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Correspondence

Effects on left ventricular performance of changes in cardiac loading conditions depend on 'relative load'

De Hert, S. G.; Van der Linden, P. J.

Author Information
European Journal of Anaesthesiology: February 2004 - Volume 21 - Issue 2 - p 158-159

EDITOR:

We read with interest the article by Reuter and colleagues in which they analysed the effects of Trendelenburg positioning after cardiac surgery [1]. They observed that the Trendelenburg manoeuvre only slightly increased preload volume, without improvement of cardiac performance, but with a marked increase in cardiac filling pressures. The authors therefore concluded that the Trendelenburg head-down tilt was not an efficient manoeuvre after cardiac surgery. It should be noted that manoeuvres intended to increase cardiac preload may elicit a variety of responses, which have been related among others to the type of manoeuvre (Trendelenburg, leg elevation, etc.), the presence of mechanical ventilation of the lungs and the type of anaesthesia (general versus combined general and epidural) [2]. Apart from this, there is a pathophysiological aspect in the study by Reuter and colleagues that we would like to emphasize. The study was performed in 12 patients, and in our opinion it is very possible that with the selection of this limited number of patients, the authors may have overlooked the wide spectrum of responses that can be elicited when performing manoeuvres intended to increase cardiac preload.

It has been shown that the response of the cardiac performance to leg elevation is highly variable. Indeed, some patients show an improvement in myocardial function as manifested by an increase in left ventricular (LV) dP/dtmax and stroke volume and an acceleration of LV relaxation. Other patients show hardly any change in cardiac function, and a number of patients develop impairment of myocardial function, manifested by a decrease in dP/dtmax and stroke volume, a slowing of LV relaxation with increased load dependence of myocardial relaxation, and a marked increase in LV end-diastolic pressure [3]. This latter response was related to a deficient length-dependent regulation of myocardial function [4]. Note that in the presence of a closed pericardium or closed chest conditions, the length-dependent regulation of myocardial function may be further impaired compared with the open chest conditions [5].

The variability of responses in cardiac performance to an increase in cardiac load has been related to the physiological concept of relative load [6,7]. Relative load relates to the capacity of the ventricle to respond to an elevation in cardiac load. A low relative cardiac load is associated with normal cardiac function, whereas a high relative load is indicative of cardiac dysfunction. At a low relative load, any increase in cardiac load is associated with a limited increase in systolic volume and no slowing of LV pressure fall. At high relative load, on the contrary, the same increase in cardiac load slows the LV pressure fall and results in an upward shift of the diastolic pressure-volume relation with increased end-diastolic pressures and diastolic failure [6]. Transposed to the clinical setting, this means that an improvement in LV function associated with an acceleration of LV pressure fall in response to an increased cardiac load indicates that the ventricle is working at low relative load. Conversely, a decrease in LV function - associated with a deceleration of LV pressure fall in the same conditions - indicates that the ventricle is working at a high relative load. The response observed by Reuter and colleagues corresponds to what can be expected of ventricles working at high relative load. The conclusion that Trendelenburg's manoeuvre does not significantly improve cardiac performance may therefore be related to the limited number of patients with a selection of ventricles working at high relative load. Further studies should analyse whether the findings obtained in the current study population also are valid for ventricles working at a low relative cardiac load and whether differences exits between the haemodynamic effects of leg elevation and the effects of the Trendelenburg position.

S. G. De Hert

Department of Anaesthesiology; University Hospital Antwerp; Edegem, Belgium

P. J. Van der Linden

Department of Cardiac Anaesthesia; Centre Hospitalier Universitaire; Charleroi, Belgium

References

1. Reuter DA, Felbinger TW, Schmidt C, et al. Trendelenburg positioning after cardiac surgery: effects of intrathoracic blood volume index and cardiac performance. Eur J Anaesthesiol 2003; 20: 17-20.
2. Nakajima Y, Mizobe T, Matsukawa T, Sessler DI, Kitamura Y, Tanaka Y. Thermoregulatory response to intraoperative head-down tilt. Anesth Analg 2002; 94: 221-226.
3. De Hert SG, Gillebert TC, ten Broecke PW, Mertens E, Rodrigus IE, Moulijn AC. Contraction-relaxation coupling and impaired left ventricular performance in coronary surgery patients. Anesthesiology 1999; 90: 748-757.
4. De Hert SG, Gillebert TC, ten Broecke PW, Moulijn AC. Length-dependent regulation of left ventricular function in coronary surgery patients. Anesthesiology 1999; 91: 379-387.
5. De Hert SG, ten Broecke PW, Rodrigus IE, Mertens E, Stockman BA, Vermeyen KA. The effects of the pericardium on length-dependent regulation of left ventricular function in coronary artery surgery patients. J Cardiothor Vasc Anesth 2001; 15: 300-305.
6. Gillebert TC, Leite-Moreira AF, De Hert SG. Relaxation-systolic pressure relation: a load-independent assessment of left ventricular contractility. Circulation 1997; 95: 745-752.
7. De Hert SG, ten Broecke PW, Mertens E, Rodrigus IE, Stockman BA. Effects of phosphodiesterase III inhibition on length-dependent regulation of myocardial function in coronary surgery patients. Br J Anaesth 2002; 88: 779-784.
© 2004 European Academy of Anaesthesiology