In Reply:—

We appreciate the letter from Dr. Riess et al.  and fully agree that ecarin clotting time (ECT) is the method of choice for monitoring the anticoagulant effectiveness of recombinant hirudin (r-hirudin) in cases that necessitate cardiopulmonary bypass (CPB). However, ECT is not available in many institutions, including ours, and, in an emergent case, it may be necessary to use the activated partial thromboplastin time (aPTT) as an alternative method of monitoring.

Potsch et al.  1clearly demonstrated that plasma concentrations of free r-hirudin correlate much better with ECT than with aPTT, and that there is a poor relation between aPTT prolongation and plasma concentrations of free r-hirudin. 1Consequently, use of the aPTT makes it difficult to assess accurately the degree of anticoagulation after r-hirudin administration. Thrombotic complications from inadequate anticoagulation during CPB are severe and potentially lethal; therefore, it seems prudent to err on the side of over-anticoagulation if forced to rely on aPTT monitoring. Based on our experience, we recommend maintaining the aPTT around 200 s, a level higher than was recommended previously. 2 

Despite the benefits of monitoring ECT, it is not in widespread use in the United States for several reasons. ECT is not yet approved by the Food and Drug Administration, and its use may necessitate previous approval from the Food and Drug Administration (for individual patients) or from the institutional review board. Hospital laboratories do not have protocols for ECT monitoring, and it is still labor intensive, necessitating a calibration curve for each patient, and relatively expensive. Therefore, further information and education is needed so that hospitals anticipate the need for ECT, protocols are established, and the equipment is available before an urgent r-hirudin–requiring CPB case.

Pötzsch B, Madlener K, Seeling C, Reiss F-C, Greinacher A, Muller-Berghaus G: Monitoring of r-hirudin anticoagulation during cardiopulmonary bypass: Assessment of the whole blood ecarin clotting time. Throm Haemost 1997; 77: 920–5
Latham P, Revelis AF, Joshi GP, DiMaio JM, Jessen ME: Use of recombinant hirudin in patients with heparin-induced thrombocytopenia with thrombosis requiring cardiopulmonary bypass. A nesthesiology 2000; 92: 263–6