Living Anatomy of the Ventricular Myocardial Crescents Supporting the Coronary Aortic Sinuses

Three-dimensional modelling of aortic leaflet coaptation and load-bearing surfaces: in silico design of aortic valve neocuspidizations

OBJECTIVES

Three-dimensional (3D) modelling of aortic leaflets remains difficult due to insufficient resolution of medical imaging. We aimed to model the coaptation and load-bearing surfaces of the aortic leaflets and adapt this workflow to aid in the design of aortic valve neocuspidizations.

METHODS

Geometric morphometrics, using landmarks and semilandmarks, was applied to the geometric determinants of the aortic leaflets from computed tomography, followed by an isogeometric analysis using Non-Uniform Rational Basis Splines (NURBS). Ten aortic valve models were generated, measuring determinants of leaflet geometry defined as 3D NURBS curves, and leaflet coaptation and load-bearing surfaces were defined as 3D NURBS surfaces. Neocuspidizations were obtained by either shifting the upper central coaptation landmark towards the sinotubular junction or using parametric neo-landmarks placed on a centreline drawn between the centroid of the aortic root base and centroid of a circle circumscribing the 3 upper commissural landmarks.

RESULTS

The ratio of the leaflet free margin length to the geometric height was 1.83, whereas the ratio of the commissural coaptation height to the central coaptation height was 1.93. The median coaptation surface was 137 mm2 (IQR 58) and the median load-bearing surface was 203 mm2 (60) per leaflet. Neocuspidization multiplied the central coaptation height by 3.7 and the coaptation surfaces by 1.97 and 1.92 using the native coaptation axis and centroid coaptation axis, respectively.

CONCLUSIONS

Geometric morphometrics reliably defined the coaptation and load-bearing surfaces of aortic leaflets, enabling an experimental 3D design for the in silico neocuspidization of aortic valves.

Perioperative Assessment of the Hemodynamic Ventriculoarterial Junction of the Aortic Root by Three-Dimensional Echocardiography

Improved strategies in aortic valve-preserving operations appreciate the dynamic, three-dimensional complexity of the aortic root and its valve. This depends not only on detailed four-dimensional imaging of the planar dimensions of the aortic root but also on quantitative assessment of the valvar leaflets and their competency. The zones of apposition and resulting hemodynamic ventriculoarterial junction formed in diastole determine valvar competency. Current understanding and assessment of this junction is limited, often relying on intraoperative direct surgical inspection. However, this direct inspection itself is limited by evaluation in a nonhemodynamic state with limited field of view. In this review, we discuss the anatomy of the aortic root, including its hemodynamic junction. We review current echocardiographic approaches toward interrogating the incompetent aortic valve for presurgical planning. Furthermore, we introduce and standardize a complementary approach to assessing this hemodynamic ventriculoarterial junction by three-dimensional echocardiography to further personalize presurgical planning for aortic valve surgery.

Development of the arterial roots and ventricular outflow tracts

The separation of the outflow tract of the developing heart into the systemic and pulmonary arterial channels remains controversial and poorly understood. The definitive outflow tracts have three components. The developing outflow tract, in contrast, has usually been described in two parts. When the tract has exclusively myocardial walls, such bipartite description is justified, with an obvious dogleg bend separating proximal and distal components. With the addition of non-myocardial walls distally, it becomes possible to recognise three parts. The middle part, which initially still has myocardial walls, contains within its lumen a pair of intercalated valvar swellings. The swellings interdigitate with the distal ends of major outflow cushions, formed by the remodelling of cardiac jelly, to form the primordiums of the arterial roots. The proximal parts of the major cushions, occupying the proximal part of the outflow tract, which also has myocardial walls, themselves fuse and muscularise. The myocardial shelf thus formed remodels to become the free-standing subpulmonary infundibulum. Details of all these processes are currently lacking. In this account, we describe the anatomical changes seen during the overall remodelling. Our interpretations are based on the interrogation of serially sectioned histological and high-resolution episcopic microscopy datasets prepared from developing human and mouse embryos, with some of the datasets processed and reconstructed to reveal the specific nature of the tissues contributing to the separation of the outflow channels. Our findings confirm that the tripartite postnatal arrangement can be correlated with the changes occurring during development.

