Myocardial fiber orientation is oblique in the epicardium and undergoes a transition in direction through the left ventricular wall that spans approximately 100 degrees. Although fiber anatomy has been studied in detail for at least 300 years, the functional consequences of this intricate arrangement are not fully understood. Fibers are joined together in a connective tissue matrix, and each may be functionally tethered to near or distant neighbors. indeed, recent studies have suggested that tethering may allow myocardial shortening to occur both in the direction of the fibers and also perpendicular to them. This """"""""cross-fiber"""""""" shortening could result in the ability of the heart wall to shorten in two directions and thicken extensively in the third, a potent mechanism for ejection of blood. Magnetic Resonance Imaging tissue tagging is a new imaging method which allows the nonsurgical placement of short-lived magnetic markers into myocardium, and thus permits the tracking of tissue through the cardiac cycle, and accurate measurement of local deformations in the entire left ventricle. In this proposal, tagging is used to characterize regional left ventricular normal and shear strains during systole. To define how the heart's architecture enables extensive thickening to occur in systole, we will first determine whether the layers of the heart wall are tethered to each by correlating the angle at which maximum shortening occurs to the histologic fiber angle, at multiple regions in the left ventricle. We will describe myocardial deformation in detail by measuring left ventricular strains with respect to the fiber angle of each layer. This will allow us to define the importance of crossfiber shortening for systolic thickening by determining whether they co-vary from region to region of the left ventricle. The effect of epicardial fibers on the deformation of the perpendicular endocardial fibers will be assessed by selectively destroying epicardial layers with liquid nitrogen, and measuring the consequences on endocardial strains. Our findings will have relevance to the study of disease states such as cardiomyopathy and ischemia, in which a disturbed interaction between fibers may affect thickening and result in ventricular dysfunction.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL046223-02
Application #
3365301
Study Section
Cardiovascular and Pulmonary Research A Study Section (CVA)
Project Start
1992-02-27
Project End
1995-01-31
Budget Start
1993-02-01
Budget End
1994-01-31
Support Year
2
Fiscal Year
1993
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Hees, Paul S; Fleg, Jerome L; Mirza, Zulfiqar A et al. (2006) Effects of normal aging on left ventricular lusitropic, inotropic, and chronotropic responses to dobutamine. J Am Coll Cardiol 47:1440-7
Hees, Paul S; Fleg, Jerome L; Dong, Sheng-Jing et al. (2004) MRI and echocardiographic assessment of the diastolic dysfunction of normal aging: altered LV pressure decline or load? Am J Physiol Heart Circ Physiol 286:H782-8
Hees, Paul S; Fleg, Jerome L; Lakatta, Edward G et al. (2002) Left ventricular remodeling with age in normal men versus women: novel insights using three-dimensional magnetic resonance imaging. Am J Cardiol 90:1231-6
Dong, S J; Hees, P S; Siu, C O et al. (2001) MRI assessment of LV relaxation by untwisting rate: a new isovolumic phase measure of tau. Am J Physiol Heart Circ Physiol 281:H2002-9
Dong, S J; Hees, P S; Huang, W M et al. (1999) Independent effects of preload, afterload, and contractility on left ventricular torsion. Am J Physiol 277:H1053-60
MacGowan, G A; Shapiro, E P; Azhari, H et al. (1997) Noninvasive measurement of shortening in the fiber and cross-fiber directions in the normal human left ventricle and in idiopathic dilated cardiomyopathy. Circulation 96:535-41
Denisova, O; Shapiro, E P; Weiss, J L et al. (1997) Localization of ischemia in canine hearts using tagged rotated long axis MR images, endocardial surface stretch and wall thickening. Magn Reson Imaging 15:1037-43
MacGowan, G A; Burkhoff, D; Rogers, W J et al. (1996) Effects of afterload on regional left ventricular torsion. Cardiovasc Res 31:917-25
Azhari, H; Denisova, O E; Montag, A et al. (1996) Circular sampling: perspective of a time-saving scanning procedure. Magn Reson Imaging 14:625-31
Azhari, H; Weiss, J L; Rogers, W J et al. (1995) A noninvasive comparative study of myocardial strains in ischemic canine hearts using tagged MRI in 3-D. Am J Physiol 268:H1918-26

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