective neochordae loops in seven consecutive patients who were candidates for mitral valve replacement at Rajaie Cardiovascular Medical and Research Center. Preoperative TTE was performed for all patients, and the device was set up for each individual patient. The patient’s excised mitral valve was preserved to measure the size of his/her normal chordae. A chorda with no rheumatic change or fusion and shortening or elongation was considered normal and the gold standard for evaluating the accuracy of the Neochordae Loop Maker. The length of each normal chorda (gold standard) and its corresponding artificial chorda on the Neochordae Loop Maker was measured. The Bland-Altman analysis was used to assess the agreement between these lengths.
After calibrating the device, this technique is applied in an ongoing prospective randomized clinical trial (NCT01811537) to assess its efficacy in mitral valve repair.
The patients included two men (29%) and five women (71%) with a mean ± SD age of 56.57 ± 9.18 years. Twenty-one pairs of normal chordae (gold standard) and their respective neochordae were assessed. The mean ± SD length of the gold standard (1.92 ± 0.67) and the mean ± SD length of neochordae (1.93 ± 0.69) were not statistically different (P = 0.96). Figure 7 shows the Bland-Altman plot, which also confirmed the agreement between the two measured lengths.
Clinical Experiences With Mitral Valve Repair
So far, five patients have been enrolled in the ongoing clinical trial. No intraoperative length modification or additional suture was required for all of the applied neochordae loops. All of these patients had none or trivial mitral regurgitation by intraoperative and also 6-month follow-up transesophageal echocardiography.
Mitral valve repair has shown superior results compared with mitral valve replacement and has become the procedure of choice for the treatment of mitral regurgitation.1 A broad spectrum of reconstructive techniques, including ring annuloplasty, leaflet resection, edge-to-edge stitch, and chordal replacement, have been developed. These techniques are not mutually exclusive and can be applied together. Furthermore, all of them have been used in both conventional and minimally invasive mitral valve repair surgeries.
Recent studies have emphasized valve-sparing techniques because the resection of a large segment may not be feasible in more complex pathologies,8,9 and left ventricular outflow tract obstruction has been observed after this technique.10 However, ring annuloplasty and edge-to-edge techniques are not enough for more complex pathologies, and chordal replacement should also be performed. Moreover, unsatisfactory results were observed in the patients who needed a ring size of less than 30 mm with the edge-to-edge technique.11 Chordal replacement with expanded polytetrafluoroethylene sutures was introduced in the 1980s, and various reports have published its excellent early and long-term results.12
Various types of chordal replacement methods have been proposed during the past decades, but none of them have succeeded in reducing the complexity of minimally invasive mitral valve repair. One of the most popular ones is saline test during the surgery. Although this technique seems simple, it is time consuming and requires at least one nonprolapsed scallop as a reference. Another technique is using a ruler during surgery to measure the length of the normal chordae and making three or four loops with this length.13 This technique also needs length refinement during surgery, which increases the cardiopulmonary bypass time.
In our study, the agreement between the length of the normal chordae of the excised mitral valves and their respective neochordae loops demonstrated the accuracy of this new method. The successful preliminary results in the clinical phase of this study also confirmed that our proposed technology would be able to lessen the complexity of mitral valve repair surgery. Because all the steps in developing neochordae loops are taken preoperatively, this method would decrease procedure time and increase the quality of repair. The preliminary results showed that no change is needed during surgery and neochordae replacement. This method, accordingly, reduces the complexity inherent in previous techniques when measuring the length or changing the size of required neochordae, especially in minimally invasive and robotic surgeries.
Newer devices are under development to avoid cardiopulmonary bypass in mitral valve repair. The concept of beating heart transapical insertion of artificial chordae for mitral valve repair has been introduced and explored in few human subjects.14 The left ventricular apex is used as the anchoring point for the artificial chordae. However, recent studies have shown that the anchoring of the neochordae at the papillary muscles, thereby mimicking the real anatomy, should be preferred over the left ventricular apex.15 So far, techniques have focused on postimplantation adjustment in the beating heart.16 Our technique is a breakthrough in making premeasured neochordae loops and is applicable in beating heart mitral valve repair as well. This method anchors the papillary muscle’s head instead of the apex and also obviates length adjustment after implantation.
In conclusion, our proposed technology is a practical, unique, and simple method for making neochorda loops before starting cardiopulmonary bypass. Accordingly, the ability of this technique to develop premeasured neochordae loops in a couple of minutes and preclude postimplantation length adjustment could lessen the complexity and procedure time in minimally invasive and robotic mitral valve repair. Moreover, measuring all distances in a beating heart with preoperative TTE may lead to better physiological and coaptation level. Further studies are required to confirm these results with minimally invasive mitral valve repair.
The authors thank Anita Sadeghpour, MD, Yalda Mirmesdagh, MD, Golrokh Bateni, and Pedram Amouzadeh for their assistance in our study.
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