Echographic evaluation of ICU patients with tissue Doppler imaging: more studies and more consensus are still needed

Abstract

In many intensive care units (ICUs), cardiac transthoracic echocardio graphy (TTE) has replaced invasive monitoring in routine evaluation of acutely ill patients. Since the mid ’80s, there have been many studies of ICU patients, most of whom were receiving mechanical ventilation (MV). With the emergence of new TTE modalities such as tissue Doppler imaging (TDI) and strain rate or threedimensional imaging, new studies are currently available. TDI is now widely used in cardiology and is a powerful tool in the assessment of left ventricular fi lling pressures (LVFPs), relaxation, or right ventricular function. It was suggested that the ratio of pulsed Doppler mitral fl ow in early diastole (E wave) over early diastolic mitral annulus velocity (E a with TDI), known as E/E a , was closely related to LVFP. However, in many clinical situations, a lack of correlation between E/E a and LVFP was observed, even in patients with spontaneous breathing [1]. Th ree studies focusing on TDI and left ventricular function in ICU patients were recently published [2-4], two of them in Critical Care [2,4]. Th ese studies provide new approaches in the assessment of systolic or diastolic function during septic shock and weaning from MV. In all studies, patients were mechanically ventilated, adding complexity to the TTE examination. For years, invasive pressure measurements in patients under MV have been performed at the end-expiratory time, when intra-thoracic pressure is closer to atmospheric pressure in most cases. For TTE study, things are slightly diff erent. Doppler study (such as E wave) aims to determine direction and velocity of blood fl ow. Th at fl ow, as intra-cardiac pressure, depends of the respiratory cycle. By contrast, TDI determines the velocity of the myocardium and is considered relatively load-independent. So the necessity to perform measure ments (E a ) at a certain time of the respiratory cycle may be questioned. Moreover, methodo logical diff erences between studies may be confusing (Table 1). Th ese diff erences may lead to a loss of information in some cases and eventually may explain the diff erences observed between TTE and invasive monitoring. At the bedside, the clinician may be tempted to use a simple beat measurement and disregard the res pira tory time. Further studies focusing on the feasibility and infl uence of MV on TDI parameters are needed [5]. Guidelines regarding the methods and designs of future trials in the ICU will be valuable, as these studies demon strate that a quantitative assessment of cardiovascular parameters over a simple qualitative approach is possible with TTE in patients on MV. As in the study by Moschietto and colleagues [2], evolution of these values may provide crucial information for the clinician.