Midterm results of transapical aortic valve replacement via real-time magnetic resonance imaging guidance

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.

Finite Element Analysis of a Novel Aortic Valve Stent

Worldwide, one of the leading causes of death for patients with cardiovascular disease is aortic valve failure or insufficiency as a result of calcification and cardiovascular disease. The surgical treatment consists of repair or total replacement of the aortic valve. Artificial aortic valve implantation via a percutaneous or endovascular procedure is the minimally invasive alternative to open chest surgery, and the only option for high-risk or older patients. Due to the complex anatomical location between the left ventricle and the aorta, there are still engineering design optimization challenges which influence the long-term durability of the valve. In this study we developed a computer model and performed a numerical analysis of an original self-expanding stent for transcatheter aortic valve in order to optimize its design and materials. The study demonstrates the current valve design could be a good alternative to the existing commercially available valve devices.

Augmented Reality System for Ultrasound Guidance of Transcatheter Aortic Valve Implantation

OBJECTIVE

Transcatheter aortic valve implantation (TAVI) relies on fluoroscopy and nephrotoxic contrast medium for valve deployment. We propose an alternative guidance system using augmented reality (AR) and transesophageal echocardiography (TEE) to guide TAVI deployment. The goals of this study were to determine how consistently the aortic valve annulus is defined from TEE using different aortic valve landmarks and to compare AR guidance with fluoroscopic guidance of TAVI deployment in an aortic root model.

METHODS

Magnetic tracking sensors were integrated into the TAVI catheter and TEE probe, allowing these tools to be displayed in an AR environment. Variability in identifying aortic valve commissures and cuspal nadirs was assessed using TEE aortic root images. To compare AR guidance of TAVI deployment with fluoroscopic guidance, a TAVI stent was deployed 10 times in the aortic root model using each of the two guidance systems.

RESULTS

Commissures and nadirs were both investigated as features for defining the valve annulus in the AR guidance system. The commissures were identified more consistently than the nadirs, with intraobserver variability of 2.2 and 3.8 mm, respectively, and interobserver variability of 3.3 and 4.7 mm, respectively. The precision of TAVI deployment using fluoroscopic guidance was 3.4 mm, whereas the precision of AR guidance was 2.9 mm, and its overall accuracy was 3.4 mm. This indicates that both have similar performance.

CONCLUSIONS

Aortic valve commissures can be identified more reliably than cuspal nadirs from TEE. The AR guidance system achieved similar deployment accuracy to that of fluoroscopy while eliminating the use and consequences of nephrotoxic contrast and radiation.

Robotic-assisted real-time MRI-guided TAVR: from system deployment to in vivo experiment in swine model

PURPOSE

Real-time magnetic resonance imaging (rtMRI) guidance provides significant advantages during transcatheter aortic valve replacement (TAVR) as it provides superior real-time visualization and accurate device delivery tracking. However, performing a TAVR within an MRI scanner remains difficult due to a constrained procedural environment. To address these concerns, a magnetic resonance (MR)-compatible robotic system to assist in TAVR deployments was developed. This study evaluates the technical design and interface considerations of an MR-compatible robotic-assisted TAVR system with the purpose of demonstrating that such a system can be developed and executed safely and precisely in a preclinical model.

METHODS

An MR-compatible robotic surgical assistant system was built for TAVR deployment. This system integrates a 5-degrees of freedom (DoF) robotic arm with a 3-DoF robotic valve delivery module. A user interface system was designed for procedural planning and real-time intraoperative manipulation of the robot. The robotic device was constructed of plastic materials, pneumatic actuators, and fiber-optical encoders.

RESULTS

The mechanical profile and MR compatibility of the robotic system were evaluated. The system-level error based on a phantom model was 1.14 ± 0.33 mm. A self-expanding prosthesis was successfully deployed in eight Yorkshire swine under rtMRI guidance. Post-deployment imaging and necropsy confirmed placement of the stent within 3 mm of the aortic valve annulus.

