Activated clotting times in acute coronary syndromes and percutaneous transluminal coronary angioplasty

Angiographic and clinical outcomes of bivalirudin versus heparin in patients with acute coronary syndrome undergoing percutaneous coronary intervention

BACKGROUND

Heparin with adjunctive glycoprotein IIb/IIIa platelet receptor (GP IIb/IIIa) inhibitors has demonstrated its effectiveness in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI). Bivalirudin, a direct thrombin inhibitor, has recently been shown to be an effective alternative for patients undergoing elective PCI.

OBJECTIVES

To assess the angiographic and clinical outcomes of adjunctive pharmacological strategies in a high-risk population presenting with ACS.

METHODS

Of 891 consecutive PCI patients with ACS, 304 received bivalirudin (60.5% male, 68+/-11 years) and were compared with 283 who received heparin (58.7% male, 66+/-12 years). A 30-day major adverse cardiac event was defined as the occurrence of cardiac death, nonfatal myocardial infarction, urgent revascularization or major hemorrhage.

RESULTS

Adjunctive GP IIb/IIIa inhibitors were used in 14.1% of the bivalirudin group and in 72.4% of the heparin group (P<0.010). The occurrence of Thrombolysis In Myocardial Infarction (TIMI) flow less than grade 3 was lower and the achievement of angiographic success was higher in the bivalirudin group than in the heparin group (5.2% versus 8.2%, 94.7% versus 89.7%, P=0.039 and P<0.010, respectively). There was no difference between groups in the incidence of bleeding events (bivalirudin 2.0% versus heparin 3.5%, P not significant) and in 30-day major adverse cardiac events (bivalirudin 8.3% versus heparin 5.7%, P=0.223).

CONCLUSIONS

In the high-risk cohort undergoing PCI, bivalirudin with provisional GP IIb/IIIa inhibitors achieved better angiographic results. Although not powered to show a difference, and while acknowledging that a selection bias could have affected the data, the present study showed that bivalirudin may be as clinically effective and safe as heparin with adjunctive GP IIb/IIIa inhibitors.

Reproducibility and variability of activated clotting time measurements in the cardiac catheterization laboratory

The objective of this study was to characterize the reproducibility and variability in the measurement to the activated clotting time (ACT) when performed on two different types of instruments, the HemoTec ACT (Medtronic) and the Hemochron 801 (International Technidyne). The ACT has evolved into the most common point-of-care test used in the cardiac catheterization lab to manage patient heparinization. Since the test has not been standardized, different systems frequently produce different results under the same clinical conditions. Duplicate paired ACT tests (n = 885) from 359 patients were performed on both instruments. Prothrombin times (PT) and activated partial thromboplastin times (aPTT) were also determined on subsets of these same samples (PT = 533; aPTT = 487). The performance and relationships between the two tests were determined using a variety of statistical analytical techniques. The average difference between the ACT devices was only 8 sec, yet more than 60% of the measurements varied by more than 10%. Over one-fourth of measurements varied by more than 20%. The reproducibility to the HemoTec instrument was superior to the Hemochron instrument across the entire range of ACTs measured (mean coefficient of variation 2.4% +/- 3.1% vs. 7.2% +/- 6.1% for HemoTec and Hemochron, respectively; P < 0.00001; range = 65-555 sec). The relationship between the two ACTs was nonlinear. In therapeutic ranges used for interventional procedures (200-350 sec), HemoTec and Hemochron ACTs are not comparable to one another. Statistical comparative analysis indicated that the HemoTec ACT has better overall performance.

Bivalirudin administration during percutaneous coronary intervention: emphasis on high-risk patients

In a large phase III study of patients with unstable angina treated with percutaneous transluminal coronary angioplasty (PTCA), the thrombin-specific anticoagulant bivalirudin produced relative risk reductions of 22% (p = 0.039) for ischemic complications and 62% (p < 0.001) for bleeding complications compared with heparin. Subsequent reports have shown that between-treatment differences favoring fewer complications with bivalirudin also extend to high-risk patients. Early heparinization promotes heparin resistance and decreases activated clotting time achieved during PTCA. These effects are relevant to patients with postinfarction angina, which is associated with a greater likelihood of early vessel closure and procedural failure. In 1006 patients with one or both of these risk factors, bivalirudin significantly reduced combined ischemic and bleeding complications compared with heparin (8.6% vs 18%, p < 0.001). Treatment separations favoring bivalirudin increased with risk, suggesting decreased heparin effectiveness in patients at heightened risk. Findings in three additional risk groups-women, the elderly, and patients not receiving glycoprotein IIb/IIIa inhibitors-also showed fewer complications with bivalirudin therapy. Preliminary data suggest that bivalirudin can be combined safely with glycoprotein IIb/Illa antagonists in percutaneous coronary intervention (PCI), including PTCA. An ongoing trial is aimed at determining the efficacy and safety of heparin with planned glycoprotein IIb/IIIa therapy versus bivalirudin with provisional glycoprotein IIb/IIIa therapy. The use of bivalirudin in patients with heparin-induced thrombocytopenia also is being evaluated after favorable findings in early compassionate-use studies. The fact that between-treatment differences favoring bivalirudin were especially outstanding among the high-risk patients considered in this review reinforces the impression that bivalirudin is a promising and unprecedented alternative to heparin in PCI.

Activated clotting times in the setting of eptifibatide use during percutaneous coronary intervention

BACKGROUND

Previous studies have demonstrated a prolongation of activated clotting times (ACT) with abciximab administration during percutaneous coronary interventions (PCI). The impact of the short acting glycoprotein (GP) IIb-IIIa inhibitor, eptifibatide, on ACT measurements has not been studied.

