Myocardial Contractile Performance, Preload Recruitable Stroke Work Relationships, and Histomorphometric Changes Following Off-Pump and On-Pump Coronary Bypass Grafting of the Left Internal Thoracic Artery to the Left Anterior Descending Artery
Background: It has been shown that coronary artery bypass grafting without cardiopulmonary bypass (off-pump or OPCABG) preserves better cerebrocognitive, pulmonary, hepatorenal, and blood cell functions compared with on-pump surgery because of an attenuated inflammatory response. The degrees of ischemia/reperfusion injury, myocardial protection, and quantitative changes in myocardial contractile performance following OPCABG have not been well documented.
Methods: A canine myocardial ischemic injury model (60-minute occlusion of the left anterior descending artery [LAD]; n = 30, 27-35 kg body weight) was used to quantitatively assess postoperative regional left ventricular function (sonomicrometry, micromanometry, preload recruitable stroke work [PRSW]). The left internal thoracic artery (LITA) was anastomosed to the distal LAD in off-pump and on-pump CABG with antegrade/retrograde cold blood cardioplegic arrest (cardiopulmonary bypass time, 58 ± 2 minutes; cross-clamp time, 28 ± 3 minutes). Anastomosis patency and endothelial changes at the anastomoses were analyzed with light microscopy and histopathologic techniques.
Results: LAD occlusion resulted in ischemia/infarction (creatine kinase-MB levels on-pump and off-pump versus the baselines were, respectively, 17.5 ± 1.4 mg/L versus 1.5 ± 0.3 mg/L [P < .05 by analysis of variance and t test] and 19.5 ± 1.8 mg/L versus 2.1 ± 0.4 mg/L [P < .05]) and a significant decrease in regional myocardial function in both groups (50% decrease of PRSW). Revascularization led to reestablishment of myocardial function to baseline (on-pump and off-pump PRSW were, respectively, 57-196 3 103 erg · cm-2 [mean, 127
3 103 ± 25 3 103 erg · cm-2] and 81-98 3 103 erg · cm-2 [mean, 90 3 103 ± 15 3 103 erg · cm-2]). All anastomoses were widely patent in all animals 14 days after surgery. There was a significantly increased intimal thickening at the 8-0 monofilament suture line in the off-pump LITA-to-LAD anastomoses.
Conclusions: Compared with most commonly applied myocardial preservation techniques (cardiopulmonary bypass, hypothermic blood cardioplegic arrest), OPCABG provides at least equal myocardial protection, because there were no significant quantitative differences between off-pump and on-pump CABG in myocardial contractile performance following LITA-to-LAD revascularization. The more prominent intimal thickening observed in OPCABG procedures is worrisome and deserves further investigation.
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