Peter Agger

The Three-Dimensional Arrangement of the Myocytes Aggregated Together Within the Mammalian Ventricular Myocardium

Although myocardial architecture has been investigated extensively, as yet no evidence exists for the anatomic segregation of discrete myocardial pathways. We performed post‐mortem diffusion tensor imaging on 14 pig hearts. Pathway tracking was done from 22 standardized voxel groups from within the left ventricle, the left ventricular papillary muscles, and the right ventricular outflow tract. We generated pathways with comparable patterns in the different hearts when tracking from all chosen voxels. We were unable to demonstrate discrete circular or longitudinal pathways, nor to trace any solitary tract of myocardial cells extending throughout the ventricular mass. Instead, each pathway possessed endocardial, midwall, and epicardial components, merging one into another in consistent fashion. Endocardial tracks, when followed towards the basal or apical parts of the left ventricle, changed smoothly their helical and transmural angulations, becoming continuous with circular pathways in the midwall, these circular tracks further transforming into epicardial tracks, again by smooth change of the helical and transmural angles. Tracks originating from voxels in the papillary muscles behaved similarly to endocardial tracks. This is the first study to show myocardial pathways that run through the mammalian left and right ventricles in a highly reproducible manner according to varying local helical and transmural intrusion angles. The patterns generated are an inherent feature of the three‐dimensional arrangement of the individual myocytes aggregated within the walls, differing according to the regional orientation and branching of individual myocytes. We found no evidence to support the existence of individual muscles or bands. Anat Rec, 2009.

Inside out: modern imaging techniques to reveal animal anatomy.

Animal anatomy has traditionally relied on detailed dissections to produce anatomical illustrations, but modern imaging modalities, such as MRI and CT, now represent an enormous resource that allows for fast non-invasive visualizations of animal anatomy in living animals. These modalities also allow for creation of three-dimensional representations that can be of considerable value in the dissemination of anatomical studies. In this methodological review, we present our experiences using MRI, CT and μCT to create advanced representation of animal anatomy, including bones, inner organs and blood vessels in a variety of animals, including fish, amphibians, reptiles, mammals, and spiders. The images have a similar quality to most traditional anatomical drawings and are presented together with interactive movies of the anatomical structures, where the object can be viewed from different angles. Given that clinical scanners found in the majority of larger hospitals are fully suitable for these purposes, we encourage biologists to take advantage of these imaging techniques in creation of three-dimensional graphical representations of internal structures.

Normal right ventricular three-dimensional architecture, as assessed with diffusion tensor magnetic resonance imaging, is preserved during experimentally induced right ventricular hypertrophy.

The three‐dimensional architecture of the right ventricular myocardium is a major determinant of function, but as yet no investigator‐independent methods have been used to characterize either the normal or hypertrophied state. We aimed to assess and compare, using diffusion tensor magnetic resonance imaging, the normal architecture with the arrangement induced by chronic hypertrophy. We randomized 20 female 5 kg piglets into pulmonary trunk banding (N = 16) and sham operation (N = 4). Right ventricular hypertrophy was assessed after 8 weeks. The excised and fixed hearts were subject to diffusion tensor imaging to determine myocyte helical angles, and the presence of any reproducible tracks formed by the aggregated myocytes. All banding animals developed significant right ventricular hypertrophy, albeit that no difference was observed in terms of helical angles or myocardial pathways between the banded animals and sham group animals. Helical angles varied from ∼70 degrees endocardially to −50 degrees epicardially. Very few tracks were circular, with helical angles approximating zero. Reproducible patterns of chains of aggregated myocytes were observed in all hearts, regardless of group. The architecture of the myocytes aggregated in the walls of the right ventricle is comparable to that found in the left ventricle in terms of endocardial and epicardial helical angles, however the right ventricle both in the normal and the hypertrophied state lacks the extensive zone of circular myocytes seen in the mid‐portion of the left ventricular walls. Without such beneficial architectural remodelling, the porcine right ventricle seems unsuited structurally to sustain a permanent increase in afterload. Anat Rec, 2009.

