Percutaneous Heart Valve Replacement

The power of disruptive technological innovation: Transcatheter aortic valve implantation

We sought to evaluate the principles of disruptive innovation, defined as technology innovation that fundamentally shifts performance and utility metrics, as applied to transcatheter aortic valve implantation (TAVI). In particular, we considered implantation procedure, device design, cost, and patient population. Generally cheaper and lower performing, classical disruptive innovations are first commercialized in insignificant markets, promise lower margins, and often parasitize existing usage, representing unattractive investments for established market participants. However, despite presently high unit cost, TAVI is less invasive, treats a "new," generally high risk, patient population, and is generally done by a multidisciplinary integrated heart team. Moreover, at least in the short-term TAVI has not been lower-performing than open surgical aortic valve replacement in high-risk patients. We conclude that TAVI extends the paradigm of disruptive innovation and represents an attractive commercial opportunity space. Moreover, should the long-term performance and durability of TAVI approach that of conventional prostheses, TAVI will be an increasingly attractive commercial opportunity.

A novel heart valve stent design: mechanical interaction with the aortic root

Percutaneous aortic valve implantation has become an alternative technique to surgical valve replacement in patients with high risk for open chest surgery. Vascular stents clinically used today for non-invasive aortic valve replacement tend, however, to impede the dimension changes of the compliant aortic root over the cardiac cycle. The purpose of the present work is to assess the influence of a novel heart valve stent, designed specifically to limit the traumatism in tissue, on the compliance of the aortic root. A theoretical approach is adopted to model the mechanical behaviour of the different stent parts and assess the compliance modification induced by the stent. The validity of the model is then tested experimentally. Both approaches show that the specific geometry of the stent makes it possible to keep the compliance of the aortic root close to the native root values.

Percutaneous valve procedures: Present and future

Percutaneous mitral commissurotomy and aortic valvuloplasty have been being performed since the mid-1980s. Balloon commissurotomy has been used in thousands of cases worldwide and it provides good short- and long-term results in a wide range of patients. It has virtually replaced surgical commissurotomy in the treatment of mitral stenosis. In contrast, percutaneous aortic valvuloplasty is almost abandoned worldwide due to its lack of efficacy and the risks involved. The new techniques of percutaneous valve intervention: aortic valve replacement and mitral valve repair are at an early stage: the first in-man applications of these fledgling techniques started in 2002. Preliminary series show that they are feasible; however, they need to be further evaluated in comparison with contemporary treatment to assess accurately how efficient they are and the risks involved. Currently potential applications concern high-risk patients, however, in the future, after thorough evaluation, this may be extended to others. Thus, percutaneous interventions already play an important role in treatment of valvular heart disease, a role that seems set for future expansion.

Hydrodynamic Evaluation of a Minimally Invasive Heart Valve in an Isolated Aortic Root Using a Modified In Vitro Model

Implantation methods for commercially available heart valve prostheses require open-chest access to the heart to perform the suturing process. In order to alleviate this complicated surgical implant technique, a “stent-valve” design was developed that will provide a less cumbersome implantation method and therefore a less invasive access to the heart. The purpose of this study is to verify its hydrodynamic performance and migration characteristics to assess its feasibility for use as a replacement heart valve. Hydrodynamic evaluation of the novel stent-valve combination device was carried out using a Vivitro left heart simulator and by setting up a comparison with the same 19 mm trileaflet valve under a traditional implantation (suture) method. To assess implantation ability under normal physiological conditions, porcine aortic root tissue was mounted into the left heart simulator to replace the original glass sinus. A comparison experiment was conducted to study the change in the total compliance and resistance of the testing system using the modified Windkessel model. For the range of test conditions investigated, the stent-valve combination device produced an average pressure gradient of 41.2 mm Hg(±19.6 mm Hg), an average effective orifice area (EOA) of 1.06 cm2(±0.08 cm2), and an average regurgitation percentage of 4.5% (±3.3%), while the sutured valve produced an average pressure gradient of 48.7 mm Hg(±17.4 mm Hg), an average EOA of 0.88 cm2(±0.14 cm2), and an average regurgitation percentage of 0.8% (±0.4%). The total compliance and resistance of the system was 0.37 ml/mm Hg(±0.01 ml/mm Hg) and 1.1 mm Hg/ml/s(±0.29 mm Hg/ml/s), with the original Windkessel model, and 0.33 ml/mm Hg(±0.01 ml/mm Hg) and 1.1 mm Hg/ml/s(±0.24 mm Hg/ml/s) for the system with the aortic tissue. The stent-valve combination device has demonstrated favorable hydrodynamic performance when compared with the same trileaflet valve under the traditional suturing method, and the arterial stent makes it possible to secure the valve at its required position without migration.

