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Competitive Flow & Graft Patency Assessment
Competitive flow (residual flow from the native coronary in a grafted coronary vessel) is often considered a good sign. The
coronary artery is not totally occluded, and myocardial tissue is less impaired. However, during a Flow-QC® test of the coronary graft, competitive flow may obscure the maximum flow capacity by reducing flow through the graft. The Flow-QC tests consists of analyzing the average and pulsatile flow through the graft. Competitive flow reduces average graft flow, increases its pulsatility, and brings into question the patency of a perfectly good graft. For a simplified explantion, please see our alternative analogy.
A telltale sign of competitive flow is a negative peak in flow during systole. The cardiac pressure pulse arrives in the
native coronary before it has traveled the longer route through the coronary graft. Therefore, flow will run backwards into the graft during the beginning of systole if there is
competitive flow.
If competitive flow is anticipated, simply occlude the coronary during the Flow-QC test. This will eliminate competitive flow during the test, and let you test the graft under conditions of maximum flow. When the competitive flow is occluded, graft flow can increase significantly as illustrated in this case study.
For a complete explanation and illustrations, please see section II-I of our Flow-Based Intraoperative Coronary Graft Patency
Assessment guide. For techniques on on Occluding Competitive Flow, please see section III-F.
Request a hard copy of our guide book.
Pitfalls in Pulsatility Index
The Pulsatility Index (PI) is defined as the minimum-to-maximum flow waveform excursion divided by mean flow. A high PI is a combined measure of low flow and high pulsatility in the graft flow. A PI between one and five is considered an indication of a good graft.
PI is a useful quick assessment of graft patency – but it may be misleading if used as the sole basis for graft patency assessment.
- These case examples show a low PI in grafts with a technical error – the PI on its own would have yielded a false negative.
- Pulsatility of the waveform may be increased to give false positives, when the waveform has excessive motion artifacts (see: focus note). The same
may happen when there is competitive flow (see the In Focus story, above).
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