Vortices Formed on the Mitral Valve Tips Aid Normal Left Ventricular Filling
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Vortices Formed on the Mitral Valve Tips Aid Normal Left Ventricular Filling JOHN J. CHARONKO,1 RAHUL KUMAR,2 KELLEY STEWART,1,3 WILLIAM C. LITTLE,2 and PAVLOS P. VLACHOS1 1 Department of Mechanical Engineering, Virginia Tech, 100 Randolph Hall, Blacksburg, VA 24060, USA; 2Department of Cardiology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; and 3Department of Mechanical and Aerospace Engineering, The George Washington University, 801 22nd Street NW, Academic Center, Suite 739, Washington, DC 20052, USA
(Received 26 August 2012; accepted 23 January 2013; published online 7 February 2013) Associate Editor Aleksander S. Popel oversaw the review of this article.
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Abstract—For the left ventricle (LV) to function as an effective pump it must be able to fill from a low left atrial pressure. However, this ability is lost in patients with heart failure. We investigated LV filling by measuring the cardiac blood flow using 2D phase contrast magnetic resonance imaging and quantified the intraventricular pressure gradients and the strength and location of vortices. In normal subjects, blood flows towards the apex prior to the mitral valve opening, and the mitral annulus moves rapidly away after the valve opens, with both effects enhancing the vortex ring at the mitral valve tips. Instead of being a passive by-product of the process as was previously believed, this ring facilitates filling by reducing convective losses and enhancing the function of the LV as a suction pump. The virtual channel thus created by the vortices may help insure efficient mass transfer for the left atrium to the LV apex. Impairment of this mechanism contributes to diastolic dysfunction, with LV filling becoming dependent on left atrial pressure, which can lead to eventual heart failure. Better understanding of the mechanics of this progression may lead to more accurate diagnosis and treatment of this disease.
INTRODUCTION The left ventricle (LV) normally functions as a suction pump,22 filling rapidly during early diastole, and can increase the rate of filling during stress (such as exercise) without an elevation of left atrial (LA) pressure.8,28,34 Many conditions including aging, coronary artery disease, hypertension, LV hypertrophy, myocardial ischemia, dilated cardiomyopathy (DCM), and restrictive cardiomyopathy impair early diastolic filling, diminishing the ability of the LV to function as a suction pump.14,27,40,41 In these conditions filling becomes dependent on increased LA pressure,9,27,28 such as that generated by elevated pulmonary pressure or LA contraction during late diastole. This diastolic dysfunction (LVDD) is present in patients with heart failure whether their LV ejection fraction is preserved or decreased3,29 making it a unifying element of the condition. Furthermore, abnormalities of LV filling dynamics in asymptomatic subjects indicate groups with increased risk for subsequently developing heart failure.38 There is thus a clear clinical need to understand what characteristics are needed to create stro
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