Myocardial perfusion can be quantified from time-intensity curves derived from the anterior myocardium after LA injection of contrast. Background-subtracted peak video intensity in this situation correlates closely with MBV. When MBV and MBF are closely coupled, such as during inotropic stimulation of the heart, background-subtracted peak video intensity also correlates closely with MBF. Since there are similarities in the models of LA and venous injections, these data indicate that it may be feasible to quantify myocardial perfusion with myocardial contrast echocardiography after venous injection of contrast.

Vasodilation of microvessels distal to a stenosis results in an increase in myocardial blood volume (MBV). The purpose of this study was to examine the changes in MBV induced by graded coronary artery stenoses by using myocardial contrast echocardiography (MCE). Accordingly, 21 dogs underwent progressive stenosis of a coronary artery in a random order, the severity of which was judged by the pressure distal to it. Total myocardial blood flow (MBF) to the bed distal to the artery (both anterograde and collateral) was measured by injection of radiolabeled microspheres into the left atrium. In seven dogs, anterograde and total MBF were measured at each stenosis stage by injection of different microspheres into the left atrium and directly into the coronary artery, respectively. MBV was calculated by dividing MBF by the mean transit rate of microbubbles injected directly into the coronary artery during MCE. The perfusion bed size of the artery was also measured by MCE. Our major findings are as follows: 1) there is a nonlinear increase in MBV with increasing degrees of coronary stenosis until the coronary stenosis becomes critical; 2) at moderate levels of coronary stenosis, MBV remains constant despite ongoing autoregulation because of reduction in the size of the perfusion bed supplied by the stenotic vessel; and 3) after exhaustion of autoregulation, a decrease in MBV is noted with increasing levels of stenosis. We conclude that assessment of MBV provides insights into myocardial perfusion distal to a coronary stenosis above and beyond that provided by the measurement of MBF alone.

FS-069 produces no changes in hemodynamic function, myocardial blood flow, left ventricular wall thickening or pulmonary gas exchange when injected intravenously in large amounts. When diluted FS-069 is injected into the coronary artery, a very small fraction of the larger bubbles are entrapped within the microcirculation, resulting in a persistent contrast effect. Thus, although FS-069 is a safe intravenous echocardiographic contrast agent, it cannot provide information on myocardial blood flow when injected directly into a coronary artery.

RF catheter ablation not only results in a marked reduction in blood flow within the acute pathological lesion but also causes reduced flow beyond the borders of the acute lesion because of microvascular endothelial cell injury. The progression or resolution of tissue injury within the region beyond the border of the pathological lesion may explain the late electrophysiological effects of RF ablation.

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Background-Currently, the detection of noncritical coronary stenoses requires some form of stress. We hypothesized that these stenoses can be detected at rest without recourse to stress by assessing adaptive changes that occur distally in the microcirculation. Methods and Results-Phasic changes in myocardial video intensity (VI) were measured at rest with continuous high-mechanical-index (MI) contrast echocardiography in 15 open-chest dogs. Data were acquired at baseline and in the presence of different degrees of noncritical coronary stenosis. In 6 of these dogs, capillary blood volume was also measured at baseline using high-MI intermittent imaging with triggering performed separately at both end diastole and end systole. During continuous high-MI imaging, a significant increase in systolic VI was noted with coronary stenoses that resulted in progressive increases in the systolic/diastolic VI ratio with greater degrees of stenosis (Pϭ0.003), with a mildly quadratic relation noted between the two: yϭ1.3 · 10 Ϫ6 · x 2 ϩ0.01xϩ0.32, PϽ0.001, rϭ0.76, SEEϭ0.14. There was no difference in capillary blood volume between end diastole and end systole at baseline. Conclusions-Capillary blood volume does not change between diastole and systole in vivo. Phasic changes in VI are noted at baseline during high-MI continuous imaging. The systolic component is negligible at baseline but increases with increasing levels of noncritical coronary stenosis because of adaptive changes in the microcirculation distal to the stenosis. Thus, the measurement of phasic changes in myocardial VI has the potential to detect coronary stenosis at rest without recourse to any form of stress. Key Words: stenosis Ⅲ echocardiography Ⅲ blood volume B ecause of autoregulation, coronary blood flow (CBF) remains normal at rest until a coronary stenosis exceeds Ϸ85% in severity. 1,2 In the absence of a prior infarction, therefore, noncritical coronary stenoses cannot be detected by cardiac imaging at rest, and some form of stress is required to induce either regional dysfunction or a perfusion abnormality. The same is true even for electrocardiography.When coronary arterioles dilate in the presence of a noncritical stenosis, their blood volume (aBV) increases. 3,4 A portion of these arterioles are intramyocardial. 5 We hypothesized that because the degree of dilation of the coronary arterioles is related to the severity of stenosis, 3,4,6 aBV should increase in proportion to coronary stenosis severity. If this phenomenon could be measured noninvasively, the presence and severity of noncritical coronary stenosis could be measured at rest without recourse to any form of stress.Whereas phasic changes in intramyocardial arteriolar dimensions have been documented during cardiac contraction, 7 there is controversy regarding changes in capillary dimensions during this period. 8 -11 We postulated that because arterioles and venules are larger than capillaries, their compression would occur early in systole, causing an increase in their resistance that would re...

When myocardial necrosis coexists with post-ischemic myocardial dysfunction and no residual coronary stenosis, the absolute degree of wall thickening during dobutamine can be used to determine the extent of myocardium that has escaped necrosis. The dose of dobutamine needed to elicit maximal thickening of the postischemic myocardium is related to the amount of myocardial necrosis.

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