Anatomy of the Ventricular Outflow Tracts: An Electrophysiology Perspective

Outflow tract ventricular arrhythmias are the most common type of idiopathic ventricular arrhythmia. A systematic understanding of the outflow tract anatomy improves procedural efficacy and enables electrophysiologists to anticipate and prevent complications. This review emphasizes the three-dimensional spatial relationships between the ventricular outflow tracts using seven anatomical principles. In turn, each principle is elaborated on from a clinical perspective relevant for the practicing electrophysiologist. The developmental anatomy of the outflow tracts is also discussed and reinforced with a clinical case.

Relationship between the aortic root and the atrioventricular conduction axis

Damage to the atrioventricular conduction axis continues to be a problem subsequent to transcatheter implantation of aortic valvar prostheses. Accurate knowledge of the precise relationships of the conduction axis relative to the aortic root could greatly reduce the risk of such problems. Current diagrams highlighting these relationships rightly focus on the membranous septum. The current depictions, however, overlook a potentially important relationship between the superior fascicle of the left bundle branch and the nadir of the semilunar hinge of the right coronary leaflet of the aortic valve. Recent histological investigations demonstrate, in many instances, a very close relationship between the left bundle branch and the right coronary aortic leaflet. The findings also highlight two additional variable features, which can be revealed by clinical imaging. The first of these is the extent of an inferoseptal recess of the left ventricular outflow tract. The second is the extent of rotation of the aortic root within the base of the left ventricle. Much more of the conduction axis is within the confines of the circumference of the outflow tract when the root is rotated in counterclockwise fashion as assessed from the perspective of the imager, with this finding itself associated with a much narrower inferoseptal recess. A clear understanding of the marked variability within the aortic root is key to avoiding future problems with atrioventricular conduction.

Acute severe aortic insufficiency during cardiopulmonary bypass in a bicuspid aortic valve with unrecognized annular displacement and fibrous strands: a case report

Background

Bicuspid aortic valve (BAV) with displacement of the attachment of the conjoined aortic leaflet and fibrous strands is a rare cardiac malformation. We report a case of BAV that presented as acute massive aortic regurgitation during cardiopulmonary bypass for a planned non-valve-related procedure and was successfully treated by emergency aortic valve replacement.

Case summary

A 70-year-old man with triple vessel coronary disease and severe left ventricular systolic dysfunction underwent coronary bypass grafting and graft replacement of the ascending aorta. Acute aortic regurgitation occurred during ventricular fibrillation and after de-clamping of the aortic graft. Intra-operative findings included a fused BAV (right-left cusp fusion), very asymmetrical leaflet (commissure angle of the non-fused leaflet 135°), three aortic sinuses, and conjoined leaflets originating from the myocardium in the inter-ventricular septum. The aortic leaflets were resected and replaced with a prosthetic aortic valve at the attachment site of the conjoined leaflets. Post-operatively, no peri-valvular leaks were observed, and left ventricular function was improved.

Discussion

Intra-operative acute massive aortic regurgitation may be caused by a morphologically abnormal aortic leaflet and root complex in patients with a BAV. The dilated aortic root, asymmetrical leaflet, and abnormal aortic leaflet insertion, with thick septal myocardium of the coronary aortic sinus, might have caused unstable leaflet co-aptation, leading to deformation of the aortic leaflets influenced by the change in myocardial tone and intra-operative change in the sinotubular junction. Familiarity with the classification of congenital BAV, and the anatomy of the normal and abnormal aortic root complex, is important.

