Paul P. Lunkenheimer

The three‐dimensional arrangement of the myocytes in the ventricular walls

Tche arrangement of the myocytes aggregated together within the ventricular walls has been the subject of anatomic investigation for more than four centuries. The dangers of analyzing the myocardium on the basis of arrangement of the skeletal myocytes have long been appreciated, yet some still described the ventricular myocardium in terms of a unique band extending from the pulmonary trunk to the aorta. Another current interpretation, with much support, is that the ventricular myocytes are compartmentalized in the form of sheets, albeit that the extent of division, and interrelations, of the sheets is less well explained. Histological examination, however, shows that the only muscular unit to be found within the myocardial walls is the cardiac myocyte itself. Our own investigations show that, rather than forming a continuous band, or being arranged as sheets, the myocytes are aggregated together as a three‐dimensional mesh within a supporting matrix of fibrous tissue. Within the mesh of aggregated myocytes, it is then possible to recognize two populations, depending on the orientations of their long axes. The first population is aligned with the long axis of the aggregated myocytes tangential to the epicardial and endocardial borders, albeit with marked variation in the angulation relative to the ventricular equator. Correlation with measurements taken using force probes shows that these myocytes produce the major unloading of the blood during ventricular systole. The second population is aligned at angles of up to 40° from the epicardium toward the endocardium. The correlation with measurements from force probes reveals that these intruding myocytes produce auxotonic forces during the cardiac cycle. The three‐dimensional arrangement of the mesh also serves to account for the realignment of the myocytes that must take place during ventricular contraction so as to account for the extent of systolic mural thickening. Clin. Anat. 22:64–76, 2009.

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.

A finite element model of the human left ventricular systole

Local wall stress is the pivotal determinant of the heart muscles systolic function. Under in vivo conditions, however, such stresses cannot be measured systematically and quantitatively. In contrast, imaging techniques based on magnetic resonance (MR) allow the determination of the deformation pattern of the left ventricle (LV) in vivo with high accuracy. The question arises to what extent deformation measurements are significant and might provide a possibility for future diagnostic purposes. The contractile forces cause deformation of LV myocardial tissue in terms of wall thickening, longitudinal shortening, twisting rotation and radial constriction. The myocardium is thereby understood to act as a densely interlaced mesh. Yet, whole cycle image sequences display a distribution of wall strains as function of space and time heralding a significant amount of inhomogeneity even under healthy conditions. We made similar observations previously by direct measurement of local contractile activity. The major reasons for these inhomogeneities derive from regional deviations of the ventricular walls from an ideal spheroidal shape along with marked disparities in focal fibre orientation. In response to a lack of diagnostic tools able to measure wall stress in clinical routine, this communication is aimed at an analysis and functional interpretation of the deformation pattern of an exemplary human heart at end-systole. To this end, the finite element (FE) method was used to simulate the three-dimensional deformations of the left ventricular myocardium due to contractile fibre forces at end-systole. The anisotropy associated with the fibre structure of the myocardial tissue was included in the form of a fibre orientation vector field which was reconstructed from the measured fibre trajectories in a post mortem human heart. Contraction was modelled by an additive second Piola–Kirchhoff active stress tensor. As a first conclusion, it became evident that longitudinal fibre forces, cross-fibre forces and shear along with systolic fibre rearrangement have to be taken into account for a useful modelling of systolic deformation. Second, a realistic geometry and fibre architecture lead to typical and substantially inhomogeneous deformation patterns as they are recorded in real hearts. We therefore, expect that the measurement of systolic deformation might provide useful diagnostic information.

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.

Statistical Analysis of the Angle of Intrusion of Porcine Ventricular Myocytes from Epicardium to Endocardium Using Diffusion Tensor Magnetic Resonance Imaging

Pairs of cylindrical knives were used to punch semicircular slices from the left basal, sub‐basal, equatorial, and apical ventricular wall of porcine hearts. The sections extended from the epicardium to the endocardium. Their semicircular shape compensated for the depth‐related changing orientation of the myocytes relative to the equatorial plane. The slices were analyzed by diffusion tensor magnetic resonance imaging. The primary eigenvector of the diffusion tensor was determined in each pixel to calculate the number and angle of intrusion of the long axis of the aggregated myocytes relative to the epicardial surface. Arrays of axially sectioned aggregates were found in which 53% of the approximately two million segments evaluated intruded up to ±15°, 40% exhibited an angle of intrusion between ±15° and ±45°, and 7% exceeded an angle of ±45°, the positive sign thereby denoting an epi‐ to endocardial spiral in clockwise direction seen from the apex, while a negative sign denotes an anticlockwise spiral from the epicardium to the endocardium. In the basal and apical slices, the greater number of segments intruded in positive direction, while in the sub‐basal and equatorial slices, negative angles of intrusion prevailed. The sampling of the primary eigenvectors was insensitive to postmortem decomposition of the tissue. In a previous histological study, we also documented the presence of large numbers of myocytes aggregated with their long axis intruding obliquely from the epicardial to the endocardial ventricular surfaces. We used magnetic resonance diffusion tensor imaging in this study to provide a comprehensive statistical analysis. Anat Rec, 290:1413–1423, 2007.

