Jonathan R. Mazal

Transatrial Intrapericardial Tricuspid Annuloplasty

OBJECTIVES This study sought to demonstrate transcatheter deployment of a circumferential device within the pericardial space to modify tricuspid annular dimensions interactively and to reduce functional tricuspid regurgitation (TR) in swine. BACKGROUND Functional TR is common and is associated with increased morbidity and mortality. There are no reported transcatheter tricuspid valve repairs. We describe a transcatheter extracardiac tricuspid annuloplasty device positioned in the pericardial space and delivered by puncture through the right atrial appendage. We demonstrate acute and chronic feasibility in swine. METHODS Transatrial intrapericardial tricuspid annuloplasty (TRAIPTA) was performed in 16 Yorkshire swine, including 4 with functional TR. Invasive hemodynamics and cardiac magnetic resonance imaging (MRI) were performed at baseline, immediately after annuloplasty and at follow-up. RESULTS Pericardial access via a right atrial appendage puncture was uncomplicated. In 9 naïve animals, tricuspid septal-lateral and anteroposterior dimensions, the annular area and perimeter, were reduced by 49%, 31%, 59%, and 24% (p < 0.001), respectively. Tricuspid leaflet coaptation length was increased by 53% (p < 0.001). Tricuspid geometric changes were maintained after 9.7 days (range, 7 to 14 days). Small effusions (mean, 46 ml) were observed immediately post-procedure but resolved completely at follow-up. In 4 animals with functional TR, severity of regurgitation by intracardiac echocardiography was reduced. CONCLUSIONS Transatrial intrapericardial tricuspid annuloplasty is a transcatheter extracardiac tricuspid valve repair performed by exiting the heart from within via a transatrial puncture. The geometry of the tricuspid annulus can interactively be modified to reduce severity of functional TR in an animal model.

An efficient, free-breathing protocol for MR right heart catheterization

Methods The baseline MR examination begins with cardiac localizers. At this stage it is important to verify isocenter because if the patient is too deep in the bore then femoral vascular access sheaths are inaccessible to the operator. Through-plane phase contrast (PC) scans in the ascending aorta and main pulmonary artery follow for quantification of Qp and Qs. To avoid the need to repeat long PC scans (3 averages), we first perform brief PC ‘localizer’ scans with a single average to confirm the selected velocityencoding factor is correct. For cardiac volumetric analysis, long and short axis views are obtained using a real-time SSFP sequence that sacrifices some spatial resolution for increased temporal resolution. Data is collected over one and a half heartbeats to ensure the entire cardiac cycle is captured. Because of the delay in image reconstruction, the short axis stack is acquired last while the operator prepares for catheterization. A dedicated user interface (Interactive Front End, Siemens; Erlangen, Germany) is used for real-time imaging during catheterization. This interface permits interactive manipulation of imaging planes, slice thickness, saturation pre-pulse, and cine loop recordings. To minimize catheterization time, reference images

Real-Time Magnetic Resonance Imaging Guidance Improves the Diagnostic Yield of Endomyocardial Biopsy

Summary Diagnostic yield of endomyocardial biopsy is low, particularly in disease that affects the myocardium in a nonuniform distribution. The authors hypothesized that real-time MRI guidance could improve the yield through targeted biopsy of focal myocardial pathology. They tested this hypothesis in an animal model of focal myocardial pathology using intracoronary ethanol and microspheres. The authors compared real-time MRI-guided endomyocardial biopsy in swine using a custom actively visualized MRI bioptome against x-ray–guided biopsy using a commercial bioptome by skilled operators. Real-time MRI guidance significantly increased the diagnostic yield of endomyocardial biopsy.

Segmented nitinol guidewires with stiffness-matched connectors for cardiovascular magnetic resonance catheterization: preserved mechanical performance and freedom from heating

BackgroundConventional guidewires are not suitable for use during cardiovascular magnetic resonance (CMR) catheterization. They employ metallic shafts for mechanical performance, but which are conductors subject to radiofrequency (RF) induced heating. To date, non-metallic CMR guidewire designs have provided inadequate mechanical support, trackability, and torquability. We propose a metallic guidewire for CMR that is by design intrinsically safe and that retains mechanical performance of commercial guidewires.MethodsThe NHLBI passive guidewire is a 0.035” CMR-safe, segmented-core nitinol device constructed using short nitinol rod segments. The electrical length of each segment is less than one-quarter wavelength at 1.5 Tesla, which eliminates standing wave formation, and which therefore eliminates RF heating along the shaft. Each of the electrically insulated segments is connected with nitinol tubes for stiffness matching to assure uniform flexion. Iron oxide markers on the distal shaft impart conspicuity.Mechanical integrity was tested according to International Organization for Standardization (ISO) standards. CMR RF heating safety was tested in vitro in a phantom according to American Society for Testing and Materials (ASTM) F-2182 standard, and in vivo in seven swine. Results were compared with a high-performance commercial nitinol guidewire.ResultsThe NHLBI passive guidewire exhibited similar mechanical behavior to the commercial comparator. RF heating was reduced from 13 °C in the commercial guidewire to 1.2 °C in the NHLBI passive guidewire in vitro, using a flip angle of 75°. The maximum temperature increase was 1.1 ± 0.3 °C in vivo, using a flip angle of 45°. The guidewire was conspicuous during left heart catheterization in swine.ConclusionsWe describe a simple and intrinsically safe design of a metallic guidewire for CMR cardiovascular catheterization. The guidewire exhibits negligible heating at high flip angles in conformance with regulatory guidelines, yet mechanically resembles a high-performance commercial guidewire. Iron oxide markers along the length of the guidewire impart passive visibility during real-time CMR. Clinical translation is imminent.

