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 onpump 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 10(3) erg.cm-2; [mean, 127 x10(3) +/- 25 x 10(3) erg . cm-2] and 81-98 10(3) erg.cm-2; [mean, 90 x 10(3) +/- 15 x 10(3) 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 onpump 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.