Experimental investigation of hypercoagulant conditions associated with angiography

To evaluate changes in blood coagulability after high-velocity intravascular fluid injections under conditions relevant to angiography.

In 101 rabbits, fluids were injected at 1,000 psi (6,890 kPa) via a multiple-side-hole catheter in the abdominal aorta, while blood was simultaneously aspirated via a second downstream catheter. The fluids injected included saline, contrast media, blood, tissue plasminogen activator, and heparin. The aspirate was evaluated for clotting time with an activated clotting time (ACT) device, for elevated levels of plasma hemoglobin to confirm capture of at least part of the injection bolus in the sample, and sometimes for hematocrit or fibrin degradation products (FDP).

A single high-pressure injection of 2 mL of saline briefly accelerated the ACT of a blood-saline bolus (mean, 38% +/- 4). The mean volume of the hypercoagulable bolus was 15 mL. Systemic FDP levels became elevated within a few minutes after initial injection, suggesting activation of the fibrinolytic system by intravascular clot formation. Subsequent injections produced less hypercoagulability, probably reflecting the anticoagulant effects of FDP. Pressure-injected contrast agents had anticoagulant effects. The ACT was accelerated by up to 80% after injection of blood that had remained within the catheter for 3-10 minutes. Glove powder or gauze lint from wiping the guide wire markedly accelerated intracatheter clotting. Hypercoagulability after injection of clotting blood was partially prevented by injections with contrast agent and was completely inhibited by low-dose systemic heparinization.

A hypercoagulable bolus may occur after angiographically relevant high-pressure fluid injections. The major contributing factors appear to be high jet velocities and injection of small amounts of clotting blood. Heparinization provides a simple and effective means of prevention.