Percutaneous Treatment for Mitral Regurgitation: The QuantumCor System

Future Technology

Mitral regurgitation is the most common valvular disease and significant (moderate/severe) mitral regurgitation is found in 2.3% of the population older than 65 years. New transcatheter minimally invasive technologies are being developed to address mitral valve disease in patients deemed too high a risk for conventional open-heart surgery. There are several features of the mitral valve (saddle-shaped noncalcified annulus with irregular leaflet geometry) that make a transcatheter approach to repair or replacing the valve more challenging compared with the aortic valve. Several devices are under investigation for transcatheter mitral valve replacement, and also for mitral valve repair targeting the mitral valve leaflets, chordae tendinae, and mitral annulus. The MitraClip device is the only Food and Drug Administration-approved device to treat mitral regurgitation by targeting the mitral leaflets. There are eight minimally invasive devices being studied in humans that target the mitral annulus, and at least two devices being studied in animal models. There are 5 devices in clinical trials for minimally invasive approaches targeting the chordae tendinae. More than 10 different transcatheter mitral valves are in various stages of development and clinical trials. These transcatheter mitral valves can be delivered either through a transseptal, transapical, transaortic, or left atriotomy approach. It seems likely that transcatheter treatment approaches to mitral valve disease will become more common, at least in the sick and elderly patient population.

Percutaneous Mitral Valve Interventions and Heart Failure

Mitral regurgitation (MR) is the most frequent Valvular Heart Disease (VHD) and is an important cause of heart failure. MR can be caused by primary valve abnormality (Degenerative MR/Primary MR) or it can be secondary to cardiomyopathy (Functional MR/Secondary MR). Medical management alleviates symptoms but does not alter the progression of the disease. Current guidelines recommend surgery for moderate-to-severe (Grade > 3) MR in patients with symptoms or evidence of left ventricular dysfunction. Despite current practice guidelines, the majority of patients with severe MR do not undergo surgery. The reasons include high surgical risk from advanced age or multiple comorbidities, and a lack of clear data supporting valve surgery for secondary MR with LV dysfunction. The recent emergence of percutaneous interventional approaches in treating MR has expanded therapeutic options for patients who are at high risk for conventional Mitral Valve (MV) surgery. In this chapter, we will review the novel advancements in the field of percutaneous MV interventions that could potentially become the standard of care for patients with MR and heart failure.

Echocardiographic imaging options in ovine research subjects

OBJECTIVES

To determine the feasibility of acquiring quality transesophageal (TEE), epicardial (EE), and intracardiac (ICE) echocardiographic images in ovine subjects and to discuss the merits of each technique with a focus on ICE image acquisition.

ANIMALS

Eleven male castrated Dorset adult sheep.

METHODS

Transesophageal echocardiography was performed under general anesthesia. Epicardial echocardiography was performed as part of an open chest (thoracotomy or sternotomy) experiment. Subjects were recovered with permanent jugular vein indwelling catheter and ICE from this approach was described. Feasibility of each technique was qualitatively assessed based on subjective image quality from three images for each image plane in each sheep.

RESULTS

Transesophageal echocardiography was technically challenging and did not provide adequate image quality for consistent interpretation. Epicardial echocardiography and ICE had more favorable results with ICE demonstrating unique benefits for post-operative serial monitoring.

CONCLUSIONS

Epicardial echocardiography and ICE were effective imaging techniques. Epicardial echocardiography required the least specialized training but was considered to have limited feasibility due to its requirement for an open chest procedure. Even with the necessity for permanent indwelling jugular cannulation, ICE was the least invasive of the three imaging techniques and potentially the most practical approach for chronic studies by minimizing post-operative stress. Transesophageal echocardiography was not a feasible technique in this study.