The hypertrabeculated (noncompacted) left ventricle is different from the ventricle of embryos and ectothermic vertebrates

Ventricular hypertrabeculation (noncompaction) is a poorly characterized condition associated with heart failure. The condition is widely assumed to be the retention of the trabeculated ventricular design of the embryo and ectothermic (cold-blooded) vertebrates. This assumption appears simplistic and counterfactual. Here, we measured a set of anatomical parameters in hypertrabeculation in man and in the ventricles of embryos and animals. We compared humans with left ventricular hypertrabeculation (N=21) with humans with structurally normal left ventricles (N=54). We measured ejection fraction and ventricular trabeculation using cardiovascular MRI. Ventricular trabeculation was further measured in series of embryonic human and 9 animal species, and in hearts of 15 adult animal species using MRI, CT, or histology. In human, hypertrabeculated left ventricles were significantly different from structurally normal left ventricles by all structural measures and ejection fraction. They were far less trabeculated than human embryonic hearts (15-40% trabeculated volume versus 55-80%). Early in development all vertebrate embryos acquired a ventricle with approximately 80% trabeculations, but only ectotherms retained the 80% trabeculation throughout development. Endothermic (warm-blooded) animals including human slowly matured in fetal and postnatal stages towards ventricles with little trabeculations, generally less than 30%. Further, the trabeculations of all embryos and adult ectotherms were very thin, less than 50 μm wide, whereas the trabeculations in adult endotherms and in the setting of hypertrabeculation were wider by orders of magnitude. It is concluded in contrast to a prevailing assumption, the hypertrabeculated left ventricle is not like the ventricle of the embryo or of adult ectotherms. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

A mathematical model of the mechanical link between shortening of the cardiomyocytes and systolic deformation of the left ventricular myocardium

BACKGROUND Left ventricular myocytes are arranged in a complex three-dimensional mesh. Since all myocytes contract approximately to the same degree, mechanisms must exist to enable force transfer from each of these onto the framework as a whole, despite the transmural differences in deformation strain. This process has hitherto not been clarified in detail. OBJECTIVE To present a geometrical model that establishes a mechanical link between the three-dimensional architecture and the function of the left ventricular myocardium. METHODS The left ventricular equator was modeled as a cylindrical tube of deformable but incompressible material, composed of virtual cardiomyocytes with known diastolic helical and transmural angles. By imposing reference circumferential, longitudinal, and torsional strains onto the model, we created a three-dimensional deformation field to calculate passive shortening of the myocyte surrogates. We tested two diastolic architectures: 1) a simple model with longitudinal myocyte surrogates in the endo- and epicardium, and circular ones in the midwall, and 2) a more accurate architecture, with progressive helical angle distribution varying from -60° in the epicardium to 60° in the endocardium, with or without torsion and transmural cardiomyocyte angulation. RESULTS The simple model caused great transmural unevenness in cardiomyocyte shortening; longitudinal surrogates shortened by 15% at all depths equal to the imposed longitudinal strain, whereas circular surrogates exhibited a maximum shortening of 23.0%. The accurate model exhibited a smooth transmural distribution of cardiomyocyte shortening, with a mean (range) of 17.0 (13.2-20.8)%. Torsion caused a shortening of 17.0 (15.2-18.9)% and transmural angulation caused a shortening of 15.2 (12.4-18.2)%. Combining the effects of transmural angulation and torsion caused a change of 15.2 (13.2-16.5)%. CONCLUSION A continuous transmural distribution of the helical angle is obligatory for smooth shortening of the cardiomyocytes, but a combination of torsional and transmural angulation changes is necessary to execute systolic mural thickening whilst keeping shortening of the cardiomyocytes within its physiological range.

