Closed-chest transthoracic magnetic resonance imaging-guided ventricular septal defect closure in swine

MRI-guided endovascular intervention: current methods and future potential

INTRODUCTION

Image-guided endovascular interventions, performed using the insertion and navigation of catheters through the vasculature, have been increasing in number over the years, as minimally invasive procedures continue to replace invasive surgical procedures. Such endovascular interventions are almost exclusively performed under x-ray fluoroscopy, which has the best spatial and temporal resolution of all clinical imaging modalities. Magnetic resonance imaging (MRI) offers unique advantages and could be an attractive alternative to conventional x-ray guidance, but also brings with it distinctive challenges.

AREAS COVERED

In this review, the benefits and limitations of MRI-guided endovascular interventions are addressed, systems and devices for guiding such interventions are summarized, and clinical applications are discussed.

EXPERT OPINION

MRI-guided endovascular interventions are still relatively new to the interventional radiology field, since significant technical hurdles remain to justify significant costs and demonstrate safety, design, and robustness. Clinical applications of MRI-guided interventions are promising but their full potential may not be realized until proper tools designed to function in the MRI environment are available. Translational research and further preclinical studies are needed before MRI-guided interventions will be practical in a clinical interventional setting.

MRI-Guided Cardiac Catheterization in Congenital Heart Disease: How to Get Started

PURPOSE OF REVIEW

Cardiac magnetic resonance imaging provides radiation-free, 3-dimensional soft tissue visualization with adjunct hemodynamic data, making it a promising candidate for image-guided transcatheter interventions. This review focuses on the benefits and background of real-time magnetic resonance imaging (MRI)-guided cardiac catheterization, guidance on starting a clinical program, and recent research developments.

RECENT FINDINGS

Interventional cardiac magnetic resonance (iCMR) has an established track record with the first entirely MRI-guided cardiac catheterization for congenital heart disease reported nearly 20 years ago. Since then, many centers have embarked upon clinical iCMR programs primarily performing diagnostic MRI-guided cardiac catheterization. There have also been limited reports of successful real-time MRI-guided transcatheter interventions. Growing experience in performing cardiac catheterization in the magnetic resonance environment has facilitated practical workflows appropriate for efficiency-focused cardiac catheterization laboratories. Most exciting developments in imaging technology, MRI-compatible equipment and MRI-guided novel transcatheter interventions have been limited to preclinical research. Many of these research developments are ready for clinical translation. With increasing iCMR clinical experience and translation of preclinical research innovations, the time to make the leap to radiation-free procedures is now.

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.

MRI Catheterization: Ready for Broad Adoption

In recent years, interventional cardiac magnetic resonance imaging (iCMR) has evolved from attractive theory to clinical routine at several centers. Real-time cardiac magnetic resonance imaging (CMR fluoroscopy) adds value by combining soft-tissue visualization, concurrent hemodynamic measurement, and freedom from radiation. Clinical iCMR applications are expanding because of advances in catheter devices and imaging. In the near future, iCMR promises novel procedures otherwise unsafe under standalone X-Ray guidance.

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.

Interventional CMR: Clinical applications and future directions

Interventional cardiovascular magnetic resonance (iCMR) promises to enable radiation-free catheterization procedures and to enhance contemporary image guidance for structural heart and electrophysiological interventions. However, clinical translation of exciting pre-clinical interventions has been limited by availability of devices that are safe to use in the magnetic resonance (MR) environment. We discuss challenges and solutions for clinical translation, including MR-conditional and MR-safe device design, and how to configure an interventional suite. We review the recent advances that have already enabled diagnostic MR right heart catheterization and simple electrophysiologic ablation to be performed in humans and explore future clinical applications.

Magnetic Resonance Imaging-Guided Cardiac Interventions

Performing intraoperative cardiovascular procedures inside an MR imaging scanner can potentially provide substantial advantage in clinical outcomes by reducing the risk and increasing the success rate relative to the way such procedures are performed today, in which the primary surgical guidance is provided by X-ray fluoroscopy, by electromagnetically tracked intraoperative devices, and by ultrasound. Both noninvasive and invasive cardiologists are becoming increasingly familiar with the capabilities of MR imaging for providing anatomic and physiologic information that is unequaled by other modalities. As a result, researchers began performing animal (preclinical) interventions in the cardiovascular system in the early 1990s.

Results of comparing transthoracic device closure and surgical repair with right infra-axillary thoracotomy for perimembranous ventricular septal defects

OBJECTIVES

Transthoracic device closure (TTDC) and surgical repair with right infra-axillary thoracotomy (SRRIAT) are two main alternative minimally invasive approaches for restrictive perimembranous ventricular septal defect (VSD); however, few studies have compared them with each other in terms of effectiveness and cost.

METHODS

Patients with perimembranous VSD undergoing TTDC or SRRIAT from January 2012 to July 2013 were reviewed in a comparative investigation between the two procedures.