Expert Consensus Statement: Anatomy, Imaging, and Nomenclature of Congenital Aortic Root Malformations

Over the past 2 decades, several categorizations have been proposed for the abnormalities of the aortic root. These schemes have mostly been devoid of input from specialists of congenital cardiac disease. The aim of this review is to provide a classification, from the perspective of these specialists, based on an understanding of normal and abnormal morphogenesis and anatomy, with emphasis placed on the features of clinical and surgical relevance. We contend that the description of the congenitally malformed aortic root is simplified when approached in a fashion that recognizes the normal root to be made up of 3 leaflets, supported by their own sinuses, with the sinuses themselves separated by the interleaflet triangles. The malformed root, usually found in the setting of 3 sinuses, can also be found with 2 sinuses, and very rarely with 4 sinuses. This permits description of trisinuate, bisinuate, and quadrisinuate variants, respectively. This feature then provides the basis for classification of the anatomical and functional number of leaflets present. By offering standardized terms and definitions, we submit that our classification will be suitable for those working in all cardiac specialties, whether pediatric or adult. It is of equal value in the settings of acquired or congenital cardiac disease. Our recommendations will serve to amend and/or add to the existing International Paediatric and Congenital Cardiac Code, along with the Eleventh iteration of the International Classification of Diseases provided by the World Health Organization.

Expert Consensus Statement: Anatomy, Imaging, and Nomenclature of Congenital Aortic Root Malformations

Over the past 2 decades, several categorizations have been proposed for the abnormalities of the aortic root. These schemes have mostly been devoid of input from specialists of congenital cardiac disease. The aim of this review is to provide a classification, from the perspective of these specialists, based on an understanding of normal and abnormal morphogenesis and anatomy, with emphasis placed on the features of clinical and surgical relevance. We contend that the description of the congenitally malformed aortic root is simplified when approached in a fashion that recognizes the normal root to be made up of 3 leaflets, supported by their own sinuses, with the sinuses themselves separated by the interleaflet triangles. The malformed root, usually found in the setting of 3 sinuses, can also be found with 2 sinuses, and very rarely with 4 sinuses. This permits description of trisinuate, bisinuate, and quadrisinuate variants, respectively. This feature then provides the basis for classification of the anatomical and functional number of leaflets present. By offering standardized terms and definitions, we submit that our classification will be suitable for those working in all cardiac specialties, whether pediatric or adult. It is of equal value in the settings of acquired or congenital cardiac disease. Our recommendations will serve to amend and/or add to the existing International Paediatric and Congenital Cardiac Code, along with the Eleventh iteration of the International Classification of Diseases provided by the World Health Organization.

Revisiting the Anatomy of the Left Ventricular Summit

The left ventricular summit corresponds to the epicardial side of the basal superior free wall, extending from the base of the left coronary aortic sinus. The summit composes the floor of the compartment surrounded by the aortic root, infundibulum, pulmonary root, and left atrial appendage. The compartment is filled with thick adipose tissue, carrying the coronary vessels. Thus, the treatment of ventricular tachycardia originating from the summit is challenging, and three-dimensional understanding of this complicated region is fundamental. We revisit the clinical anatomy of the left ventricular summit with original images from the Wallace A. McAlpine collection.

Aortic root rotational position associates with aortic valvar incompetence and aortic dilation after arterial switch operation for transposition of the great arteries

PURPOSE

Aortic dilation and valvar regurgitation can develop in transposition of the great arteries (TGA) after the arterial switch operation (ASO). Variation in aortic root rotational position affects flow dynamics in patients without congenital heart disease. The aim of this study was to assess neo-aortic root (neo-AoR) rotational position and its association with neo-AoR dilation, ascending aorta (AAo) dilation, and neo-aortic valvar regurgitation in TGA following ASO.

