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Address for reprints: Tom C. Nguyen, MD, Division of Cardiothoracic Surgery, Department of Surgery, University of California San Francisco, 500 Parnassus Ave, MU-West 405 Box 0118, San Francisco, CA 94143.
Mitral valve disease in presence of severe mitral annular calcification (MAC) remains a challenge for surgeons to address. Conventional surgical techniques have potential for heightened morbidity and mortality. The advent of transcatheter heart valve technology and transcatheter mitral valve replacement (TMVR) holds promise to treat mitral valve disease with MAC with excellent clinical outcomes.
Methods
We review current treatment strategies for MAC and studies in which TMVR techniques were used.
Results
Several studies and a global registry describe outcomes of TMVR for mitral valve disease with MAC. We describe our specific technique on how to perform a minimally invasive transatrial approach for TMVR.
Conclusions
TMVR demonstrates strong promise as a safe and effective way to treat mitral valve disease with MAC. We advocate for a minimally invasive transatrial approach when performing TMVR for mitral valve disease with MAC.
Strategic use of minimally invasive, transatrial, transcatheter mitral valve replacement offers an innovative approach to safe, effective treatment of mitral valve disease with MAC.
Mitral valve disease with MAC remains a challenge for surgeons, and conventional surgical approaches have potential for heightened morbidity. Use of TMVR technology has demonstrated strong promise with excellent clinical outcomes. We advocate for a minimally invasive transatrial approach for TMVR when mitral valve disease with severe MAC is present.
See Commentary on page 51.
Mitral annular calcification (MAC) is a chronic, degenerative process that leads to progressive calcium deposition on the mitral valve (MV) annulus.
MV replacement in the setting of severe MAC is associated with heightened cardiovascular morbidity and mortality. Acute perioperative mortality can range from 3% to 9%, and there is a 1% to 2% associated risk of the devastating complication of atrioventricular groove disruption or left ventricular perforation (each with an associated >80% mortality).
Treatment of MV disease with MAC remains a challenge for cardiac surgeons. However, with an improved understanding of MAC pathophysiology, and the advent of transcatheter heart valve (THV) technology, new strategies can be applied that enable surgeons to more safely and effectively treat MV disease with MAC.
In this topic overview, we will delve into the pathophysiology of MAC and how it is distinct from rheumatic mitral stenosis (MS), review the existing literature on the use of THV for transcatheter mitral valve replacement (TMVR) in MAC, and describe our approach for a minimally invasive transatrial approach for TMVR.
Defining the Disease and Pathophysiology
Although rheumatic heart disease is the most common cause of MS, it is important to understand that MV disease with MAC is a distinct entity from rheumatic MS.
In contrast to rheumatic MS, MAC is a condition that often presents in older patients with multiple medical comorbidities and involves the base of the leaflets, and annulus, with circular narrowing from outside inward. Risk factors for MAC include advanced age, female gender, chronic kidney disease, conditions that are associated with increased stress on the MV (eg, hypertension, aortic stenosis, hypertrophic cardiomyopathy, and MV prolapse), osteoporosis, and metabolic disorders such as Marfan syndrome and Hurler syndrome.
In rheumatic MS, fusion of the leaflets at the commissures is present, and the greatest narrowing occurs at the leaflet tips. Although balloon valvuloplasty is helpful in relieving rheumatic MS (leading to a marked decrease in left atrial pressure), it is less so for MAC given that the leaflet tips in MAC are often unrestricted and there is no leaflet commissural fusion.
The hemodynamics of transmitral valve pressures tracing for both conditions yields insight into their differing pathophysiology. In rheumatic MS, there is leaflet impedance to atrial emptying. The left atrial catheterization tracing sine qua non for rheumatic MS is elevation of the left atrial pressure greater than left ventricle pressure during diastole with persistent diastolic separation of the left atrial and left ventricular pressures.
