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(Circulation. 2007;115:918-927.)
© 2007 American Heart Association, Inc.

Contemporary Reviews in Cardiovascular Medicine

Myocardial Energetics and Efficiency

Current Status of the Noninvasive Approach

Paul Knaapen, MD, PhD; Tjeerd Germans, MD; Juhani Knuuti, MD, PhD; Walter J. Paulus, MD, PhD; Pieter A. Dijkmans, MD; Cornelis P. Allaart, MD, PhD; Adriaan A. Lammertsma, PhD; Frans C. Visser, MD, PhD

From the Department of Cardiology (P.K., T.G., P.A.D., C.P.A., F.C.V.), the Laboratory of Physiology (W.J.P.), and the Department of Nuclear Medicine & PET Research (A.A.L.), VU University Medical Center, Institute for Cardiovascular Research, Amsterdam, The Netherlands, and the Turku PET Center (J.K.), University of Turku, Turku, Finland.

Correspondence to Dr Paul Knaapen, Department of Cardiology, 6D 120, VU University Medical Center, De Boelelaan 1117, 1081 HV, Amsterdam, The Netherlands. E-mail p.knaapen@vumc.nl

Key Words: hemodynamics • imaging • metabolism

An extract of the first 250 words of the full text is provided, because this article has no abstract.

	Introduction

 
The heart is an aerobic organ that relies almost exclusively on the aerobic oxidation of substrates for generation of energy. Consequently, there is close coupling between myocardial oxygen consumption (MO₂) and the main determinants of systolic function: heart rate, contractile state, and wall stress.¹ As in any mechanical pump, only part of the energy invested is converted to external power. In the case of the heart, the ratio of useful energy produced (ie, stroke work [SW]) to oxygen consumed is defined as mechanical efficiency, as originally proposed by Bing et al.² Under normal conditions this ratio is 25%, and the residual energy mainly dissipates as heat.³ In pathophysiological disease states, such as heart failure, mechanical efficiency is reduced, and it has been hypothesized that the increased energy expenditure relative to work contributes to progression of the disease.^4,5 Moreover, therapeutic interventions that enhance mechanical efficiency have proven to be beneficial with respect to outcome.⁶ It is therefore desirable to quantify efficiency of the heart to study disease processes and monitor interventions.

Both cardiac oxidative metabolism and mechanical work, and thus efficiency, can be quantified through invasive measurements. Although these measurements are accurate and currently considered the gold standard, in clinical practice they are limited because of the need for dual-sided heart catheterization and selective catheterization of the coronary sinus. Recent advances in imaging techniques, however, offer the possibility to noninvasively estimate MO₂ and mechanical work by positron emission tomography and echocardiography or by magnetic resonance imaging, respectively.

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