The clinical development of percutaneous heart valve technology

Predicting target vessel location for improved planning of robot-assisted CABG procedures

Prior to performing a robot-assisted coronary artery bypass grafting procedure, a pre-operative computed tomography scan is used to assess patient candidacy and to identify the location of the target vessel. The surgeon then determines the optimal port locations to ensure proper reach to the target with the robotic instruments, while assuming that the heart does not undergo any significant changes between the pre- and intra-operative stages. However, the peri-operative workflow itself leads to changes in heart position and consequently the intra-operative target vessel location. As such, the pre-operative plan must be adequately updated to adjust the target vessel location to better suit the intraoperative condition. Here we propose a technique to predict the position of the peri-operative target vessel location with approximately 3.5 mm RMS accuracy. We believe this technique will potentially reduce the rate of conversion of robot-assisted procedures to traditional open-chest surgery due to poor planning.

Evaluation of model-enhanced ultrasound-assisted interventional guidance in a cardiac phantom

Minimizing invasiveness associated with cardiac procedures has led to limited visual access to the target tissues. To address these limitations, we have developed a visualization environment that integrates interventional ultrasound (US) imaging with preoperative anatomical models and virtual representations of the surgical instruments tracked in real time. In this paper, we present a comprehensive evaluation of our model-enhanced US-guidance environment by simulating clinically relevant interventions in vitro . We have demonstrated that model-enhanced US guidance provides a clinically desired targeting accuracy better than 3-mm rms and maintains this level of accuracy even in the case of image-to-patient misalignments that are often encountered in the clinic. These studies emphasize the benefits of integrating real-time imaging with preoperative data to enhance surgical navigation in the absence of direct vision during minimally invasive cardiac interventions.

Characterization and outcome of patients with severe symptomatic aortic stenosis referred for percutaneous aortic valve replacement

OBJECTIVE

Many high-risk patients with severe symptomatic aortic stenosis are not referred for surgical aortic valve replacement. Although this patient population remains ill-defined, many of these patients are now being referred for percutaneous aortic valve replacement. We sought to define the characteristics and outcomes of patients referred for percutaneous aortic valve replacement.

METHODS

Between February 2006 and March 2007, 92 patients were screened for percutaneous aortic valve replacement. Clinical and echocardiographic characteristics of patients undergoing surgical aortic valve replacement, percutaneous aortic valve replacement, balloon aortic valvuloplasty, or no intervention were compared. The primary end point was all-cause mortality.

RESULTS

Nineteen patients underwent successful surgical aortic valve replacement, 18 patients underwent percutaneous aortic valve replacement, and 36 patients had no intervention. Thirty patients underwent balloon aortic valvuloplasty, and of these, 8 patients were bridged to percutaneous aortic valve replacement and 3 were bridged to surgical aortic valve replacement. Of the remaining 19 patients undergoing balloon aortic valvuloplasty, bridging to percutaneous aortic valve replacement could not be accomplished because of death (n = 9 [47%)], exclusion from the percutaneous aortic valve replacement protocol (n = 6 [32%]), and some patients improved after balloon aortic valvuloplasty and declined percutaneous aortic valve replacement (n = 4 [21%]). The most common reasons for no intervention included death while awaiting definitive treatment (n = 10 [28%]), patient uninterested in percutaneous aortic valve replacement (n = 10 [28%]), and questionable severity of symptoms or aortic stenosis (n = 9 [25%]). Patients not undergoing aortic valve replacement had higher mortality compared with those undergoing aortic valve replacement (44% vs 14%) over a mean duration of 220 days.

CONCLUSION

Symptomatic patients with severe aortic stenosis have high mortality if timely aortic valve replacement is not feasible. Twenty percent of the patients referred for percutaneous aortic valve replacement underwent surgical aortic valve replacement with good outcome. Patients undergoing balloon aortic valvuloplasty alone or no intervention had unfavorable outcomes.

