Towards real-time cardiovascular magnetic resonance-guided transarterial aortic valve implantation: in vitro evaluation and modification of existing devices

Interventional cardiac magnetic resonance imaging: current applications, technology readiness level, and future perspectives

BACKGROUND

Cardiac magnetic resonance (CMR) provides excellent temporal and spatial resolution, tissue characterization, and flow measurements. This enables major advantages when guiding cardiac invasive procedures compared with X-ray fluoroscopy or ultrasound guidance. However, clinical implementation is limited due to limited availability of technological advancements in magnetic resonance imaging (MRI) compatible equipment. A systematic review of the available literature on past and present applications of interventional MR and its technology readiness level (TRL) was performed, also suggesting future applications.

METHODS

A structured literature search was performed using PubMed. Search terms were focused on interventional CMR, cardiac catheterization, and other cardiac invasive procedures. All search results were screened for relevance by language, title, and abstract. TRL was adjusted for use in this article, level 1 being in a hypothetical stage and level 9 being widespread clinical translation. The papers were categorized by the type of procedure and the TRL was estimated.

RESULTS

Of 466 papers, 117 papers met the inclusion criteria. TRL was most frequently estimated at level 5 meaning only applicable to in vivo animal studies. Diagnostic right heart catheterization and cavotricuspid isthmus ablation had the highest TRL of 8, meaning proven feasibility and efficacy in a series of humans.

CONCLUSION

This article shows that interventional CMR has a potential widespread application although clinical translation is at a modest level with TRL usually at 5. Future development should be directed toward availability of MR-compatible equipment and further improvement of the CMR techniques. This could lead to increased TRL of interventional CMR providing better treatment.

Effects of heart valve prostheses on phase contrast flow measurements in Cardiovascular Magnetic Resonance - a phantom study

BACKGROUND

Cardiovascular Magnetic Resonance is often used to evaluate patients after heart valve replacement. This study systematically analyses the influence of heart valve prostheses on phase contrast measurements in a phantom trial.

METHODS

Two biological and one mechanical aortic valve prostheses were integrated in a flow phantom. B0 maps and phase contrast measurements were acquired at a 1.5 T MR scanner using conventional gradient-echo sequences in predefined distances to the prostheses. Results were compared to measurements with a synthetic metal-free aortic valve.

RESULTS

The flow results at the level of the prosthesis differed significantly from the reference flow acquired before the level of the prosthesis. The maximum flow miscalculation was 154 ml/s for one of the biological prostheses and 140 ml/s for the mechanical prosthesis. Measurements with the synthetic aortic valve did not show significant deviations. Flow values measured approximately 20 mm distal to the level of the prosthesis agreed with the reference flow for all tested all prostheses.

CONCLUSIONS

The tested heart valve prostheses lead to a significant deviation of the measured flow rates compared to a reference. A distance of 20 mm was effective in our setting to avoid this influence.

Magnetic Resonance Imaging-Guided Transcatheter Cavopulmonary Shunt

OBJECTIVES

The aim of this study was to test the hypothesis that real-time magnetic resonance imaging (MRI) would enable closed-chest percutaneous cavopulmonary anastomosis and shunt by facilitating needle guidance along a curvilinear trajectory, around critical structures, and between a superior vena cava "donor" vessel and a pulmonary artery "target."

BACKGROUND

Children with single-ventricle physiology require multiple open heart operations for palliation, including sternotomies and cardiopulmonary bypass. The reduced morbidity of a catheter-based approach would be attractive.

METHODS

Fifteen naive swine underwent transcatheter cavopulmonary anastomosis and shunt creation under 1.5-T MRI guidance. An MRI antenna-needle was advanced from the superior vena cava into the target pulmonary artery bifurcation using real-time MRI guidance. In 10 animals, balloon-expanded off-the-shelf endografts secured a proximal end-to-end caval anastomosis and a distal end-to-side pulmonary anastomosis that preserved blood flow to both branch pulmonary arteries. In 5 animals, this was achieved with a novel, purpose-built, self-expanding device.

