The standard high-range activated clotting time (sHR ACT) is used to monitor anticoagulation postangioplasty (PTCA), but may be unreliable. We assessed the accuracy of a new method we termed the ACT differential (ACT Diff), obtained by measuring the difference between an sHR ACT and a heparinase ACT from the same sample. Heparinase removes heparin from its sample and provides a current heparin-free baseline. For phase 1 of the study, the sHR ACT, ACT Diff, and laboratory APTT were measured in 250 samples from 75 PTCA patients. In 125 samples with an APIT prolonged but within measurement range, linear regression against the APTT was performed. The correlation coefficient was 0.74 for the ACT Diff and 0.24 for the sHR ACT. An ACT Diff of 15-25 sec was found to equal an APTT of 2.5-3.5 x control. In 50 samples with a normal activated partial thromboplastin time (APT), there was good differentiation by the ACT Diff of results from those adequately heparinired, with a value of 0.9 2 4.4 sec. The sHR ACT was 114 f 15.5 sec, and could not reliably distinguish between anticoagulated and nonanticoagulated samples. In 75 samples obtained with a high APTT (above measurement range), the ACT Diff was >30 sec in 95% of samples, and again this allowed differentiation from therapeutic samples. The equivalent sHR ACT was 148 sec, and could not reliably distinguish between anticoagulated and overanticoagulated samples as the ACT Diff could. In phase 2, to examine the clinical usefulness of the ACT Diff, 286 patients were managed post-PTCA by starting heparin when ACT Diff fell to <50 sec, maintaining ACT Diff at 15-25 sec during heparin infusions, and following cessation of heparin, by removing sheaths when the ACT Diff was <7 sec. These patients were compared to a control group of 250 patients. Major bleeding (5% vs. 0.5%, P < 0.005) and minor bleeding (30% vs. 13%, P < 0.001) were significantly reduced in the group managed using the ACT Diff. The reduction in bleeding was thought to be due to the rapid availability of reliable results. Abrupt closure was low in both groups (0% with ACT Diff vs. 0.8%). No other thrombotic events occurred. Following phases 1 and 2, the ACT Diff replaced the APlT in all PTCA patients at this institution. In the 18 mo from July 1993, 1,104 patients were managed this way. Incidence of major bleeding (0.2%), transfusion requirement (O.lYo), false anneurysm (O.6%), and abrupt closure during heparin infusion (0.17'0) remained low.
In conclusion, the ACT Diff is more accurate than an sHR ACT, and its clinical use in PTCA patients is associated with a very low incidence of complications from anticoagulation. Its routine use should be considered by units unable to obtain rapid APTT results.