Regional and Epi‐ to Endocardial Differences in Transmural Angles of Left Ventricular Cardiomyocytes Measured in Ex Vivo Pig Hearts: Functional Implications

Recent studies point toward the existence of a significant population of cardiomyocytes that intrude transmurally, in addition to those aligned tangentially. Our aim was to investigate the extent of transmural angulation in the porcine left ventricle using diffusion tensor magnetic resonance imaging (DTMRI). Hearts from eight 15 kg pigs were arrested in diastole. The ventricles were filled with polymer to maintain the end‐diastolic dimensions. All hearts were examined using DTMRI to assess the distribution of transmural angulation of the cardiomyocytes at 12 predetermined locations covering the entirety of the left ventricle. We found significant differences between the regions, as well as within the transmural subcomponents. In eight out of the 12 predetermined mural segments, the highest mean transmural angle was located sub‐endocardially. The greatest mean transmural angles were found in the anterior basal region, specifically 14.9 ± 6.0‐degree angle, with the greatest absolute value being 34.3‐degree angle. This is the first study to show the significant heterogeneities in the distribution of helical and transmural angles within the entirety of the left ventricular walls, not only for different depths within the ventricular walls, but also between different ventricular regions. The results show unequivocally that not all the contractile elements are aligned exclusively in tangential fashion within the left ventricle. The main function of the transmurally intruding component is most likely to equalize and normalize shortening of the cardiomyocytes at all depths within the myocardium, but our findings also support the notion of antagonistic forces existing within the myocardial walls. Anat Rec, 296:1724–1734, 2013.

Assessment of the Helical Ventricular Myocardial Band Using Standard Echocardiography

In the discussion of their recent article, Hayabuchi and his colleagues acknowledge that the “helical myocardial band” remains controversial. In the accompanying editorial, Buckberg harbored no such doubts. Are the limited echocardiographic findings illustrated truly sufficient for Hayabuchi and his colleagues to conclude that there is a “helical ventricular myocardial band”? They refer to a model that Torrent-Guasp had carved out of the ventricular muscular mass by disrupting myriads of myocardial branches, suggesting moreover that this band is freely moveable on itself. The histological studies produced by Hort and Feneis, however, provided evidence that the ventricular cone does not have discrete origins and insertions of the cardiomyocytes as found in skeletal muscle. Pettigrew had demonstrated more than a century ago the multiple interleaving sheets of cardiomyocytes to be found within the cone. Lev and Simkins, cited by Buckberg, also had emphasized that the cone can be dissected at the whim of the prosector, as achieved by Torrent-Guasp when subjectively producing the preparations now modeled by Buckberg. Our investigations, cited by Hayabuchi and colleagues, endorse the works of Feneis and Hort. The histological findings show no obvious anatomical substrate, other than the obvious change in alignment of the aggregated chains of cardiomyocytes, to explain the echocardiographic feature emphasized by the Japanese workers. They certainly provide none that represent a substantial proportion of the width of the septum, as the echocardiograms seem to suggest. The echogenic band is seen in the equatorial and basal regions of each of the walls of the left ventricle when viewed from the apex. No such band is seen when the ventricular mass is viewed using the parasternal window. We suggest that the echogenic band represents an area of distinct myocyte orientation within the continuous mesh of the septum, where the reflected ultrasound is perpendicular to the dominant orientation of the cardiomyocytes, thus giving maximum intensity compared with the surrounding tissue. The echogenic band, when viewed from the apex, therefore, is likely to represent no more than the chains of cardiomyocytes located within the mid-wall of the ventricular cone which are aligned circumferentially. The concept of the helical ventricular myocardial band does not model the circumferential orientation in this region. There are further problems, however, with the concepts advanced by Buckberg, His inferences are based on imaging systems that measure only strain, as opposed to assessing the local development of force. The onset of shortening is not identical with the onset of contraction, so it is his mistake to interpret late shortening as delayed contraction. We have shown that within the ventricular cone, there are extended zones in which the myocardium contracts auxotonically, that is, the force increases during systole. The features of such auxotonic contraction are delayed onset, restricted shortening, and delayed termination.

