Real-time MRI guided atrial septal puncture and balloon septostomy in swine

Abstract

Cardiac perforation during atrial septal puncture (ASP) might be avoided by improved image guidance. X-ray fluoroscopy (XRF), which guides ASP, visualizes tissue poorly and does not convey depth information. Ultrasound is limited by device shadows and constrained imaging windows. Alternatively, real-time MRI (rtMRI) provides excellent tissue contrast in any orientation and may enable ASP and balloon atrial septostomy (BAS) in swine. Custom MRI catheters incorporated "active" (receiver antenna) and "passive" (iron or gadolinium) elements. Wholly rtMRI-guided transfemoral ASP and BAS were performed in 10 swine in a 1.5T interventional suite. Hemodynamic results were measured with catheters and velocity encoded MRI. Successful ASP was performed in all 10 animals. Necropsy confirmed septostomy confined within the fossa ovalis in all. BAS was successful in 9/10 animals. Antenna failure in a re-used needle led to inadvertent vena cava tear prior to BAS in 1 animal. ASP in the same animal was easily performed using a new needle. rtMRI illustrated clear device-tissue-lumen relationships in multiple orientations, and facilitated simple ASP and BAS. The mean procedure time was 19 +/- 10 minutes. Septostomy achieved a mean left to right shunt ratio of 1.3:1 in these healthy animals. Interactive rtMRI permits rapid transcatheter ASP and BAS in swine. Further technical development may enable novel applications.

Figure 1

“Active” ASP needle. A. Schematic of the custom modified loopless antenna ASP needle. To enhance tip visibility, a microcoil is affixed to the distal tip (positive) and connected to the outer shaft (ground). Appropriate tuning, matching and decoupling circuitry connect the needle to a MRI receiver channel. B. Photograph of 6F ASP needle. C. Image of the active ASP needle colored green in a water phantom.

Figure 2

Atrial septal puncture procedure sequence. (A) Baseline transverse slice imaged in real-time. Ao=aorta, RA=right atrium, LA=left atrium, FO=fossa ovalis (white arrow), PV=pulmonary vein. (B) The modified “active” ASP needle (green) can be seen tenting the interatrial septum at the level of the fossa ovalis. (C) The needle tip has entered into the LA. (D) A floppy-tipped 0.018” wire is advanced through the needle into the LA and subsequently left atrial appendage (LAA). It has coupled with the needle signal and therefore appears green. The dilator sheath tip susceptibility marker can be seen abutting the RA side of the septum (yellow arrow).

Figure 3

Selective real-time MR angiogram confirming ASP needle entry into the left atrium. After visual confirmation of ASP needle entry in the left atrium, 3–5mL of 30mM dilute Gd-DTPA is injected through the ASP needle wire port. A saturation pre-pulse is applied to suppress the background as contrast sequentially enhances the lumen of the left atrium (LA), left ventricle (LV) and out the aorta (Ao). Note there is no contrast enhancement of the right ventricle (RV) or outlined pulmonary artery (PA), indicating successful ASP.

Figure 4

Balloon Atrial Septostomy. A 14 mm x 40mm peripheral angioplasty balloon (red) inflated with dilute Gd-DTPA across the interatrial septum. A platinum marker indicates the distal aspect of the balloon (white arrow). The proximal marker is out of plane. Ao = aorta.

Figure 5

Atrial septal measurements. Atrial septal dimensions (A-C) obtained from SSFP short axis view. A=posterior aortic wall to anterior edge of fossa ovalis. B=fossa ovalis. C= posterior edge of fossa ovalis to posterior atrial wall. LA=left atrium, RA=right atrium, RVOT=right ventricular outflow track, SD=standard deviation.

Figure 6

Necropsy photograph after BAS view from the left atrium. The septostomy is centered within the fossa ovalis (FO). There is no gross evidence of thermal injury or valve disruption. MA =mitral annulus, MV=mitral valve