Descriptive Analysis of In Vitro Cutting of Swine Mitral Cusps: Comparison of High-Power Laser and Scalpel Blade Cutting Techniques

BACKGROUND AND OBJECTIVES

The most common injury to the heart valve with rheumatic involvement is mitral stenosis, which is the reason for a big number of cardiac operations in Brazil. Commissurotomy is the traditional technique that is still widely used for this condition, although late postoperative restenosis is concerning. This study's purpose was to compare the histological findings of porcine cusp mitral valves treated in vitro with commissurotomy with a scalpel blade to those treated with high-power laser (HPL) cutting, using appropriate staining techniques.

MATERIALS AND METHODS

Five mitral valves from healthy swine were randomly divided into two groups: Cusp group (G1), cut with a scalpel blade (n = 5), and Cusp group (G2), cut with a laser (n = 5). G2 cusps were treated using a diode laser (λ = 980 nm, power = 9.0 W, time = 12 sec, irradiance = 5625 W/cm², and energy = 108 J).

RESULTS

In G1, no histological change was observed in tissue. A hyaline basophilic aspect was focally observed in G2, along with a dark red color on the edges and areas of lower birefringence, when stained with hematoxylin-eosin, Masson's trichrome, and Sirius red. Further, the mean distances from the cutting edge in cusps submitted to laser application and stained with Masson's trichrome and Sirius red were 416.7 and 778.6 μm, respectively, never overcoming 1 mm in length.

CONCLUSIONS

Thermal changes were unique in the group submitted to HPL and not observed in the cusp group cut with a scalpel blade. The mean distance of the cusps' collagen injury from the cutting edge was less than 1 mm with laser treatment. Additional studies are needed to establish the histological evolution of the laser cutting and to answer whether laser cutting may avoid valvular restenosis better than blade cutting.

Current challenges in interventional mitral valve treatment

Transcatheter mitral valve therapies have emerged as an alternative option in high surgical risk or inoperable patients with severe and symptomatic mitral regurgitation (MR). As multiple technologies and different approaches will become available in the field of mitral valve interventions, different challenges are emerging, both patient- (clinical challenges) and procedure-related (technical challenges). This review will briefly explore the current open challenges in the evolving fields of interventional mitral valve treatment.

Percutaneous Mitral Annuloplasty

Percutaneous mitral valve therapies are emerging as an alternative option for high-risk patients who are not good candidates for conventional open-heart surgery. Recently, multiple technologies and diversified approaches have been developed and are under clinical study or in preclinical development. This article on transcatheter mitral annuloplasty devices, describes the different technologies, and reports on the initial clinical and preclinical experiences.

Transcatheter mitral valve repair therapies for primary and secondary mitral regurgitation

Mitral regurgitation is one of the most prevalent valvular heart diseases and its prevalence is related to population aging. Elderly patients with age-associated co-morbidities have an increased risk for conventional mitral valve surgery. Transcatheter mitral valve repair has emerged as a feasible and safe alternative in patients with contraindications for surgery or high operative risk. Several transcatheter mitral repair technologies have been developed during the last decade. While the development of some devices was abandoned due to suboptimal results, others demonstrated to be safe and effective and have been included in current practice guidelines. Not all technologies are suitable for all mitral anatomies and regurgitation mechanisms. Therefore, accurate evaluation of mitral valve anatomy and function are pivotal to the success of these therapies. Cardiac imaging plays a central role in selecting patients, guiding the procedure and evaluating the durability of the repair at follow-up.

Ischemic mitral regurgitation: mechanisms, intraoperative echocardiographic evaluation, and surgical considerations

Ischemic mitral regurgitation (IMR) is a subcategory of functional rather than organic, mitral valve (MV) disease. Whether reversible or permanent, left ventricular remodeling creates IMR that is complex and multifactorial. A comprehensive TEE examination in patients with IMR may have important implications for perioperative clinical decision making. Several TEE measures predictive of MV repair failure have been identified. Current practice among most surgeons is to typically repair the MV in patients with IMR. MV replacement is usually reserved for situations in which the valve cannot be reasonably repaired, or repair is unlikely to be tolerated clinically.