In MAC, there is a high left atrial v-wave with rapid y-descent and equilibration of the atrial-ventricular pressure gradient indicative of minimal valvular impedance to flow. Doppler echocardiography is often used to determine whether or not MS is severe, but the contour of the transmitral flow velocity should be carefully examined and cardiac catheterization may help to determine relative contributions of left atrial pressure elevation from MV resistance versus abnormal left ventricular filling.
Treatment Options for Mitral Annular Calcification
Up to 20% of patients who undergo MV surgery have some degree of MAC, and MAC has been associated with several-fold higher mortality in isolated MV surgery compared with patients without MAC.
Aside from the more advanced age and accompanying comorbidities that add perioperative risk, several technical challenges arise from the annular calcium deposits. The calcium can prevent adequate apposition of the replacement MV to the annulus resulting in perivalvular leak (PVL).
Placing stitches in the calcified annulus also risks injury to the left circumflex coronary artery, which may require urgent bypass, thereby adding procedural complexity. Annular decalcification to permit better replacement mitral valve seating is possible but may weaken the annulus resulting in atrioventricular groove disruption, which can incur exceedingly high mortality.
The alternative is to leave the calcified annulus in place and try to minimize manipulation or debridement of the existing calcium. This is balanced against the risk of settling for a smaller valve size, which may leave patients with residual MS. Brescia and colleagues
recently described their experience using the Sonopet ultrasonic aspirator (Stryker) to remodel the calcifications in MAC. In a series of 15 patients, a median 27-mm replacement MV was implanted, resulting in reduced mean MV gradient and 0% operative mortality. No atrioventricular groove disruptions occurred. Technology such as this ultrasonic aspirator may be helpful to perform calcification debridement more safely when called for.
The goals of treatment for MV disease with MAC include replacing the valve safely in a patient population already at greater risk, using the largest valve prosthesis possible to produce the greatest effective orifice area, and using techniques to minimize PVL, left ventricle outflow tract obstruction (LVOTO), and device embolization. With its expandable frame, the THV can tolerate expansion in a nonperfectly circular annulus while maximizing orifice area and preserving valve function. Furthermore, expansion under direct vision allows a surgeon to carefully control the ultimate size given a patient's anatomy. The combined techniques of an open or minimally invasive surgical approach with a THV is particularly well suited to help achieve these goals for the surgical treatment of MAC
Transcatheter mitral valve replacement in native mitral valve disease with severe mitral annular calcification: results from the first multicenter global registry.
reported results from a global registry that includes 64 patients from 32 international sites who underwent TMVR for severe MAC with the Edwards Sapien, Sapien XT, or Sapien S3 platform (Edwards Lifesciences). The cohort had a mean Society of Thoracic Surgeons mortality score of 14.4%. TMVR was technically successful in 72% of all cases, and 30-day mortality was 30%. Among the 3 access options—transseptal, transapical, and transatrial—transatrial had the highest technical success at 89%, and the lowest 30-day mortality rate at 20%. With follow-up out to a year post-TMVR, the surviving cohort demonstrated clinical improvement, with lower New York Heart Association (NYHA) functional class scores over time. This study also highlights the merits of the transatrial approach. LVOTO occurred in 9.3% of cases, but none were from the transatrial approach. THV embolization occurred in 6.25% of cases, of which only 1 case occurred with the transatrial approach, and left ventricle perforation occurred in 3.1% of cases, none of which were from the transatrial approach. A follow-up report on the global registry reinforced the superior safety of the transatrial approach because mortality risk was nearly 2.5-fold greater when comparing the transseptal and transapical approaches to the transatrial approach.
published the largest series to date describing 26 patients who underwent sternotomy for TMVR; 100% of these procedures were technically successful, and NYHA functional class improved significantly at 30-day follow-up.
However, data from case reports and case series can be pooled together for a total of 74 cases of TMVR. Forty-one cases were performed via the transatrial approach, which had a 93% technical success rate, 14.6% 30-day mortality, and 2.4% risk of LVOTO.
