Kanishka Ratnayaka, MD and Robert J. Lederman, MD
Introduction
Interventional cardiologists specializing in Congenital Heart Disease (CHD) have grown adept at using what is available, whether devices or imaging modalities, to treat their patients. Nevertheless, while procedures increase in complexity, operators continue to rely on two-dimensional imaging guidance of gray and white shadows, pattern recognition, and contrast angiography. Complex 3-dimensional spatial relationships are not addressed by current techniques, which can expose patients to significant radiation. Growing and developing children are particularly radiosensitive and carry a lifetime of oncologic risk. Chromosomal damage in the peripheral blood of children exposed to catheterization-related radiation has been detected.[1,2] Interventional cardiac MRI (ICMR) guidance offers a potential solution.[3]
Cardiac MRI is a radiation-free, robust imaging modality used to: evaluate cardiac anatomy and function, measure volume and flow, measure tissue infarction, evaluate perfusion and viability, and allow for three-dimensional reconstruction of cardiac and vascular anatomy. Real-time cardiac MRI can provide excellent soft tissue imaging at approximately 5-15 frames/second in many simultaneous planes in any orientation. Combining invasive catheter hemodynamic measurements and MRI physiologic assessment power enables us to realize the full potential of catheterization diagnosis and intervention.
FIGURE 1 Real-time MRI Right and Left Heart Catheterization in Complete Atrioventricular Canal.
State of the Art
Diagnostic (Invasive)
In patients requiring invasive diagnostic studies, particularly serial studies (single ventricle, heart transplant) the radiation-sparing argument may be most compelling; the cumulative X-ray dose may be significant.[4] MRI offers a radiation and contrast-free alternative to those patients who may benefit most from the wealth of structural, functional, and biochemical information MRI can provide. In some critical instances, such as calculating pulmonary vascular resistance in patients with pulmonary artery hypertension and undergoing staged surgical palliation, MRI catheterization evaluation can be superior to the current methods.[5] While MRI guided catheterization emerged over a decade ago,[6] it has been non-glamourous, incremental workflow and user interface enhancements that have fueled steady progress. The worldwide experience approaches one-thousand patients. An understandable critique of ICMR is the lack of compatible catheter and guidewire tools, but for invasive diagnostic studies, off-the-shelf balloon endhole wedge catheters are sufficient (Figure 1).
A commercially available MR safe and visible guidewire would enable MRI guidance for most patients requiring diagnostic cardiac catheterization. A polymer guidewire is undergoing final stage clinical testing in Europe,[7] and safe metallic guidewires are approaching clinical testing.[8] Another typical critique is that MRI catheterization is time- consuming when compared to current standard X-ray catheterization. In our experience, simple workflow enhancements and experience have substantially decreased time to approximately 15 minutes per hemodynamic condition tested.
The majority of worldwide experience has been performed at three centers (King College London, Great Ormond Street, and National Institutes of Health), but clinical progress has increased attention. Attendance at the Society for Cardiovascular Magnetic Resonance annual scientific sessions “interventional cardiac MRI” one day pre-conference has steadily grown with over one hundred participants each of the last three years. In the past year, the National Institutes of Health (NIH) has hosted two hands-on MRI catheterization courses for eighty guests coming from twenty centers in the North America and Europe; future training courses are being scheduled for interested centers.
To read the full article, please go to the August 2016 Issue of CCT.