The once and future state of percutaneous mitral valve repair

There has been a great deal of interest in percutaneous mitral valve repair techniques in recent years, with several devices undergoing animal testing and clinical trials. Percutaneous annuloplasty and leaflet repair devices are currently in development, and while safety rates have generally been equal or superior to conventional surgical techniques, efficacy has been suboptimal. Most current percutaneous mitral valve repair devices can only reduce regurgitant volumes by approximately 20-40%, but these reductions may be enough to treat high-risk patients, including the elderly and those with comorbidities, who are otherwise ineligible for surgery. An analysis of how these devices alter the geometry and mechanics of the mitral valve apparatus can provide insight into long-term efficacy and durability and may lead to improvements in the reduction of mitral regurgitation. In the future, multiple percutaneous techniques may be utilized in combination to increase overall efficacy. In this article, we report on percutaneous mitral valve repair techniques with published clinical or animal data.

Percutanenous therapies for mitral regurgitation

Percutaneous therapies for the treatment of mitral regurgitation have emerged rapidly over the past several years. Most of the percutaneous approaches are modifications of existing surgical approaches to mitral annuloplasty or leaflet repair. Most of the percutaneous devices are based on surgical approaches. Catheter-based leaflet repair with the MitraClip is accomplished using an implantable clip to mimic the surgical edge-to-edge technique. Percutaneous annuloplasty can be achieved indirectly via the coronary sinus, or directly from retrograde left ventricular access. Several of these percutaneous approaches have been successfully used in trials or are in the early stages of use in practice.

Percutaneous Techniques for the Treatment of Patients with Functional Mitral Valve Regurgitation

Percutaneous approaches to mitral regurgitation remain largely investigational. In the last decade, novel percutaneous strategies have opened new options in the treatment of valvular heart disease. Several studies are currently underway to determine the benefits of transcatheter mitral valve repair therapy. Transcatheter chordal procedures are being developed, including chordal cutting and chordal implantation. Transcatheter valve implantation in the mitral position might offer a desirable alternative in selected patients and has been accomplished in a compassionate fashion on rare occasions in patients who are not candidates for surgical valve repair or replacement.

Percutaneous approaches to mitral regurgitation

Percutaneous therapy for mitral repair has emerged over the past several years as an investigational option for treating mitral regurgitation (MR). A variety of novel methods to treat MR using a percutaneous route have been developed. Most of these approaches are modifications of surgical techniques, some established and some obscure. The basic surgical approaches to mitral repair are annuloplasty and leaflet repair. Catheter-based devices mimic or approximate these surgical approaches. MR as a disease process is heterogeneous, and different therapeutic approaches are needed for different etiologies of MR and morphologies of the mitral apparatus. Primary leaflet diseases are mitral prolapse and fibroelastic deficiency. Secondary, or functional, MR exists when the leaflets are normal. Functional ischemic MR and functional MR related to heart failure occur in different populations and historically have had different responses to surgical therapy. Leaflet repair using a percutaneous clip has been accomplished for patients with mitral valve prolapse and also some patients with functional MR. Indirect annuloplasty via the coronary sinus has shown promising early human trial results in patients with functional MR. Direct annuloplasty and left ventricular chamber remodeling technologies are in the earliest stages of human application. This group of approaches is being studied as an alternative to surgery for selected patients. The MitraClip (Evalve, Menlo Park, CA) for leaflet repair has been approved for use in Europe and is being applied predominantly to high-risk surgical patients with either functional or degenerative, organic MR. One of the coronary sinus devices has received approval in Europe as well. This complex clinical landscape has made device development, trial design, and patient selection complicated. Steady progress in the field is being made. Many patients with functional MR who are currently treated medically will be the subject of upcoming trials. Catheter methods for mitral repair promise to serve some patients currently considered high risk for surgery, and some patients may have catheter therapy as an alternative to surgery.

The QuantumCor device for treating mitral regurgitation: an animal study

OBJECTIVES

The mitral annular contraction achieved could help reduce mitral regurgitation (MR), and with appropriate modifications, be applied to human subjects providing a potentially effective percutaneous method of valve repair.