High-frequency oscillation in an adult porcine model

Objective: Controversy exists as to whether high‐frequency oscillatory ventilation can be used on babies and small laboratory animals only, or whether high‐frequency oscillatory ventilation can also be efficient in the adult patient and large (>65 kg body weight) laboratory animals. Moreover, controversy exists as to whether limitations in high‐frequency oscillation efficiency are caused by the size and shape of the bronchial system, by the lack of low impedant intersegmental gas flow in lung parenchyma, or by inappropriate high‐frequency ventilators and ancillary hardware. Therefore, our objective in this study using the adult pig as a model of the adult patient was to test whether the adult airway system is suited to the use of high‐frequency oscillatory ventilation or whether there are geometrical, structural, or functional limitations to efficient ventilation by high‐frequency oscillation. Design: Prospective, controlled, randomized comparison over 8 to 16 hrs of ventilatory management. Setting: Experimental thoracovascular surgery laboratory in a university hospital. Subjects: Fifteen adult, female, house swine (weight 90 to 140 kg). Interventions: We evaluated the ventilatory effect of a wide range of oscillation frequencies (10–15 to 35–45 Hz), tidal volumes (0.5 to 2.2 mL/kg), and bias flow volumes (10 to 70 L/min) at a mean airway pressure of 12 ± 1 cm H2O in anesthetized and relaxed pigs who did not have lung injury. Measurements and Main Results: Arterial blood gases are mainly dependent on tidal volume, frequency, and mean airway pressure. A threshold bias flow volume of 35 ± 5 L/min is required to prevent CO2 rebreathing. In the group of lightweight animals (65 to 99 kg), the most efficient frequency band for CO2 elimination was ∽25 Hz. The most efficient frequency band for arterial oxygenation was found to vary between individuals more than the most efficient frequency band for CO2 elimination. In the group of heavy animals (100 to 140 kg), no most efficient mean frequency could be assessed, probably because the excitation system was limited. We confirmed that tidal volume on its own had an effect on CO2 elimination (“tidal‐volume effect”), although CO2 elimination was mainly determined by the product of tidal volume and oscillation frequency (oscillated minute volume), at least up to a critical frequency. Beyond that frequency, CO2 elimination could not be enhanced. The most efficient mean airway pressure in unimpaired lungs was assessed at 12 ± 1 cm H2O. Conclusions: Adult pigs with a body weight in the range of the weight of clinical adult patients can be ventilated by high‐frequency oscillation at tidal volumes smaller than, equal to, or slightly more than anatomical deadspace. The most efficient frequency for gas exchange varied between individuals. Tidal volume had an enhancing effect on CO2 elimination. The frequency dependency of Pao2 may have been related to a frequency‐dependent structural remodeling of the airway system, which occurred even though the mean airway pressure was kept constant. These results demonstrate that failure of adequate ventilation by high‐frequency oscillation is caused by a) CO2 rebreathing, b) the avoidance of an appropriate alveolar recruitment strategy, and c) an underpowered, high‐frequency ventilatory system (oscillator) that is unable to deliver appropriate pressure oscillations. These limitations led to insufficient CO2 elimination and/or inadequate arterial oxygenation. (Crit Care Med 1994; 22:S37‐S48)

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.

Immediate Effects of Partial Left Ventriculectomy on Left Ventricular Function

Abstract Background: Attempts to prolong life or to improve the quality of life by partial left ventriculectomy in patients suffering from dilated cardiomyopathy have yielded strikingly variable results in leading surgical centers. Hypothesis: The outcome of patients after partiat left ventriculectomy depends on intraoperative myocardial protection together with appropriate long‐term pharmacotherapy. We further assume that partial removal of the fibrotic ventricular wall may lead to a particularly inhomogeneous pattern of wall stress, giving rise to the potential of a paradoxical increase in wall stress and the creation of arrhythmogenic foci. Methods: During surgery in 24 patients, local mesh tension was measured using needle‐force probes in up to five sites within the left ventricular wall before and after resection of the interpapillary mural segment. The data were used to calculate regional peak developed force and to identify any differences in the timing of local mechanical activity between the measured regions. Results: Mean decrease in regional wall stress was 42% (76 sites of measurement). However, we discovered a paradoxicat increase of 42% in 18 sites of measurement. The time delay in the onset of force development between the measured regions prior to surgery was 0 msec in 10 patients, up to 30 msec in 7 patients, and beyond 80 msec in 7 patients. After resection, the time delay increased considerably in incidence and duration. Conclusion: Ventriculectomy is an effective means of reducing wall stress. The unexpectedly high incidence of inhomogeneities in wall stress after asymmetrical surgical ventricular remodeling, currently typical for the classical Batista procedure, together with the asynchronous regional ventricular function that we found to increase after partial left ventriculectomy, needs further elucidation by electrophysiological investigations.

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.

Three-dimensional alignment of the aggregated myocytes in the normal and hypertrophic murine heart

Several observations suggest that the transmission of myocardial forces is influenced in part by the spatial arrangement of the myocytes aggregated together within ventricular mass. Our aim was to assess, using diffusion tensor magnetic resonance imaging (DT-MRI), any differences in the three-dimensional arrangement of these myocytes in the normal heart compared with the hypertrophic murine myocardium. We induced ventricular hypertrophy in seven mice by infusion of angiotensin II through a subcutaneous pump, with seven other mice serving as controls. DT-MRI of explanted hearts was performed at 3.0 Tesla. We used the primary eigenvector in each voxel to determine the three-dimensional orientation of aggregated myocytes in respect to their helical angles and their transmural courses (intruding angles). Compared with controls, the hypertrophic hearts showed significant increases in myocardial mass and the outer radius of the left ventricular chamber (P < 0.05). In both groups, a significant change was noted from positive intruding angles at the base to negative angles at the ventricular apex (P < 0.01). Compared with controls, the hypertrophied hearts had significantly larger intruding angles of the aggregated myocytes, notably in the apical and basal slices (P < 0.001). In both groups, the helical angles were greatest in midventricular sections, albeit with significantly smaller angles in the mice with hypertrophied myocardium (P < 0.01). The use of DT-MRI revealed significant differences in helix and intruding angles of the myocytes in the mice with hypertrophied myocardium.