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Cardiovascular Research 2004 61(1):94-104; doi:10.1016/j.cardiores.2003.09.032
© 2004 by European Society of Cardiology
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Copyright © 2004, European Society of Cardiology

Altered oscillatory work by ventricular myofilaments from a rabbit coronary artery ligation model of heart failure

David J Miller*, Niall G MacFarlane and Gayle Wilson

Institute of Biomedical and Life Sciences, West Medical Building, University of Glasgow, G12 8QQ, Glasgow, UK

* Corresponding author. d.j.miller{at}bio.gla.ac.uk

Objectives: Understanding the changed ability of cardiac myofilaments to produce pump work requires knowledge of kinetics of crossbridge function as well as more widely studied parameters such as Ca-sensitivity and isometric force development. We tested the hypothesis that altered crossbridge kinetics contribute to reduced myofilament work in early-stage heart failure (left ventricular dysfunction, LVD). Methods: The sinusoidal oscillation technique can yield insights into crossbridge function. Dynamic stiffness, oscillatory work and power were assessed in chemically skinned, Ca-activated trabeculae from rabbit ventricles in early-stage failure, 8 weeks after infarction induced by coronary artery ligation (LIG). Results were compared with sham-operated controls (SH). LVD was assessed by echocardiography. Results: Ca-activated force and myofilament Ca-sensitivity were not significantly altered at this early stage of LVD. In maximally Ca-activated preparations, the frequency of minimal dynamic stiffness (fmin) was 23% lower in LIG. fmin increases by >80% between pCa 5.8 and 4 in SH but not in LIG. Maximal phase lead and lag angles (between length and tension) were lower in LIG at frequencies near fmin, lowering oscillatory work and power. The Lissajous figures (oscillatory work loops) of imposed length vs. tension are often asymmetric near fmin. The degree of asymmetry was greater in LIG. Conclusions: Reduced capacity for mechanical power, consistent with depressed haemodynamic performance in LVD hearts, is only partially attributable to crossbridge slowing; changes in the phase relationship will also contribute. These changes are not readily attributable to known alterations in contractile protein isoforms. Some deductions are drawn about which steps in the crossbridge cycle are modified in this model of LVD. Altered cardiac myocyte Ca-transients, reported to be associated with LVD, will be translated into pump work by a contractile machinery that is functionally altered, even though isometric force and myofilament Ca-sensitivity might remain near-normal at this stage.

KEYWORDS Heart failure; Contractile function; e–c coupling; Ventricular function; Rabbit

Time for primary reviews 23 days


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