METHODS

Patients with TGA repaired by ASO who underwent cardiac magnetic resonance (CMR) were reviewed. Neo-AoR rotational angle, neo-AoR and AAo dimensions indexed (to height), indexed left ventricular end diastolic volume (LVEDVI), and neo-aortic valvar regurgitant fraction (RF) were obtained from CMR.

RESULTS

Among 36 patients, the median age at CMR was 17.1 years (12.3, 21.9). Neo-AoR rotational angle (range - 52 to + 78°) was clockwise ( ≥ + 15°) in 50%, counterclockwise (<-9°) in 25%, and central (-9 to + 14°) in 25% of patients. A quadratic term for neo-AoR rotational angle, indicating increasing extremes of counterclockwise and clockwise angles, was associated with neo-AoR dilation (R² = 0.132, p = 0.03), AAo dilation (R² = 0.160, p = 0.016), and LVEDVI (R² = 0.20, p = 0.007). These associations remained statistically significant on multivariable analyses. Rotational angle was negatively associated with neo-aortic valvar RF on univariable (p < 0.05) and multivariable analyses (p < 0.02). Rotational angle was associated with smaller bilateral branch pulmonary arteries (p = 0.02).

CONCLUSION

In patients with TGA after ASO, neo-AoR rotational position likely affects valvar function and hemodynamics, leading to a risk of neo-AoR and AAo dilation, aortic valvar incompetence, increasing left ventricular size, and smaller branch pulmonary arteries.

Diversity and determinants of the sigmoid septum and its impact on morphology of the outflow tract as revealed using cardiac computed tomography

BACKGROUND

The sigmoid septum has been generally evaluated subjectively and qualitatively, without detailed examination of its diversity, impact on the morphology of the left ventricular outflow tract (LVOT), and anatomical background.

METHODS

We enrolled 100 patients without any background cardiac diseases (67.5 ± 12.8 years old; 43% women) who underwent cardiac computed tomography. Basal septal morphology was evaluated using antero-superior and medial bulging angles (bidirectional angulation of the basal septum relative to the LVOT). The eccentricity index of the LVOT, area narrowing ratio (LVOT/virtual basal ring area), aortic-to-left ventricular axial angle (angulation of the aortic root relative to the left ventricle), and wedged height (non-coronary aortic sinus to inferior epicardium distance) were also quantified.

RESULTS

The antero-superior bulging, medial bulging, aortic-to-left ventricular axial angles, LVOT eccentricity index, area narrowing ratio, and wedged height were 76° ± 17°, 166° ± 27°, 127° ± 9°, 1.8 ± 0.5, 1.0 ± 0.2, and 41.2 ± 9.1 mm, respectively. Both bulging angles were correlated with each other and contributed to the narrowing and deformation of the LVOT. Angulated aortic root was not correlated with either bidirectional septal bulge or LVOT narrowing. Clockwise rotation of the aortic root rotation was an independent predictor of prominent antero-superior septal bulge. Deeper aortic wedging was a common independent predictor of bidirectional septal bulge.

CONCLUSIONS

The extent of septal bulge varies in normal hearts. Along with deep aortic wedging, the bidirectional bulge of the basal septum deforms and narrows the LVOT without affecting the virtual basal ring morphology.

Understanding the Aortic Root Using Computed Tomographic Assessment: A Potential Pathway to Improved Customized Surgical Repair

There is continued interest in surgical repair of both the congenitally malformed aortic valve, and the valve with acquired dysfunction. Aortic valvar repair based on a geometric approach has demonstrated improved durability and outcomes. Such an approach requires a thorough comprehension of the complex 3-dimensional anatomy of both the normal and congenitally malformed aortic root. In this review, we provide an understanding of this anatomy based on the features that can accurately be revealed by contrast-enhanced computed tomographic imaging. We highlight the complimentary role that such imaging, with multiplanar reformatting and 3-dimensional reconstructions, can play in selection of patients, and subsequent presurgical planning for valvar repair. The technique compliments other established techniques for perioperative imaging, with echocardiography maintaining its central role in assessment, and enhances direct surgical evaluation. This additive morphological and functional information holds the potential for improving selection of patients, surgical planning, subsequent surgical repair, and hopefully the subsequent outcomes.