CONCLUSIONS

These phantom and in vivo studies demonstrate the feasibility and advantages of robotic-assisted TAVR under rtMRI guidance. This robotic system increases the precision of valve deployments, diminishes environmental constraints, and improves the overall success of TAVR.

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.

Computer Vision Techniques for Transcatheter Intervention

Minimally invasive transcatheter technologies have demonstrated substantial promise for the diagnosis and the treatment of cardiovascular diseases. For example, transcatheter aortic valve implantation is an alternative to aortic valve replacement for the treatment of severe aortic stenosis, and transcatheter atrial fibrillation ablation is widely used for the treatment and the cure of atrial fibrillation. In addition, catheter-based intravascular ultrasound and optical coherence tomography imaging of coronary arteries provides important information about the coronary lumen, wall, and plaque characteristics. Qualitative and quantitative analysis of these cross-sectional image data will be beneficial to the evaluation and the treatment of coronary artery diseases such as atherosclerosis. In all the phases (preoperative, intraoperative, and postoperative) during the transcatheter intervention procedure, computer vision techniques (e.g., image segmentation and motion tracking) have been largely applied in the field to accomplish tasks like annulus measurement, valve selection, catheter placement control, and vessel centerline extraction. This provides beneficial guidance for the clinicians in surgical planning, disease diagnosis, and treatment assessment. In this paper, we present a systematical review on these state-of-the-art methods. We aim to give a comprehensive overview for researchers in the area of computer vision on the subject of transcatheter intervention. Research in medical computing is multi-disciplinary due to its nature, and hence, it is important to understand the application domain, clinical background, and imaging modality, so that methods and quantitative measurements derived from analyzing the imaging data are appropriate and meaningful. We thus provide an overview on the background information of the transcatheter intervention procedures, as well as a review of the computer vision techniques and methodologies applied in this area.

Phantom study of an ultrasound guidance system for transcatheter aortic valve implantation

A guidance system using transesophageal echocardiography and magnetic tracking is presented which avoids the use of nephrotoxic contrast agents and ionizing radiation required for traditional fluoroscopically guided procedures. The aortic valve is identified in tracked biplane transesophageal echocardiography and used to guide stent deployment in a mixed reality environment. Additionally, a transapical delivery tool with intracardiac echocardiography capable of monitoring stent deployment was created. This system resulted in a deployment depth error of 3.4mm in a phantom. This was further improved to 2.3mm with the custom-made delivery tool. In comparison, the variability in deployment depth for traditional fluoroscopic guidance was estimated at 3.4mm.

Real-time magnetic resonance-guided aortic valve replacement using Engager valve

PURPOSE

New-generation stented bioprostheses coupled with better imaging modalities are expanding the clinical utility of transcatheter aortic valve replacement (TAVR). This study aimed at evaluating the feasibility of real-time cardiovascular magnetic resonance (rtCMR) -guided TAVR using the Medtronic Engager aortic valve system in a preclinical model.

DESCRIPTION

The Engager delivery device was slightly modified to make it CMR-compatible. Ten Yucatan swine underwent rtCMR-guided transapical TAVR. Postplacement phase-contrast and first-pass perfusion CMR sequences were used to evaluate for aortic regurgitation and myocardial perfusion, respectively.

EVALUATION

Real-time CMR provided excellent visualization of cardiac anatomy during TAVR. Nine of 10 animals had proper valve placement in the aortic annulus as determined by CMR and confirmed by necropsy inspection. Postplacement phase-contrast scans confirmed no intravalvular or paravalvular leaks. Perfusion scans demonstrated sufficient coronary flow. Roentgenographs confirmed proper placement of the prostheses.

CONCLUSIONS

The Engager valve can be implanted transapically under rtCMR guidance with a modified, CMR-compatible delivery device in a preclinical model. Cardiovascular magnetic resonance allowed for accurate preplacement evaluation, real-time guidance, and postplacement functional assessment.

