SIMULATED FLOW PATTERN IN MASSIVE PULMONARY-EMBOLISM - SIGNIFICANCE FOR SELECTIVE INTRAPULMONARY THROMBOLYSIS

Purpose: The flow pattern in the central pulmonary arteries proximal t o large pulmonary emboli was studied experimentally. The currents to w hich thrombolytic agents are exposed when administered via an intrapul monary catheter were visualized in order to explain the lack of benefi t of local versus systemic administration. Methods: By illumination of suspended microspheres, the flow pattern proximal to an obstructing e mbolus was visualized in an in vitro pulmonary arterial flow model. In six dogs massive pulmonary embolism was created. A pigtail catheter w as positioned in the pulmonary artery immediately proximal to the cent ral edge of the occluding embolus, To allow visualization of the local flow pattern, a small amount of contrast material (4 ml) was injected through the catheter at a high flow rate (25 ml/sec). The course of t he radiopaque spot that emerged from the catheter tip within 160 msec was monitored with digital subtraction angiography at a frame rate of 12.5 frames/sec. In two dogs, the study was repeated after embolus fra gmentation with the same catheter position. Results: The flow model st udy revealed formation of a vortex proximal to the occluding embolus. In vivo experiments showed that the radiopaque spot was whirled by the vortex proximal to the embolus and made only evanescent contact with the edge of the embolus. Regardless of the embolus location, the contr ast spot was washed into the non-occluded ipsilateral and contralatera l pulmonary arteries within 0.40-0.64 sec. After embolus fragmentation , the contrast spot was carried completely into the formerly occluded artery,. Conclusion: Flow studies explain why thrombolytic agents admi nistered via a catheter positioned adjacent to the embolus may have no more effect than systemically administered agents. An enhanced local effect is precluded by the rapid washout into the non-occluded pulmona ry arteries and subsequent systemic dilution. These results support th e practice of direct intrathrombic injection of thrombolytics or local thrombolysis as an adjunct to embolus fragmentation.