An improved method for detecting and quantifying cardiac muscle disarray in hypertrophic cardiomyopathy

Prevalence of Left Ventricular Myocardial Crypts in Japanese Patients

Objective Myocardial crypts are congenital abnormalities associated with hypertrophic cardiomyopathy (HCM) and other conditions. This study assessed the prevalence of myocardial crypts in Japanese patients. Methods Myocardial crypts were evaluated in a consecutive series of 300 patients (13-92 years old) who underwent computed tomography angiography (CTA) because of clinical suspicion of ischemic heart disease. Results We found a myocardial crypt incidence of 9.7% (29 patients) in our study population, with multiple crypts observed in 2.3% (7 patients). Among these, myocardial crypts were found in 2 out of 8 (25%) patients with hypertrophic cardiomyopathy (HCM), 1 of which was apical-type HCM. In patients with a single crypt (22 patients), the most common location of the crypt was at the left ventricular apex (16/22 patients, 72.7%), followed by the inferior wall (5/22 patients, 22.7%) and the interventricular septum (1/22 patients, 4.6%). Conclusion The incidence of myocardial crypts observed in our study aligns with that reported in previous studies, although the most common location among the Japanese population was the left ventricular apex.

Collagenase treatment reduces the anisotropy of ultrasonic backscatter in rat myocardium by reducing collagen crosslinks

Dysregulation of collagen deposition, degradation, and crosslinking in the heart occur in response to increased physiological stress. Collagen content has been associated with ultrasonic backscatter (brightness), and we have shown that the anisotropy of backscatter can be used to measure myofiber alignment, that is, variation in the brightness of a left ventricular short-axis ultrasound. This study investigated collagen's role in anisotropy of ultrasonic backscatter; female Sprague-Dawley rat hearts were treated with a collagenase-containing solution, for either 10 or 30 min, or control solution for 30 min. Serial ultrasound images were acquired at 2.5-min intervals throughout collagenase treatment. Ultrasonic backscatter was assessed from anterior and posterior walls, where collagen fibrils are predominately aligned perpendicular to the angle of insonification, and the lateral and septal walls, where collagen is predominately aligned parallel to the angle of insonification. Collagenase digestion reduced backscatter anisotropy within the myocardium. Collagen remains present in the myocardium throughout collagenase treatment, but crosslinking is altered within 10 min. These data suggest that crosslinking of collagen modulates the anisotropy of ultrasonic backscatter. An Anisotropy Index, derived from differences in backscatter from parallel and perpendicularly aligned fibers, may provide a noninvasive index to monitor the progression and state of myocardial fibrosis.

Cellular orientational fluctuations, rotational diffusion and nematic order under periodic driving

The ability of living cells to sense the physical properties of their microenvironment and to respond to dynamic forces acting on them plays a central role in regulating their structure, function and fate. Of particular importance is the cellular sensitivity and response to periodic driving forces in noisy environments, encountered in vital physiological conditions such as heart beating, blood vessel pulsation and breathing. Here, we first test and validate two predictions of a mean-field theory of cellular reorientation under periodic driving, which combines the minimization of cellular anisotropic elastic energy with active remodeling forces. We then extend the mean-field theory to include uncorrelated, additive nonequilibrium fluctuations, and show that the theory quantitatively agrees with the experimentally observed stationary probability distributions of the cell body orientation, under a range of biaxial periodic driving forces. The fluctuations theory allows the extraction of the dimensionless active noise amplitude of various cell types, and consequently their rotational diffusion coefficient. We then focus on intra-cellular nematic order, i.e. on orientational fluctuations of actin stress fibers around the cell body orientation, and show experimentally that intra-cellular nematic order increases with both the magnitude of the driving forces and the biaxiality strain ratio. These results are semi-quantitatively explained by applying the same cell body fluctuations theory to orientationally correlated actin stress fiber domains. Finally, an estimate of the energy scale of cellular orientational fluctuations for one cell type is shown to be about six order of magnitude larger than the thermal energy at room temperature. The implications of our findings, which make the quantitative analysis of cell mechanosensitivity more accessible, are discussed.

