Effect of topically-applied milrinone or nitroglycerin on internal mammary artery free flow

Surgical mobilization of the internal mammary artery (IMA) can induce graft vasospasm, which is commonly managed by wrapping the IMA in a vasodilator-soaked swab before grafting. However, the choice of the most effective topical vasodilator remains the subject of continued investigation. We carried out a prospective randomized controlled trial to compare the effect of topically-applied milrinone, nitroglycerin and normal saline on IMA free flow.<b><i>Methods </i></b>Forty-six consecutive patients undergoing elective primary coronary artery bypass grafting were enrolled. After the left IMA was harvested, free flow was measured under controlled hemodynamic conditions before any intervention (flow 1) and at a mean of 12.5 minutes after the topical application of one of three agents (milrinone, nitroglycerin or normal saline) on the IMA (flow 2).<b><i>Results </i></b>All agents induced a significant increase in IMA flow, and flow 2 was significantly higher in the nitroglycerin and milrinone groups compared to the normal saline group, even while controlling for flow 1 as a centered continuous variable. Nevertheless, there was no statistically significant difference in flow 2 between the nitroglycerin and milrinone groups.<b><i>Conclusions</i></b>Topically-applied milrinone and nitroglycerin can increase blood flow of the IMA significantly in the early period after surgical mobilization. IMA blood flow was greater after the topical application of milrinone compared to nitroglycerin, but this has failed to reach statistical significance in the present study setting.

外科游离内乳动脉（internal mammary artery, IMA）可诱发移植血管痉挛，临床通常在移植前使用浸有血管扩张剂的拭子包裹IMA以应对该问题。然而，目前临床仍需进一步探索最为有效的局部外用血管扩张剂选择方案。本研究开展了一项前瞻性随机对照试验，对比局部外用米力农（milrinone）、硝酸甘油（nitroglycerin）与生理盐水（normal saline）对IMA自由血流量的影响。**<i>方法</i>**：本研究共纳入46例连续入组的择期原发性冠状动脉旁路移植术患者。在获取左侧IMA后，于血流动力学稳定的受控条件下，分别在干预前测量IMA自由血流量（记为flow 1）；并于局部外用三种受试药物之一后的平均12.5分钟时，再次测量IMA自由血流量（记为flow 2）。**<i>结果</i>**：三种受试药物均可显著提升IMA血流量。在校正flow 1作为中心化连续变量后，硝酸甘油组与米力农组的flow 2均显著高于生理盐水组。但硝酸甘油组与米力农组的flow 2未达到统计学意义上的显著差异。**<i>结论</i>**：在外科游离后的早期阶段，局部外用米力农与硝酸甘油均可显著提升IMA血流量。尽管局部外用米力农后的IMA血流量较硝酸甘油组更高，但本研究场景下该差异未达到统计学显著性水平。