Balloon catheter with check valves for experimental relief of acute aortic regurgitation

Calculation of left ventricular diastolic time constant (Tau) in dogs with aortic regurgitation using continuous-wave Doppler spectra

OBJECTIVE

To investigate a new noninvasive method for calculating left ventricular diastolic time constant (Tau) through a continuous-wave aortic regurgitation Doppler spectrum.

METHODS

According to ultrasound guidance, twenty-four animal models (beagles) of aortic regurgitation and acute ischemic left ventricular diastolic dysfunction were created. The left ventricular diastolic function was manipulated with dobutamine or esmolol and fifty-nine hemodynamic stages were achieved. Raw audio signals of the continuous-wave Doppler spectra were collected, and new aortic regurgitation Doppler spectra were built after reprocessing by a personal computer. The updating time of the spectral line was 0.3 ms. The new Doppler spectra contour line was automated using MATLAB (MATrix LABoratory, MathWorks, Natick, MA, USA), and two time intervals, (t2-t1) and (t3-t1) were measured on the ascending branch of the aortic regurgitation Doppler spectrum. Then, the two time intervals were substituted into Bai's equations, and Doppler-derived Tau (Tau-D) was resolved and compared with catheter-derived Tau (Tau-c).

RESULTS

There is no significant difference between Tau-D and Tau-c (45.95 ± 16.90 ms and 46.81 ± 17.31 ms, respectively; P > 0.05). Correlation analysis between Tau-c and Tau-D suggested a strong positive relationship ( r = 0.97, P = 0.000). A Bland-Altman plot of Tau-c and Tau-D revealed fair agreement.

CONCLUSIONS

This new calculation method is simple, convenient, and shows a strong positive relationship and fair agreement with the catheter method.

Evolution of Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement emerged ≈20 years ago and changed the landscape of structural interventional cardiology. The first experiments in animal models provided proofs of the concept and the substrate for the first percutaneous valve implantation in patients. The initial promising results in a clinical setting drew the attention of the industry and of the scientific community, and an effort was made for the past 12 years to address the limitations of the technology, facilitate the procedure, minimize the risk of complications, and broaden the applications of transcatheter aortic valve replacement. This article reviews the evolution of transcatheter aortic valve replacement, presents the first steps in this field, cites the evidence from registries and clinical trials, highlights the limitations of this treatment, and discusses the future perspectives and the developments proposed to address the current pitfalls.

[Transcatheter aortic valve replacement: when should it be used in aortic stenosis?]

30% of patients with significant aortic stenosis are not considered for operative aortic valve replacement because of the high perioperative risk. An alternative catheter based option for these patients is the transcatheter aortic valve replacement (TAVI). In general, there are two approaches for TAVI: transfemoral and transapical. Transfemoral aortic valve replacement is performed by transcatheter replacement of an aortic valve via the femoral arteries. Transapical valve replacement is achieved by transcatheter implantation via the fifth intercostal space. The most common complications are vessel injuries, bleeding complications, new onset of AV-block, development of paravalvular insufficiency, acute kidney injury, stroke and TIA. The first long-term observations suggest positive results. First clinical trials in a high-risk population show a promising outcome. Therefore TAVI offers a reasonable therapy option for patients with high perioperative risk. Further long-term clinical trials are still pending.

Transcatheter aortic valve implantation: the evolution of prostheses, delivery systems and approaches

It is two decades since the first report of transcatheter implantation of a stented aortic valve in an animal. The first implantation of a transcatheter aortic valve in a human was accomplished just one decade ago dramatically demonstrating the promise and feasibility of this new therapy. Over the past 10 years, there have been rapid developments in valves, delivery systems and technical approaches. Today, transcatheter valve implantation is a technical possibility for the great majority of patients with aortic stenosis. The next 10 years may well see this become the dominant therapy for aortic stenosis.