Transapical sutureless aortic valve implantation under magnetic resonance imaging guidance: Acute and short-term results

OBJECTIVES

Despite the increasing success and applicability of transcatheter aortic valve replacement, 2 critical issues remain: the durability of the valves, and the ideal imaging to aid implantation. This study was designed to investigate the transapical implantation of a device of known durability using real-time magnetic resonance imaging (MRI) guidance.

METHODS

A sutureless aortic valve was used that employs a self-expanding nitinol stent and is amenable to transapical delivery. MRI (1.5-T) was used to identify the anatomic landmarks in 60-kg Yucatan swine. Prostheses were loaded into an MRI-compatible delivery device with an active guidewire to enhance visualization. A series of acute feasibility experiments were conducted (n = 10). Additional animals (n = 6) were allowed to survive and had follow-up MRI scans and echocardiography at 90 days postoperatively. Postmortem gross examination was performed.

RESULTS

The valve was MRI compatible and created no significant MRI artifacts. The 3 commissural struts were visible on short-axis view; therefore, coronary ostia obstruction was easily avoided. The average implantation time was 65 seconds. Final results demonstrated stability of the implants with preservation of myocardial perfusion and function over 90 days: the ejection fraction was 48% ± 15%; the peak gradient was 17.3 ± 11.3 mm Hg; the mean gradient was 9.8 ± 7.2 mm Hg. Mild aortic regurgitation was seen in 4 cases, trace in 1 case, and a severe central jet in 1 case. Prosthesis positioning was evaluated during gross examination.

CONCLUSIONS

We demonstrated that a sutureless aortic valve can be safely and expeditiously implanted through a transapical approach under real-time MRI guidance. Postimplantation results showed a well-functioning prosthesis, with minimal regurgitation, and stability over time.

Intra-operative 2-D ultrasound and dynamic 3-D aortic model registration for magnetic navigation of transcatheter aortic valve implantation

We propose a navigation system for transcatheter aortic valve implantation that employs a magnetic tracking system (MTS) along with a dynamic aortic model and intra-operative ultrasound (US) images. This work is motivated by the desire of our cardiology and cardiac surgical colleagues to minimize or eliminate the use of radiation in the interventional suite or operating room. The dynamic 3-D aortic model is constructed from a preoperative 4-D computed tomography dataset that is animated in synchrony with the real time electrocardiograph input of patient, and then preoperative planning is performed to determine the target position of the aortic valve prosthesis. The contours of the aortic root are extracted automatically from short axis US images in real-time for registering the 2-D intra-operative US image to the preoperative dynamic aortic model. The augmented MTS guides the interventionist during positioning and deployment of the aortic valve prosthesis to the target. The results of the aortic root segmentation algorithm demonstrate an error of 0.92±0.85 mm with a computational time of 36.13±6.26 ms. The navigation approach was validated in porcine studies, yielding fiducial localization errors, target registration errors, deployment distance, and tilting errors of 3.02±0.39 mm, 3.31±1.55 mm, 3.23±0.94 mm, and 5.85±3.06(°) , respectively.

An augmented magnetic navigation system for Transcatheter Aortic Valve Implantation

This research proposes an augmented magnetic navigation system for Transcatheter Aortic Valve Implantation (TAVI) employing a magnetic tracking system (MTS) combined with a dynamic aortic model and intra-operative ultrasound (US) images. The dynamic 3D aortic model is constructed based on the preoperative 4D computed tomography (CT), which is animated according to the real time electrocardiograph (ECG) input of patient. And a preoperative planning is performed to determine the target position of the aortic valve prosthesis. The temporal alignment is performed to synchronize the ECG signals, intra-operative US image and tracking information. Afterwards, with the assistance of synchronized ECG signals, the contour of aortic root automatic extracted from short axis US image is registered to the dynamic aortic model by a feature based registration intra-operatively. Then the augmented MTS guides the interventionist to confidently position and deploy the aortic valve prosthesis to target. The system was validated by animal studies on three porcine subjects, the deployment and tilting errors of which are 3.17 ± 0.91 mm and 7.40 ± 2.89° respectively.

