Heparin resistance after preoperative heparin therapy or intraaortic balloon pumping

Abstract Heparin resistance, defined as failure of 500 IU per kilogram of body weight of heparin to prolong the activated clotting time (ACT) to 480 seconds or longer, was noted during 949 of 4,280 (22%) consecutive open heart surgical procedures performed on adults between 1986 and 1991. The total population was divided into the following four groups; group 1, preoperative intraaortic balloon support without concomitant heparin therapy (n = 138 patients); group 2, preoperative intravenous heparin therapy (n = 741 patients); group 3, intraaortic balloon support with concomitant intravenous heparin therapy (n = 137 patients); and group 4, controls, not receiving preoperatively the therapy given groups 1, 2, or 3 (n = 3,264 patients). The ACT response to an initial dose of 500 lU/kg of heparin and the incidence of heparin resistance were 596 ± 203 seconds and 30% in group 1; 506 ± 149 seconds and 50% in group 2; 520 ± 159 seconds and 53% in group 3; and 705 ± 234 seconds and 14% in group 4, respectively. These results indicate that preoperative intravenous therapy and intraaortic balloon support are associated with a decreased ACT response to intraoperative heparin. Baseline ACT levels and preoperative platelet counts were not predictive of heparin resistance. A reduced ACT response to the initial dose of heparin was associated with increased requirements for supplementary anticoagulant therapy during the ensuing period on cardiopulmonary bypass, indicating that the decreased sensitivity to heparin extends beyond the initial episode of heparinization. These data reveal that preoperative intraaortic balloon support and intravenous heparin therapy are associated with a heightened resistance to heparin, necessitating modifications in the standard heparin dose schedule and mandating close surveillance of ACT for the duration of cardiopulmonary bypass.