Validation of transit time flow measurement in coronary artery bypass surgery using 3-Tesla magnetic resonance phase contrast imaging

Objectives: Validation of intra-operative transit time flow measurement in coronary artery bypass surgery with the help of 3-Tesla magnetic resonance (MR) phase contrast imaging.

Methods: Fifty-six coronary bypasses (arteries: left internal thoracic artery to left anterior descending artery n=16, right internal thoracic artery to right coronary artery n=1; veins to right coronary artery n=18, marginal branch n=7, circumflex branch n=7, diagonal branch n=6, left anterior descending n=1) were studied in 27 patients. In this prospective study, each bypass was studied intra-operatively using Doppler flow measurement. Within one week post surgery, patients were studied using a 3-Tesla MR scanner (Magnetom Verio, Siemens, Erlangen, Germany) using velocity encoded phase-contrast flow measurements.

Results: Intra-operative Doppler flow measurements demonstrated regular flow patterns in all territories supplied. For all bypasses, MRI flow measurement results were as follows: median flow 60ml/min (interquartile range (IQR): 37.5–78.5ml/min). For comparison, the corresponding median intra-operative flow was 58ml/min (IQR: 41–80ml/min). All grafts were patent during MR imaging. There was a good agreement between intra-operative flow measurements and postoperative MR flow measurements with a mean difference between the two methods of -1.02ml/min and a range between limits of agreement of -67.37–65.33ml/min. Linear regression analysis of pooled data revealed a highly significant correlation (p<0.001; R=0.44).

Conclusions: This study demonstrates that TTFM correlates significantly with postoperative MR phase contrast imaging. This underlines that TTFM is a very helpful intraoperative tool predicting peri-operative graft patency.