Influence of inotropy and chronotropy on the mitral valve sphincter mechanism

Mitral Annulus Geometry and Dynamic Motion Changes in Patients With Aortic Regurgitation: A Three-Dimensional Transesophageal Echocardiographic Study

OBJECTIVE

The aim of the present study was to investigate the mitral annulus (MA) geometry and dynamic motion changes in patients with aortic regurgitation (AR) before and after aortic valve replacement (AVR). Moreover, the difference in the effect of the type of prosthetic aortic valve on MA was compared.

DESIGN

Prospective observational study.

SETTING

Cardiac operating room at a single hospital.

PARTICIPANTS

Eighty-two patients with isolated moderate-to-severe AR who underwent AVR. Forty patients with normal valves were enrolled as controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The MA geometry and dynamic motion throughout the cardiac cycle were evaluated semiautomatically by three-dimensional transesophageal echocardiography. The severity of functional mitral regurgitation was intraoperatively evaluated. All patients were divided into 2 groups depending on the type of prosthetic valve (mechanical valve and bioprosthetic valve groups). Before AVR, compared with the control group without AR, the AR group demonstrated larger MA dimensions and the MA geometry was flatter. The contraction fraction of the MA area, perimeter, and height during the whole cardiac cycle were larger in the AR group (p < 0.05 for all). After AVR, most MA geometric and dynamic parameters decreased and functional mitral regurgitation also improved. In the postoperative subset analyses, the mechanical valve group showed a larger contraction fraction of the MA area and perimeter than the bioprosthetic valve group (p < 0.05 for both).

CONCLUSIONS

The MA geometry and dynamic motion changed markedly in patients with AR. These spatial and dynamic changes were restored to a certain extent after surgical correction of the aortic valve. However, the effects produced by mechanical and bioprosthetic valves on MA were different.

Mechanics of healthy and functionally diseased mitral valves: a critical review

The mitral valve is a complex apparatus with multiple constituents that work cohesively to ensure unidirectional flow between the left atrium and ventricle. Disruption to any or all of the components-the annulus, leaflets, chordae, and papillary muscles-can lead to backflow of blood, or regurgitation, into the left atrium, which deleteriously effects patient health. Through the years, a myriad of surgical repairs have been proposed; however, a careful appreciation for the underlying structural mechanics can help optimize long-term repair durability and inform medical device design. In this review, we aim to present the experimental methods and significant results that have shaped the current understanding of mitral valve mechanics. Data will be presented for all components of the mitral valve apparatus in control, pathological, and repaired conditions from human, animal, and in vitro studies. Finally, current strategies of patient specific and noninvasive surgical planning will be critically outlined.

Contribution of mitral annular dynamics to LV diastolic filling with alteration in preload and inotropic state

Mitral annular (MA) excursion during diastole encompasses a volume that is part of total left ventricular (LV) filling volume (LVFV). Altered excursion or area variation of the MA due to changes in preload or inotropic state could affect LV filling. We hypothesized that changes in LV preload and inotropic state would not alter the contribution of MA dynamics to LVFV. Six sheep underwent marker implantation in the LV wall and around the MA. After 7–10 days, biplane fluoroscopy was used to obtain three-dimensional marker dynamics from sedated, closed-chest animals during control conditions, inotropic augmentation with calcium (Ca), preload reduction with nitroprusside (N), and vena caval occlusion (VCO). The contribution of MA dynamics to total LVFV was assessed using volume estimates based on multiple tetrahedra defined by the three-dimensional marker positions. Neither the absolute nor the relative contribution of MA dynamics to LVFV changed with Ca or N, although MA area decreased (Ca, P < 0.01; and N, P < 0.05) and excursion increased (Ca, P < 0.01). During VCO, the absolute contribution of MA dynamics to LVFV decreased ( P < 0.001), based on a reduction in both area ( P < 0.001) and excursion ( P < 0.01), but the relative contribution to LVFV increased from 18 ± 4 to 45 ± 13% ( P < 0.001). Thus MA dynamics contribute substantially to LV diastolic filling. Although MA excursion and mean area change with moderate preload reduction and inotropic augmentation, the contribution of MA dynamics to total LVFV is constant with sizeable magnitude. With marked preload reduction (VCO), the contribution of MA dynamics to LVFV becomes even more important.

Effects of hemodynamic alterations on anterior mitral leaflet curvature during systole

OBJECTIVES

The application of repair techniques to treat mitral valve incompetence has increased progressively during the past 20 years. Unfortunately, recent reports have demonstrated the longevity of these repairs to be less than previously believed. Most repair failures are stress related. Computational models to optimize valve repair are in development, but to be brought to fruition, a better understanding of dynamic leaflet geometry is necessary. In this study, sonomicrometry was used in an ovine model to compute systolic leaflet curvature at varying afterloads and states of contractility.

METHODS

The anterior leaflet of 12 sheep was instrumented with 5 piezoelectric transducers in a cruciate array. Systolic blood pressure ranged from 90 to 200 mm Hg with increasing phenylephrine hydrochloride infusion. Epinephrine was used to vary contractile state. Leaflet curvature was calculated continuously (200 Hz) during systole.

RESULTS

Anterior leaflet curvature in the septolateral direction was double that in the intercommisural direction. There were also significant changes in leaflet curvature during systole. Curvature in neither direction was affected by afterload. Epinephrine augmented intercommisural curvature in a dose-independent fashion, whereas it had no effect on curvature in the septolateral direction.

CONCLUSIONS

Dynamic mitral anterior leaflet geometry was found to be amazingly constant over a wide range of hemodynamic conditions. These data provide information about leaflet geometry that will aid in the construction of realistic computational models. Such models may facilitate the design of annuloplasty rings and surgical techniques that minimize leaflet stress and increase mitral valve repair longevity.

The Dynamic Anterior Mitral Annulus

BACKGROUND

The anterior mitral annulus is considered a fixed structure. Recent data suggest otherwise. This study tested the hypothesis that the size of the anterior annulus varies with hemodynamic loading and ventricular contractility.

METHODS

Sonomicrometry array localization measured annular area, total annular circumference, anterior circumference, and posterior circumference in 6 sheep before and after neosynephrine increased systolic blood pressure by at least 150% during atrial pacing at 120 beats/min. In 6 additional animals the same dimensions were measured during atrial pacing (at 120 and 150 beats/min) and during isoproteronol infusions to increase heart rate to 120 and 150 beats/min.

RESULTS

Neosynephrine increased systolic total annular circumference from 99.7 +/- 5.5 mm to 106.9 +/- 9.6 mm. Anterior circumference increased from 40.8 +/- 4.0 mm to 45.3 +/- 5.7 mm whereas posterior circumference only increased from 59.0 +/- 5.5 mm to 61.6 +/- 7.0 mm. Low isoproteronol infusion decreased systolic total annular circumference from 107.5 +/- 8.3 mm to 101.9 +/- 10.6 mm. Most of this change occurred in the posterior circumference. Higher infusions of isoproteronol decreased total annular circumference from 106.8 +/- 8.3 mm to 98.3 +/- 9.7 mm. At this higher inotropic state the decrease in annular size was similar in the anterior and posterior annulus.

CONCLUSIONS

In sheep, the anterior annulus is a dynamic structure that varies in size in response to changes in hemodynamic loading and ventricular contractility.