Systolic ejection of the left ventricle (LV) is a complex co-ordinated action, which involves fiber shortening in multiple directions along with systolic torsion (see Figure 1). These actions produce wall thickening and blood displacement, thus generating a stroke volume. The most commonly used index of LV contractile function is the ejection fraction (EF), which represents volume strain├óÔé¼ÔÇØa change in volume divided by initial volume. EF, by definition, is ├óÔé¼´åİinternally™ normalized, and does not require correction for body size. Therefore, the EF of a normal├óÔé¼ÔÇ£sized adult can be compared with that of an infant and, likewise, systolic function in small, experimental animals can be compared with that of humans. Furthermore, a large volume of published literature supports the clinical utility of the EF in clinical medicine. However, the EF does not convey information about regional function,1 which is important in diagnosing coronary artery disease. Furthermore, chronic changes in left ventricular geometry also affect myocardial function, but may not be detected by the EF. Such geometric changes are common among patients with hypertension, aortic stenosis and
diastolic heart failure.2
How Prevalent is Hypertrophic Remodeling Among Patients with Diastolic Heart Failure?
A recent survey of patients admitted to the New York area hospitals with heart failure and a normal EF showed that left ventricular hypertrophy was present in over 80% of such patients.3 Our laboratory has devoted much attention to the study of LV systolic function in hypertensive heart disease, valvular heart disease and diastolic heart failure├óÔé¼ÔÇØthree conditions that are commonly associated with hypertrophic remodeling. As noted above, a mostly to measure regional, as opposed to global LV systolic function. Standard tissue Doppler imaging allows a Doppler sample volume├óÔé¼ÔÇØ region of interest├óÔé¼ÔÇØto be placed in any myocardial structure as long as it is reasonably parallel to the ultrasound beam. For this reason, regional shortening and lengthening are usually measured in the longitudinal, and more recently, in the radial direction. Myocardial longitudinal strain, expressed as a percentage, throughout the cardiac cycle can be derived from the velocity gradient, or strain rate, between any two points. Conceptually, it should be kept in mind that strain rate represents the rate of systolic deformation and strain represents the normalized extent of deformation in this region of interest.
Advantages/Disadvantages of Doppler Imaging in the Study of Myocardial Function
Strain rate imaging has the advantage of measuring a vector component of regional myocardial contraction independent of the effect of tethering and translation. However, analysis of regional function by velocity and/or displacement measurements is bedeviled by inability to discriminate between actively contracting and ├óÔé¼´åİtethered™ myocardium. In this situation, an akinetic segment may demonstrate motion if it is pulled by an adjacent segment that is functioning normally.
- Aurigemma GP, Zile MR, Gaasch WH, Contractile behavior of the left ventricle in diastolic heart failure ├óÔé¼ÔÇ£ with emphasis on regional systolic function. Circulation. 2006;113(2):296├óÔé¼ÔÇ£304..
- Aurigemma GP, Gaasch WH, Clinical practice. Diastolic heart failure. N Engl J Med. 2004;351(11):1097├óÔé¼ÔÇ£105.
- Klapholz M, Maurer M, Lowe AM, et al,. Hospitalization for heart failure in the presence of a normal left ventricular ejection fraction: results of the New York Heart Failure Registry, J Am Coll Cardiol. 2004;43(8):1432├óÔé¼ÔÇ£8.
- Aurigemma GP, Silver KH, Priest MA, et al. Geometric changes allow normal ejection fraction despite depressed myocardial shortening in hypertensive left ventricular hypertrophy. J Am Coll Cardiol. 1995;26(1):195├óÔé¼ÔÇ£202.
- Hurlburt HM, Aurigemma GP, Hill JC et al. Direct ultrasound measurement of longitudinal, circumferential, and radial strain using 2-dimensional strain imaging in normal adults, Echocardiography. 2007; in press.
- DeCara JM, Toledo E, Salgo IS, et al, Evaluation of left ventricular systolic function using automated angleindependent motion tracking of mitral annular displacement, J Am Soc Echocardiogr, 2005;18(12):1266├óÔé¼ÔÇ£9.