Shuji Matsuoka

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 less than .01) by the graft occlusion.

Comparison of blood-flow velocity waveforms in different coronary artery bypass grafts. Sequential saphenous vein grafts and internal mammary artery grafts.

Characteristics of blood-flow velocities were investigated at different sites in two types of coronary artery bypass grafts, sequential saphenous vein grafts (SSVG) and internal mammary artery grafts (IMAG). The latter appear to have the longest life span. The patency rate of the side-to-side anastomosis of the SSVG is better than that of the end-to-side anastomosis. The SSVG was anastomosed to the major diagonal branch by side-to-side anastomosis and to the left anterior descending coronary artery (LAD) by end-to-side anastomosis in 13 patients who had 75-100% and 75-90% stenoses in the LAD and major diagonal branch, respectively. IMAG anastomoses were performed to the LAD in 10 patients with 75-100% stenoses of the artery. The blood-flow velocities were measured by the 20-MHz, eighty-channel ultrasound pulsed Doppler method during surgery. In six patients in the SSVG group, we investigated the configuration of velocity profiles at the region just proximal to the side-to-side anastomosis and at the bridge portion between the side-to-side and end-to-side anastomosis. In the other seven patients, we measured the blood-flow velocity at several centimeters proximal to the side-to-side anastomosis and compared it with that in the IMAG. At the region just proximal to the side-to-side anastomosis, the velocity profile skewed toward the anastomosis side wall in all patients, and the flow velocity near the wall opposite to the side-to-side anastomosis was reversed in five of six patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Flow Velocity Waveforms in Aortic Stenosis and the Effects of Valve Replacement

In 6 patients with pure aortic stenosis, the flow velocity waveforms in the left anterior descending coronary artery were studied using an 80-channel 20-MHz pulsed Doppler velocimeter before and immediately after aortic valve replacement. All patients showed normal coronary arteriograms. The left anterior descending coronary artery flow velocity waveform in aortic stenosis was characterized by a reverse flow in the first half of systole and a slowly increasing diastolic inflow. After aortic valve replacement, the reverse flow in the first half of systole disappeared in all patients, but an end-systolic reverse flow was discerned in 5 of 6 patients. The increasing rate of the diastolic inflow was augmented in all patients. After aortic valve replacement, the time from onset of diastole to the diastolic peak velocity was shortened from 176.8 +/- 28.8 to 90.5 +/- 18.8 ms (p less than 0.01), and the diastolic peak velocity increased from 90.5 +/- 28.0 to 122.5 +/- 17.2 cm/s (p less than 0.05). Blood pressure and heart rate, however, did not change significantly before and after valve replacement. These changes in the left coronary artery velocity waveforms after valve replacement suggest the beneficial effects of removal of aortic stenosis on human coronary artery inflow.

Coronary flow characteristics of left coronary artery in aortic regurgitation before and after aortic valve replacement

In 6 patients with pure aortic regurgitation, the velocity waveform in the left anterior descending coronary artery (LAD) was measured using an 80-channel 20-MHz-pulse Doppler velocimeter before and immediately after aortic valve replacement. All patients showed normal coronary angiograms. Flow velocity was analyzed by both zero-cross and fast Fourier transform methods in real time. The LAD flow in severe aortic regurgitation was characterized by an increase in the systolic flow component, a small and rapidly decreased diastolic flow, an irregular velocity profile across the vessel, and a wider velocity spectrum. After aortic valve replacement, systolic flow decreased by 36.3 +/- 21.7% (p less than 0.01), whereas diastolic flow increased by 81.4 +/- 51.8% (p less than 0.05). The ratio of diastolic flow to total LAD flow increased from 63 +/- 13% to 82 +/- 7% (p less than 0.05). The velocity profile became more parabolic and had a narrow spectrum. These results suggest that operation for aortic regurgitation induces beneficial effects on the myocardial inflow immediately after valve replacement.

Normal and Stenotic Blood Flow Velocities in Human Left Coronary Artery Measured by an 80 Channel 20 MHz Pulsed Doppler Velocimeter

The purpose of our studies was two-fold: [1] to investigate the phasic characteristics of normal coronary artery flow as well as velocity profiles across the vessel, and [2] to analyze the characteristics of the post-stenotic coronary artery flow in man. We measured blood velocities in the left anterior descending coronary artery (LAD) by an 80 channel 20 MHz pulsed Doppler velocimeter. To investigate the characteristics of normal coronary artery flow, blood flow velocity measurements were performed in segments 7 or 8 of LAD in ten patients with an atrial septal defect (ASD) after the defect closure. None of these patients had any detectable coronary artery stenosis or left ventricular hypertrophy. The velocity waveform displayed diastolic predominant pattern, which is a characteristic of left coronary artery flow. The diastolic-to-total velocity area ratio of normal coronary velocity waveforms was about 80%. During systole, two different types of reverse flow were observed time sequentially, i.e., an early-systolic reverse flow and a mid- (and late-) systolic one. During diastole, the blood velocity profiles were classified into three types: a parabolic pattern, a skewed pattern (toward the near wall or far wall) and an M-shaped pattern. The direction of skewing was not consistent among patients, but the number of parabolic profiles increased in late diastole. Post-stenotic blood flow velocities were measured in nine patients with 75% to 99% stenosis of the LAD during coronary artery bypass graft surgery in the nine patients. The coronary artery velocity waveform through a severe stenosis was characterized by augmentation of the systolic velocity component and a relatively small diastolic velocity component. The diastolic-to-total velocity area ratio was about 50%. The velocity spectrum of post-stenotic coronary artery was wider in the distant distal portion than the immediately distal portion. The velocity profile in the vicinity of the vessel wall was irregular in the immediately distal portion, indicating the presence of flow separation.