Pushing the limits-further evolutions of transcatheter valve procedures in the mitral position, including valve-in-valve, valve-in-ring, and valve-in-native-ring.
The rate of any-degree PVL was 3% for the 41 transatrial cases compared with 20% any-degree PVL for the 30 transseptal cases, and 0% for the 3 transapical cases.
New technology and TMVR devices continue to be developed and clinical studies are currently underway. Gossl and colleagues
report favorable early feasibility results of the Tendyne TMVR platform (Abbott Laboratories) in 20 patients with MAC-associated mitral regurgitation. No procedural mortality occurred, 1 patient died within 30 days of the procedure, and 8 patients had died by 1 year. At the 1-year follow up, mitral regurgitation remained absent and NYHA functional class had improved in 11 of 12 patients who were alive. The Apollo Trial for the Medtronic Intrepid TMVR system is currently enrolling patients, and will include a cohort of patients with MAC. There remain strong research and innovation opportunities for TMVR with the goal of engineering devices to treat MAC safely and effectively.
How We Do It: Minimally Invasive Transatrial TMVR
We advocate for a minimally invasive transatrial approach given the direct approach to the MV offered for patients of all habitus, along with reduced risk of PVL and valve embolization.
To date, we have treated approximately 20 patients with this method. A preprocedural cardiac computed tomography scan is obtained for every patient to view the MV position and geometry (Figure 2). Although clinician judgment and experience leads to identification of severe MAC when seen on imaging, the scoring system devised by Guerrero and colleagues
provides an organized manner to describe the nature and severity of MAC. We consider some patients with moderate MAC and all patients with severe MAC for minimally invasive TMVR in our practice.
Figure 2Computed tomography scan of a patient with severe mitral annular calcification.
A right minithoracotomy is performed at the third or fourth intercostal space. After dissection of pericardial fat and entry into the pericardium lateral to the phrenic nerve, several retraction sutures are placed. The left atrium is accessed via the interatrial groove, and the atriotomy extended with angled Potts scissors (Figure 3). A left atrial retractor is placed, stabilized by a retractor post inserted through a separate chest incision. Care is taken to avoid excessive retraction that could distort or dislodge any previously placed THV in the aortic position, if present.
Figure 3Left atriotomy performed at Sondergaard's groove, extended with Potts scissors.
The noncalcified portion of the anterior mitral leaflet and its cordal attachments are excised, leaving a 2- to 3-mm rim of leaflet tissue to prevent LVOTO (Figure 4). To minimize risk of atrioventricular groove disruption, we do not routinely resect the posterior leaflet or associated MAC. If a septal myectomy is necessary, this should be done before THV placement.
Figure 4Resection of the anterior mitral valve leaflet, leaving a rim of tissue 2 to 3 mm at the annulus.
Annular 2–0 pledgeted Ethibond sutures are placed in an everting manner around the mitral annulus with the pledgets on the atrial side. We use a SH-1 needle to enable us to take bites around denser annular calcifications. In regions with heavy calcifications, we err on taking more left atrial tissue to create a seal, whereas other sutures around less-dense calcifications or normal tissue will help anchor the valve (Figure 4). Areas of key annular suture placement include each commissure, the junction of P1-P2, P2-P3, and any areas of deep indentation along the annulus. If dense MAC prevents annular suture placement, the suture can be placed in the residual leaflet tissue or atrial tissue.
The annulus is then sized with the Sapien transcatheter delivery balloon (Figure 5). The balloon should be inflated until it fits snugly, but not overinflated. Intraoperative balloon sizing remains a crucial step, and we emphasize that it is important to not rely solely on computed tomography measurements because THV oversizing may lead to LVOTO. In our institutional experience, most patients undergoing TMVR receive a Sapien 26 mm or 29-mm S3 valve. Before the valve is crimped, a 1–cm-wide felt strip is sewn to the S3 skirt with 5–0 polypropylene suture taking care to not incorporate any of the bioprosthetic leaflet tissue (Figure 6). The felt strip should not be taller than 1 cm to eliminate this as a potential contributor to LVOTO.
