The interaction between the left ventricle and the arterial system has been described by a theoretic model. Indeed, Sunagawa et al. 1 suggested that, by using the end-systolic pressure to volume relation to define left ventricular (LV) inotropic state (Ees) and the end-sys- tolic pressure to stroke volume relation to define effec- tive arterial elastance (Ea), the interaction between Ees and Ea could usefully characterize LV pump function under various conditions. In this model, Ea is defined as a steady-state arterial parameter that incorporates the principal elements of vascular load, including peripheral resistance, vascular compliance, characteristic imped- ance, and systolic and diastolic time intervals. This para- meter can be estimated from the ratio of end-systolic pressure to stroke volume. Given a constant heart rate, in fact, the stroke volume varies in response to changes in LV end-systolic pressure following a linear relation, with a slope that is proportional to the impedance that the arterial tree opposes to LV ejection. 2 Several studies confirmed in animal models 3 and in human beings 4,5 that Ea characterizes the major compo- nents of arterial load, thereby providing an appropriate and useful tool to assess the impact of such load on LV chamber function. Furthermore, some clinical investiga- tions, 6-8 assuming that Ea was an appropriate index of arterial impedance, evaluated the effects of afterload reduction in patients with heart failure in terms of opti- mal coupling between the end-systolic pressure to vol- ume relation and Ea. The purposes of the present study were to evaluate the effect of intraaortic balloon counterpulsation (IABC) Effective arterial elastance and the hemodynamic effects of intraaortic balloon counterpulsation in patients with coronary heart disease Niccolò Marchionni, MD, a Stefano Fumagalli, MD, a Giorgio Baldereschi, MD, a Mauro Di Bari, MD, a and Fabio Fantini, MD b Florence, Italy Objectives The goal of the present study was to analyze the effects of different intraaortic balloon counterpulsation (IABC) inflation volumes on effective arterial elastance (Ea) in patients with complicated coronary heart disease and to determine whether Ea can predict the hemodynamic response to IABC. Background Ea (the central aortic end-systolic pressure to stroke volume ratio) incorporates the principal elements of input arterial impedance and has been proved useful to evaluate the effects of afterload reduction in patients with left ven- tricular (LV) failure. However, although the hemodynamic action of IABC can be considered as a typical example of “pure” afterload reduction, it has never been assessed in terms of changes in Ea. Methods After clinical stabilization, 18 patients treated with IABC for complicated acute myocardial infarction or unsta- ble angina were enrolled in the study. Systemic hemodynamics were measured by use of right cardiac thermodilution catheters with IABC off (control) and IABC on at balloon inflation volumes of 20 and 40 ml, in randomized sequence. Aortic pressure was recorded through the central lumen of the IABC catheter to calculate Ea as the ratio of aortic dicrotic pressure to stroke volume. Results A higher control Ea was associated with a lower control LV stroke work and a larger IABC-related hemodynamic improvement (that was maximal with the 40 ml inflation volume). The increase in LV stroke work was closely related to the decrease in Ea. Accordingly, hemodynamic benefits from IABC were less evident in patients with lower control Ea. In conclu- sion, effects of IABC were related to both balloon inflation volume and control hemodynamics, reflecting the afterload dependence of a depressed LV function. (Am Heart J 1998;135:855-61.) From the a Department of Gerontology and Geriatric Medicine and the b Cardiology Unit, Department of Internal Medicine, University of Florence. Submitted July 18, 1997; accepted Nov. 12, 1997. Supported in part by a grant from the Special Project (40%) on Cardiac Failure through the Italian Ministry of the University and Scientific and Technological Research. Reprint requests: Niccolò Marchionni, MD, Coronary Care Unit, Department of Gerontology and Geriatric Medicine, University of Florence, Via delle Oblate, 4. 50141, Florence, Italy. E-mail: nmarchionni@cesit1.unifi.it Copyright © 1998 by Mosby, Inc. 0002-8703/98/$5.00 + 0 4/1/87838