Recovery of coronary flow and left ventricular function after abciximab.

Function After Abciximab To the Editor: I read with great interest the article by Neumann et al1 on the “Effect of Glycoprotein IIb/IIIa Receptor Blockade on Recovery of Coronary Flow and Left Ventricular Function After the Placement of Coronary-Artery Stents in Acute Myocardial Infarction.” In particular, the recovery of coronary flow and left ventricular function provided by abciximab were related to improvement of perfusion of the coronary microvasculature beyond mere restoration of epicardial vessel patency. Indeed, the efficacy of abciximab in preventing distal embolization and reducing periprocedural myocardial infarction was observed previously among various subsets of patients in the EPIC (Evaluation of c7E3 for the Prevention of Ischemic Complications) trial.2,3 In the article by Neumann et al,1 patients with myocardial infarction were randomized to receiving standard-dose heparin or abciximab plus low-dose heparin. A total of 15 000 U was administered to those in the standard-heparin group compared with 30 000 U of heparin for those treated with abciximab plus low-dose heparin. In addition, patients in the standard-heparin group continued to receive heparin infusion for 12 hours after sheath removal. I suppose the total dose of heparin in the abciximab plus low-dose heparin group was 7500 U (typographical error in the text, I believe). Nonetheless, this dose is not particularly low, because the median dose among patients in the low-dose heparin group of the EPILOG (Evaluation in PTCA to Improve Long-term Outcome with abciximab GP IIb/IIIa blockade) study4 was 5500 U (interquartile range 4700 to 6600 U). On the other hand, the median doses for those patients in the standard-dose heparin and standard-dose plus abciximab groups were 9400 U (interquartile range 7800 to 11 800 U) and 8600 U (interquartile range 7000 to 10 000 U), respectively. It would be useful to know the activated clotting and partial thromboplastin times, because subsequent complications may be related to the level of anticoagulation.5 Immediately after stent placement, the basal and peak flow velocity reserve, degree of angiographic residual stenosis, and hemodynamic data were similar between these 2 groups, which suggests that optimal results were obtained between these 2 groups of patients. However, at 14 days, the recovery of coronary flow and left ventricular function was substantially greater among those treated with abciximab. The authors attributed these benefits to platelet glycoprotein IIb/IIIa blockade. Although these results are impressive, an important confounding factor was that heparin infusion was continued for 12 hours in the standarddose group. Its significance was not discussed. The sudden discontinuation of heparin after 12 hours may promote coagulation, the so-called “rebound” phenomenon,6 and hence lead to formation of microthrombi and subsequent “clogging” of the coronary microvasculature. This effect may account, in part, for the results at 14 days.