History of percutaneous aortic valve prosthesis

This review describes the development of percutaneous transluminal catheter-mounted heart valves for permanent implantation. The time period from the first surgically implanted valve in 1952, through catheter- mounted valves inserted for temporal relief, until the conception of the percutaneous transcatheter heart valve for permanent implantation is summarized. The process involved in the construction of the new valve is detailed in Figure 1, and the future of this new treatment modality is discussed.

[Transcatheter-based aortic valve implantation. Present and future technologies]

The calcified aortic stenosis is the dominating valve disease. Patients affected are most common elderly people in the 8th or 9th decade of their life who often show associated comorbidities like reduced left ventricular function, impaired renal function, pulmonary hypertension, and further diseases (diabetes mellitus, stroke, chronic obstructive pulmonary disease). In many cases perioperative morbidity and mortality are too high for surgical valve replacement and patients are rejected. Nevertheless, prognosis of aortic stenosis is worse, if the typical symptoms like dyspnea on exertion, syncope, and angina occur. The transcatheter aortic valve implantation is an alternative treatment for this particular group of patients. The aortic valve bioprosthesis consists of a balloon-expandable stent or a self-expandable frame, in which a valve of bovine or porcine pericardium is incorporated. The implantation is performed by retrograde access via the femoral artery; the balloon-expandable prosthesis can also be implanted by transapical approach. Alternatively, the subclavian artery is chosen for access. More frequently, the implantation is performed in analgosedation with the patient awake that favors the transfemoral approach. A further reduction of the available prosthesis and new types of valves which are under current experimental tests and clinical evaluation contribute to this development.

Catheter-based modification of heart valve diseases: from experimental to clinical application

Efforts to modify cardiac valve defects using catheter-based techniques are increasing at the present time. We present observations on cardiac valve morphology and disease and review the progress being made to address valve defects with these innovative methods. Some new procedures developed through animal experimentation have already been put to use in clinical practice, but the newness of these techniques and the small number of cases in which they have been applied to date precludes an evaluation of their long-term durability. Although at the present time cardiac surgery remains the standard for treating most cases of valve disease, in certain situations a catheter-based treatment might provide a reasonable alternative, even if only temporary, especially for individuals with serious disease who are not suitable candidates for surgery.

[Percutaneous cardiac valve replacement: a review]

Surgery is no longer the only technique to replace a cardiac valve. New percutaneous procedures allow aortic or pulmonary valve implantation. Even if the feasibility of these procedures has been proved, cases reported are very rare and selected. This emergent technology is still at an early stage of development and new prospective studies will be necessary to evaluate these procedures correctly before concluding their clinical benefit. At this time surgery remains the gold standard in terms of cardiac valve replacement.

Percutaneous stent-mounted valve for treatment of aortic or pulmonary valve disease

The objective of this study was to develop a prosthetic cardiac valve designed for percutaneous transcatheter implantation. Percutaneous catheter-based therapies play a limited role in the management of cardiac valve disease. Surgical implantation of prosthetic valves usually requires thoracotomy and cardiopulmonary bypass. The stent-valve is constructed of a rolled sheet of heat-treated nitinol. Although malleable when cooled, once released from a restraining sheath at body temperature the stent unrolls, becomes rigid, and assumes its predetermined cylindrical conformation. A ratcheting lock-out mechanism prevents recoil and external protrusions facilitate anchoring. Valve leaflets are constructed of bovine pericardium. The feasibility of catheter implantation, prosthetic valve function, and survival were investigated in an animal model. In vitro and pulse duplicator testing documented valve durability. Endovascular delivery of the prototype stent-valve to the aortic or pulmonary position was feasible. Accurate positioning was required to ensure exclusion of the native valve leaflets and, in the case of the aortic valve, to avoid compromise of the coronary ostia or mitral apparatus. Oversizing of the stent in relation to the valve annulus was desirable to facilitate anchoring and prevent paravalvular insufficiency. Stent-valve implantation proved feasible and compatible with survival in an animal model. Transcatheter implantation of prosthetic valves is possible. Further evolution of this technology will involve lower-profile devices with design features that facilitate vascular delivery, visualization, positioning, deployment, and valvular function.