Transcatheter and transapical aortic valve replacement

Minimally invasive valve replacement is limited to bioprosthetic aortic and pulmonary valves for use in very specific populations of patients. Replacement via trans-catheter and transapical techniques should be used only in patients in whom traditional surgical replacement is deemed an unacceptable risk. Nursing management will focus heavily on care for comorbid conditions because of the high-risk nature of the patients in whom these valves will initially be implanted.

Targeting accuracy under model-to-subject misalignments in model-guided cardiac surgery

In image-guided interventions, anatomical models of organs are often generated from pre-operative images and further employed in planning and guiding therapeutic procedures. However, the accuracy of these models, along with their registration to the subject are crucial for successful therapy delivery. These factors are amplified when manipulating soft tissue undergoing large deformations, such as the heart. When used in guiding beating-heart procedures, pre-operative models may not be sufficient for guidance and they are often complemented with real-time, intra-operative cardiac imaging. Here we demonstrate via in vitro endocardial "therapy" that ultrasound-enhanced model-guided navigation provides sufficient guidance to preserve a clinically-desired targeting accuracy of under 3 mm independently of the model-to-subject misregistrations. These results emphasize the direct benefit of integrating real-time imaging within intra-operative visualization environments considering that model-to-subject misalignments are often encountered clinically.

Percutaneous and Minimally Invasive Valve Procedures

The incidence of valvular heart disease is expected to increase over the next several decades as a large proportion of the US demographic advances into the later decades of life. At the same time, the next several years can be anticipated to bring a broad transition of surgical therapy to minimally invasive (minithoracotomy and small port) access and the more gradual introduction of percutaneous approaches for the correction of valvular heart disease. Broad acceptance of these technologies will require careful and sometimes perplexing comparisons of the outcomes of these new technologies with existing standards of care. The validation of percutaneous techniques, in particular, will require the collaboration of cardiologists and cardiac surgeons in centers with excellent surgical and catheter experience and a commitment to trial participation. For the near term, percutaneous techniques will likely remain investigational and will be limited in use to patients considered to be high risk or to inoperable surgical candidates. Although current-generation devices and techniques require significant modification before widespread clinical use can be adopted, it must be expected that less invasive and even percutaneous valve therapies will likely have a major impact on the management of patients with valvular heart disease over the next several years.

Sutureless Stented Aortic Valve Implantation Under Direct Vision: Lessons From a Negative Experience in Sheep

BACKGROUND AND AIM OF THE STUDY

Percutaneous aortic valve replacement has been proposed as a valid alternative to surgery in selected cases; however, it still has many problems. As a less radical preliminary step, we implanted a balloon-expandable stented aortic valve under direct vision in sheep.

METHODS

Under cardiopulmonary bypass (CPB) and through a transverse aortotomy, an aortic valve mounted in a long tubular balloon-expandable stent was implanted in six acute sheep. The leaflets were not excised and no anchoring sutures were used between stent and native annulus. Epicardial, two-dimensional color Doppler echocardiography was used to assess the function of the stented valve followed by macroscopic inspection at necropsy.

RESULTS

Direct visualization of the entire annulus when the collapsed, valved stent was placed within the aortic root was difficult in all animals. Valve deployment took less than 1 minute. The surgical procedure resulted in major complications in all cases. Migration (3/6), paravalvular leak (2/6), mitral conflicts resulting in mitral regurgitation (1/6), and coronary ostia obstruction (2/6) were the major events at the origin of the failure. Only three animals could be weaned from CPB but did not recover enough to survive the procedure.

CONCLUSIONS

Sutureless implantation of a stented aortic valve through standard CPB and aortotomy is far more complex than expected. Changes in stent design and surgical approach are indicated.

Cardiac surgery in the elderly: indications and management options to optimize outcomes

The elderly have increasingly benefited from the advances in cardiac surgical techniques and perioperative care. Compared to the same procedures in younger patients their operations can be more technically demanding and their level of reserve leaves less margin should complications occur. The importance of using realistic indications for operations with a focus on improving the quality of their lives and of optimal preoperative preparation of patients is emphasized.

