Submitted on July 14, 2006
Accepted on October 17, 2006
NON-INVASIVE ASSESSMENT OF LEFT VENTRICULAR AND MYOCARDIAL CONTRACTILITY IN MIDDLE-AGED MEN AND WOMEN: DISPARATE EVOLUTION ABOVE THE AGE OF 50 ?
Tom E Claessens1*, Ernst R Rietzschel2, Marc L De Buyzere2, Dirk De Bacquer3, Guy De Backer3, Thierry C Gillebert2, Pascal Verdonck4, and Patrick Segers5
1 Cardiovascular Mechanics and Biofluid Dynamics Research Unit, Ghent University, Ghent, Belgium
2 Department of Cardiovascular Diseases, Ghent University Hospital, Ghent, Belgium
3 Department of Epidemiology and Public Health, Ghent University, Ghent, Belgium
4 Ghent University, United States; Ghent University
5 University of Ghent, Belgium
* To whom correspondence should be addressed. E-mail: tom.claessens{at}ugent.be.
End-systolic elastance (Ees) is a frequently used index of left ventricular (LV) contractility. However, due to its inherent dependence on LV geometry, Ees cannot be used to compare myocardial contractile state between ventricles with different geometries, which is the case in any cross-sectional study. Various normalization methods for Ees have been proposed in literature, but a standardized method is still lacking. In this study, we introduced a novel alternative normalization technique and compared it with three previously suggested methods. We tested all normalization methods to assess the age- and gender-related differences in myocardial contractility in a large population sample of 2184 middle-aged (age 35-55 years) untreated subjects free from overt cardiovascular disease. Ventricular contractility Ees was determined using a previously validated non-invasive single-beat method, based on 2D echocardiographic and brachial blood pressure measurements. Myocardial contractility was estimated as (i) Ees·EDV, (ii) Ees·LVM, (iii) 0.433·Ees·LVM/RWT, based on a theoretical LV model, and (iv) 0.0941·Ees·LVM0.455·RWT-0.159, a novel semi-empirical expression derived in this study (EDV = end-diastolic volume, LVM = LV mass, RWT = relative wall thickness). Due to the difference in their underlying assumptions, the various myocardial contractility indices do not provide consistent information with respect to gender differences. Despite these discrepancies, it was found that myocardial contractility in women appears to be better preserved after the age of 50 compared to men. The physiologic mechanisms behind this potentially clinically important phenomenon at population level require further investigation.