BACKGROUND

MR is an important source of morbidity and is an independent predictor of mortality. A variety of percutaneous approaches are being developed to address this issue. We introduce a novel potential method utilizing radiofrequency (RF) energy to heat and shrink the mitral valve annulus in an animal model.

METHODS

In open-heart procedures in 16 healthy sheep (six with naturally occurring MR), we used a malleable probe (QuantumCor, Lake Forest, CA) that conforms to the annular shape to deliver RF energy via a standard generator to replicate a surgical mitral annular ring. Seven sheep were followed chronically and their mitral annulus dimensions measured serially.

RESULTS

All sheep underwent intracardiac echocardiography or direct circumferential measurement of the mitral annulus before and after RF therapy. RF therapy was administered in less than 4 min in each case, and the mean anteroposterior (AP) annular distance was reduced by a mean of 23.8% (AP diameter reduction 5.75 +/- 0.86 mm, P < 0.001) acutely. In the six sheep with nonischemic MR, regurgitation was eliminated. Acute histopathology (HP) demonstrated no damage to the leaflets, coronary sinuses, or coronary arteries. At the end of the intended 6-month period of the chronic part of the study, four of the seven animals survived. The four treatment animals showed significant reductions in mitral A-P dimension, with a percent diameter reduction of 26.4% (AP diameter reduction 7 +/- 2.3 mm).

CONCLUSION

The application of RF directly to heat the mitral annulus has resulted in sustained contraction of the annulus in this limited preclinical animal study. With further study and possible modifications, it holds promise for future application in human subjects with MR.

Percutaneous mitral annuloplasty

Mitral annuloplasty is the most common surgical procedure performed for mitral valve regurgitation, whether performed alone or as part of a more complex repair. A less invasive percutaneous approach to mitral annuloplasty associated with lesser morbidity might offer advantages over a surgical procedure in some patients, even if less efficacious. We review current experimental percutaneous approaches to mitral annuloplasty.

Influence of left atrial and ventricular volumes on the relation between mitral valve annulus and coronary sinus

The aim of this study was to evaluate the anatomic relation between the coronary sinus (CS), mitral annulus, and coronary arteries using 64-multislice computed tomography (MSCT) in patients presenting with a wide range of atrial volumes and left ventricular functions to determine the potential clinical use for percutaneous mitral annuloplasty (PMA). The MSCT data of 165 patients (age 63.65 +/- 12.89 years, 67.3% men) were evaluated. The following variables were measured: CS length, CS ostium area, area of the section of CS when it becomes great cardiac vein, area between CS and atrioventricular groove assessed in volume-rendered 3-dimensional images, axial angle measured as the angle between CS and mitral annulus assessed in axial section, mitral valve annulus (MVA) area, left atrium volume, and left circumflex artery/marginal branch-CS relation referring to mitral annulus. The correlation was inversed between the reduction of the axial angle and all following variables: enlargement of both left ventricular end-systolic (r = -0.429, p <0.001) and end-diastolic (r = -0.428, p <0.001) volumes, left atrial volume (r = -0.361, p <0.001), and MVA (r = -0.324, p <0.001). Similarly, there was inverse correlation between the reduction of the area between CS and atrioventricular groove, and enlargement of both left ventricular end-systolic (r = -0.376, p <0.001) and end-diastolic (r = -0.291, p <0.001) volumes, left atrial volume (r = -0.221, p = 0.001), and MVA (r = -0.155, p = 0.019). Of note, circumflex artery was located between CS and MVA in 77% of the patients, but in patients with severe mitral regurgitation CS crossed circumflex/marginal branch artery more frequently (97% of cases). In conclusion, a close proximity of the CS to the mitral annulus but also to circumflex artery is more likely to occur with left atrial and ventricular enlargement. Thus, MSCT should be considered as part of the selection process of potential candidate to PMA to avoid external compression of circumflex artery/marginal branch by the device.