RESULTS

Real-time MRI needle access of target vessels (pulmonary artery), endograft delivery, and superior vena cava shunt to pulmonary arteries were successful in all animals. All survived the procedure without complications. Intraprocedural real-time MRI, post-procedural MRI, x-ray angiography, computed tomography, and necropsy showed patent shunts with bidirectional pulmonary artery blood flow.

CONCLUSIONS

MRI guidance enabled a complex, closed-chest, beating-heart, pediatric, transcatheter structural heart procedure. In this study, MRI guided trajectory planning and reproducible, reliable bidirectional cavopulmonary shunt creation.

Robot-assisted real-time magnetic resonance image-guided transcatheter aortic valve replacement

BACKGROUND

Real-time magnetic resonance imaging (rtMRI)-guided transcatheter aortic valve replacement (TAVR) offers improved visualization, real-time imaging, and pinpoint accuracy with device delivery. Unfortunately, performing a TAVR in a MRI scanner can be a difficult task owing to limited space and an awkward working environment. Our solution was to design a MRI-compatible robot-assisted device to insert and deploy a self-expanding valve from a remote computer console. We present our preliminary results in a swine model.

METHODS

We used an MRI-compatible robotic arm and developed a valve delivery module. A 12-mm trocar was inserted in the apex of the heart via a subxiphoid incision. The delivery device and nitinol stented prosthesis were mounted on the robot. Two continuous real-time imaging planes provided a virtual real-time 3-dimensional reconstruction. The valve was deployed remotely by the surgeon via a graphic user interface.

RESULTS

In this acute nonsurvival study, 8 swine underwent robot-assisted rtMRI TAVR for evaluation of feasibility. Device deployment took a mean of 61 ± 5 seconds. Postdeployment necropsy was performed to confirm correlations between imaging and actual valve positions.

CONCLUSIONS

These results demonstrate the feasibility of robotic-assisted TAVR using rtMRI guidance. This approach may eliminate some of the challenges of performing a procedure while working inside of an MRI scanner, and may improve the success of TAVR. It provides superior visualization during the insertion process, pinpoint accuracy of deployment, and, potentially, communication between the imaging device and the robotic module to prevent incorrect or misaligned deployment.

Real-time magnetic resonance imaging-guided transcatheter aortic valve replacement

OBJECTIVES

To demonstrate the feasibility of Real-time magnetic resonance imaging (rtMRI) guided transcatheter aortic valve replacement (TAVR) with an active guidewire and an MRI compatible valve delivery catheter system in a swine model.

METHODS

The CoreValve system was minimally modified to be MRI-compatible by replacing the stainless steel components with fluoroplastic resin and high-density polyethylene components. Eight swine weighing 60-90 kg underwent rtMRI-guided TAVR with an active guidewire through a left subclavian approach.

RESULTS

Two imaging planes (long-axis view and short-axis view) were used simultaneously for real-time imaging during implantation. Successful deployment was performed without rapid ventricular pacing or cardiopulmonary bypass. Postdeployment images were acquired to evaluate the final valve position in addition to valvular and cardiac function.

CONCLUSIONS

Our results show that the CoreValve can be easily and effectively deployed through a left subclavian approach using rtMRI guidance, a minimally modified valve delivery catheter system, and an active guidewire. This method allows superior visualization before deployment, thereby allowing placement of the valve with pinpoint accuracy. rtMRI has the added benefit of the ability to perform immediate postprocedural functional assessment, while eliminating the morbidity associated with radiation exposure, rapid ventricular pacing, contrast media renal toxicity, and a more invasive procedure. Use of a commercially available device brings this rtMRI-guided approach closer to clinical reality.

