LABORATORY INVESTIGATION TISSUE CHARACTERIZATION The dependence of myocardial ultrasonic integrated backscatter on contractile performance*

We have recently shown that the cardiac cycle-dependent variation in myocardial ultrasonic integrated backscatter is blunted with regional ischemia in dogs. To determine if global and intramural regional myocardial contractile performance can be quantified by integrated backscatter, we analyzed ultrasonic responses after induction of increased and decreased contractility in five dogs. A recently developed analog data-acquisition system for measuring integrated backscatter in real time was used to sample radiofrequency signals gated from subepicardial or subendocardial regions. Baseline recordings of integrated backscatter, left ventricular pressure, left ventricular dP/dt, and wall thickness were made at 12 left ventricular sites for both intramural regions. Contractility was modified subsequently by either paired pacing or propranolol to produce significantly elevated or depressed values for maximum left ventricular dP/dt compared with baseline (1083 + 289 to 1868 + 398 to 3001 + 570 mm Hg/sec; p < .01 for all). The amplitude of the cyclic variation of integrated backscatter was 50% greater (arithmetically) in subendocardial than in subepicardial regions for all treatments (7.6 -+ 0.3 vs 6.0 ± 0.5 dB, p < .001). The maximum rate of change in integrated backscatter waveforms during isovolumetric contraction was faster with paired pacing and slower with propranolol than at baseline for all regions (56 + 6 to 74 6 to 82 ± 5 dB/sec, p < .005). The maximum rate of change in integrated backscatter also was greater in subendocardial than subepicardial regions (p < .001). Thus, both regional and global differences in myocardial contractile performance are manifest quantitatively in integrated backscatter waveforms. We propose that the physiologic determinants of these differences may depend on regional and global variations in myofibril elastic characteristics. Circulation 72, No. 1, 183-192, 1985. CHARACTERIZATION OF MYOCARDIUM based on quantitative ultrasonic integrated backscatter measurements may permit noninvasive elucidation of cardiac pathology.'-' The physical basis for ultrasonic tissue differentiation of pathologic properties of the heart is reflected by the variation in intrinsic scattering properties among individual tissue types. For the heart, the scattering properties are determined in part by the local variations in density and compressibility of discrete intramural regions, and may vary throughout a selected volume of tissue.` Ultrasonic backscatter paFrom the Department of Medicine, Cardiovascular Division, and Department of Physics, Washington University, St. Louis. Supported in part by National Institutes of Health grants HL17646 (SCOR in Ischemic Heart Disease), HL28998, a Squibb Cardiovascular Research Fellowship (Dr. Perez), and NASA grant NSG-1601. Address for correspondence: Julio E. Perez, M.D., Box 8086, Cardiovascular Division, Washington University School of Medicine, 660 South Euclid Ave., St. Louis, MO 63110. Received Nov. 26, 1984; revision accepted April 4, 1985. *All editorial decisions for this article, including selection of reviewers and the final disposition, were made by a guest editor. This procedure applies to all manuscripts with authors from the Washington University School of Medicine. Vol. 72, No. 1, July 1985 rameters are modified substantially by pathologic changes. We have previously shown that irreversible morphologic changes accompanying experimental myocardial infarction or cardiomyopathy are associated with significant elevations in time-averaged ultrasonic integrated backscatter measurements.7 1 Furthermore, we found recently that physiologic myocardial contraction and relaxation are associated with a parallel, cyclic variation in integrated backscatter. 12 The magnitude of this cardiac cycle-dependent variation in integrated backscatter is reduced greatly with even brief ischemia in dogs and recovers with reperfus1ion.3, 14 However, the temporal association between segmental akinesis and blunted cyclic variation in backscatter does not establish that the magnitude of cyclic variation reflects myocardial contractile function quantitatively. The purpose of this study was to determine the dependence of ultrasonic integrated backscatter measurements on global and intramural regional myocardial contractile performance by analysis of ultrasonic responses after induced increased or decreased con183 by gest on A ril 4, 2017 http://ciajournals.org/ D ow nladed from