Prevalence and extent of mitral annular disjunction in structurally normal hearts: comprehensive 3D analysis using cardiac computed tomography

AIMS

Mitral annular disjunction is fibrous separation between the attachment of the posterior mitral leaflet and the basal left ventricular myocardium initially described in dissected hearts. Currently, it is commonly evaluated by echocardiography, and potential relationships with mitral valve prolapse and ventricular arrhythmia have been suggested. However, controversy remains as its prevalence and extent have not been fully elucidated in normal living subjects.

METHODS AND RESULTS

Systolic datasets of cardiac computed tomography obtained from 98 patients (mean age, 69.1 ± 12.6 years; 81% men) with structurally normal hearts were assessed retrospectively. Circumferential extent of both mitral leaflets and disjunction was determined by rotating orthogonal multiplanar reconstruction images around the central axis of the mitral valvar orifice. Distribution angle within the circumference of the mitral valvar attachment and maximal height of disjunction were quantified. In total, 96.0% of patients demonstrated disjunction. Average distribution angles of the anterior and posterior mitral leaflets were 91.3 ± 9.4° and 269.8 ± 9.7°, respectively. Average distribution angle of the disjunction was 105.1 ± 49.2°, corresponding to 39.0 ± 18.2% of the entire posterior mitral valvar attachment. Median value of the maximal height of disjunction was 3.0 (1.5-7.0) mm. Distribution prevalence map of the disjunction revealed characteristic double peaks, with frequent sites of the disjunction located at the anterior to antero-lateral and inferior to infero-septal regions.

CONCLUSION

Mitral annular disjunction is a rather common finding in the normal adult heart with bimodal distribution predominantly observed involving the P1 and P3 scallops of the posterior mitral leaflet.

Successful catheter ablation approach above the aortic sinus cusp eliminating a ventricular arrhythmia arising from the myocardial crescent beneath the interleaflet triangle: Late gadolinium enhancement magnetic resonance imaging assessment

A 61-year-old female with 50 000 ventricular premature contractions and a reduced left ventricular ejection fraction of 35% was referred to our center. Although the origin was considered to originate from the junction between the left and right coronary cusp, a single radiofrequency application above the aortic sinus cusp could eliminate it. LGE-MRI was able to reveal the exact location of the single RF lesion.

Rotational Position of the Aortic Root is Associated with Increased Aortic Dimensions in Marfan and Loeys-Dietz Syndrome

Progressive aortic dilation is common in Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS). Risk factors for progression are poorly understood. Normal variation in the aortic root (AoR) rotational position relative to the left ventricular base may impact this risk. We aimed to assess the relationship between the rotational position of the AoR and aortic dimensions in this population. Patients with a genetic diagnosis of MFS or LDS were included. AoR and ascending aorta (AAo) dimensions were measured from the first and most recent transthoracic echocardiogram. The AoR rotational angle was measured in the parasternal short-axis plane in diastole. Linear regression was used to study the correlation between AoR rotation angle and aortic dimensions. 53 MFS and 14 LDS patients were included (age 11.5 ± 5.8 years at first TTE and 21.2 ± 7.2 years at most recent, 68% male). The mean indexed AoR and AAo values were 2.26 ± 0.58 cm/m² and 1.64 ± 0.35 cm/m² at the first TTE and 1.98 ± 0.39 cm/m² and 1.45 ± 0.25 cm/m² at the most recent TTE, respectively. The mean AoR rotational angle was 8 ± 14°. AoR rotational angle was central (- 9 to + 14°) in 42, clockwise (≥ + 15°) in 19, and counterclockwise (≤ -10°) in 6. The six outliers with counterclockwise position were excluded. There was a positive association between the AoR rotation angle and most recent TTE indexed AoR (r² = 0.08, p = 0.02) and AAo sizes (r² = 0.08, p = 0.02). There was no association between AoR rotational angle and rate of change in indexed AoR size (p = 0.8). There was a positive association between AoR rotation angle and rate of change in indexed AAo size (r² = 0.10, p = 0.01). There is an association between clockwise rotational position of the AoR and increased AoR and AAo dimensions in children and young adults with MFS and LDS patients. The rotational position of the AoR may guide follow-up in these patient populations. However, this potential risk factor for dilation warrants further investigation.

