Radiation-Free Right Heart Catheterization Feasible, Safe with MRI Guidance

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A small, preliminary study of unselected patients undergoing right heart catheterization suggests that it may be possible to offer patients an effective, radiation-free alternative to the traditional X-ray-directed procedure via magnetic resonance imaging (MRI) guidance. The study, published online August 1, 2012, ahead of print in the European Heart Journal, provides early evidence that cardiovascular interventional MRI can be used in clinical practice to take advantage of better tissue visualization and reduced radiation exposure.

Researchers led by Robert J. Lederman, MD, of the National Institutes of Health (Bethesda, MD), performed investigational MRI-guided transfemoral right heart catheterization in 16 patients. Following standard X-ray catheterization, patients were transferred to an adjoining room to undergo continuous real-time MRI-guided catheterization twice—once with an air-filled balloon catheter, and then with a balloon filled with a 2% solution of diluted gadolinium.

High Rate of Success

Of the 16 catheterizations, 15 were successful without use of a guidewire—since no MRI-safe guidewires are currently available—despite the fact that 81% of patients had pulmonary artery hypertension. The only procedural failure occurred in a patient with a large secundum atrial septal defect with large pulmonary arteries and moderate pulmonary hypertension. Both X-ray and MRI catheterization failed in this patient without a guidewire.

Overall, real-time MRI allowed for continuous visualization of transfemoral catheterization during navigation into all selected vessels and chambers. There were no clinical differences between pressure measurements or between hemoglobin-oximetry measurements obtained among the 3 approaches. In addition, success rates were similar for all chamber-entry tasks, regardless of technique (table 1).

Table 1. Procedural Step Success with X-Ray vs. MRI-Guidance

There also was no difference in total right heart catheterization times among the 3 approaches (table 2).

Table 2. Total Catheterization Times

^a P = 0.347 for all comparisons.

All 3 image-guidance techniques provided equivalent operator confidence that the catheter was inside the targeted chamber or vessel. In entering the left pulmonary artery from the main pulmonary artery, however, MRI with gadolinium-filled catheters tended to navigate faster than X-ray or MRI with air-filled balloons.

With X-ray guidance, the catheter tip and shaft were always visible, whereas MRI-guidance provided inferior visibility because only the tip was visible. However, compared with the air-filled balloons, the gadolinium-filled balloons were more consistently conspicuous than under MRI and could be selectively visualized using a ‘saturation preparation’ MRI mode, which specifically enhanced the appearance of gadolinium inside the catheter tip.

Early Experience Encouraging

According to the study authors, although there was a learning curve for the MRI approaches, the procedural steps became faster with practice. For example, the transfer time from the X-ray catheterization procedure to MRI was 17.3 ± 3.1 minutes for the first 8 patients and 12.0 ± 4.7 minutes for the second 8 patients (P = 0.027). In addition, the MRI with gadolinium-filled balloon was performed in half the time in the last 8 patients compared with the first 8 (15.4 ± 1.2 vs. 31.5 ± 9.5; P = 0.002).

“This is the first experience of comprehensive right heart catheterization (sampling both cava and both pulmonary artery branches) performed entirely using MRI guidance in an unselected cohort of subjects, and the only paired comparison of X-ray and MRI catheterization in the same subjects,” Dr. Lederman and colleagues write.

Based on their early work, they conclude that structural heart interventions may be realistic targets for MRI catheterization in a range of therapeutic areas including delivery and repair of aortic valves, repair of other cardiac structural defects, and enhanced image guidance of peripheral artery interventions, among others.

Still, “MRI catheterization is not ready for broad clinical adoption,” they write. “With improved catheter devices and workflows, even simple MRI catheterization procedures may one day be justified.”

Study Details

All procedures were performed transfemorally. Patients were excluded for cardiovascular instability (including STEMI, refractory angina, or refractory heart failure), pregnancy or nursing, an estimated glomerular filtration rate < 30 mL/min/1.73 m² (in case a gadolinium-filled balloon were to rupture), or ineligibility for MRI.

Source:

Ratnayaka K, Faranesh AZ, Hansen MS, et al. Real-time MRI-guided right heart catheterization in adults using passive catheters. Eur Heart J. 2012;Epub ahead of print.

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