A pilot study on magnetic navigation for transcatheter aortic valve implantation using dynamic aortic model and US image guidance

PURPOSE

In this paper, we propose a pilot study for transcatheter aortic valve implantation guided by an augmented magnetic tracking system (MTS) with a dynamic aortic model and intra-operative ultrasound (US) images.

METHODS

The dynamic 3D aortic model is constructed from the preoperative 4D computed tomography, which is animated according to the real-time electrocardiograph (ECG) input of patient. Before the procedure, the US probe calibration is performed to map the US image coordinate to the tracked device coordinate. A temporal alignment is performed to synchronize the ECG signals, the intra-operative US image and the tracking information. Thereafter, with the assistance of synchronized ECG signals, the spatial registration is performed by using a feature-based registration. Then the augmented MTS guides the surgeon to confidently position and deploy the transcatheter aortic valve prosthesis to the target.

RESULTS

The approach was validated by US probe calibration evaluation and animal study. The US calibration accuracy achieved [Formula: see text], whereas in the animal study on three porcine subjects, fiducial, target, deployment distance and tilting errors reached [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], respectively.

CONCLUSION

Our pilot study has revealed that the proposed approach is feasible and accurate for delivery and deployment of transcatheter aortic valve prosthesis.

Minimally invasive cardiac surgery: transapical aortic valve replacement

Minimally invasive cardiac surgery is less traumatic and therefore leads to quicker recovery. With the assistance of engineering technologies on devices, imaging, and robotics, in conjunction with surgical technique, minimally invasive cardiac surgery will improve clinical outcomes and expand the cohort of patients that can be treated. We used transapical aortic valve implantation as an example to demonstrate that minimally invasive cardiac surgery can be implemented with the integration of surgical techniques and engineering technologies. Feasibility studies and long-term evaluation results prove that transapical aortic valve implantation under MRI guidance is feasible and practical. We are investigating an MRI compatible robotic surgical system to further assist the surgeon to precisely deliver aortic valve prostheses via a transapical approach. Ex vivo experimentation results indicate that a robotic system can also be employed in in vivo models.

Self-Expanding Stent and Delivery System for Aortic Valve Replacement

Currently, aortic valve replacement procedures require a sternotomy and use of cardiopulmonary bypass (CPB) to arrest the heart and provide a bloodless field in which to operate. A less invasive alternative to open heart surgery is transapical or transcatheter aortic valve replacement (TAVR), already emerging as a feasible treatment for patients with high surgical risk. The bioprosthetic valves are delivered via catheters using transarterial or transapical approaches and are implanted within diseased aortic valves. This paper reports the development of a new self-expanding stent for minimally invasive aortic valve replacement and its delivery device for the transapical approach under real-time magnetic resonance imaging (MRI) guidance. Made of nitinol, the new stent is designed to implant and embed a commercially available bioprosthetic aortic valve in aortic root. An MRI passive marker was affixed onto the stent and an MRI active marker to the delivery device. These capabilities were tested in ex vivo and in vivo experiments. Radial resistive force, chronic outward force, and the integrity of bioprosthesis on stent were measured through custom design dedicated test equipment. In vivo experimental evaluation was done using a porcine large animal model. Both ex vivo and in vivo experiment results indicate that the self-expanding stent provides adequate reinforcement of the bioprosthetic aortic valve and it is easier to implant the valve in the correct position. The orientation and positioning of the implanted valve is more precise and predictable with the help of the passive marker on stent and the active marker on delivery device. The new self-expanding nitinol stent was designed to exert a constant radial force and, therefore, a better fixation of the prosthesis in the aorta, which would result in better preservation of long-term heart function. The passive marker affixed on the stent and active marker embedded in the delivery devices helps to achieve precise orientation and positioning of the stent under MRI guidance. The design allows the stent to be retracted in the delivery device with a snaring catheter if necessary. Histopathology reports reveal that the stent is biocompatible and fully functional. All the stented bioprosthesis appeared to be properly seated in the aortic root.

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.