Brugada syndrome

First introduced as a new clinical entity in 1992, the Brugada syndrome is associated with a relatively high risk of sudden death in young adults, and occasionally in children and infants. Recent years have witnessed a striking proliferation of papers dealing with the clinical and basic aspects of the disease. Characterized by a coved-type ST-segment elevation in the right precordial leads of the electrocardiogram (ECG), the Brugada syndrome has a genetic basis that thus far has been linked only to mutations in SCN5A, the gene that encodes the alpha-subunit of the sodium channel. The Brugada ECG is often concealed, but can be unmasked or modulated by a number of drugs and pathophysiological states including sodium channel blockers, a febrile state, vagotonic agents, tricyclic antidepressants, as well as cocaine and propranolol intoxication. Average age at the time of initial diagnosis or sudden death is 40 +/- 22, with the youngest patient diagnosed at 2 days of age and the oldest at 84 years. This review provides an overview of the clinical, genetic, molecular, and cellular aspects of the Brugada syndrome, incorporating the results of two recent consensus conferences. Controversies with regard to risk stratification and newly proposed pharmacologic strategies are discussed.

Current status of percutaneous valvular procedures

OPINION STATEMENT

During the past few decades, percutaneous valvular procedures have been used in mitral and aortic stenosis. Percutaneous mitral commissurotomy, which has virtually replaced surgical commissurotomy in the treatment of mitral stenosis, has been performed since the mid-1980s and has provided good results in thousands of patients worldwide. Percutaneous balloon aortic valvuloplasty has largely been abandoned due to its limited efficacy and the risks involved. New percutaneous procedures are currently being developed in mitral regurgitation and aortic stenosis, which represent the two most frequent valve diseases in industrialized countries. They are in the early stages of development but have opened a very exciting field of investigation. Two percutaneous mitral valve treatment techniques have been used: the edge-to-edge technique and the prosthetic ring annuloplasty. Preliminary series show that they are feasible; however, they need to be further evaluated in comparison with contemporary treatment to accurately assess their effectiveness and the risks involved. Since 2003, percutaneous aortic valve replacement has been performed in approximately 100 compassionate cases with end-stage aortic stenosis, formally declined for surgery. It results in hemodynamic and clinical improvement, with an acceptable risk in this highly selected population. The evaluation of these new percutaneous procedures requires a close collaboration between interventionalists, echocardiographers, engineers, and surgeons. It is probable that they will play an important role in the treatment of valve disease in the future.

Percutaneous transcatheter one-step mechanical aortic disc valve prosthesis implantation: a preliminary feasibility study in swine

PURPOSE

To evaluate the feasibility of one-step implantation of a new type of stent-based mechanical aortic disc valve prosthesis (MADVP) above and across the native aortic valve and its short-term function in swine with both functional and dysfunctional native valves.

METHODS

The MADVP consisted of a folding disc valve made of silicone elastomer attached to either a nitinol Z-stent (Z model) or a nitinol cross-braided stent (SX model). Implantation of 10 MADVPs (6 Z and 4 SX models) was attempted in 10 swine: 4 (2 Z and 2 SX models) with a functional native valve and 6 (4 Z and 2 SX models) with aortic regurgitation induced either by intentional valve injury or by MADVP placement across the native valve. MADVP function was observed for up to 3 hr after implantation.

RESULTS

MADVP implantation was successful in 9 swine. One animal died of induced massive regurgitation prior to implantation. Four MADVPs implanted above functioning native valves exhibited good function. In 5 swine with regurgitation, MADVP implantation corrected the induced native valve dysfunction and the device's continuous good function was observed in 4 animals. One MADVP (SX model) placed across native valve gradually migrated into the left ventricle.

CONCLUSION

The tested MADVP can be implanted above and across the native valve in a one-step procedure and can replace the function of the regurgitating native valve. Further technical development and testing are warranted, preferably with a manufactured MADVP.

Therapy for the Brugada syndrome

The Brugada syndrome is a congenital syndrome of sudden cardiac death first described as a new clinical entity in 1992. Electrocardiographically characterized by a distinct coved-type ST segment elevation in the right precordial leads, the syndrome is associated with a high risk for sudden cardiac death in young and otherwise healthy adults, and less frequently in infants and children. The ECG manifestations of the Brugada syndrome are often dynamic or concealed and may be revealed or modulated by sodium channel blockers. The syndrome may also be unmasked or precipitated by a febrile state, vagotonic agents, alpha-adrenergic agonists, beta-adrenergic blockers, tricyclic or tetracyclic antidepressants, a combination of glucose and insulin, and hypokalemia, as well as by alcohol and cocaine toxicity. An implantable cardioverter-defibrillator (ICD) is the most widely accepted approach to therapy. Pharmacological therapy aimed at rebalancing the currents active during phase 1 of the right ventricular action potential is used to abort electrical storms, as an adjunct to device therapy, and as an alternative to device therapy when use of an ICD is not possible. Isoproterenol and cilostazol boost calcium channel current, and drugs like quinidine inhibit the transient outward current, acting to diminish the action potential notch and thus suppress the substrate and trigger for ventricular tachycardia/fibrillation (VT/VF).