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Torsion of the left ventricle (LV) is associated with rotation of the apex with respect to the base around the long axis of the LV. A mathematical model of LV mechanics, which relates torsion to transmural distribution of fibre shortening, was evaluated with two-dimensional echocardiography in nine anaesthetised closed-chest dogs. Torsion was calculated as the difference between the angles of rotation (radians) of echo-derived transverse cross-section projections of the LV obtained at the mitral valve and low papillary level, divided by the axial distance between these projections measured in a long-axis cross-section, and multiplied by the outer radius in a mid-papillary transverse projection of the LV. A shortening to torsion ratio (STR) was defined as the ratio of inner wall shortening to torsion occurring during ejection. In a series of 11 measurements, each based on frame-to-frame analysis of 15 cardiac cycles, STR was found to be 2.31 +/- 0.23 rad-1 (mean +/- SD), whereas the mathematical model predicted a STR value of 2.4 rad-1 over a wide range of preload, afterload and contractility levels. We conclude that two-dimensional echocardiography validates the presence of torsion in the normal canine left ventricle, as predicted by the model of left ventricular mechanics.

To facilitate the passage of echo contrast agents through the microcirculation and the echocardiographic study of myocardial perfusion, ultrasonic energy (sonication) was employed to produce contrast agents consisting of relatively uniform, stable and small (less than 10 mu diameter) gaseous microbubbles suspended in liquid solutions. The size and persistence of the microbubbles was verified by light microscopy and an in vitro system were employed for comparative assessment of peak echo amplitude and echo persistence characteristics of various contrast agents. The study indicated that although a variety of hand-agitated and sonicated contrast agents provided satisfactory echo intensities, sonication was clearly superior to the hand-agitation method, because sonication produced smaller, more uniform and more stable microbubbles that may be suitable for myocardial contrast echocardiography. It is concluded that of the contrast agents examined, sonicated solutions of sorbitol (70%) and dextrose (70%) appeared to have particular potential because of the small sizes of the microbubbles (6 +/- 2 and 8 +/- 3 mu, respectively) and their prolonged in vitro persistence. The use of sonication to produce standardized, small and stable microbubbles should facilitate physiologic passage of the contrast agent through the capillary beds and allow two-dimensional imaging of the left heart myocardium during right-sided, aortic root, coronary sinus or intracoronary contrast injections.

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SUMMARY Regional differences in wall motion and wall thickening were quantitated in the normal left ventricle using two-dimensional echocardiography (2-D echo). Using a computer-aided system, the left ventricle was subdivided in a standardized manner into 40 segments of five 2-D echo short-axis cross sections from the mitral valve level to the low left ventricle or apex. Measurements of sectional and segmental cavity areas, muscle areas and endocardial as well as epicardial peritneters, allowed assessment of contractile function using such indexes as endocardial systolic fractional area change (FAC), wall thickening (WTh), and circumferential fiber shortening (shortening). In 50 normal anesthetized, closed-chest dogs (including 10 studies in the conscious state) and in 32 normal humans, left ventricular contractile function increased significantly from base to apex. Thus, in anesthetized dogs, sectional FAC, WTh and shortening increased from left ventricular base to apex as follows: 39.4 ± 5.1% to 61.6 ± 7.2%, 20.5 ± 6.6% to 46.7 11.5% and 22.7 ± 3.4% to 35.4 5.9%, respectively. Similar trends were noted in conscious dogs. In man, sectional FAC, WTh and shortening also increased from the mitral valve to the low left ventricular level: 38.8 3.3% to 60.7 4.5%, 23.9 ± 5.6% to 28.9 ± 7.6% and 21.4 ± 5.0% to 30.6 ± 5.6%, respectively. Detailed segmental analysis in individual cross sections also revealed regional differences in contraction. Generally, contraction was most vigorous in posterior regions of the left ventricle. The septal regions exhibited lowest contraction at the base, but also the greatest increase from base to apex, both in the canine and human. Lateral regions did not show significant changes along the length of the left ventricle. Diastolic wall thickness also varied. We conclude that contraction in the normal left ventricle cannot be assumed to be uniform or symmetrical. These normal regional differences in function should be taken into account when evaluating altered physiologic states and in studying effects of therapeutic interventions.FOR MANY YEARS cardiologists have assumed that the pattern of contraction in the normal left ventricle is concentric and uniform, classically defined as synergic motion. i Most of the earlier studies aimed at characterizing ventricular function were therefore based on models and assumed myocardial fiber structure consistent with uniform contraction.2 3 However, animal investigations have shown that the distribution of fiber angles is complex and changes during systolic contraction; endocardial and epicardial fibers tend to be oriented longitudinally and midwall fibers circumferentially.4 A study by Greenbaum et al.5 indicates that the human cardiac fiber architecture is even more complex than previously thought. Thus, models based on uniform wall motion may not adequately describe LV function in normal states, a prerequisite for studying altered physiologic conditions. Clinical studies using cineventriculography in man have indicated that myocardial performance ...

The potential for the use of contrast echocardiography to study myocardial perfusion has generated efforts to develop standardized echo contrast agents. The two methods used in this laboratory to generate microbubbles in solutions serving as contrast agents included the widely used hand-agitation method and the newer ultrasonic microcavitation (sonication) method. The latter has been demonstrated to generate smaller and more uniform microbubbles in an in vitro system. The present study was designed to observe, by direct microscopic examination of a cat mesentery preparation, the behavior and fate of the microbubbles in an in vivo system. The in vivo mesentery observations confirm the critical role of microbubble size in its unhindered passage through the capillary vasculature. The smaller and more uniform sonicated microbubbles passed rapidly through the microcirculation along with the red blood cells, whereas the larger microbubbles were observed to coalesce and interrupt the flow of blood and subsequently collapse or shrink.

Two-dimensional echocardiography during agitated saline contrast injections into the left ventricle was applied in eight closed chest dogs to examine the degree of mitral valve regurgitation encountered with pacing from two sites: 1) at the right ventricular apex and 2) within the coronary sinus at the base of the left ventricle. Pacing was at a rate of 10 beats/min above the sinus rate, and ranged from 60 to 120 beats/min. Hemodynamic variables were monitored, and data on global and regional left ventricular function were derived from a series of short- and long-axis cross-sectional echographic images. The degree of valvular regurgitation was assessed independently by two observers, and systolic appearance of echo contrast in the left atrium was graded as 0 to +4. Although no mitral regurgitation was noted in sinus rhythm, regurgitation was severe with right ventricular apical pacing (3.2 +/- 0.7, mean +/- standard deviation) and relatively mild (0.9 +/- 0.7) with basal pacing (p less than 0.01 and 0.05, respectively). Relative to sinus rhythm, thermodilution stroke volume was significantly (p less than 0.05) depressed by both apical and basal pacing (from 32.6 +/- 14.6 to 25.0 +/- 7.9 and 26.0 +/- 7.6 cc, respectively), but there was no significant difference between the two pacing sites. Mapping of regional function at six levels of the left ventricle revealed significant heterogeneities, with maximal dysfunction noted in the vicinity of the pacing site. It is concluded that significant differences in mitral regurgitation exist depending on the site of pacing, with apical pacing causing severe regurgitation and abnormal regional contraction near the pacing site.