RESULTS

Success from the procedures was achieved in 30 TTDC (30/33, 91%) and 96 SRRIAT patients (100%). Operation duration in the TTDC group was significantly shorter than that of the SRRIAT group (115.8 ± 43.8 vs 175.6 ± 41.3 min, P < 0.01). The total perioperative drainage, use of red blood cells, mechanical ventilation time, stay in the intensive care unit and hospital stay for the TTDC group were significantly less than those in the SRRIAT group. No deaths or complete atrioventricular block occurred in either group. One SRRIAT patient accepted a second surgery for residual shunt. TTDC costs slightly more than SRRIAT (40270.6 ± 2741.3 renmingbi [RMB] vs 32964.5 ± 8221.6 RMB, P < 0.01).

CONCLUSIONS

Both TTDC and SRRIAT showed excellent outcomes and cosmetic appearance for suitable VSD candidates. Although its costs were higher, TTDC had the advantages over SRRIAT of a short operation duration and intensive care unit stay and fewer days in the hospital.

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.

MRI catheterization in cardiopulmonary disease

Diagnosis and prognostication in patients with complex cardiopulmonary disease can be a clinical challenge. A new procedure, MRI catheterization, involves invasive right-sided heart catheterization performed inside the MRI scanner using MRI instead of traditional radiographic fluoroscopic guidance. MRI catheterization combines simultaneous invasive hemodynamic and MRI functional assessment in a single radiation-free procedure. By combining both modalities, the many individual limitations of invasive catheterization and noninvasive imaging can be overcome, and additional clinical questions can be addressed. Today, MRI catheterization is a clinical reality in specialist centers in the United States and Europe. Advances in medical device design for the MRI environment will enable not only diagnostic but also interventional MRI procedures to be performed within the next few years.

Integration of MDCT and fluoroscopy using C-arm computed tomography to guide structural cardiac interventions in the cardiac catheterization laboratory

OBJECTIVES

Our study was aimed at evaluation of three-dimensional (3D)-CT overlay onto the catheterization laboratory fluoroscopy to guide structural cardiac interventions.

BACKGROUND

Current imaging for structural cardiac interventions (fluoroscopy, echocardiography) may not provide adequate guidance. The ability to integrate intracardiac 3D-CT imaging data in the cardiac catheterization laboratory may be beneficial, but has not yet been systematically studied.

METHODS

Thirty-two patients undergoing various catheterization laboratory procedures (transcatheter aortic valve replacement, paravalvular leak (PVL) closure, pulmonary vein (PV) stenting, etc.) were prospectively enrolled. The goal was to evaluate the feasibility and benefit of overlaying pre-procedural CT data onto the real-time procedural fluoroscopic image using the Syngo DynaCT Cardiac C-arm CT system (Siemens Healthcare, Forcheim, Germany).

RESULTS

The overlay was considered most helpful for patients undergoing PVL closure and PV stenting. The additional radiation exposure of the C-arm CT was a fraction of the total procedural dose (3.5% of total skin dose and 9.1% of total DAP).

CONCLUSIONS

Overlay of 3D-CT data onto the real-time procedural fluoroscopy in the cardiac catheterization laboratory is feasible to aide procedural guidance. The overlay was considered most helpful for patients undergoing PVL closure and PV stenting. The additional radiation dose is a small fraction of the total dose. © 2014 Wiley Periodicals, Inc.

Real-time cardiovascular magnetic resonance subxiphoid pericardial access and pericardiocentesis using off-the-shelf devices in swine

BACKGROUND

Needle access or drainage of pericardial effusion, especially when small, entails risk of bystander tissue injury or operator uncertainty about proposed trajectories. Cardiovascular magnetic resonance (CMR) might allow enhanced imaging guidance.

METHODS AND RESULTS

We used real-time CMR to guide subxiphoid pericardial access in naïve swine using commercial 18G titanium puncture needles, which were exchanged for pericardial catheters. To test the value of CMR needle pericardiocentesis, we also created intentional pericardial effusions of a range of volumes, via a separate transvenous-transatrial catheter. We performed these procedures in 12 animals.

CONCLUSIONS

CMR guided pericardiocentesis is attractive because the large field of view and soft tissue imaging depict global anatomic context in arbitrary planes, and allow the operator to plan trajectories that limit inadvertent bystander tissue injury. More important, CMR provides continuous visualization of the needle and target throughout the procedure. Using even passive needle devices, CMR enabled rapid pericardial needle access and drainage. We believe this experience supports clinical testing of real-time CMR guided needle access or drainage of the pericardial space. We suspect this would be especially helpful in "difficult" pericardial access, for example, in distorted thoracic anatomy or loculated effusion.