Transcatheter real-time MRI guided myocardial chemoablation using acetic acid

Background In patients with ischemic cardiomyopathy, radiofrequency ablation for ventricular arrhythmias can have limited efficacy because of the mismatch between lesion depth and substrate thickness, and because radiofrequency-induced edema surrounding the lesion is reversible resulting in only temporary conduction block. We hypothesized that transcatheter needle injection under real-time magnetic resonance imaging (MRI) of caustic agents doped with gadolinium contrast could achieve deep targeted and irreversible myocardial ablation which could be assessed acutely.

Transcatheter bidirectional Glenn shunt guided by real-time MRI

Methods Ten swine underwent transcatheter bidirectional Glenn procedures under MRI at 1.5T. An MRI antenna-needle was advanced from the superior vena cava (SVC) into the target pulmonary artery (PA) bifurcation using realtime MRI guidance. A caval-pulmonary sheath introduced endografts. Balloon-expansion secured a proximal end-to-end caval anastomosis that also occluded the azygos, and a distal end-to-side pulmonary anastomosis that preserved blood flow to both branch pulmonary arteries.

Transcatheter Myocardial Needle Chemoablation During Real-Time Magnetic Resonance Imaging A New Approach to Ablation Therapy for Rhythm Disorders

Background—Radiofrequency ablation for ventricular arrhythmias is limited by inability to visualize tissue destruction, by reversible conduction block resulting from edema surrounding lesions, and by insufficient lesion depth. We hypothesized that transcatheter needle injection of caustic agents doped with gadolinium contrast under real-time magnetic resonance imaging (MRI) could achieve deep, targeted, and irreversible myocardial ablation, which would be immediately visible. Methods and Results—Under real-time MRI guidance, ethanol or acetic acid was injected into the myocardium of 8 swine using MRI-conspicuous needle catheters. Chemoablation lesions had identical geometry by in vivo and ex vivo MRI and histopathology, both immediately and after 12 (7–17) days. Ethanol caused stellate lesions with patchy areas of normal myocardium, whereas acetic acid caused homogeneous circumscribed lesions of irreversible necrosis. Ischemic cardiomyopathy was created in 10 additional swine by subselective transcoronary ethanol administration into noncontiguous territories. After 12 (8–15) days, real-time MRI–guided chemoablation—with 2 to 5 injections to create a linear lesion—successfully eliminated the isthmus and local abnormal voltage activities. Conclusions—Real-time MRI–guided chemoablation with acetic acid enabled the intended arrhythmic substrate, whether deep or superficial, to be visualized immediately and ablated irreversibly. In an animal model of ischemic cardiomyopathy, obliteration of a conductive isthmus both anatomically and functionally and abolition of local abnormal voltage activities in areas of heterogeneous scar were feasible. This represents the first report of MRI-guided myocardial chemoablation, an approach that could improve the efficacy of arrhythmic substrate ablation in the thick ventricular myocardium.

Fully Percutaneous Transthoracic Left Atrial Entry and Closure as a Potential Access Route for Transcatheter Mitral Valve Interventions

Background—Percutaneous access for mitral interventions is currently limited to transapical and transseptal routes, both of which have shortcomings. We hypothesized that the left atrium could be accessed directly through the posterior chest wall under imaging guidance. Methods and Results—We tested percutaneous transthoracic left atrial access in 12 animals (10 pigs and 2 sheep) under real-time magnetic resonance imaging or x-ray fluoroscopy plus C-arm computed tomographic guidance. The pleural space was insufflated with CO2 to displace the lung, an 18F sheath was delivered to the left atrium, and the left atrial port was closed using an off-the-shelf nitinol cardiac occluder. Animals were survived for a minimum of 7 days. The left atrial was accessed, and the port was closed successfully in 12/12 animals. There was no procedural mortality and only 1 hemodynamically insignificant pericardial effusion was observed at follow-up. We also successfully performed the procedure on 3 human cadavers. A simulated trajectory to the left atrium was present in all of 10 human cardiac computed tomographic angiograms analyzed. Conclusions—Percutaneous transthoracic left atrial access is feasible without instrumenting the left ventricular myocardium. In our experience, magnetic resonance imaging offers superb visualization of anatomic structures with the ability to monitor and address complications in real-time, although x-ray guidance seems feasible. Clinical translation seems realistic based on human cardiac computed tomographic analysis and cadaver testing. This technique could provide a direct nonsurgical access route for future transcatheter mitral implantation.

Real-time inversion recovery for infarct visualization during MR-guided interventions

Background Real-time MR imaging is appealing for dynamic procedural guidance. Some MRI-guided procedures, such as catheter ablation or myocardial biopsy, may require the interventionist to visualize infarcted tissue in real-time in order to navigate devices relative to the lesion. Methods to interleave late gadolinium enhancement (LGE) images into a real-time imaging stream (1 in 5 frames) have been described previously for infarct visualization (1). Here, we implemented a real-time inversion recovery sequence to provide a stream of LGE images for procedural guidance, designed to rapidly toggle between high-frame rate “navigation mode” and lower-frame rate “infarct visualization mode”.

Real-time magnetic resonance imaging guidance improves the yield of endomyocardial biopsy

Background In current practice, the diagnostic yield of endomyocardial biopsy is low because the procedure is performed ‘blind’ using X-ray fluoroscopy guidance and because many pathologies affect the myocardium in a patchy distribution. We hypothesized that biopsy performed under direct realtime MRI guidance would have superior diagnostic yield, in an animal model of focal myocardium pathology.