Aortic valve opening and closure: the clover dynamics.

BACKGROUND: Systolic aortic root expansion is reported to facilitate valve opening, but the precise dynamics remain unknown. A sonometric study with a high data sampling rate (200 to 800 Hz) was conducted in an acute ovine model to better understand the timing, mechanisms, and shape of aortic valve opening and closure. METHODS: Eighteen piezoelectric crystals were implanted in 8 sheep at each annular base, commissures, sinus of Valsalva, sinotubular junction, nodulus of Arantius, and ascending aorta (AA). Geometric changes were time related to pressures and flows. RESULTS: The aortic root was hemodynamically divided into left ventricular (LV) and aortic compartments situated, respectively, below and above the leaflets. During isovolumetric contraction (IVC), aortic root expansion started in the LV compartment, most likely due to volume redistribution in the LV outflow tract below the leaflets. This expansion initiated leaflet separation prior to ejection (2.1%±0.5% of total opening area). Aortic compartment expansion was delayed toward the end of IVC, likely related to volume redistribution above the leaflets due to accelerating aortic backflow toward the aortic valve and coronary flow reduction due to myocardial contraction. Maximum valve opening during the first third of ejection acquired a truncated cone shape [leaflet free edge area smaller than annular base area (-41.5%±5.5%)]. The distal orifice became clover shaped because the leaflet free edge area is larger than the commissural area by 16.3%±2.0%. CONCLUSIONS: Aortic valve opening is initiated prior to ejection related to delicate balance between LV, aortic root, and coronary dynamics. It is clover shaped at maximum opening in systole. A better understanding of these mechanisms should stimulate more physiological surgical approaches of valve repair and replacement.

Ventriculo-aortic junction in human root. A geometric approach.

With advances in tissue engineering and improvement of surgical techniques, stentless biological valves and valve-sparing procedures have become alternatives to traditional aortic valve replacement with stented bioprostheses or mechanical valves. New surgical techniques preserve the advantages of native valves but require better understanding of the anatomical structure of the aortic root. Silicone rubber was injected in fresh aortic roots of nine human cadavers under the physiological closing pressure of 80 mmHg. The casts reproduced every detail of the aortic root anatomy and were used to digitize 27 leaflet attachment lines (LALs) of the aortic valves. LALs were normalized and described with a mathematical model. LALs were found to follow a pattern with the right coronary being the largest followed by the non-coronary and then the left coronary. During diastole, the aortic valve LAL can be described by an intersection between a created tube and an extruded parabolic surface. This geometrical definition of the LAL during end diastole gives a better understanding of the aortic root anatomy and could be useful for heart valve design and improvement of aortic valve reconstruction technique.

Kinking of the atrioventricular plane during the cardiac cycle.

Systolic descent of the atrioventricular plane toward the relatively stationary left ventricular apex is well described. As the atrioventricular plane includes two separate valvular units, systolic atrioventricular plane displacement should not be homogenous. In 6 sheep, sonomicrometric crystals were implanted at the base of the right coronary sinus, anterolateral and posteromedial fibrous trigones, posterior mitral annulus, left ventricular apex, and the tips of the anterior and posterior mitral leaflets. The aortomitral angle was calculated and related to simultaneous left ventricular and aortic pressures and mitral valve movement. The aortomitral angle was largest at end diastole (150.73 degrees +/- 15.48 degrees ). During isovolumic contraction, it narrowed rapidly to 144.90 degrees +/- 16.64 degrees , followed by a slower narrowing during ejection until it reached its smallest angle at end systole (139.66 degrees +/- 16.78 degrees ). During isovolumic relaxation, the aortomitral angle increased to 143.66 degrees +/- 16.02 degrees at the beginning of diastole. During the first third of diastole, it narrowed again to 141 degrees +/- 16.24 degrees before re-expanding to maximum at end diastole. During systole, the atrioventricular plane descended non-homogeneously toward the apex, with kinking at the hinge between the aortic and mitral annulus plane. This deformation of the atrioventricular plane has relevance in valve surgery.