Percutaneous Mitral Valve Repair

Surgical mitral valve repair is the procedure of choice to treat mitral regurgitation of all etiologies. Whereas annuloplasty is the cornerstone of mitral valve repair, a variety of other surgical techniques are utilized to correct dysfunction of the leaflets and subvalvular apparatus; in most cases, surgical repair entails application of multiple repair techniques in each patient. Preclinical studies and early human experience have demonstrated that some of these surgical repair techniques can be performed using percutaneous approaches. Specifically, there has been great progress in the development of novel technology to facilitate percutaneous annuloplasty and percutaneous edge-to-edge repair. The objectives of this report were to (1) discuss the surgical foundations for these percutaneous approaches; (2) review device design and experimental and clinical results of percutaneous valve repair; and (3) address future directions, including the key challenges of patient selection and clinical trial design.

Midterm Results of the Edge-to-Edge Technique for Complex Mitral Valve Repair

BACKGROUND

The edge-to-edge technique (E2E) has been advocated for the complex repair of myxomatous mitral valves. We compared outcomes of E2E performed in patients at risk for systolic anterior motion (SAM) versus outcomes in patients with residual mitral regurgitation (MR) after repair completion.

METHODS

A total of 1,612 patients had repair of myxomatous mitral valves between June 1997 and December 2003 at Brigham and Women's Hospital. The E2E was used in 72 (4.5%) patients. Fifty-two patients (52/72; group I) had E2E for persistent MR after complex repair. Twenty patients (20/72; group II) had E2E for high risk of post-repair SAM and left ventricular outflow tract obstruction. Mean age of the patients was 61 +/- 14 years; 47 were male, average New York Heart Association class at admission was 2.4 +/- 0.6, and mean left ventricular ejection fraction was 56 +/- 12%.

RESULTS

The operative mortality was zero. Immediate postoperative MR was significantly improved in all patients compared with the preoperative grade (p value < 0.0005). Mean follow-up was 388 days. In those in whom E2E was used for residual MR without SAM risk (group I), postoperative MR (> or = 2+) was detected in 15 of 52 patients at 6 months. In group II, SAM was completely eliminated and the mean MR grade in the immediate postoperative period was 0.5 +/- 0.7. There was no long-term recurrence of MR in group II.

CONCLUSIONS

This study suggests that E2E eliminates SAM and long-term MR in patients with pre-repair echocardiographic predictors of SAM. The E2E is not efficacious in preventing long-term recurrent MR if performed for residual MR after complex mitral repair.

Intracardiac Echocardiography for Percutaneous Mitral Valve Repair in a Swine Model

BACKGROUND

High-quality live imaging assessment of cardiac valves and cardiac anatomy is crucial for the success of percutaneous catheter-based mitral valve (MV) repair techniques. We examined the use of intracardiac echocardiography (ICE) in providing online ICE images necessary for successful perctunaneous MV repair by Alfieri stitch technique-based percutaneous edge-to-edge device in a swine model.

METHODS

ICE was performed in 20 healthy adult pigs (90 +/- 8 kg, mean +/- SEM). A 10F ICE catheter was advanced through the left femoral vein and the right jugular vein. Images were obtained from the right atrium, left atrium, right ventricle, and pulmonary artery. Fluoroscopy was used to locate the position of ICE catheter tip in different imaging windows.

RESULTS

An echocardiographic protocol was developed for focused visualization of target cardiac structures during the process of percutaneous MV repair. This included visualization of interatrial septum to guide transeptal puncture; to confirm transit of guidewire into the left atrium, across the MV into the left ventricle and across the aortic valve into the aorta; to assist in central positioning of guide catheter in the left atrium above and then across MV leaflets; and to visualize middle scallops of anterior and posterior MV leaflets in short- and long-axis views. Finally, location and orientation of the orifice of the therapy catheter against each MV leaflet was visualized to enable successful capture of MV leaflets, to confirm successful deployment of suture and double orifice (figure of 8" appearance of MV, and finally to confirm central deployment of clip at the site of suture.

CONCLUSION

An ICE protocol was developed to visualize serial cardiac structures to guide deployment of suture into the A2-P2 scallops of the MV and to confirm final result before release of clip.