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Coronary Microvascular Functional Reserve: Quantification of Long-term Changes with Electron-Beam CT—Preliminary Results in a Porcine Model¹

¹ From the Departments of Physiology and Biophysics (S.M., E.L.R.), the Department of Internal Medicine, Divisions of Cardiovascular Diseases (T.R.B., A.L.) and Hypertension (L.O.L.), the Section of Biostatistics (A.L.W., V.S.P.), and the Department of Diagnostic Radiology (P.F.S.), Mayo Clinic and Foundation, 200 First St SW, Alfred 2-409, Rochester, MN 55905. Received May 25, 2000; revision requested July 12; final revision received March 5, 2001; accepted March 23. Supported in part by National Institutes of Health research grant HL-43025. Address correspondence to E.L.R. (e-mail: elran@mayo.edu).

View larger version (48K): [in a new window]   Figure 1. Electron-beam CT scan (left) obtained during peak attenuation of the LV chamber at end diastole. The perfusion territory of the LAD is outlined in the anterior cardiac wall. The imaging sequence provided time-intensity curves (right), where each data point represents the average attenuation (in Hounsfield units [HU]) within the region of interest. These curves are used to obtain indexes of intramyocardial blood volume and perfusion (see text for details).

View larger version (25K): [in a new window]   Figure 2a. Graphs show absolute values (and mean ± SD) of (a) Doppler US-based intracoronary blood flow (CBF), (b) electron-beam CT-based intramyocardial blood volume (BV), and (c) perfusion (F) at rest and in response to adenosine at baseline and at follow-up. Within the baseline and follow-up studies separately, intracoronary blood flow, blood volume, and perfusion significantly increased in response to adenosine (P < .001, respectively). The increase in blood volume and perfusion at follow-up in response to adenosine was greater than that at baseline, and this is consistent with intracoronary blood flow measurements (P < .001 for blood volume, perfusion, and intracoronary blood flow).

View larger version (26K): [in a new window]   Figure 2b. Graphs show absolute values (and mean ± SD) of (a) Doppler US-based intracoronary blood flow (CBF), (b) electron-beam CT-based intramyocardial blood volume (BV), and (c) perfusion (F) at rest and in response to adenosine at baseline and at follow-up. Within the baseline and follow-up studies separately, intracoronary blood flow, blood volume, and perfusion significantly increased in response to adenosine (P < .001, respectively). The increase in blood volume and perfusion at follow-up in response to adenosine was greater than that at baseline, and this is consistent with intracoronary blood flow measurements (P < .001 for blood volume, perfusion, and intracoronary blood flow).

View larger version (24K): [in a new window]   Figure 2c. Graphs show absolute values (and mean ± SD) of (a) Doppler US-based intracoronary blood flow (CBF), (b) electron-beam CT-based intramyocardial blood volume (BV), and (c) perfusion (F) at rest and in response to adenosine at baseline and at follow-up. Within the baseline and follow-up studies separately, intracoronary blood flow, blood volume, and perfusion significantly increased in response to adenosine (P < .001, respectively). The increase in blood volume and perfusion at follow-up in response to adenosine was greater than that at baseline, and this is consistent with intracoronary blood flow measurements (P < .001 for blood volume, perfusion, and intracoronary blood flow).

View larger version (21K): [in a new window]   Figure 3. Graph shows the relationship between baseline and follow-up values of Doppler US-based intracoronary blood flow (CBF) and electron-beam CT-based perfusion (F) at rest and after adenosine. There is a good correlation between intracoronary blood flow and perfusion over the entire range of flow values. Variation of measurements around the regression line is primarily attributable to nonsimultaneous data acquisition (ie, temporal heterogeneity of myocardial perfusion) and to tomographic sampling of a myocardial subsection within the perfusion territory with electron-beam CT versus upstream assessment of blood flow through the entire perfusion bed with Doppler US (ie, spatial heterogeneity of myocardial perfusion).

View larger version (19K): [in a new window]   Figure 4. Graph shows the relationship between blood volume (BV) and perfusion (F) on the basis of parameters derived from electron-beam CT. Values are given at baseline (resting conditions = , adenosine = ) and at follow-up (resting conditions = , adenosine = ). Despite a different microvascular functional response to adenosine at baseline and follow-up, all values follow the same curvilinear line, which suggests that the relative distribution of recruitable and nonrecruitable vessels remained fairly constant in normal porcine hearts during the 3-month follow-up period (see text for details).

View larger version (22K): [in a new window]   Figure 5. Graphs show variation in (left) intramyocardial blood volume (BV) and (right) perfusion (F) measurements. Perfect alignment of these data with the line of identity would mean absence of temporal variation.