Copyright © 1990 by the European Society of Cardiology.
© 1990 The European Society of Cardiology
Diastolic dysfunction and myocardial energetics
Department of Physiology and Division of Cardiology, University of Louvain, School of Medicine Brussels, Belgium
Correspondence: Hubert Pouleur MD, University of Louvain, School of Medicine, av. Hippocrate 55 HEDY/5560, 1200 Brussels, Belgium
Myocardial relaxation is an energy-dependent process. Indeed, adenosine triphosphate (ATP) is required to pump free myoplasmic calcium back into the sarcoplasmic reticulum. It is also nessary to extrude the calcium ions which enter the cell during the plateau phase of the action potential. The calcium-sodium exchange mechanism does not seem to require energy in itself, but sodium exchanged for calcium eventually needs to be extruded via sodium/potassium ATPase and there is also an ATP-dependent calcium pump. Thus when ATP production is limited, calcium may remain fixed to troponin for part or for the whole of diastole, resulting in a slower rate of isovolumic relaxation and reahced distensibility of the myocardium.
Alterations in diastolic function caused by inadequate energy production occur in the high-demand type of myocardial ischaemia. There is also growing evidence that most forms of heart failure are accompanied by a state of energy depletion. Alterations in mitochondria1 density and enzymatic activity are common in the failing myocardium and may partially explain the reduction in ATP production. Inadequate growth of the capillary network in hypertrophied myocardium, impaired subendocardial perfusion due to increased diastolic wall stress and/or coronary artery disease, probably aiso contribute to an imbalance between energy production and utilization. As relaxation is intrinsically a much slower process than activation and since changes in ATP concentration may also affect calcium efflux by allosteric effects, impaired relaxation and reduced diastolic distensibility are almost universal in chronic congestive heart failure. Optimal therapy of heart failure should, therefore, also aim at improving this phase of the cardiac cycle.
Key Words: Diastolic dysfunction • myocardial energeties • coronary artery disease • heart failure
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