CORONARY ARTERY DISEASE Analysis of flow characteristics in poststenotic regions of the human coronary artery during bypass graft surgery

Poststenotic blood flow velocities were evaluated in nine patients with 75% to 99% stenosis of the left anterior descending coronary artery (LAD) during coronary artery bypass graft surgery. We used the 20 MHz 80-channel pulsed Doppler velocimeter developed in our laboratory. An operator placed a specially designed probe on the native LAD with his fingers. Before induction of extracorporeal circulation, LAD blood velocities were measured at several locations distal to the stenosis. The poststenotic flow velocities were rich in systolic flow component with reduced diastolic component. The velocity configuration in the poststenotic portions was characterized by the presence of reverse flow velocities and/or irregularity of the velocity pattern near the vessel wall, indicating the existence of flow separation and recirculation in the regions. The broadening of the velocity spectrum observed at central axial regions suggested the occurrence of flow disturbances. After grafting, the velocity waveform in the LAD beyond a vein bypass graft changed to a diastolic-predominant pattern with a relatively small systolic component. A transient bypass graft occlusion caused a marked reduction in diastolic flow velocity. The systolic-to-diastolic velocity ratio increased from 0.27 ± 0.07 to 1.50 + 0.50 (p < .01) by the graft occlusion. Circulation 76, No. 5, 1092-1100, 1987. PHASIC FLOW in the left coronary artery of animals is high during diastole and remains low during systole. This pattern is thought to be caused by transmural compression of the intramyocardial vessels during systole and by release of the compression force during diastole." 2 Partial obstruction of the left coronary artery in the dog reduced the ratio of diastolic-to-systolic flow as measured by an electromagnetic flowmeter. 3 However, measurements of phasic poststenotic blood flow velocity in a human native coronary artery have been hampered by methodologic limitations. In addition, the velocity profile across the vessel in the poststenotic region has not been clarified in man or in animals. Such data, if obtainable, could provide From the Department of Medical Engineering and Systems Cardiology and the Department of Thoracic and Cardiovascular Surgery, Kawasaki Medical School, Kurashiki, Japan. Supported in part by Research Grant for Cardiovascular Diseases 60-C2 from the Ministry of Health and Welfare, Japan, and by a grant from the Uehara Memorial Foundation, Japan. Address for correspondence: Fumihiko Kajiya, M.D., Department of Medical Engineering and Systems Cardiology, Kawasaki Medical School, 577-Matsushima, Kurashiki, 701-01, Japan. Received Feb. 20, 1987; revision accepted July 23, 1987. 1092 a means for evaluating the pathophysiologic significance of stenotic coronary artery disease. Ultrasound pulsed Doppler velocimeters are useful for measuring local blood flow velocity in vessels noninvasively. However, a conventional pulsed Doppler velocimeter with low carrier frequencies cannot obtain detailed blood velocity profiles of small vessels like the coronary artery. Hartley and Cole5 were the first to develop a 20 MHz pulsed Doppler velocimeter to measure blood flow velocity in small vessels. Marcus et al.6 measured phasic velocity in human coronary arteries without surgical isolation of the artery during cardiac surgery by using a 20 MHz transducer and by introducing a unique suction probe. In their studies, the Doppler shift frequency was detected by a zero-cross method, and the number of channels of measurement was limited. Recently, we have developed an 80-channel 20 MHz pulsed Doppler velocimeter7-9 that detects Doppler signals from 80 channels by a zero-cross method and analyzes Doppler signals from one optional channel by a fast Fourier transform method, both in real time. With this method, we have been able to analyze detailed blood velocity profiles across vessels, as well CIRCULATION by gest on N ovem er 6, 2017 http://ciajournals.org/ D ow nladed from THERAPY AND PREVENTION-CORONARY ARTERY DISEASE as velocity distribution (spectrum) in a sample volume. The multichannel system makes it easy to detect the Doppler signals from vessels covered by tissue, such as human coronary arteries. The purpose of our study was twofold: (1) to analyze the characteristics of the coronary artery flow-velocity profile distal to severe stenosis before bypass grafting and (2) to investigate the change in the diastolic and systolic blood flow velocities in a distal native coronary artery after grafting.