HEPARIN RESISTANCE AFTER PREOPERATIVE HEPARIN-THERAPY OR INTRAAORTIC BALLOON PUMPING

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 ope n heart surgical procedures performed on adults between 1986 and 1991. The total population was divided into the following four groups: grou p 1, preoperative intraaortic balloon support without concomitant hepa rin therapy (n = 138 patients); group 2, preoperative intravenous hepa rin therapy (n = 741 patients); group 3, intraaortic balloon support w ith concomitant intravenous heparin therapy (n = 137 patients); and gr oup 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 IU/kg of heparin and the incidence of heparin resistance were 5 96 +/- 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 secon ds and 14% in group 4, respectively. These results indicate that preop erative intravenous therapy and intraaortic balloon support are associ ated with a decreased ACT response to intraoperative heparin. Baseline ACT levels and preoperative platelet counts were not predictive of he parin resistance. A reduced ACT response to the initial dose of hepari n was associated with increased requirements for supplementary anticoa gulant therapy during the ensuing period on cardiopulmonary bypass,; i ndicating that the decreased sensitivity to heparin extends beyond the initial episode of heparinization. These data reveal that preoperativ e intraaortic balloon support and intravenous heparin therapy are asso ciated with a heightened resistance to heparin, necessitating modifica tions in the standard heparin dose schedule and mandating close survei llance of ACT for the duration of cardiopulmonary bypass.