Identification of Myocardial Disarray in Patients With Hypertrophic Cardiomyopathy and Ventricular Arrhythmias

Background

Myocardial disarray is a likely focus for fatal arrhythmia in hypertrophic cardiomyopathy (HCM). This microstructural abnormality can be inferred by mapping the preferential diffusion of water along cardiac muscle fibers using diffusion tensor cardiac magnetic resonance (DT-CMR) imaging. Fractional anisotropy (FA) quantifies directionality of diffusion in 3 dimensions. The authors hypothesized that FA would be reduced in HCM due to disarray and fibrosis that may represent the anatomic substrate for ventricular arrhythmia.

Objectives

This study sought to assess FA as a noninvasive in vivo biomarker of HCM myoarchitecture and its association with ventricular arrhythmia.

Methods

A total of 50 HCM patients (47 ± 15 years of age, 77% male) and 30 healthy control subjects (46 ± 16 years of age, 70% male) underwent DT-CMR in diastole, cine, late gadolinium enhancement (LGE), and extracellular volume (ECV) imaging at 3-T.

Results

Diastolic FA was reduced in HCM compared with control subjects (0.49 ± 0.05 vs. 0.52 ± 0.03; p = 0.0005). Control subjects had a mid-wall ring of high FA. In HCM, this ring was disrupted by reduced FA, consistent with published histology demonstrating that disarray and fibrosis invade circumferentially aligned mid-wall myocytes. LGE and ECV were significant predictors of FA, in line with fibrosis contributing to low FA. Yet FA adjusted for LGE and ECV remained reduced in HCM (p = 0.028). FA in the hypertrophied segment was reduced in HCM patients with ventricular arrhythmia compared to patients without (n = 15; 0.41 ± 0.03 vs. 0.46 ± 0.06; p = 0.007). A decrease in FA of 0.05 increased odds of ventricular arrhythmia by 2.5 (95% confidence interval: 1.2 to 5.3; p = 0.015) in HCM and remained significant even after correcting for LGE, ECV, and wall thickness (p = 0.036).

Conclusions

DT-CMR assessment of left ventricular myoarchitecture matched patterns reported previously on histology. Low diastolic FA in HCM was associated with ventricular arrhythmia and is likely to represent disarray after accounting for fibrosis. The authors propose that diastolic FA could be the first in vivo marker of disarray in HCM and a potential independent risk factor.

Novel α-Actin Gene Mutation p.(Ala21Val) Causing Familial Hypertrophic Cardiomyopathy, Myocardial Noncompaction, and Transmural Crypts. Clinical-Pathologic Correlation

Background

Mutations of α‐actin gene (ACTC1) have been phenotypically related to various cardiac anomalies, including hypertrophic cardiomyopathy and dilated cardiomyopathy and left ventricular (LV) myocardial noncompaction. A novel ACTC mutation is reported as cosegregating for familial hypertrophic cardiomyopathy and LV myocardial noncompaction with transmural crypts.

Methods and Results

In an Italian family of 7 subjects, 4 aged 10 (II‐1), 14 (II‐2), 43 (I‐4) and 46 years (I‐5), presenting abnormal ECG changes, dyspnea and palpitation (II‐2, I‐4, and I‐5), and recurrent cerebral ischemic attack (I‐5), underwent 2‐dimensional echo, cardiac magnetic resonance, Holter monitoring, and next‐generation sequencing gene analysis. Patients II‐2 and I‐5 with ventricular tachycardia underwent a cardiac invasive study, including coronary with LV angiography and endomyocardial biopsy. In all the affected members, ECG showed right bundle branch block and left anterior hemiblock with age‐related prolongation of QRS duration. Two‐dimensional echo and cardiac magnetic resonance documented LV myocardial noncompaction in all and in I‐4, I‐5, and II‐2 a progressive LV hypertrophy up to 22‐mm maximal wall thickness. Coronary arteries were normal. LV angiography showed transmural crypts progressing to spongeous myocardial transformation with LV dilatation and dysfunction in the oldest subject. At histology and electron microscopy detachment of myocardiocytes were associated with cell and myofibrillar disarray and degradation of intercalated discs causing disanchorage of myofilaments to cell membrane. Next‐generation sequencing showed in affected members an unreported p.(Ala21Val) mutation of ACTC.