Flow Dynamics in Coronary Stenosis

The pressure loss across coronary artery stenosis is mainly caused by two factors: viscous friction loss by stenotic segments and separation loss by the flow separation after (and before) stenosis. When the percentage diameter stenosis increases, the coronary flow reserve decreases. In addition to percentage stenosis, the length of the stenosis and the number of stenotic segments affect the hemodynamic significance of stenosis. The eccentric type stenosis is not only mechanically compliant, but it also changes the area of stenosis with the alteration of vasomotor tone. Accordingly, pressure-dependent and vasomotor tone-dependent diameter change should be taken into consideration in the compliant stenosis. Following our intraoperative measurements of blood flow velocities, the flow separation and flow disturbance were observed in the poststenotic region in human coronary arteries. The systolic-to-diastolic flow ratio was high in stenotic coronary arteries, while the ratio was normalized after bypass grafting in most patients.

Intraoperative Evaluation of Blood Velocity Waveforms in Different Types of Coronary Artery Bypass Grafts-Sequential Saphenous Vein Graft and Internal Mammary Artery Graft

The patency of the aorta-coronary bypass grafting may closely relate to the velocity profile and flow disturbance in the graft as well as the volume flow rate. In this study, we investigated the blood velocity in two different types of graft, i.e., sequential saphenous vein graft (SSVG) and internal mammary artery graft (IMAG). The SSVG was anastomosed to the major diagonal branch (DIAG) by side-to-side (SSA) anastomosis and to the left anterior descending coronary artery (LAD) by end-to-side anastomosis (EDA in 13 patients who had 75–100% and 75–90% stenoses in the LAD and major diagonal branch, respectively. The IMAG anastomoses were performed to the LAD in 10 patients with 75–100% stenoses of the artery. The blood velocity measurements were performed by 10 MHz 80 channel pulsed Doppler method during surgery. In six patients in the SSVG group, we investigated the configuration of the velocity profile at the region just proximal to the SSA and at the bridge portion between the SSA and EDA. In the other seven patients, we measured the blood flow velocity at several centimeters proximal to the SSA and compared it with that in the IMAG. At the region just proximal to the SSA, the velocity profile skewed toward the anastomosis side wall in all patients, and the flow velocity near the wall opposite to the SSA was reversed in five of six patients. In the bridge portion, directional changes in skewing of the velocity profile were recognized, that is, a skewed pattern toward the wall opposite to the anastomosis (four patients) or a symmetric pattern (two patients). The peak diastolic velocity in the region was 25.4±5.8 cm/sec, significantly lower than that (46.6±12.3 cm/sec) just proximal to the SSA. The velocity profile across the IMAG several centimeters proximal to the graft-coronary anastomosis showed a parabolic configuration with a narrow spectrum. The peak diastolic velocity in the IMAG (26.6±2.0 cm/sec) was almost the same as that in the SSVG (26.6±5.5 cm/sec), but the estimated graft diameter of the IMAG (2.3±0.2mm) was significantly smaller than that of the SSVG (3.4±0.5 mm). These findings may provide insight into the underlying mechanism of graft viability because the patterns of blood flow seem to be a contributory factor in determining the fate of the graft.

Intraoperative Evaluation of Blood Velocity Waveforms in Different Coronary Artery Bypass Graft

We investigated the characteristics of blood velocities in different types of coronary bypass grafts, i.e., the saphenous vein graft (SVG; 6 cases) vs the internal mammary artery graft (IMAG; 6 cases) and for different positioning of the sequential saphenous vein bypass graft (SSVG), i.e., the side-to-side anastomosis (SSA) vs the end-to-side anastomosis (ESA), the life span of which are known to be different. The blood velocities were measured by the dual mode (zerocross and FFT), multichannel, high frequency ultrasound Doppler method during bypass graft surgery. Comparing the blood velocities in the SVG with those in the IMAG (longer life span), the velocity profile was much more parabolic and the velocity spectrum was narrower in the IMAG. Regarding the velocities in the SSVG (the SSA has longer life span), the skew of the velocity profile and the reverse flow at the position just proximal to the SSA were always recognized near the probe-side wall (the opposite side of the SSA), indicating the existence of flow separation and recirculation in this region. The direction of skew changed between the SSA and the ESA in almost all cases. These patterns of blood flow seem to be a contributory factor in determining the fate of the graft.