Coronary vascular injury after transient coronary artery occlusion.

BACKGROUND: Microvascular function was examined in dog hearts subjected to transient coronary artery occlusion. EXPERIMENTAL DESIGN: Temporary coronary artery occlusion (15 or 30 minutes) followed by prolonged reperfusion (24 to 72 hours) was performed in dogs. Myocardial blood flow (radioactive microspheres), vascular permeability (human serum albumin uptake), and apparent vascular volume (radioactively labeled erythrocytes) were used as measures of vascular function. Myeloperoxidase was used as a measure of leukocyte uptake. Free radical formation was measured by electron spin resonance using a spin trapping agent (phenyl N-tert-butylnitrone). RESULTS: A 30-minute occlusion followed by reperfusion produced prolonged hyperemia, increased vascular permeability, increased apparent vascular volume, and increased leukocyte uptake. Extravasation of red blood cells and carbon black was present within the coronary artery distribution. The altered vascular function was temporally correlated with prolonged leukocyte uptake and free radical production, returning to control values only at 72 hours. A 15-minute occlusion increased vascular permeability at 24 hours, without altering myocardial blood flow or apparent vascular volume. Transmural myocardial leukocyte accumulation after a 15-minute occlusion was minimal in the absence of myocardial infarction or other histologic alterations. Active free radical formation was minimal at 24 hours, with a return of vascular permeability to control values at 48 hours. CONCLUSIONS: The data demonstrate prolonged dysfunction of the coronary microvasculature after a transient 30-minute occlusion of the left anterior descending coronary artery. The prolonged injury is associated temporally with leukocyte uptake and free radical formation in the presence of minimal infarction. A transient 15-minute occlusion produces a different pattern of vascular dysfunction with an abbreviated duration (24 hours), not associated with myocardial necrosis, extensive leukocyte uptake, nor prolonged free radical formation.

Digitizing and signal averaging of left ventricular pressure signals using a dedicated radionuclide imaging system.

A method for obtaining left ventricular (LV) volume curves, synchronized with average LV pressure (LVP) curves for calculation of LV contractility, is described. Multiple gated blood pool imaging was performed to calculate average LV volume curves. Simultaneously with this acquisition, LVPs and aortic pressures were measured by indwelling catheters and recorded on an FM tape recorder. These signals were fed to the computer as image information and averaged and processed by the software developed for this purpose. Pressure resolution of the calibrated images was 4 mmHg/pixel when provision was made for a maximum pressure of 200 mmHg. A good correlation (r = 0.99) was obtained between the calculated peak LVPs and mean peak LVPs read from the chart recorder. The regression equation was: digitized peak LVP = 1.04 x chart recording--5.11 mmHg and the standard error of the estimate was 2.9 mmHg. Similar results were obtained with the aortic pressure (AP) measurements (digitized AP = 0.94 x chart recording + 6.37 mmHg, the standard error of the estimate was 3.8 mmHg). The digitized data also allowed the construction of pressure-volume loops for interpretation of ventricular contractility.

New method for measuring myocardial blood flow by high resolution scintigraphy in the excised dog heart.

The standard method for measuring myocardial blood flow (MBF) with radioactive microspheres requires processing of selected tissue samples usually from the excised heart, and consequent loss of exact relation to myocardial morphology. A computer-based image processing method was developed by using [99mTc]microspheres (mean particle size 20 microns) for quantitative analysis of MBF in 25 dogs. A computer-controlled gamma camera was used to obtain the images of radioactive microsphere distribution in transaxial slices of the ex vivo heart. Any portion of these slice images could be quantitated by using a computer program based on modification of the formula for determining MBF by the standard microsphere method. Regional myocardial perfusion calculated by this technique correlated well with values obtained with reference microspheres (r = 0.96) over a broad range of MBF. The results show that our new method, accurately and with high resolution, delineated zones of differing MBF and confirmed the increase of MBF in surviving myocardium with healing.

Influence of attenuation on radionuclide stroke volume determinations.

Using a method for determination of absolute volumes, including correcting for attenuation, we have explored the ability of the method to determine stroke volume in humans by radionuclide techniques. Thermodilution cardiac output determinations and multigated equilibrium blood-pool scintigraphy in the LAO view were performed simultaneously in twenty patients in which no evidence of intracardiac shunts or valvular disease was present. The correlation was good between the attenuated radionuclide and thermodilution stroke volume (r = 0.80, s.e.e. of estimate = 12 ml; SVtd = 2.31 x SVr + 18 ml). When correction for attenuation was made, the correlation improved (r = 0.96, s.e.e. = 6 ml) and approached the line of identity (SVtd = 0.99 x SVr + 1.2 ml). The correlation was also good between radionuclide cardiac output, corrected for attenuation, and the thermodilution cardiac output (r = 0.89, s.e.e. = 0.36 l/min; COtd = 0.86 x COr + 0.67 l/min). Thus our method of correction for attenuation in the determination of absolute left-ventricular volumes has been shown to provide a reliable, noninvasive means of calculating stroke volume and cardiac output in humans, without the use of geometric assumptions or regression equations.

Comparison of Indium-111 platelet scintigraphy and two-dimensional echocardiography in the diagnosis of left ventricular thrombi.

In a study comparing indium-111 platelet scintigraphy and two-dimensional echocardiography as methods of identifying left ventricular thrombi, the results obtained with both techniques were verified at surgery or autopsy in 53 patients--34 with left ventricular aneurysms, and 19 with mitral-valve disease. Left ventricular thrombi were found at surgery or autopsy in 14 of the patients with aneurysms and in none of those with mitral-valve disease. Thirteen of 53 echocardiograms (25 per cent) were technically inadequate and excluded from the analysis. In the group with aneurysms, the sensitivity of scintigraphy in detecting thrombi was 71 per cent, and that of echocardiography was 77 per cent. The specificity of scintigraphy was 100 per cent, and that of echocardiography was 93 per cent. We conclude that indium-111 platelet scintigraphy and two-dimensional echocardiography have useful and complementary roles in the detection of left ventricular thrombi. Both these noninvasive techniques can be used to monitor therapy.

"Circumferential profiles:" a new method for computer analysis of thallium-201 myocardial perfusion images.

A method for computer analysis of thallium-201 scintigrams is described, in which the left-ventricular activity is measured along radii constructed from the center of the left ventricle (LV) to each point on the LV circumference. Data are then displayed graphically as a "circumferential profile" of normalized activity against radial location. Thallium defects are identified and scored by comparison of the profile curve with empirically determined normal limits. In patients with coronary artery disease, defect scores were found to be quantitative and reproducible, and to agree generally with subjective visual analysis.

Analysis of left ventricular function from multiple gated acquisition cardiac blood pool imaging. Comparison to contrast angiography.

Global ventricular function was evaluated by both multiple gated cardiac blood pool scans (MUGA) and contrast ventriculograms in a group of 17 patients with suspected coronary artery disease. The contrast ventriculograms were analyzed frame by frame to generate a volume versus time curve for each patient, while the tracer data were analyzed by two methods: 1) the standard method, in which the left ventricle is identified on the end-diastolic frame and the background corrected activity under the region of interest obtained from the entire cardiac cycle, and displayed as a time versus activity curve; and 2) by a semi-automatic method in which the computer applies a threshold detection program to define the ventricular borders, and activity in the chamber at each point in the cardiac cycle is defined after background correction. The tracer data in each patient were analyzed independently by four observers. The tracer data correlated with the contrast data on a point by point basis r = 0.87 for the standard method, and 0.93 for the semi-automatic technique. An F test of variance revealed the semi-automatic method superior to the standard approach (P less than 0.05).