Aortic root dynamics are asymmetric.

BACKGROUND AND AIM OF THE STUDY: The presence of conformational changes in the aortic root during the cardiac cycle is well known, but precise information on time-related changes at each level of the root is lacking. METHODS: High-resolution, 3D sonomicrometry (200 Hz) was applied in an acute sheep model. Twelve crystals were implanted in eight sheep at each base (n = 3), commissure (n = 3), sinotubular junction (n = 3) and ascending aorta (n = 3). Under stable hemodynamic conditions, geometric changes of the perimeter of each sinus of Valsalva, sinus height, and twist and root tilt angles were time-related to left ventricluar (LV) and aortic pressures. RESULTS: Expansion of the perimeter of the three sinuses of Valsalva was homogeneous, but in significantly different proportions (p < 0.001): the right sinus expanded (+32.4 +/- 2.4%) more than the left (+29.3 +/- 3.2%), and more than the non-coronary (NC) sinus (+25.8 +/- 1.7%). A similar pattern was found for aortic root height: right greater than left, and left greater than NC sinus (p < 0.001). This asymmetry resulted in changes of the root's twist and tilt angles. Although the twist deformation was consistent for each sheep, no general pattern was found. The aortic root tilt angle (between the basal plane and the commissural plane) was 16.3 +/- 1.5 degrees at end-diastole (angle oriented posteriorly and to the left). During systole, it was reduced by 6.6 +/- 0.5 degrees, aligning the LV outflow tract with the ascending aorta. This tilt angle returned to its original value after valve closure. CONCLUSION: Aortic root expansion is asymmetric, generating precise changes in its tilt angle. During systole, tilt angle reduction resulted in a straight cylinder that probably facilitates ejection; during diastole, the tilt angle increased, probably reducing leaflet stress. These findings should impact upon surgical procedures and the design of new prostheses.

Anterior mitral basal 'stay' chords are essential for left ventricular geometry and function.

BACKGROUND AND AIM OF THE STUDY: Among the anterior mitral basal chords, two particularly strong and thick stay chords (SC) remain under tension during the entire cardiac cycle. Collagen fibers of the anterior mitral leaflet (AML) are oriented from insertion of the SC on the AML to the fibrous trigones (FT), suggesting that local stress is directed from the papillary muscles (PM) over the SC and AML to the FT, maintaining left ventricular (LV) geometry. METHODS: Sonomicrometry crystals were implanted in sheep at the LV apex (A), the anterior (AW) and septal (SW) LV wall, the PM tips (M1 and M2), the SC insertion into the AML (S1 and S2), the posterior (PMA) and lateral (P1 and P2) mitral annulus, the FT (T1 and T2), the tips of the anterior (AL) and posterior (PL) mitral leaflets, and the base of the aortic right coronary sinus (RCS). Changes in distances, areas, and volume were time-related to aortic flow and LV and ascending aorta pressures. Recordings were taken at baseline and after transection of the SC. RESULTS: After transection of the SC, the systolic distance from M1-T1 increased by +0.96 +/- 0.41 mm (p < 0.05) and from M2-T2 by +0.97 +/- 0.42 mm (p < 0.05). The LV length increased at T1-A by +1.14 +/- 0.60 mm (p < 0.05) and at T2-A by +0.97 +/- 0.37 mm (p < 0.05). The aortomitral angle narrowed at end-systole by -3.26 +/- 0.85 degrees (p < 0.05). Transection of the SC reduced dP/dt by -11.20 +/- 5.29% (p < 0.05), maximum aortic flow by -16.89 +/- 7.86% (p < 0.05), and maximum pressure-volume ratio by -10.83 +/- 3.36% (p < 0.05). CONCLUSION: Transection of the anterior mitral SC did not result in mitral regurgitation but induced significant changes in LV geometry, including narrowing of the aortomitral angle and subsequent deterioration of LV function. The SC are essential for maintaining normal LV geometry and function.

