Can heart perfusion MRI work without ECG gating in patients with atrial fibrillation?

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Myocardial perfusion cardiovascular magnetic resonance (CMR) is a well-established method for detecting ischemic heart disease. But problems with ECG gating can degrade images or make scans non-diagnostic, particularly in patients with arrhythmias.

Researchers used a turboFLASH saturation recovery pulse sequence without ECG triggering. After one saturation pulse, they rapidly acquired 4–5 slices of undersampled radial k-space images, taking approximately 40–50 milliseconds per image. Acquisition of the 4–5-slice set was repeated continuously about 4 times per second. An iterative constrained reconstruction method reconstructed the ungated images. The perfusion images were then post-processed into three sets: ungated, self-gated to near systole, and self-gated to near diastole.

To test the ungated approach and compare processing methods, 8 patients scheduled for coronary angiography underwent stress and rest perfusion imaging using the ungated acquisition. Six had a history of atrial fibrillation (AF). Three blinded readers assessed image quality and whether disease was present.

All 8 patients completed the perfusion CMR protocol, and 7 of 8 underwent coronary angiography. Three patients were in AF during CMR. The three readers rated the CMR images as high quality overall. Image quality differed little between patients in AF and those in sinus rhythm: 3.6±0.7 versus 3.3±0.5.

Stress/rest imaging showed normal perfusion in 4 patients, fixed perfusion defects in 2, and reversible perfusion defects in 2, corresponding with angiographic results. Pooled results from the independent readers gave ungated imaging a sensitivity of 0.92 (CI 0.65–0.99) and specificity of 0.92 (CI 0.65–0.99) for detecting coronary artery disease. Images self-gated after acquisition to near systole or near diastole had the same sensitivity and a specificity of 1 (CI 0.76–1).

The researchers concluded that ungated radial dynamic perfusion CMR can provide high-quality images in sinus rhythm and during AF. High diagnostic accuracy was possible with this rapid sequence in the small cohort. They said an ungated approach simplifies acquisition and could expand perfusion CMR to patients with arrhythmias and those with gating problems.