Conclusions

Novel p.(Ala21Val) mutation of ACTC1 causes myofibrillar and intercalated disc alteration leading to familial hypertrophic cardiomyopathy and LV myocardial noncompaction with transmural crypts.

Venous thromboembolism in an industrial north american city: temporal distribution and association with particulate matter air pollution

BACKGROUND

Emerging evidence, mainly from Europe and Asia, indicates that venous thromboembolism (VTE) occurs most often in winter. Factors implicated in such seasonality are low temperature-mediated exacerbation of coagulation and high levels of particulate matter (PM) air pollution. However, in contrast to most European and Asian cities, particulate matter pollution peaks in the summer in many North American cities.

OBJECTIVES

We aimed to exploit this geographical difference and examine the temporal distribution of VTE in a cold-weather, North American city, Detroit, with a summer PM peak. Our goal was thereby to resolve the influence of temperature and PM levels on VTE.

METHODS

Our retrospective, analytical semi-ecological study used chart review to confirm 1,907 acute, ambulatory VTE cases, divided them by location (Detroit versus suburban), and plotted monthly VTE frequency distributions. We used Environmental Protection Agency data to determine the temporal distribution of PM pollution components in Detroit. Suburban PM air pollution is presumed negligible and therefore not monitored.

RESULTS

Acute VTE cases in Detroit (1,490) exhibited a summer peak (June 24(th)) and differed from both a uniform distribution (P<0.01) and also that of 1,123 no-VTE cases (P<0.02). Levels of 10 µm diameter PM and coarse particle (2.5 to 10 µm) PM also exhibited summer peaks versus a winter peak for 2.5 µm diameter PM. Contrary to their urban counterparts, suburban cases of acute VTE (417) showed no monthly variation.

CONCLUSIONS

The summer peak of acute VTE in Detroit indicates that low temperature is not a major factor in VTE pathogenesis. In contrast, concordance of the 10 µm diameter PM, coarse particle, and the Detroit VTE monthly distributions, combined with no monthly suburban VTE variation, is consistent with a role for PM pollution. Furthermore, divergence of the VTE and 2.5 µm PM distributions suggests that particle size may play a role.

Visualizing collagen network within human and rhesus monkey vocal folds using polarized light microscopy

OBJECTIVES

Collagen fiber content and orientation affect the viscoelastic properties of the vocal folds, determining oscillation characteristics during speech and other vocalization. The investigation and reconstruction of the collagen network in vocal folds remains a challenge, because the collagen network requires at least micron-scale resolution. In this study, we used polarized light microscopy to investigate the distribution and alignment of collagen fibers within the vocal folds.

METHODS

Data were collected in sections of human and rhesus monkey (Macaca mulatta) vocal folds cut at 3 different angles and stained with picrosirius red.

RESULTS

Statistically significant differences were found between different section angles, implying that more than one section angle is required to capture the network's complexity. In the human vocal folds, the collagen fiber distribution continuously varied across the lamina propria (medial to lateral). Distinct differences in birefringence distribution were observed between the species. For the human vocal folds, high birefringence was observed near the thyroarytenoid muscle and near the epithelium. However, in the rhesus monkey vocal folds, high birefringence was observed near the epithelium, and lower birefringence was seen near the thyroarytenoid muscle.

CONCLUSIONS

The differences between the collagen networks in human and rhesus monkey vocal folds provide a morphological basis for differences in viscoelastic properties between species.

Prevalence and clinical profile of myocardial crypts in hypertrophic cardiomyopathy

BACKGROUND

In hypertrophic cardiomyopathy (HCM), cardiovascular MR can detect morphological abnormalities of the left ventricle (LV) not visualized with echocardiography. Although myocardial crypts (ie, narrow, blood-filled invaginations within the LV wall) have been recognized in HCM, all clinical implications of these structural abnormalities within the broad clinical HCM spectrum are not completely resolved. Therefore, we sought to characterize the prevalence and diagnostic significance of myocardial crypts in HCM patients.

