Velocity quantification by electrocardiography-gated phase contrast magnetic resonance imaging in patients with cardiac arrhythmia: a simulation study based on real time transesophageal echocardiography data in atrial fibrillation.

OBJECTIVE: To systematically investigate the impact of beat-to-beat variations on electrocardiography (ECG)-gated multibeat flow imaging with phase contrast (PC) magnetic resonance imaging (MRI) based on real time in vivo transesophageal echocardiography (TEE) data in patients with known arrhythmia.
METHODS: Real-time 2-dimensional Doppler TEE was performed in five patients with atrial fibrillation (4 men, age = 64 ± 8.7 years). The TEE data provided real-time left atrial (LA) and left ventricular (LV) flow velocities in consecutive cardiac cycles with different RR interval durations. The PC MRI acquisitions were simulated from the TEE velocity measures by constructing time-resolved k-space data for segmented sampling schemes typically used for ECG-gated 2-dimensional PC MRI. Each simulation was repeated 100 times to minimize effects from data that may be weighted to a particular beat in the center of k-space. The resulting LA and LV velocities were compared to the average TEE velocities and data from individual cardiac cycles.
RESULTS: Despite beat-to-beat variations of velocities in TEE data, ECG-gated flow imaging with MRI could reproduce persistent average LA and LV mean velocities within 7.0% to 7.4% compared to TEE.
CONCLUSIONS: The PC MRI velocity measurements in patients with varying RR interval durations are not significantly different from time-averaged real-time velocity data for a typical segmented k-space data acquisition schemes. Though beat-to-beat variations in atrial velocities that were observed with TEE cannot be detected with ECG-gated multibeat PC MRI, it can reliably assess average flow patterns across multiple beats.