Quantitative Ischemia Detection During Cardiac Magnetic Resonance Stress Testing by Use of FastHARP

Abstract

Background— Because ECG alterations caused by ischemia cannot be reliably detected in the high-field MRI environment, detection of wall motion abnormalities is often used to ensure patient safety during stress testing. However, an experienced observer is needed to detect these abnormalities. In this study, we investigate the use of fast harmonic phase (FastHARP) MRI for the quantitative, operator-independent detection of the onset of ischemia during acute coronary occlusion. Methods and Results— Eight mongrel dogs underwent an acute 2-minute closed-chest coronary artery occlusion while continuous FastHARP images were acquired. Full regional wall strain was determined every other heartbeat in a single short-axis imaging slice. After 5 minutes of reperfusion, a second 2-minute ischemic episode was induced during the acquisition of conventional cine wall-motion images. The time at which ECG alterations were observed during the first ischemic period was recorded. The time from occlusion to the detection of ischemia, based on a consensus of 2 blinded observers, was determined for MRI. No significant ischemia was present in 2 animals. In the remaining animals, the onset of ischemia was detected significantly earlier by FastHARP than by cine MRI (9.5±5 versus 33±14 seconds, P <0.01). HARP ischemia detection preceded ECG changes, on average, by 54 seconds. Conclusions— The rapid acquisition and detection of induced ischemia with FastHARP MRI shows promise as a nonsubjective method to diagnose significant coronary lesions during MR stress testing.