Comparison between TachoComb and TachoSil for surgical hemostasis in arterial bleeding: an animal experimental study.

BACKGROUND TachoComb has frequently been used for the treatment of both venous and arterial bleeding. However, anaphylactic reactions have been reported after repeated use of hemostatic agents containing aprotinin such as TachoComb. Because aprotinin is also associated with risk of renal failure, manufacturing of a new product--TachoSil--which lacks aprotinin seems a logic evolvement. Furthermore, thrombin on the TachoSil material has been changed from bovine in TachoComb to human origin. These changes in the biochemical composition could lead to changes in the hemostatic performance. Therefore, we aimed to disclose any difference in hemostatic efficacy of the two products. METHODS Twelve 70-kg pigs had controlled insults to the thoracic aorta with and without heparin administration. The iatrogenic lesion was randomly covered with either TachoComb or TachoSil and the time to hemostasis was measured. RESULTS Time to hemostasis when using TachoSil compared with TachoComb was increased 14% (-13% to 48%) with heparin and 10% (-26% to 66%) without heparin (mean +/- 95% confidence interval; p > 0.05 in both). Time to hemostasis with heparin administration increased significantly in both treatments: TachoComb 80% (26%-156%) (p = 0.001) and TachoSil 75% (18%-158%) (p = 0.005). CONCLUSION We found neither statistical nor clinical evidence that TachoComb should have better hemostatic properties than does TachoSil in arterial bleeding. Both TachoSil and TachoComb can be used with heparin administration, but significant prolongation of the time to hemostasis is to be expected for both products. TachoSil should be preferred to TachoComb due to the potential lower risk of side effects when using the former.

Insights from echocardiography, magnetic resonance imaging, and microcomputed tomography relative to the mid-myocardial left ventricular echogenic zone.

The anatomical substrate for the mid‐mural ventricular hyperechogenic zone remains uncertain, but it may represent no more than ultrasound reflected from cardiomyocytes orientated orthogonally to the ultrasonic beam. We sought to ascertain the relationship between the echogenic zone and the orientation of the cardiomyocytes.

The functional architecture of skeletal compared to cardiac musculature: Myocyte orientation, lamellar unit morphology, and the helical ventricular myocardial band.

How the cardiomyocytes are aggregated within the heart walls remains contentious. We still do not fully understand how the end‐to‐end longitudinal myocytic chains are arranged, nor the true extent and shape of the lamellar units they aggregate to form. In this article, we show that an understanding of the complex arrangement of cardiac musculature requires knowledge of three‐dimensional myocyte orientation (helical and intrusion angle), and appreciation of myocyte packing within the connective tissue matrix. We show how visualization and segmentation of high‐resolution three‐dimensional image data can accurately identify the morphology and orientation of the myocytic chains, and the lamellar units. Some maintain that the ventricles can be unwrapped in the form of a “helical ventricular myocardial band,” that is, as a compartmentalized band with selective regional innervation and deformation, and a defined origin and insertion like most skeletal muscles. In contrast to the simpler interpretation of the helical ventricular myocardial band, we provide insight as to how the complex myocytic chains, the heterogeneous lamellar units, and connective tissue matrix form an interconnected meshwork, which facilitates the complex internal deformations of the ventricular wall. We highlight the dangers of disregarding the intruding cardiomyocytes. Preparation of the band destroys intruding myocytic chains, and thus disregards the functional implications of the antagonistic auxotonic forces they produce. We conclude that the ventricular myocardium is not analogous to skeletal muscle, but is a complex three‐dimensional meshwork, with a heterogeneous branching lamellar architecture. Clin. Anat. 29:316–332, 2016.