METHODS

Seventy consecutive patients undergoing PCI in the setting of eptifibatide administration were prospectively enrolled in a single center study. Eptifibatide was administered as two 180 microg/kg boluses 10 minutes apart followed by a continuous infusion of 2.0 microg/kg/min. In 15 patients (Group I), the initial eptifibatide and heparin boluses were separated by 5 minutes, and ACT's were assessed after each bolus as well as at 3 subsequent time points. In 55 patients (Group II), an ACT level was drawn 10 minutes after the initial heparin/eptifibatide bolus and 20 minutes following the second eptifibatide bolus. Two different ACT measuring devices--CoaguChek Pro DM and Hemochron 801--were used to examine the impact of eptifibatide on ACT values.

RESULTS

The devices differed in the reproducibility of their measurements, but the overall trends were consistent with both devices. The ACT value was unchanged after the initial eptifibatide bolus (with a delta of 0.6 seconds by CoaguChek Pro DM and 4.2 seconds by Hemochron). While the ACT value rose significantly after the heparin bolus, the second eptifibatide bolus did not result in any further rise in ACT values.

CONCLUSIONS

Unlike abciximab, eptifibatide does not significantly prolong the ACT in patients undergoing PCI. This may have implications regarding the need for separate heparin dosing algorithms for patients undergoing PCI in the setting of different GPIIb-IIIa inhibitors.

Safety of low dose heparin in elective coronary angioplasty

OBJECTIVES

To evaluate the safety of a low dose of heparin in consecutive stable patients undergoing elective percutaneous transluminal coronary angioplasty (PTCA).

DESIGN

Open prospective study in a single centre.

PATIENTS

1375 consecutive patients had elective PTCA (1952 lesions: type A 11%, B1 34%, B2 36%, and C 19%). There were no angiographic exclusion criteria.

INTERVENTIONS

A bolus of 5000 IU heparin was used as the standard anticoagulation regimen during PTCA. The sheaths were removed immediately after successful completion of the procedure. Prolongation of heparin treatment was left to the operator's discretion.

MAIN OUTCOME MEASURES

Procedural success was defined as < 50% residual stenosis without death from any cause, acute myocardial infarction, urgent coronary bypass surgery, or repeat angioplasty within 48 hours for acute recurrent ischaemia; the need for prolonged heparinisation; and the occurrence of puncture site complications.

RESULTS

Procedural success without clinical events was achieved in 90% of patients. Mortality was 0.3%; coronary bypass surgery was performed in 1.7% of the procedures. The rate of myocardial infarction was 3.3%; repeat angioplasty within 48 hours was carried out in 0.7% of patients. A total of 89.1% of the patients were treated according to the protocol. Prolonged treatment with heparin was considered necessary in 123 patients (8.9%). Repeat angioplasty for abrupt closure was performed in two patients shortly after sheath removal and in two during prolonged heparinisation. Puncture site complications occurred in 2.1% of patients (low dose heparin 1.9% and prolonged heparinisation 4.9%).

CONCLUSION

Elective PTCA can be safely performed using a low dose of heparin, with a negligible risk for subacute closure. Low dose heparin may reduce the incidence of puncture site complications, shorten hospitalisation, and enable out-patient angioplasty.

Association of heparin-resistant thrombin activity with acute ischemic complications of coronary interventions

BACKGROUND

Acute thrombosis is thought to contribute to abrupt coronary occlusion during percutaneous coronary revascularization despite the administration of heparin and aspirin. This study was designed to detect the presence of heparin-resistant thrombin activity and to define its relationship to the acute ischemic complications of coronary interventions.

METHODS AND RESULTS

Plasma levels of fibrinopeptide A (FPA) and prothrombin fragment 1.2 (F1.2), markers of thrombin and factor Xa activity, respectively, were measured in the coronary sinus with heparin-bonded catheters in 58 patients undergoing coronary interventions. Activated coagulation times were maintained > 300 seconds by the Hemochron method. Mean FPA levels decreased significantly, from 7.0 +/- 0.9 nmol/L before the procedure to 5.2 +/- 0.5 nmol/L after the heparin bolus and to 2.9 +/- 0.2 nmol/L after the procedure (P = .0001). In 26 patients (45%), FPA levels remained above the threshold for suppression angioplasty of thrombin activity determined during angiography in 7 patients without coronary artery disease (> 3.0 nmol/L). FPA concentrations after coronary interventions were increased in patients with intracoronary thrombus (P = .01), abrupt coronary occlusion (P = .06), postprocedural non-Q-wave myocardial infarction (P = .04), and clinically unsuccessful procedures (P = .04). F1.2 levels were relatively low before the procedures and did not change significantly.

CONCLUSIONS

Heparin administration suppresses thrombin activity in most but not all patients undergoing coronary interventions. Heparin-resistant thrombin activity is associated with angiographic evidence of intracoronary thrombus and ischemic complications of coronary interventions.

Activated clotting time differential is a superior method of monitoring anticoagulation following coronary angioplasty

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 APTT 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 heparinized, with a value of 0.9 +/- 4.4 sec. The sHR ACT was 114 +/- 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 APTT 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 (0.1%), false anneurysm (0.6%), and abrupt closure during heparin infusion (0.1%) 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.

When we "act" on ACT levels: activated clotting time measurements to guide heparin administration during and after interventional procedures

The establishment and monitoring of anticoagulation before, during, and after interventional and invasive procedures are crucial responsibilities. However, few prospective studies exist to rationally guide us in how and when to "act" in response to ACT values in specific clinical situations. Definitive studies to reach a uniform and safe ++approach are needed. The articles published in this issue of Catheterization and Cardiovascular Diagnosis represent an important step in understanding the role and value of ACT levels.