The truth about activated clotting time measurements

A Pilot Study to Assess the Clinical Onset of IV Heparin in Interventional Cardiology and Cardiac Surgery

OBJECTIVES

To determine the onset of heparin anticoagulation, using 2 different measures of activated clotting times (ACT), thromboelastography (TEG; R-time), and anti-Xa levels, after administering low- (100 U/kg) and high- (300 U/kg) dose intravenous (IV) heparin to patients undergoing transcatheter aortic valve replacement (TAVR) and cardiac surgery, respectively.

DESIGN

Prospective study.

SETTING

Single academic institution.

PARTICIPANTS

Patients with normal baseline coagulation presenting for TAVR or cardiac valve surgery.

INTERVENTIONS

Coagulation studies were performed at baseline, 30 seconds, 90 seconds, and 180 seconds after IV heparin administration. The tests included iSTAT (iACT) and Hemochron ACT (hACT), TEG R-Time, and anti-Xa levels. At the authors' institution, anti-Xa is the preferred measure of heparin anticoagulation when time permits. ACT, a rapid point- of-care test, is used to assess intraprocedural anticoagulation.

MEASUREMENTS AND MAIN RESULTS

After both low- and high-dose heparin, there are peak increases in ACT and anti-Xa at 30 seconds, followed by a decline at 90 seconds and plateau at 180 seconds. The TEG R-time remained elevated (>80 minutes) throughout. For TAVR cases, all anti-Xa was >1.5 IU/mL, and was associated with an iACT >180 seconds and an hACT >200 seconds. For cardiac valve surgery cases, all anti-Xa was >2.4 and associated with an iACT >420 seconds and and hACT >340 seconds. Compared with hACT, iACTs were significantly lower at all time points after low-dose heparin, but not after high-dose heparin.

CONCLUSIONS

In this pilot study, heparin anticoagulation was detected as early as 30 seconds after IV administration, based on ACT, anti-Xa levels, and TEG R-time.

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