METHODS AND RESULTS

Cine and late gadolinium enhancement cardiovascular MR and 2-dimensional echocardiography were obtained in 292 consecutive patients with HCM including 31 genotype-positive/phenotype-negative family members without LV hypertrophy (28 ± 16 years; 51% male) and 261 patients with LV hypertrophy (46 ± 18 years; 60% male). Ninety-eight subjects without cardiovascular disease were controls. Myocardial crypts (1-6/patient) were identified only by cardiovascular MR in 19 of 31 genotype-positive/phenotype-negative patients (61%) compared with only 10 of 261 (4%) patients with HCM with LV hypertrophy (P<0.001) and were absent in control subjects. Twelve-lead electrocardiograms were normal in 10 (53%) of the genotype-positive/phenotype-negative patients with crypts. Crypts were confined to the basal LV, most commonly in the ventricular septum (n=21) or posterior LV free wall (n=4), and associated with normal LV contractility and absence of late gadolinium enhancement in all but one patient.

CONCLUSIONS

LV myocardial crypts represent a distinctive morphological expression of HCM, occurring with different frequency in HCM patients with or without LV hypertrophy. Crypts are a novel cardiovascular MR imaging marker, which may identify individual HCM family members who should also be considered for diagnostic genetic testing. These data support an expanded role for cardiovascular MR in early evaluation of HCM families.

Fibrin architecture in clots: a quantitative polarized light microscopy analysis

Fibrin plays a vital structural role in thrombus integrity. Thus, the ability to assess fibrin architecture has a potential to provide insight into thrombosis and thrombolysis. Fibrin has an anisotropic molecular structure, which enables it to be seen with polarized light. Therefore, we aimed to determine if automated polarized light microscopy methods of quantifying two structural parameters; fibrin fiber bundle orientation and fibrin's optical retardation (OR: a measure of molecular anisotropy) could be used to assess thrombi. To compare fibrin fiber bundle orientation we analyzed picrosirius red-stained sections obtained from clots formed: (A) in vitro, (B) in injured and stenotic coronary arteries, and (C) in surgically created aortic aneurysms (n=6 for each group). To assess potential changes in OR, we examined fibrin in picrosirius red-stained clots formed after ischemic preconditioning (10 min ischemia+10 min reflow; a circumstance shown to enhance lysability) and in control clots (n=8 each group). The degree of fibrin organization differed significantly according to the location of clot formation; fibrin was most aligned in the aneurysms and least aligned in vitro whereas fibrin in the coronary clots had an intermediate organization. The OR of fibrin in the clots formed after ischemic preconditioning was lower than that in controls (2.9+/-0.5 nm versus 5.4+/-1.0 nm, P<0.05). The automated polarized light analysis methods not only enabled fibrin architecture to be assessed, but also revealed structural differences in clots formed under different circumstances.

Development of abnormal tissue architecture in transplanted neonatal rat myocytes

BACKGROUND

Most myocardial cell transplant studies focus on demonstration of improved function; however, such improvement depends on the development of appropriate tissue structure. Thus, our aim was to assess the architectural changes that occurred after cell transplant into normal and infarcted myocardium.

METHODS

Male neonatal cells (1 to 2 days old) were injected into the left ventricular free wall of adult female rats. The tissue was examined 0 to 1 days and 1 to 2, 4 to 6, and 12 weeks later in noninfarcted hearts and 6 months after transplant into infarcts. In histologic sections, we assessed the cells' retardation of polarized light (to measure development of contractile elements), two-dimensional cell orientation, cell nuclear morphology, and collagen content.

RESULTS

The transplant cells' retardation of polarized light gradually increased to 81% of that of host cells after 6 months (p < 0.001). The transplant cells were disorganized and although their nuclei increased in size, they always had a rounded appearance. Collagen content in the transplant was 210% to 430% higher than in host tissue (p < 0.01). In addition, scar collagen always separated transplant and host cells.

CONCLUSIONS

One architectural feature, the rounded nuclei, provided a distinctive marker to identify transplanted cells. Nevertheless, the transplants' inhibited muscle development together with disorganization, separation from the host muscle, and a substantial increase in collagen resulted in a structure unlikely to play an active role in systolic function.