Multimodality imaging in interventional cardiology

'Multimodality' imaging--the side-by-side interpretation of data obtained from various noninvasive imaging techniques, such as echocardiography, radionuclide techniques, multidetector CT (MDCT), and MRI--allows anatomical, morphological, and functional data to be combined, increases diagnostic accuracy, and improves the efficacy of cardiovascular interventions and clinical outcomes. During the past decade, advances in software and hardware have allowed co-registration of various imaging modalities, resulting in cardiac 'hybrid' or 'fusion' imaging. In this Review, we discuss the roles of both multimodality and hybrid imaging in three broad areas of cardiology--coronary artery disease (CAD), heart failure, and valvular heart disease. In the evaluation of CAD, integration of either single-photon emission computed tomography (SPECT) or PET with CT coronary angiography provides both morphological and functional data in a single procedure. Accordingly, the functional consequences (myocardial hypoperfusion on SPECT or PET) of anatomical pathology (coronary anatomy on MDCT or MRI) can be assessed. Co-registration of PET and MRI data sets to provide cellular and molecular information on plaque composition and stability is now possible. Furthermore, novel imaging modalities have been implemented to guide electrophysiological and transcatheter-based procedures, such as cardiac resynchronization therapy (an established treatment for patients with heart failure), and transcatheter valve repair or replacement procedures.

Magnetic resonance imaging in patients with cardiac pacemakers: era of "MR Conditional" designs

Advances in cardiac device technology have led to the first generation of magnetic resonance imaging (MRI) conditional devices, providing more diagnostic imaging options for patients with these devices, but also new controversies. Prior studies of pacemakers in patients undergoing MRI procedures have provided groundwork for design improvements. Factors related to magnetic field interactions and transfer of electromagnetic energy led to specific design changes. Ferromagnetic content was minimized. Reed switches were modified. Leads were redesigned to reduce induced currents/heating. Circuitry filters and shielding were implemented to impede or limit the transfer of certain unwanted electromagnetic effects. Prospective multicenter clinical trials to assess the safety and efficacy of the first generation of MR conditional cardiac pacemakers demonstrated no significant alterations in pacing parameters compared to controls. There were no reported complications through the one month visit including no arrhythmias, electrical reset, inhibition of generator output, or adverse sensations. The safe implementation of these new technologies requires an understanding of the well-defined patient and MR system conditions. Although scanning a patient with an MR conditional device following the strictly defined patient and MR system conditions appears straightforward, issues related to patients with pre-existing devices remain complex. Until MR conditional devices are the routine platform for all of these devices, there will still be challenging decisions regarding imaging patients with pre-existing devices where MRI is required to diagnose and manage a potentially life threatening or serious scenario. A range of other devices including ICDs, biventricular devices, and implantable physiologic monitors as well as guidance of medical procedures using MRI technology will require further biomedical device design changes and testing. The development and implementation of cardiac MR conditional devices will continue to require the expertise and collaboration of multiple disciplines and will need to prove safety, effectiveness, and cost effectiveness in patient care.

MR-based real time path planning for cardiac operations with transapical access

Minimally invasive surgeries (MIS) have been perpetually evolving due to their potential high impact on improving patient management and overall cost effectiveness. Currently, MIS are further strengthened by the incorporation of magnetic resonance imaging (MRI) for amended visualization and high precision. Motivated by the fact that real-time MRI is emerging as a feasible modality especially for guiding interventions and surgeries in the beating heart; in this paper we introduce a real-time path planning algorithm for intracardiac procedures. Our approach creates a volumetric safety zone inside a beating heart and updates it on-the-fly using real-time MRI during the deployment of a robotic device. In order to prove the concept and assess the feasibility of the introduced method, a realistic operational scenario of transapical aortic valve replacement in a beating heart is chosen as the virtual case study.

Risk of acute kidney injury after minimally invasive transapical aortic valve implantation in 270 patients

OBJECTIVE

Contrast agent is a potential risk factor for acute kidney injury (AKI). Little is known about the incidence of contrast-induced nephropathy (CIN) after trans-apical aortic valve implantation (TA-AVI) and on the impact of contrast exposure during preoperative computed tomography (CT) scan and cardiac catheterization.

