Effects of myocardial contraction on ultrasonic backscatter before and after ischemia

Abstract

To determine whether contraction and relaxation influence quantitative myocardial ultrasonic backscatter we measured systolic and diastolic integrated backscatter separately in 10 pentobarbital-anesthetized dogs with defined, paced heart rates, before and after coronary occlusion. Data were acquired from intramural sites by coupling a broadband 5-MHz transducer to the left ventricular epicardium. Integrated backscatter was obtained from seven sequential ECG gated intervals throughout the cardiac cycle over the frequencies of 2.5-7.5 MHz and referenced to values obtained with a steel reflector. Before coronary occlusion myocardium in all dogs exhibited a decrease in integrated backscatter from end diastole to end systole (P less than 0.05) in control zones and in zones destined to become ischemic (P less than 0.05). Thirty minutes after occlusion integrated backscatter did not change in control zones but was elevated in ischemic zones with blunting of the diastolic-to-systolic variation. Thus myocardium undergoing contraction exhibits a decrease in integrated backscatter, and measurement of integrated backscatter at end systole differentiates ischemic from normal myocardium.

<b>Dipyridamole Stress Echocardiography and Ultrasonic Myocardial Tissue Characterization in Predicting Myocardial Ischemia, in Comparison With Dipyridamole Stress Tc-99m MIBI SPECT Myocardial Imaging</b>

“…20) In a pooled analysis of data from 11 published series, the sensitivity and specificity of dipyridamole scintigraphy for CAD detection averaged 85% and 90%, respectively. 23) Our study results were compatible with those reported in the literature.…”

Ultrasonic tissue characterization of human hypertrophied hearts in vivo with cardiac cycle-dependent variation in integrated backscatter.

“…This hypothesis is supported by several experimental studies, [18][19][20][21][22] wherein this parameter has been demonstrated to decrease with myocardial ischemia19,22 and infarction.21,22 As opposed to measurement of absolute IB, the variation in IB in humans is obtainable with a current system because it does not require any calibration of ultrasound signals and subsequent standardization among subjects. Thus, cardiac cycle-dependent variation of IB can be used to assess alterations in the acoustic properties of the myocardium even in humans.…”

“…In seven of the 13 patients with HCM, an intracavitary pressure gradient, assessed with continuous-wave Doppler echocardiography,28 was greater than 40 mm Hg at rest, and in the other five patients, a pressure gradient equal to or greater than 40 mm Hg was provoked by exercise or inhalation of amyl nitrate. One patient with systemic hypertension (19) was included in the group of HCM because the degree of hypertrophy was considered to be much greater than expected in patients having mild to moderate hypertension alone. Sixteen normal subjects (five men and 11 women), ranging in age from 37 to 62 years (mean, 49 years), served as controls.…”

Two-dimensional ultrasonic tissue characterization: backscatter power, endocardial wall motion, and their phase relationship for normal, ischemic, and infarcted myocardium.

“…Barzilai et al 28 have shown that 30 min after coronary artery occlusion there is considerable blunting of the diastolic-to-systolic variation in integrated backscatter. We have made similar observations using a two-dimensional approach ( figure 3, A).…”

“…Thus, a variable must be free of any angle dependence with respect to the region of interest and free from attenuation effects. An absolute measurement such as mean backscatter power, which has been used by several investigators, 22,23,28,29 has certain reference difficulties that potentially limit its clinical usefulness. On the other hand, relative measurements such as the cyclic backscatter power and the phase relationship may be useful in the clinical environment.…”