Flow measurement in coronary surgery

Many of the modern less invasive approaches to coronary artery bypass grafting (CABG) are performed without the use of the heart lung machine and cardiac asystole. Even after the introduction of mechanical stabilizers, the ability to achieve a technically perfect anastomosis is less certain in beating heart bypass surgery. Our group has begun to assess the surgical results of beating heart CABG using Transit Time Flow Measurement (TTFM). Our experience indicates that a meticulous and controlled method of assessing the results of intraoperative flow measurements can improve the quality of information and increases the accuracy of diagnosing technical problems with newly constructed bypass grafts. For this reason, we developed a standard algorithm for using and interpreting intraoperative TTFM.

From January to August of 1998, 161 patients underwent off-pump CABG with a total of 323 distal anastomoses (2.0 grafts per patient). All completed grafts were tested intraoperatively with TTFM and the decision to accept or revise any individual graft was based on a decision nomogram using key values readily available from the TTFM output.

Thirty-two grafts (9.9%) were surgically revised based on unsatisfactory flow curves, the Pulsatile Index, or both. All revised grafts were found to have a significant technical error, such as an intimal flap, thrombus, conduit kinking, or dissection. There were no major complications, myocardial infarctions, or deaths in the entire series of patients.

Based on our favorable use of TTFM, we strongly recommend that patency of every graft be assessed whether the operation is performed off pump or on cardiopulmonary bypass. Guidelines for performing and interpreting TTFM ensure a high degree of confidence in the completed graft. The decision to revise a graft can be made based on simple parameters easily acquired from the TTFM device. Any concern about quality or quantity of flow should prompt immediate revision.