Abstract

The role of CMR in diagnosis and follow-up of cardiovascular disease by assessment of cardiac anatomy, function and physiology is well established. However, cardiac catheterisation procedures, where invasive pressure measurements are required or an intervention needs to be carried out the are still carried out under X-ray guidance. Innovations in CMR over the last 20 years are making CMR guided cardiac catheterisation a possibility. The combination of CMR with cardiac catheterisation has been proven to reduce the screening time and radiation dose {Razavi:2003}. This is achieved by minimising the X-Ray screening to the absolute minimum in order to obtain information that cannot be otherwise obtained by the MRI scan. In some cases, catheterisation can be carried out by CMR guidance alone. Initially CMR guided catheterisations was employed and validated against standard cardiac catheterization for the assessment of pulmonary vascular resistance (PVR){Muthurangu:2004}{Kuehne:2005}. In the past few years the indications have widened to include assessment of anatomy and function of biventricular{Kuehne:2004dp} and univentricular hearts{Schmitt:2009ks}{BellshamRevell:2011}{Schmitt:2010}, cardiac output and hemodynamic measurements during pharmacological stress{Parish:2011}{Schmitt:2010} and MR-guided diagnostic cardiac catheterisations without X-Ray{Tzifa:2011}{Ratnayaka:2012}. Advances in interventional MRI{Krueger:2006} have led to the performance of XMR guided interventions and the first-in-man clinical trial on solely MR-guided percutaneous cardiac interventions{Tzifa:2010}. Finally, most recently CMR guided cardiac catheterisation has been used to carryout ablation of cardiac arrhythmias. {Chubb2017}. The techniques of XMR catheterisation and MR-guided interventions have been described in previous publications {Razavi:2003}{Tzifa:2012}. In brief, XMR catheterizations take place in a specifically designed catheterization laboratory with combined X-Ray and MRI facilities. The safety features of the hybrid lab have been previously described ( {Razavi:2003}{White2015}. In our laboratory we use a 1.5T MR-scanner (Achieva, Philips, Best, Netherlands) and a Philips BV Pulsera cardiac X-Ray unit. In-room monitor and controls display MRI images and haemodynamic pressure traces. The tabletop design allows patients to be moved from one modality to the other in a very short time. MR compatible patient monitoring and anaesthetic equipment is used. All patients undergo a general anesthetic for the procedure. After femoral venous and arterial access is obtained patients are moved into the MRI scanner and standard cardiac MRI scans including a free breathing ECG-triggered three-dimensional (3D) steady state free precision (SSFP) scan of the heart and great vessels and 3D contrast enhanced magnetic resonance angiography (MRA) are performed to elucidate intra-cardiac and vascular anatomy. During solely MRI-guided catheterisations the likely imaging planes needed for subsequent catheter tracking are stored on the interactive scanning sequence along with the rest of the MRI protocol at the beginning of the procedure. For example, for right heart catheterisation, the following views are stored: superior vena cava (SVC)/inferior vena cava(IVC) sagittal and coronal, 4-chamber, right ventricular outflow tract (RVOT), right heart 2 chamber view (R2CH), pulmonary artery bifurcation, left pulmonary artery sagittal and right pulmonary artery coronal views. The in-room consoles display the haemodynamic pressures on one panel and four chosen imaging planes on the other. An interactive SSFP sequence (8 to 10 frames/sec) with real-time manipulation of scan parameters is used. The operators can start and stop the MRI scan independently with foot pedals and rotate through the four imaging planes displayed. Simultaneously phase contrast studies to measure flow in relevant vessels or SSFP-cine scans to measure ventricular volumes are performed with pressure recording in the relevant vessel and or chamber. These studies are repeated in different physiological states by induced pharmacologically. This includes nitric oxide administration at 20ppm with 100% oxygen during PVR assessment or dobutamine or isoprenaline during pharmacological stress testing. Dobutamine stress studies involved measurements at baseline, repeated with dobutamine infused at a rate of 10mcg/kg/min and again at 20mcg/kg/min. MR cardiac catheterisation is safe and has a wide application in the context of anatomical and haemodynamic assessments in patients with congenital heart disease both at rest and at pharmacological stress. It is particularly helpful for accurate assessment of pulmonary vascular resistance in these patients. Detailed assessment of this kind, can be extended to patients without congenital heart disease such as pre-liver transplantation patients. Although our MR-guided interventions clinical trial was stopped due to problems with the MRI compatible guide wire, there remains enthusiasm for the development of alternative MR-safe and compatible guidewires and devices. Most recent applications include MR guided ablation of arrhythmias using active catheter tracking.

Acknowledgements

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References

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