Regional comparison of midwall segment and area shortening in the canine left ventricle.

Abstract

SUMMARY. We used ultrasonic segment length gauges to examine the regional behavior of midwall fibers at different sites around the left ventricular minor axis in 12 anesthetized dogs. In six dogs (group I) with circumferentially oriented midwall gauges, significantly greater shortening of anterior than lateral or posterior wall segments was demonstrated over a range of left ventricular end-diastolic pressures from 2 to 18 mm Hg. Normalized end-diastolic segment lengths increased more in the anterior wall as end-diastolic pressure increased, suggesting that regional differences in diastolic distensibility may in part account for the observed shortening differences. To examine the extent to which shortening of longitudinally oriented fibers of the subendocardium and subepicardium might influence the behavior of the midwall circumferential fibers, we implanted mutually perpendicular midwall gauges circumferentially and longitudinally in the anterior and posterior walls in six dogs (group II). Longitudinal shortening of midwall fibers was negligible at low end-diastolic pressures, but increased significantly at higher end-diastolic pressures. In the anterior wall, there was greater circumferential than longitudinal shortening, whereas, in the posterior wall, shortening was similar in the two directions. Finally, we calculated the midwall area subtended by the mutually perpendicular gauges and found the systolic change in midwall area to be similar for the anterior and posterior walls at all end-diastolic pressures. We conclude that midwall fibers demonstrate considerable nonuniformity of contraction at different sites around the minor axis. This finding may be related in part to regional differences in diastolic distensibility or in functional interactions between fiber layers. Despite these complex regional, directional, and volume dependent differences in midwall segment function, the systolic changes in midwall area did not vary regionally. Thus, different midwall sites around the minor axis circumference appear to have similar overall contributions to the ejection of blood. (Circ Res 58: 678-691, 1986)

Relation between longitudinal, circumferential, and oblique shortening and torsional deformation in the left ventricle of the transplanted human heart.

“…In previous studies of the anterior midwall region in anesthetized, open-chest dogs, maximum shortening has been found in the Group I direction by a number of investigators, 13161929 although both Fenton et al 14 and Freeman et al 25 found this maximum in the Group II direction. We also found that circumferential (Group II) shortening was significantly greater than longitudinal (Group IV) shortening in the anterior wall, as did Lew and LeWinter 27 in their sonomicrometer studies in dogs.…”

Hyperkinesis without the Frank-Starling mechanism in a nonischemic region of acutely ischemic excised canine heart.

“…First, the pressure-length loop method can provide only unidirectional assessment of regional function, whereas myocardial fibers are variously oriented within the left ventricle30 and the extent and time course of segment shortening are different depending on the orientation of the segment. 16,[24][25][26] Second, the dimensions of the pressure-length loop area (mm Hg.cm or dyne/cm) differ from those of work or energy (dyne cm or joule). 16' 21 In contrast, the T-A loop area (mm Hg.ml) has the same dimensions as work or energy because 1 mm Hg.ml = 1.33 x 10 J.…”

Nonhomogeneous left ventricular regional shortening during acute right ventricular pressure overload.

“…End diastole was defined as the time when LV dP/dt increased to 10% of its peak value. 9 End systole was defined as the time 30 msec before peak negative dP/dt. This end-systolic timing was selected because, when we constructed LV pressure-length loops, the point 30 msec before peak negative dP/dt was consistently closer to the left upper corner of the loops than points 20 and 40 msec before peak negative dP/dt.…”

“…Plastic introducer sleeves were constructed so that the free-wall crystals were placed at the same midwall depth of 5 mm. 9 All crystals were inserted through small slits (3 mm in length) in the pericardium so that the pericardium was kept virtually intact.…”

“…The LV free-wall crystals were placed according to an external reference system similar to Freeman et al 10 and Lew and LeWinter * : The anterior long axis was the line connecting the bifurcation of the left main coronary artery and the apical dimple 10 ; the posterior long axis was the line connecting the inferior pulmonary vein and the apical dimple and roughly parallel to the posterior interventricular branches of the left circumflex coronary artery 9 ; and the lateral long axis was the line midway between the anterior and posterior external long axes. Three pairs of free-wall segment crystals, that is, anterior, lateral, and posterior, were implanted perpendicular to the corresponding external long axes.…”