Left ventricular endocardial longitudinal and transverse changes during isovolumic contraction and relaxation: a challenge.

Left ventricular (LV) longitudinal and transverse geometric changes during isovolumic contraction and relaxation are still controversial. This confusion is compounded by traditional definitions of these phases of the cardiac cycle. High-resolution sonomicrometry studies might clarify these issues. Crystals were implanted in six sheep at the LV apex, fibrous trigones, lateral and posterior mitral annulus, base of the aortic right coronary sinus, anterior and septal endocardial wall, papillary muscle tips, and edge of the anterior and posterior mitral leaflets. Changes in distances were time related to LV and aortic pressures and to mitral valve opening. At the beginning of isovolumic contraction, while the mitral valve was still open, the LV endocardial transverse diameter started to shorten while the endocardial longitudinal diameter increased. During isovolumic relaxation, while the mitral valve was closed, LV transverse diameter started to increase while the longitudinal diameter continued to decrease. These findings are inconsistent with the classic definitions of the phases of the cardiac cycle.

Sonometric study of the normal tricuspid valve annulus in sheep.

BACKGROUND AND AIM OF THE STUDY: Mitral valve dynamic changes during the cardiac cycle have been previously studied in sheep using sonomicrometry. The study aim was to analyze geometric changes of the normal tricuspid annulus in sheep using a similar methodology. This is most likely the first tricuspid valve study using high temporal resolution (200 Hz = 200 data points per second). METHODS: Thirteen crystals were implanted in seven sheep along the annulus (n = 6), at the tips of papillary muscles (n = 3), at the free edge of the leaflets (n = 3), and at the apex of the left ventricle (n = 1). Recordings (10 s) of crystal distances were used to create a three-dimensional (3D) coordinate system based on the least-squares plane of the annulus, and maximum and minimum values were calculated for length, area, and position in xyz coordinates. RESULTS: During the cardiac cycle, the tricuspid annulus area expanded 28.6 +/- 3.6% with similar maximum expansions of each segment along the annulus: septal (10.4 +/- 1.2%), anterior (13.0 +/- 1.5%), and posterior (14.0 +/- 1.6%). The annulus was saddle-shaped, with a circumferential expansion from elliptical at minimum area to more circular at maximum area. The time delay to maximum leaflet area and maximum papillary area occurred 83 +/- 13 ms and 279 +/- 30 ms respectively after maximum annulus area. CONCLUSION: The tricuspid valve undergoes continual and complex geometric changes during the cardiac cycle. In addition, the annulus expands significantly due to similar increases in length of the septal and free wall segments. The annulus is not in a single plane, but is saddle-shaped. The expansion and contraction of the tricuspid valve complex is stepwise, and sequential from base to apex.

Anterior mitral leaflet mobility is limited by the basal stay chords.

BACKGROUND: We hypothesize that 2 tendon-like anterior basal stay chords, which remain taut during the entire cardiac cycle, limit the motion of the anterior mitral leaflet. METHODS AND RESULTS: Sonomicrometric crystals were implanted in 6 sheep at the insertion of stay chords at anterior mitral leaflet (S1 and S2), papillary muscle tips, fibrous trigones, mitral annulus, and the tip of the anterior leaflet (AL). Distances between crystals were recorded before and after section of stay chords. During the cardiac cycle, the angle alpha between mitral annulus and AL changed by +54.2+/-12.4 degrees; the angles between mitral annulus and S1 (beta1) changed by +25.7+/-14.6 degrees, and between mitral annulus and S2 (beta2) by +20.4+/-7.8 degrees. During diastole, AL twice crossed the virtual plane formed by the stay chords: during E-wave by a maximum of 6.5 mm (mean, 2.5+/-2.2 mm) and during A-wave by a maximum of 3.2 mm (mean, 1.7+/-0.9 mm). After section of both stay chords, total anterior mitral leaflet motion increased as follows: AL, +6.9+/-3.4 degrees; S1, +13.1+/-4.4 degrees; and S2, +30.9+/-11.7 degrees (P<0.05). CONCLUSIONS: Although the lateral movement of anterior mitral leaflet is limited by stay chords, the midportion moves unimpaired toward the septum, like a sail, between the 2 stay chords during diastole. A diastolic left ventricular-inflow and systolic left ventricular-outflow funnel mechanism is created. Stay chord section increased lateral anterior mitral leaflet movement.