Detection and assessment of laser-mediated injury in transmyocardial revascularization

When channels are made through the myocardium with a laser, tissue surrounding the channels is injured. Thus, methods of examining and quantifying the histologic changes caused by laser-mediated injury are required both for comparison of different channel making protocols and also to help understand the mechanisms of transmyocardial revascularization. The two principal components of the myocardium, collagen and muscle, are both normally birefringent. This optical property can be exploited with the use of polarized light microscopy to assess tissue structure at the cellular and subcellular levels allowing several different types of injury to be detected. Increases in tissue temperature above 60 degrees C for muscle and 70 degrees C for collagen decrease their birefringence and, hence, result in decreased brightness when viewed with polarized light. Lower temperatures may cause cell membrane injury, calcium overload, and the formation of contraction bands, which appear as areas of increased birefringence. In this way, the extent of thermal injury can be assessed. The same optical properties can be used to measure cell and fiber orientation and, hence, enable assessment of mechanical disruption of the tissue after ablation. Long-term remodeling of the myocardium in the form of scar formation, increased interstitial fibrosis, and muscle disarray can also be quantified. The ability to measure the acute injury and the long-term structural consequences of that injury with the use of polarized light microscopy should prove vital in determining the optimal laser "dose" required and may also reveal information on the mechanism(s) of benefit found with transmyocardial revascularization.

Imaging myocardial fiber architecture in vivo with magnetic resonance

Methods are presented to image the fiber architecture of the human myocardium in vitro and in vivo. NMR images are obtained of the diffusion anisotropy tensor, indicative of local myofiber orientation. Studies of cardiac necropsy specimens demonstrate classic features of ventricular myoarchitecture including the continuous endocardial to epicardial variation of fiber helix angles (angles to the ventricular circumferential direction) of approximately +1.3 to -1.3 radians. Cross-fiber anisotropy is also observed. In the beating heart, NMR diffusion data must be corrected for the effects of myocardial deformation during the cardiac cycle. This correction can be performed using an independent MRI method to map the strain-rate tensor field of the myocardium through time. Combining fiber orientation with local myocardial strain rate, local rates of myocardial fiber shortening may be computed.

Morphological changes in the normal pattern of ventricular myoarchitecture in the developing human heart

BACKGROUND

The aim of the present study was to describe the morphological changes in the normal pattern of ventricular myoarchitecture in the prenatal and adult human heart, to understand the three-dimensional organization of the muscle fibers and their active functional role in valvular dynamics.

METHODS

We used dissection and histological techniques in 56 human hearts from fetuses and adults of both sexes.

RESULTS

In all hearts, the ventricular wall was arranged in three different layers: superficial (subepicardial), middle, and deep (subendocardial) myocardium. The superficial and deep layers are present in both ventricles, whereas the middle layer is found only in the left ventricle. Age-related differences were noted in the pattern of myoarchitecture of the superficial layer, mainly in the fetal period, and especially in the right ventricle; however, the middle layer always shows a circumferential pattern, which is specially evident in elderly hearts. The ventricular fibers in the superficial and deep layers are anchored in the ventricular orifices.

CONCLUSIONS

Our findings reveal that muscle fiber architecture showed age- but not sex-related differences. These variations may reflect a mechanism of adaptation of the heart to functional demands throughout life.

Mapping of the orientation of myocardial cells by means of polarized light and confocal scanning laser microscopy

The study of the topological organisation of myocardial cells is a basic requirement for the understanding of the mechanical design of the normal and pathological heart. We developed a technique based on multiparametric image analysis of transmitted polarized light to generate maps of the azimuth and the elevation angles of the myocardial cells. The properties of birefringence of the myocardium embedded in methylmetacrylate were measured in papillary muscles with monitored 3D orientation. This birefringence is positive uniaxial with a 0 degree extinction angle when the axis of the fiber is parallel to the axis of the polarizer or the analyzer. Thick sections were studied between crossed polars, and four images of each section were digitized for an angle of the polarizer with the section varying from 0-67.5 degrees in steps of 22.5 degrees. The amounts of transmitted light for each setup of the polarizer were combined in order to extract the values of the azimuth angle (modulo 90 degrees) and the elevation angle of the myocardial cells, according to the Johannsen equation. The respective maps of these angles were calculated and then assessed with confocal scanning laser microscopy. This method provides an efficient and accurate tool for the study of the histological architecture of the fetal and neonatal heart.

