Tuesday, December 6, 2005

Anti-Heparin Antibody Predicts Increased Risk after Heart Surgery
By Julie McKeel

As many as 13% of heart surgery patients have an antibody that makes heparin ineffective, increasing the risk of life-threatening complications after surgery, researchers reported in the Journal of Thoracic and Cardiovascular Surgery. In a study of 466 adult cardiac surgery patients, a positive test for anti-platelet factor 4/heparin antibody before surgery nearly doubled the risk of complications over the expected risk, according to the authors.

Elliott Bennett-Guerrero, MD

The study suggests that a positive anti-heparin antibody test before surgery may be associated with an increased risk of serious complications following heart surgery.

But even though the antibodies "independently predicted increased risk for in-hospital death or prolonged hospitalization," the authors did not recommend routine testing for anti-heparin antibodies before surgery.

They noted that other genetic and environmental factors are likely to contribute to the clinical outcome in patients with these antibodies.

In addition to the presence of the antibodies as an independent predictor for death or prolonged hospitalization, other significant indications included in the analysis were age, preoperative red blood cell count (hematocrit), and ejection fraction (i.e., the fraction of blood pumped from the left ventricle with each heartbeat, used as a measure of the heart's efficiency.)

All patients were screened before undergoing elective coronary artery bypass surgery, valvular heart surgery or both. Known preoperative risk factors were assessed, and patients were assigned a risk score.

A positive antibody screen was defined as an absorbance value of more than 0.5 optical density (OD) units. Preoperative serum levels of the antibody ranged from 0.02 to 3.11 OD units, with a mean of 0.29.

The study was limited in that the anti-heparin antibodies "may not be mechanistically involved in postoperative [conditions] and [death] but may merely represent a surrogate marker for sicker patients at a greater risk for adverse outcomes," the authors wrote. The authors attempted to correct for this potential limitation by incorporating a previously validated surgery risk scoring system into the analysis.

The finding comes from a single-center study, thus the authors suggest the need for larger, prospective studies before recommendations for routine pre-surgery testing can be made. They write that those studies "should investigate whether alternative forms of intraoperative and postoperative anticoagulation, antiplatelet therapy, or both could be beneficial."

Bennett-Guerrero's colleagues include William White, MPH, Ian Welsby, MD, Habib El-Moalem, PhD, and Thomas Ortel, MD, PhD, from DUMC's Department of Anesthesiology; Charles Greenberg, MD, from DUMC's Department of Hematology; and Thomas Slaughter, MD from the Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, N.C.