Can we talk? Reflections on effective communication between imager and interventionalist in congenital heart disease

The rapid proliferation of catheter-mediated treatments for congenital heart defects has brought with it a critical need for cooperation and communication among the numerous physicians supporting these new and complex procedures. New interdependencies between physicians in specialties including cardiac imaging, interventional cardiology, pediatric cardiology, anesthesia, cardiothoracic surgery, and radiology have become apparent, as centers have strived to develop the best systems to foster success. Best practices for congenital heart disease interventions mandate confident and timely input from an individual with excellent adjunctive imaging skills and a thorough understanding of the devices and procedures being used. The imager and interventionalist must share an understanding of what each offers for the procedure, use a common terminology and spatial orientation system, and convey concise and accurate information about what is needed, what is seen, and what cannot be seen. The goal of this article is to review how the cardiovascular imaging specialists and interventionalists can work together effectively to plan and execute catheter interventions for congenital heart disease.

Transthoracic delivery of large devices into the left ventricle through the right ventricle and interventricular septum: preclinical feasibility

BACKGROUND

We aim to deliver large appliances into the left ventricle through the right ventricle and across the interventricular septum. This transthoracic access route exploits immediate recoil of the septum, and lower transmyocardial pressure gradient across the right versus left ventricular free wall. The route may enhance safety and allow subxiphoid rather than intercostal traversal.

METHODS

The entire procedure was performed under real-time CMR guidance. An "active" CMR needle crossed the chest, right ventricular free wall, and then the interventricular septum to deliver a guidewire then used to deliver an 18Fr introducer. Afterwards, the right ventricular free wall was closed with a nitinol occluder. Immediate closure and late healing of the unrepaired septum and free wall were assessed by oximetry, angiography, CMR, and necropsy up to four weeks afterwards.

RESULTS

The procedure was successful in 9 of 11 pigs. One failed because of refractory ventricular fibrillation upon needle entry, and the other because of inadequate guidewire support. In all ten attempts, the right ventricular free wall was closed without hemopericardium. There was neither immediate nor late shunt on oximetry, X-ray angiography, or CMR. The interventricular septal tract fibrosed completely. Transventricular trajectories planned on human CT scans suggest comparable intracavitary working space and less acute entry angles than a conventional atrial transseptal approach.

CONCLUSION

Large closed-chest access ports can be introduced across the right ventricular free wall and interventricular septum into the left ventricle. The septum recoils immediately and heals completely without repair. A nitinol occluder immediately seals the right ventricular wall. The entry angle is more favorable to introduce, for example, prosthetic mitral valves than a conventional atrial transseptal approach.

Active delivery cable tuned to device deployment state: enhanced visibility of nitinol occluders during preclinical interventional MRI

PURPOSE

To develop an active delivery system that enhances visualization of nitinol cardiac occluder devices during deployment under real-time magnetic resonance imaging (MRI).

MATERIALS AND METHODS

We constructed an active delivery cable incorporating a loopless antenna and a custom titanium microscrew to secure the occluder devices. The delivery cable was tuned and matched to 50Ω at 64 MHz with the occluder device attached. We used real-time balanced steady state free precession in a wide-bore 1.5T scanner. Device-related images were reconstructed separately and combined with surface-coil images. The delivery cable was tested in vitro in a phantom and in vivo in swine using a variety of nitinol cardiac occluder devices.

RESULTS

In vitro, the active delivery cable provided little signal when the occluder device was detached and maximal signal with the device attached. In vivo, signal from the active delivery cable enabled clear visualization of occluder device during positioning and deployment. Device release resulted in decreased signal from the active cable. Postmortem examination confirmed proper device placement.

CONCLUSION

The active delivery cable enhanced the MRI depiction of nitinol cardiac occluder devices during positioning and deployment, both in conventional and novel applications. We expect enhanced visibility to contribute to the effectiveness and safety of new and emerging MRI-guided treatments.

Real-time MRI-guided right heart catheterization in adults using passive catheters

AIMS

Real-time MRI creates images with superb tissue contrast that may enable radiation-free catheterization. Simple procedures are the first step towards novel interventional procedures. We aim to perform comprehensive transfemoral diagnostic right heart catheterization in an unselected cohort of patients entirely using MRI guidance.

METHODS AND RESULTS

We performed X-ray and MRI-guided transfemoral right heart catheterization in consecutive patients undergoing clinical cardiac catheterization. We sampled both cavae and both pulmonary arteries. We compared success rate, time to perform key steps, and catheter visibility among X-ray and MRI procedures using air-filled or gadolinium-filled balloon-tipped catheters. Sixteen subjects (four with shunt, nine with coronary artery disease, three with other) underwent paired X-ray and MRI catheterization. Complete guidewire-free catheterization was possible in 15 of 16 under both. MRI using gadolinium-filled balloons was at least as successful as X-ray in all procedure steps, more successful than MRI using air-filled balloons, and better than both in entering the left pulmonary artery. Total catheterization time and individual procedure steps required approximately the same amount of time irrespective of image guidance modality. Catheter conspicuity was best under X-ray and next-best using gadolinium-filled MRI balloons.

CONCLUSION

In this early experience, comprehensive transfemoral right heart catheterization appears feasible using only MRI for imaging guidance. Gadolinium-filled balloon catheters were more conspicuous than air-filled ones. Further workflow and device enhancement are necessary for clinical adoption.