Three-dimensional visualization of the bovine cardiac conduction system and surrounding structures compared to the arrangements in the human heart

In the human heart, the atrioventricular node is located toward the apex of the triangle of Koch, which is also at the apex of the inferior pyramidal space. It is adjacent to the atrioventricular portion of the membranous septum, through which it penetrates to become the atrioventricular bundle. Subsequent to its penetration, the conduction axis is located on the crest of the ventricular septum, sandwiched between the muscular septum and ventricular component of the membranous septum, where it gives rise to the ramifications of the left bundle branch. In contrast, the bovine conduction axis has a long non-branching component, which penetrates into a thick muscular atrioventricular septum having skirted the main cardiac bone and the rightward half of the non-coronary sinus of the aortic root. It commonly gives rise to both right and left bundle branches within the muscular ventricular septum. Unlike the situation in man, the left bundle branch is long and thin before it branches into its fascicles. These differences from the human heart, however, have yet to be shown in three-dimensions relative to the surrounding structures. We have now achieved this goal by injecting contrast material into the insulating sheaths that surround the conduction network, evaluating the results by subsequent computed tomography. The fibrous atrioventricular membranous septum of the human heart is replaced in the ox by the main cardiac bone and the muscular atrioventricular septum. The apex of the inferior pyramidal space, which in the bovine, as in the human, is related to the atrioventricular node, is placed inferiorly relative to the left ventricular outflow tract. The bovine atrioventricular conduction axis, therefore, originates from a node itself located inferiorly compared to the human arrangement. The axis must then skirt the non-coronary sinus of the aortic root prior to penetrating the thicker muscular ventricular septum, thus accounting for its long non-branching course. We envisage that our findings will further enhance comparative anatomical research.

Normative Aortic Valvar Measurements in Adults Using Cardiac Computed Tomography - A Potential Guide to Further Sophisticate Aortic Valve-Sparing Surgery

BACKGROUND

A thorough understanding of the anatomy of the aortic valve is necessary for aortic valve-sparing surgery. Normal valvar dimensions and their relationships in the living heart, however, have yet to be fully investigated in a 3-dimensional fashion.Methods and Results:In total, 123 consecutive patients (66±12 years, Men 63%) who underwent coronary computed tomographic angiography were enrolled. Mid-diastolic morphology of the aortic roots, including height of the interleaflet triangles, geometric height, free margin length of each leaflet, effective height, and coaptation length were measured using multiplanar reconstruction images. Average height of the interleaflet triangle, geometric height, free margin length, effective height, and the coaptation length were 17.3±1.8, 14.7±1.3, 32.6±3.6, 8.6±1.4, and 3.2±0.8 mm, respectively. The right coronary aortic leaflet displayed the longest free margin length and shortest geometric height. Geometric height, free margin length, and effective height showed positive correlations with aortic root dimensions. Coaptation length, however, remained constant regardless of aortic root dimensions.

CONCLUSIONS

Diversities, as well as characteristic relationships among each value involving the aortic root, were identified using living-heart datasets. The aortic leaflets demonstrated compensatory elongation along with aortic root dilatation to maintain constant coaptation length. These measurements will serve as the standard value for revealing the underlying mechanism of aortic regurgitation to plan optimal aortic valve-sparing surgery.