METHODS

A total of 270 consecutive high-risk patients received TA-AVI for symptomatic aortic valve stenosis during a 3-year period. Different preoperative, peri-procedural, and postoperative variables were analyzed by uni- and multivariate logistic regression concerning incidence of early (<7 days) AKI and need for renal replacement therapy (RRT). Nine patients on chronic preoperative dialysis were excluded.

RESULTS

Mean age was 82 ± 5.8 years, 71% were female. LogEuroSCORE (European System for Cardiac Operative Risk Evaluation) and STS Score were 31.4 ± 15.6% and 12.1 ± 7.4%, respectively. Preoperative estimated glomerular filtration rate (eGFR) <60 ml min(-1) was present in 35.2%. CT scan and cardiac catheterization within 7 days before TA-AVI were performed in 43.7% and 20.3% of the patients and were associated with a mean contrast-agent exposition of 110 ± 21 ml for CT scans and 91 ± 65 ml for cardiac catheterization. Regarding the postoperative renal outcome, an improved or at least stable eGFR was seen in more than 50% of the patients. Intra-operative contrast-agent application was 99 ± 64 ml and correlated significantly to the development of postoperative AKI and need for RRT (p=0.013 and p=0.003). Postoperative RRT was required in 15.7%. Chronic renal insufficiency (odds ratio (OR)=6.8, p=0.025) and number of blood transfusions (OR=8.8, p=0.009) were independent risk factors for RRT. Postoperative AKI occurred in 16.1% and intra-operative contrast-agent burden >99 ml (OR=2.3, p=0.038), new thrombocytopenia (OR=4.4, p=0.005) and pathological leucocyte count (OR=2.8, p=0.009) were independent risk factors for this event. Early (within 1-7 days before TA-AVI) preoperative CT and cardiac catheterization did not significantly increase incidence of RRT or AKI. Short-term and long-term survival was explicitly lower in the AKI and in the RRT groups (p<0.001 each).

CONCLUSIONS

GFR improves after TA-AVI. Postoperative AKI and RRT depend on the amount of intra-operative contrast agent. These results strongly support the need for intra-operative tools to reduce contrast-agent exposition during TA-AVI.

Transapical aortic valve replacement under real-time magnetic resonance imaging guidance: experimental results with balloon-expandable and self-expanding stents

OBJECTIVE

Aortic valves have been implanted on self-expanding (SE) and balloon-expandable (BE) stents minimally invasively. We have demonstrated the advantages of transapical aortic valve implantation (tAVI) under real-time magnetic resonance imaging (rtMRI) guidance. Whether there are different advantages to SE or BE stents is unknown. We report rtMRI-guided tAVI in a porcine model using both SE and BE stents, and compare the differences between the stents.

METHODS

A total of 22 Yucatan pigs (45-57 kg) underwent tAVI. Commercially available stentless bioprostheses (21-25 mm) were mounted on either BE platinum-iridium stents or SE-nitinol stents. rtMRI guidance was employed as the intraoperative imaging. Markers on both types of stents were used to enhance visualization in rtMRI. Pigs were allowed to survive and had follow-up MRI scans and echocardiography at 1, 3, and 6 months postoperatively.

RESULTS

rtMRI provided excellent visualization of the aortic valve implantation mounted on both stent types. The implantation times were shorter with the SE stents (60 ± 14s) than with the BE stents (74 ± 18s), (p=0.027). The total procedure time was 31 and 37 min, respectively (p=0.12). It was considerably easier to manipulate the SE stent during deployment, without hemodynamic compromise. This was not always the case with the BE stent, and its placement occasionally resulted in coronary obstruction and death. Long-term results demonstrated stability of the implants with preservation of myocardial perfusion and function over time for both stents.

CONCLUSIONS

SE stents were easier to position and deploy, thus leading to fewer complications during tAVI. Future optimization of SE stent design should improve clinical results.