Figure 5After placement of annular stitches, a sizing balloon is snugly inflated to determine the optimal transcatheter heart valve size.
Figure 6Preparing the transcatheter heart valve. Left, a 1-cm felt strip is sewn to the skirt of the Sapien S3 valve (Edwards Lifesciences). Middle, The valve is partially crimped. Right, The trigones are marked so that proper orientation of the valve can be maintained during deployment.
The valve is partially crimped onto the balloon because it has only to fit through the atriotomy incision. Full crimping of the THV is not necessary. The commissures are marked and the trigones are aligned with the THV (Figure 6). The partially crimped THV is inserted into the left atrium, and positioned coaxially with the annular plane. In our early experience, we would implant the THV annulus flush with the MV annulus, as depicted in Figure 6, but with experience began positioning the THV such that it sat more atrially to reduce contribution to LVOTO. Our current recommendations are to implant the felt strip such that 50% to 70% of its height sits above the MV annulus in the atrial side (Figure 7). Surgeon experience and judgment with the regional anatomy may dictate the optimal position of the valve relative to the annulus. The surgical assistant then inflates the balloon slowly until it is snug. Avoid overinflation to prevent annular rupture.
Figure 7Deployment of the transcatheter heart valve. Left, The crimped Sapien 3 valve (Edwards Lifesciences) is positioned coaxially at the annular plane, where about 70% of the valve apparatus will sit supra-annularly. Middle, The balloon is inflated slowly and the valve is in good apposition with the annulus. Right, The annular stitches will then be sutured through the skirt to secure the valve in place.
After the THV is deployed, the previously placed annular sutures are passed through the valve skirt and felt strip, and tied with the knots ending up on the atrial side of the valve. The balloon can be inflated again for another 10 to 20 seconds to ensure full device expansion, followed by testing for valve leak. If PVL is detected, additional sutures at areas of deep indentation can be placed. If the valve position is satisfactory and no leaks are apparent on testing, the left atriotomy can then be closed, the heart de-aired, and crossclamp removed. Completion transesophageal echocardiography should be used to confirm adequate valve position and function without significant PVL and LVOTO.
Conclusions
In MV disease with MAC, replacement of the MV remains a challenge and is associated with increased morbidity and mortality. The pathophysiology of MAC is distinct from that of rheumatic MS. Innovative treatment approaches for MV disease with MAC include use of ultrasonic aspirator to remodel calcifications and use of THV to perform TMVR. Initial data showing excellent clinical outcomes is promising for TMVR for MAC. At our institution, we use a minimally invasive transatrial approach to TMVR. Further innovation and research are needed to devise technology specifically suited to MV disease with MAC, as well as optimal procedural techniques.
Conflict of Interest Statement
Dr Nguyen receives consulting fees from Edwards Lifesciences, Abbott Laboratories, LivaNova, and Medtronic. All other authors reported no conflicts of interest.
The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.
The authors thank Pamela Derish in the Department of Surgery, University of California San Francisco, for proofreading the manuscript.
Transcatheter mitral valve replacement in native mitral valve disease with severe mitral annular calcification: results from the first multicenter global registry.
Pushing the limits-further evolutions of transcatheter valve procedures in the mitral position, including valve-in-valve, valve-in-ring, and valve-in-native-ring.
Mitral valve replacement in the setting of severe mitral annular calcification (MAC) remains a surgical challenge. The fundamental concern with mitral valve replacement in the presence of MAC is decalcification required to pass the sutures through the mitral annulus, which can lead to annular disruption or perivalvular leak (PVL). Complex en bloc decalcification and reconstruction of the mitral annulus have been described.1,2 However, these procedures are technically challenging and only done by a few skillful surgeons, and as such they are not ready for widespread use.
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