The future of transcatheter pulmonary valvulation

Percutaneous pulmonary valve implantation now has a key role in the setting of dysfunctional right ventricle-to-pulmonary artery conduits or failing bioprosthetic pulmonary valves. However, despite the excellent results obtained with the two devices available currently (the Melody(®) valve [Medtronic Inc., Minneapolis, MN, USA] and the Edwards SAPIEN(®) valve [Edwards Lifesciences, Irvine, CA, USA]), many patients eligible for pulmonary valve replacement remain unsuitable for percutaneous pulmonary valve implantation, mainly because of large native outflow tracts. Accordingly, one of the major challenges for the future is to expand percutaneous pulmonary valve implantation to a broader population of patients. Moving forward, there is important ongoing research that is intended to improve patient outcomes, expand percutaneous pulmonary valve implantation therapy and continue to reduce the number of open-heart surgeries in this population. In this review, we underline the limitations and issues associated with the devices available currently, and we focus on the development of new strategies (such as hybrid approaches or magnetic resonance-guided procedures), new devices (such as right ventricular outflow tract reducers or the novel Native Outflow Tract valved stent from Medtronic) and new technologies (such as tissue-engineered valves), which may help to take up these challenges and represent the future of transcatheter valve implantation.

The past, present and future of minimally invasive therapy in endovascular interventions: a review and speculative outlook

Cardiovascular disease is a leading cause of death in all developed countries. In response to this need, endovascular management techniques have been developed across a large range of medical specialties. Minimally invasive percutaneous interventions were initially complex and challenging, but with the continued development of equipment and expertise their use has become routine in many fields. With routine use, it has become important to establish the safety and efficacy of endovascular treatments against the respective "gold standard" procedures, especially in light of their initial intended use for the management of patients at unacceptably high risk for standard therapy only. Such evaluation has to take into account the variety and diversity of devices and techniques, as well as the effects of operator dependability. Endovascular techniques are increasingly recognised as valid alternative management options for a variety of conditions, and it is anticipated that the current trend towards minimally invasive techniques will continue in the future, with moves towards increasingly complex endovascular techniques and hybrid interventions.

A review of most relevant complications of transcatheter aortic valve implantation

Transcatheter aortic valve implantation (TAVI) has emerged for treating aortic stenosis in patients who are poor candidates for surgical aortic valve replacement. Currently, the balloon-expandable Edwards Sapien valve—which is usually implanted via a transfemoral or transapical approach—and the self-expanding CoreValve ReValving system—which is designed for retrograde application—are the most widely implanted valves worldwide. Although a promising approach for high-risk patients, the indication may be expanded to intermediate- and eventually low-risk patients in the future; however, doing so will require a better understanding of potential complications, risk factors for these complications, and strategies to individualize each patient to a different access route and a specific valve. This paper reviews the most relevant complications that may occur in patients who undergo catheter-based aortic valve implantation.

Review of Journal of Cardiovascular Magnetic Resonance 2011

There were 83 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2011, which is an 11% increase in the number of articles since 2010. The quality of the submissions continues to increase. The editors had been delighted with the 2010 JCMR Impact Factor of 4.33, although this fell modestly to 3.72 for 2011. The impact factor undergoes natural variation according to citation rates of papers in the 2 years following publication, and is significantly influenced by highly cited papers such as official reports. However, we remain very pleased with the progress of the journal's impact over the last 5 years. Our acceptance rate is approximately 25%, and has been falling as the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. For this reason, the Editors feel it is useful to summarize the papers for the readership into broad areas of interest or theme, which we feel would be useful, so that areas of interest from the previous year can be reviewed in a single article in relation to each other and other recent JCMR articles. The papers are presented in broad themes and set in context with related literature and previously published JCMR papers to guide continuity of thought in the journal. We hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality manuscripts to JCMR for publication.