Method for the study of the three-dimensional orientation of the nuclei of myocardial cells in fetal human heart by means of confocal scanning laser microscopy

A series of three-dimensional image analysis tools are used to measure the three-dimensional orientation of nuclei of myocardial cells. Confocal scanning laser microscopy makes it possible to acquire series of sections up to 100 microns inside thick tissue sections. A mean orientation vector of unit length is calculated for each segmented nucleus. The global orientation statistics are obtained by calculating the vectorial sum of the nuclear unit vectors. The final orientation is expressed by a mean azimuth angle, an elevation angle and a measure of the angular homogeneity. The method is illustrated for two different regions of the myocardium (interventricular septum and papillary muscle) of a normal human fetal heart. This quantitative method will be used to assess and calibrate the information provided by polarized light microscopy.

Accumulation and assembly of myosin in hypertrophic cardiomyopathy with the 403 Arg to Gln beta-myosin heavy chain mutation

The sarcomeric proteins and organization of cardiac myofibrils appeared intact in multiple unrelated patients with hypertrophic cardiomyopathy. In two subjects demonstrating the missense mutation at position 403 (Arg to Gln) in the beta-myosin heavy chain gene, total myosin and immunoreactive beta-myosin heavy chain levels were similar to those found in other patients with hypertrophic cardiomyopathy and various disease control subjects. No alteration in expression of the cardiac alpha-myosin heavy chain gene was observed. These results are consistent with the examined myosin heavy chain mutation, permitting proper accumulation and assembly of myosin while primarily impairing contractile function. The characteristic myocyte disarray would appear likely to be a secondary consequence of the mutations.

Myocardial disarray at junction of ventricular septum and left and right ventricular free walls in hypertrophic cardiomyopathy

The abnormality of the myocardium in hearts with hypertrophic cardiomyopathy (HC) was assessed regarding whether the muscle bundle in the mid-wall layer maintains its normal circular and continuous orientation surrounding the left ventricular (LV) cavity. Forty-seven autopsied hearts with HC were examined. The LV wall midway between the base and apex was divided into 6 segments in the transverse plane. Histologically, the circular orientation was destroyed largely or completely due to marked fascicle disarray in 77% of the anterior and posterior junctional segments. In 33% of the middle portion of the ventricular septum and in 34% of the anterior and posterior portions of the LV free wall, the midwall layer showed disarray of muscle fibers or small fascicles. In contrast, the lateral LV free wall was devoid of disarranged fibers in its midwall layer. Myocardial fibrosis usually was predominant in the portion where disarray was marked. There were deep tissue clefts often in the area of junction. In 11 hearts (7 from patients aged > 65 years), the circular unit was intact in almost every segment, as it was in 9 of 10 control hearts. The destruction of the circular unit in the area of septal-free wall junctions in most patients with HC is a previously undescribed morphologic feature of HC. This discontinuity may result from retention of an abnormal fetal myocardial architecture in which the septal latitudinal muscle was continuous with the right ventricular free wall.

Demonstration of quantitative fabric analysis of tendon collagen using two-dimensional polarized light microscopy

The extensional behavior of tendon is closely linked to the directional organization of the collagen fibers in the tendon. We sought to demonstrate that quantitative information about this organization is accessible through the application of polarized light microscopy. Ten tendons (2 canine Achilles and 8 rat tail tendons) were sectioned in a longitudinal plane and stained with either hematoxylin and eosin or toluidine blue. One Achilles tendon was fixed without tension on the fibers, thus leaving the fibers in a wavy state, and the other was fixed while strained with longitudinal tension straightening the fibers. One hundred measurements of collagen fiber orientation were made on a 0.7 mm2 area from each tendon. Recorded orientation angles were plotted on circular histograms and analyzed using circular statistics. The strained fibers revealed a sharply peaked distribution, in contrast the unstrained fibers had a bimodal orientation distribution. The tail tendons were fixed at strains from 0-3%. Analysis of the orientation distributions revealed increasing alignment of the collagen as strain increased. These data, while matching the qualitative descriptions of the fibers, also provide quantitative assessment of organization enabling comparison among tissues of varied physical circumstances and function. This method of quantitative orientation measurement has wide application for the many birefringent tissues such as bone, smooth and striated muscle and elastin.