The extent and rate of left ventricular wall thickening during systole has previously been shown to be a useful measure of regional ventricular function and to play an important role in the ejection of blood from the left ventricle. The relation among systolic wall thickening, the directional components of contraction, ejection fraction and force velocity measurements is therefore of interest in understanding the dynamics of contraction of the intact ventricle. This report describes a theoretical basis and method for using ventricular angiograms to quantify the separate contributions of longitudinal shortening, circumferential shortening and systolic wall thickening to overall ventricular performance in man. One hundred twenty-two patients with valvular, coronary or myocardial heart disease were studied with biplane angiocardiography during diagnostic cardiac catheterizations. The percent contribution of directional components to total work or power developed by a mid-wall equatorial element of myocardium was shown to be: longitudinal, 14 percent in normal and diseased ventricles; circumferential, 45 percent in normal, increasing to 55 percent in dilated ventricles (P less than 0.005); wall thickening, 40 percent in normal, decreasing to 31 percent in dilated ventricles (P less than 0.001). Thus, left ventricular contraction, which is expressed as systolic wall thickening, quantified separately from inward wall displacement due to mid-wall circumferential shortening, accounts for nearly half of segmental left ventricular work and power. The rate and extent of ventricular wall thickening correlated closely with ejection fraction (r = 0.92 and 0.95, respectively) and with velocity of circumferential shortening (r = 0.90 and 0.80, respectively). Previous models of ventricular and myocardial mechanics that include computations of mid-wall longitudinal and circumferential stress and strain do not appear to account for the large contribution of systolic wall thickening to the performance of the intact heart. Force-velocity relations as heretofore described may therefore be partial descriptors of myocardial function in the intact ventricle.

Angiocardiography↗

PubMed1976

Intercellular coupling in the atrioventricular node and other tissues of the rabbit heart.

1. A fluorescent tracer dye, sodium fluorescein (mol.wt. 332), was used to assess the relative degree of intercellular coupling in various tissues of the rabbit heart. 2. Dye was injected intracellularly by micro-iontophoresis. Subsequent movement into contiguous cells was monitored by video microscopy. From these data the permeability of the intercellular boundaries was computed. 3. The values of boundary permeability were consistent with those expected from previous studies with tracers whose molecular weights bracketed that of fluorescein. 4. In the atrium, ventricle, Purkinje strands and His bundle, the relative magnitude of the boundary permeability correlated reasonably well with the relative profusity of gap junctional area on the intercalated disk, the latter estimated from published data. 5. The rate of passage of dye between N cells of the atrioventricular, AV, node was at least three orders of magnitude lower than between cells of the other tissues studied; this result is consistent with published reports indicating few gap junctions between cells within the region of slow conduction. 6. Quantitative considerations based on these data indicate that N cells may not be sufficiently well coupled to permit impulse propagation through the AV node by intercellular current flow, alone.

Animals↗

PubMed1976

Sarcomere dynamics in intact cardiac muscle.

Elastic properties, length-tension relations, and some characteristics of unloaded shortening were measured at the sarcomere level in rat papillary muscles. Muscle length during contraction was controlled by a servo system, while instantaneous sarcomere length was measured with a light diffraction technique. Muscles quick-released to zero load recoiled by 6% of their length; of this, sarcomere shortening amounted to only 1.6%, the remainder of the series elastic recoil occurring outside the striated region of the muscle, i.e. at the damaged ends of the specimen adjacent to the mounting clips. The length-tension relation was obtained with the sarcomere length maintained constant during contraction. Peak isometric tension increased linearly with sarcomere length from 1.6 to 2.1 mum; but between 2.1 and 2.3 mum tension appeared to be constant. The velocity of sarcomere shortening in an unloaded contraction bore a functional relation to sarcomere length which was similar to that of isometric tension. Both isometric tension and velocity of unloaded shortening reached their peak values relatively early in the contractile cycle.

Animals↗

PubMed1975

Myocardial sarcomere dynamics during isometric contraction.

1. Sarcomere lengths were measured during rest and throughout the time course of isometric contractions in thin, isolated rat papillary muscles using light diffraction techniques. 2. Shortening of the sarcomere length occurred upon contraction at all muscle lengths, averaging 7% at optimal length and more at shorter lengths. Relative to the narrow range of sarcomere lengths spanning the length--tension curve, this degree of shortening was considerable. 3. Local changes of sarcomere length were quantitatively paralleled by local changes of tissue segment length, the latter demarcated by microspheres lodged within the muscle tissue. At all but the shortest muscle lengths, sarcomere shortening was fully accounted for by equivalent lengthening of the non-striated regions near the clamped ends of the preparation. 4. It seems likely that these regions near the clamped ends of the preparation. 4. It seems constitute the source of the large series elasticity characteristic of isolated papillary muscle preparations such as this.

Animals↗

PubMed1975