This report demonstrates rapid and “comfortable” conduct of atrial septal puncture and balloon septostomy entirely using rtMRI and custom catheter devices in swine.
XRF guided ASP was first described by Ross(2
) and Cope(1
), refined by Brockenbrough(43
) and Mullins(3
), and further improved with adjunctive intracardiac(44
) and transesophageal echocardiography (45
). Examples of procedures that require transeptal access include percutaneous mitral valvuloplasty,(46
) radiofrequency ablation for arrhythmia,(47
) and balloon atrial septostomy in congenital heart diseases(49
) or severe pulmonary artery hypertension(50
). Emerging indications include left atrial appendage occlusion for chronic atrial fibrillation(51
), and percutaneous mitral(52
) or aortic valve repair(53
). Despite decades of experience, even highly skilled operators cause cardiac perforation during transeptal puncture as often as 0.9–5.4%(3
) This potentially lethal complication is more likely in patients with very small or large atria, dilated aortic root, thoracic spine deformities, and prior atrial septal defect closure.(6
) Transesophageal echo is uncomfortable, requires heavy sedation, pharyngeal and esophageal instrumentation, prolongs procedure time and inhibits patient communication. Intracardiac echo also suffers from device related shadow artifacts, requires an additional large access sheath, and can interfere mechanically with other interventional devices. With appropriate clinical grade devices, rtMRI might reduce risk and offer robust procedural guidance by better visualizing the interaction between tissue and devices.
MRI guided endovascular procedures have been successfully performed for a variety of preclinical(13
) and clinical(31
) indications. In particular, rtMRI device navigation for catheterization(23
) and atrial septal defect closure (20
), have been demonstrated using active and passive devices. These investigators performed ASP under XRF guidance(22
) or employed animals having patent foramena ovale(20
). Arepally et al
) demonstrated ASP using a similar active needle. They did not, however, test heating characteristics of the device, and did not conduct an interventional procedure or hemodynamic assessment. Moreover, they did not use a clinically-suitable rtMRI environment combining colorized device display and interactive multi-slice imaging(30
). Kee et al
investigators created transjugular intrahepatic portosystemic shunts (TIPS) using combined XRF and low-field rtMRI in swine(13
) and humans(60
). Our contribution demonstrates a complex two stage intervention, real-time multi-planar image display, clinically-relevant device visualization, and combined anatomic and hemodynamic endpoint assessment, entirely using MRI.
ASP and TIPS are examples of procedures in which devices traverse tissues boundaries, and are well suited for rtMRI guidance because of simultaneous device and soft tissue imaging. Combined with appropriate anastomotic devices, this technology might be extended to traverse greater distances for catheter-based connection of disparate vascular chambers, as in peripheral artery bypass or palliative pediatric cardiovascular shunts. Simple adaptations of these catheter devices might facilitate safer image-guided recanalization of peripheral artery occlusions.
In this experience, the rtMRI images portraying both devices and soft tissue were sufficiently information-rich to distinguish important structures simply and comfortably for the ASP operator, even though both spatial and temporal resolution were reduced compared with XRF (192x128 pixels and 8 frames/s compared with 512–1024 square and 15–30 frames/s). The enhanced tissue visualization averted iatrogenic aortic penetration, a potentially catastrophic complication that might not have been prevented using XRF or ultrasound. On a related note, interactive rtMRI may enhance procedural safety by identifying unexpected complications early. In one pig, hemorrhage was immediately evident under rtMRI; pericardial effusion would similarly be readily evident. This information might expedite emergency treatment in a clinical setting.
One limitation of this work is that catheter devices were home-made. Imaging failure in one such device led to catastrophic complication, underscoring the importance of safe, durable, conspicuous clinical-grade instruments. These experiments were performed in normal swine, and therefore do not test the potential of MRI-guided therapy in complex clinical conditions. As predicted, the observed acute shunt was low using positive pressure ventilation with positive end-expiratory pressure. Nevertheless, necropsy consistently confirmed accurate anatomic positioning of ASP in all animals within the center of the fossa ovalis.
In conclusion, rtMRI permits rapid and robust transcatheter ASP and BAS by virtue of superior visualization of complex anatomy in any orientation. Additional advantages include online hemodynamic assessment and freedom from exposure to ionizing radiation or nephrotoxic contrast agents. Further technical development may enable more novel applications.