Grinding Wheel Motion and Force Analysis in Atherosclerotic Plaque Removal by Atherectomy

Abstract

Atherectomy is a catheter-based interventional procedure to remove the atherosclerotic plaque off the arterial wall to restore the blood flow and treat cardiovascular diseases. During atherectomy, a metal bond diamond grinding wheel driven by a long flexible drive shaft is inserted into patient’s artery and rotates up to 230,000 rpm to pulverize the plaque into fine debris absorbable by blood and vessels. The grinding wheel motion inside the artery and the grinding force applied on the lesion are poorly understood though critical to the procedure complications including dissection, restenosis, vasospasm, and slow-flow/no-reflow. This dissertation studies the grinding wheel motion and the associated blood hydraulic force and plaque grinding force during atherectomy. First, an experiment utilizing a transparent tissue-mimicking artery phantom, a high-speed camera, and a piezoelectric dynamometer was conducted to visualize the grinding wheel motion and measure the force on the artery phantom. Second, a computational fluid dynamics model was established to understand the blood flow field near the grinding wheel and the hydraulic force and validated by the particle imaging velocimetry. Third, a grinding force model was built based on the Hertz contact and the smoothed particle hydrodynamics simulation to describe the impact and cutting forces on the plaque and experimentally validated. The grinding wheel orbits around the vessel lumen in the direction of its rotation. The orbital speed increases with the rotational speed and the size of the grinding wheel. This orbital motion is caused by the rotation-induced blood flow. The hydraulic force on the grinding wheel during orbiting is small comparing to the grinding force. The grinding force is 1.84, 1.92, and 2.22 N at 135,000, 155,000, and 175,000 rpm rotational speed, respectively, when a 2.38 mm diameter burr is tested in a bovine bone sample with a 4 mm lumen. While orbiting around the lumen, the grinding wheel bounces on the wall of the plaque, leaving discrete grinding marks. The bouncing grinding wheel impact force is the dominant component of the grinding force and the cutting component for plaque removal is relatively small.