Multimodality imaging throughout transcatheter aortic valve implantation

Transcatheter aortic valve implantation (TAVI) is a novel, less-invasive technique used to treat selected patients with severe aortic valve stenosis with a high surgical risk. Noninvasive imaging before, during and after the procedure is of the utmost importance in this minimally invasive procedure. Screening of the patient and sizing of the aortic root by echocardiography and multislice computed tomography is of great importance to ensure success of the TAVI procedure. Echocardiography and fluoroscopy are essential during the procedure. During follow-up of the patients, echocardiography is important to evaluate the prosthesis function, durability and integrity. Additionally, multislice computed tomography and MRI might be helpful in the follow-up of selected cases. This article outlines the evolving role of multimodality imaging throughout TAVI in patients with severe aortic valve stenosis. It describes, in a stepwise approach, how multimodality imaging by echocardiography, angiography, multislice computed tomography and MRI enhances the TAVI procedure.

Towards real-time cardiovascular magnetic resonance guided transarterial CoreValve implantation: in vivo evaluation in swine

BACKGROUND

Real-time cardiovascular magnetic resonance (rtCMR) is considered attractive for guiding TAVI. Owing to an unlimited scan plane orientation and an unsurpassed soft-tissue contrast with simultaneous device visualization, rtCMR is presumed to allow safe device navigation and to offer optimal orientation for precise axial positioning. We sought to evaluate the preclinical feasibility of rtCMR-guided transarterial aortic valve implatation (TAVI) using the nitinol-based Medtronic CoreValve bioprosthesis.

METHODS

rtCMR-guided transfemoral (n = 2) and transsubclavian (n = 6) TAVI was performed in 8 swine using the original CoreValve prosthesis and a modified, CMR-compatible delivery catheter without ferromagnetic components.

RESULTS

rtCMR using TrueFISP sequences provided reliable imaging guidance during TAVI, which was successful in 6 swine. One transfemoral attempt failed due to unsuccessful aortic arch passage and one pericardial tamponade with subsequent death occurred as a result of ventricular perforation by the device tip due to an operating error, this complication being detected without delay by rtCMR. rtCMR allowed for a detailed, simultaneous visualization of the delivery system with the mounted stent-valve and the surrounding anatomy, resulting in improved visualization during navigation through the vasculature, passage of the aortic valve, and during placement and deployment of the stent-valve. Post-interventional success could be confirmed using ECG-triggered time-resolved cine-TrueFISP and flow-sensitive phase-contrast sequences. Intended valve position was confirmed by ex-vivo histology.

CONCLUSIONS

Our study shows that rtCMR-guided TAVI using the commercial CoreValve prosthesis in conjunction with a modified delivery system is feasible in swine, allowing improved procedural guidance including immediate detection of complications and direct functional assessment with reduction of radiation and omission of contrast media.

Transcatheter aortic valve replacement: the changing paradigm of aortic stenosis treatment

Aortic stenosis is the most common cause for valvular surgery in the USA. For nearly 50 years, surgical aortic valve replacement has been the standard of care for symptomatic patients; unfortunately, a significant number of patients are not referred to surgery owing to advanced comorbidities and age. Transcatheter aortic valve replacement has emerged as an effective therapy for patients at high risk for surgery. Through device innovations and accumulated experience, the safety and efficacy of the procedure has improved since its inception. Transcatheter valve replacement has been found superior to medical therapy in inoperable patients with aortic stenosis, yet many questions remain as to which patients are appropriate for this exciting and novel therapy.

Review of journal of cardiovascular magnetic resonance 2010

There were 75 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2010, which is a 34% increase in the number of articles since 2009. The quality of the submissions continues to increase, and the editors were delighted with the recent announcement of the JCMR Impact Factor of 4.33 which showed a 90% increase since last year. Our acceptance rate is approximately 30%, but has been falling as the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. Last year for the first time, the Editors summarized the papers for the readership into broad areas of interest or theme, which we felt would be useful to practitioners of cardiovascular magnetic resonance (CMR) so that you could review areas of interest from the previous year in a single article in relation to each other and other recent JCMR articles 1. This experiment proved very popular with a very high rate of downloading, and therefore we intend to continue this review annually. The papers are presented in themes and comparison is drawn with previously published JCMR papers to identify the continuity of thought and publication in the journal. We hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality manuscripts to JCMR for publication.