Transit-time flow measurement cannot detect wrong anastomosis of an internal thoracic artery with the cardiac vein in coronary artery surgery

Clinical summary 

A 72-year-old man with effort angina was referred for coronary artery surgery. His coronary angiograms revealed occlusion of the distal right coronary artery and significant stenosis of the left main stem, the proximal left anterior descending artery, and the proximal left circumflex artery. He underwent triple coronary artery bypass grafting during cardiopulmonary bypass. The LITA was grafted to the left anterior descending artery, the left radial artery to the obtuse marginal branch of the left circumflex artery, and the saphenous vein to the atrioventricular branch of the right coronary artery. The result of transit-time flow measurement of the LITA graft is demonstrated in Figure 1. The mean flow (Qm) was 48 mL/min, the pulsatility index ([Maximal flow − Minimal flow]/Qm) was 1.6, and the percentage of insufficiency (Volume of backward flow/Volume of forward flow) was 0%. The postoperative angiogram revealed that the LITA had been anastomosed with the cardiac vein (Figure 1, B), although both aorta-coronary grafts (radial artery and saphenous vein) were patent.

View Large Image Download to PowerPoint

Figure 1. A, An intraoperative flow tracing of an in situ LITA grafted to the left anterior descending artery (LAD) in a 72-year-old man. The mean flow was 48 mL/min, the pulsatility index was 1.6, the percentage of insufficiency was 0%, and the flow was predominantly diastolic, forming a trapezoid-shaped waveform with a short systolic peak. B, A postoperative angiogram showing the LITA anastomosed wrongly with the cardiac vein.

Discussion 

In the transit-time method it is neither necessary to know the vessel diameter nor to perform any complex calibrating procedures. Therefore intraoperative transit-time flow measurement has become increasingly popular to check the anastomotic quality in coronary artery bypass grafting.5 As we have already demonstrated in the quantitative angiographic evaluation,2, 3 intraoperative Qm is closely related to the degree of the stenosis at the most stenotic portion of the anastomosis. However, we cannot completely rely on the Qm value to determine the anastomotic quality of the graft. It is possible to have a patent anastomosis with a low Qm because the optimal Qm varies with the dynamic character, including blood pressure, heart rate, coronary resistance, and graft diameter.1, 5 We cannot necessarily judge a graft with a Qm of less than 20 mL/min as nonpatent in the operating room. In contrast, surgeons can consider a graft with a Qm of greater than 20 mL/min as patent.1 In addition, on the basis of the specific physiology of coronary circulation, patent graft flow is predominantly diastolic, forming a trapezoid-shaped waveform with a short systolic peak, as demonstrated in Figure 2. On the contrary, there is no diastolic flow in an occluded graft.2, 3, 4

View Large Image Download to PowerPoint

Figure 2. A, An intraoperative flow tracing of an in situ LITA grafted to the left anterior descending artery (LAD) in a 62-year-old man. The mean flow was 48 mL/min, the pulsatility index was 1.4, the percentage of insufficiency was 0%, and the flow was predominantly diastolic, forming a trapezoid-shaped waveform with a short systolic peak. B, A postoperative angiogram showing the patent LITA anastomosed correctly to the left anterior descending artery.

In the patient in this report, the intraoperative Qm of the LITA was 48 mL/min, and its flow pattern was diastolic dominant. We considered the LITA as patent in the operating room. However, the postoperative angiogram revealed that the LITA had been accidentally anastomosed with the cardiac vein and not with the left coronary artery that we had intended to use for anastomosis. The arteriovenous flow pattern is similar to the arterioarterial flow pattern in coronary circulation. Although it is uncommon to perform incorrect grafting of the LITA to the cardiac vein, we should know that the transit-time flow measurement cannot differentiate the wrong anastomosis.