A temporarily stented, autologous pericardial aortic valve prosthesis.

BACKGROUND AND AIM OF THE STUDY: A new bioprosthesis has been developed that is: (i) constructed from glutaraldehyde-treated autologous pericardium due to its lack of antigenicity and low cost; (ii) easily constructed in the operating room; (iii) stentless but easy to implant by using a temporary stent that is removed once its function is no longer necessary; and (iv) implanted with a single proximal suture and three commissural stitches. METHODS: This prosthesis was implanted in the subcoronary aortic position of six sheep. The mean prosthesis size was 19.7 +/- 3.5 mm, and manufacturing time 16 +/- 3 min. Cardiopulmonary bypass and cross-clamp times were 142.5 +/- 26.7 min and 100.2 +/- 28.8 min, respectively. Three sheep were euthanized at three, seven, or 27 days, and the remainder at five months postoperatively. RESULTS: In all cases the valve was competent and the single commissural stitches were well-anchored. The pericardium was pliable in all cases, but one animal had obvious endocarditis (at 27 days). Small calcific nodules were found at the commissures in valves explanted at five months. Histology showed an intact collagen and elastin structure, and neointimal growth was seen covering the basal quarter of the leaflets and commissures. CONCLUSION: This new bioprosthesis might offer a particularly attractive alternative for the young patient population of the developing world. The simplicity of construction, low cost, and absence of any need for anticoagulation makes this prosthesis close to the ideal aortic valve substitute.

Dynamic balance of the aortomitral junction.

OBJECTIVE: The aortic and mitral valves have been studied in isolation, as if their functions were independent. We hypothesized that both valves work in synchrony on the basis of the shared myocardial pump and orifice. METHODS: Six sonometric crystals (7 sheep) were placed in both trigones, the midpoint of the anterior and posterior anulus, and the lateral extremities of the posterior anulus. In a separate series of animals, 3 crystals (8 sheep) were implanted in the aortic annular base of the right, left, and noncoronary sinuses of Valsalva. In an acute, open-chest model, under stable hemodynamic conditions, geometric changes were time related to simultaneous left ventricular and aortic pressures. RESULTS: From mid-diastole to end-systole, the mitral anulus area contracted by -16.1% +/- 1.9% (mean +/- SEM), whereas the aortic base area expanded by +29.8% +/- 3.3% during systole. The mitral anulus deformation was heterogeneous. In systole, the anterior mitral anulus expanded (intertrigonal distance, +11.5% +/- 2.3%) and the posterior mitral anulus contracted (distance between lateral extremities of the posterior anulus, -12.1% +/- 1.5%). The intertrigonal distance corresponded to the base of the left and noncoronary sinus of Valsalva, which expanded similarly during systole (+12.9% +/- 2.0%). The anteroposterior diameter of the mitral anulus was reduced twice that of the transverse diameter. This disparity of reduction can be explained by the posterior displacement of the intertrigonal area corresponding to the systolic aortic root expansion. CONCLUSIONS: Mitral anulus deformation is closely related to aortic root dynamics. During systole, the posterior movement of the aortic curtain allows for aortic root expansion, probably to maximize ejection, whereas during diastole, aortic root reduction participates in mitral anulus dilatation. These findings should affect mitral and aortic surgical approaches.