ALTERATIONS IN ULTRASONIC BACKSCATTER DURING EXERCISE-INDUCED MYOCARDIAL-ISCHEMIA IN HUMANS

Background Experimentally induced myocardial ischemia in animals cause s tissue modifications that alter characteristics of the ultrasonic be am backscattered from the myocardial muscle. Alterations of backscatte r parameters have been evidenced in human subjects with acute or remot e myocardial infarction and during ischemia induced by angioplasty bal loon occlusion or pharmacological stimuli. The effects of transient ef fort ischemia in humans have not been reported. The purpose of this st udy is to assess ultrasonic backscatter parameter changes induced by t ransient effort myocardial ischemia in human subjects. Methods and Res ults Nineteen patients with single left anterior descending coronary s tenosis and 15 healthy subjects underwent ultrasonic backscatter analy sis (parasternal long-axis view) at rest, immediately after a supine s tress test, and 30 minutes later. Two windows were selected in each ul trasonic study: one encompassing the septum; the other, the posterior wall. Integrated backscatter was computed throughout the cardiac cycle , yielding a power curve relative to the midmyocardial region of the m yocardial wall (excluding pericardial and endocardial borders). Five p arameters were computed from the backscatter power curve: the maximum- minimum difference, amplitude and phase of the first harmonic Fourier fitting, phase-weighted amplitude, and time-averaged integrated backsc atter difference from rest (an index of overall myocardial reflectivit y). This protocol allowed comparison of the backscatter data from a re gion at risk of ischemia (the septum) with that from a region normally perfused (posterior wall) and a comparison with the same regions of t he control group during the three ultrasonic studies. All backscatter indexes in the septum were altered significantly by exercise compared with rest values, whereas no changes were found in the normally perfus ed posterior wall or in the septum of the control group. All modified parameters returned to baseline values at the time of the recovery stu dy. Conclusions These data indicate that transient, exercise-induced i schemia is associated with reduction of the cardiac cycle-dependent va riation of the integrated backscatter power curve, a temporal shift in the nadir of the power curve with respect to the R wave (phase increa se), and a small but detectable increase of myocardial reflectivity. T hese changes may be detected noninvasively in humans with ultrasonic b ackscatter analysis.