Rate of Left Ventricular Systolic Function's Recuperation After Cardiac Surgery With Extracorporeal Circulation.

Myocardial stunning is a secondary pathophysiologic condition for a sustained reduction in myocardial perfusion, which produces kinetic abnormalities in left ventricular wall that persist for hours or days after the reperfusion phase. The physiological elements of the stunning are: a) reduction in coronary blood flow, b) a partial or complete restoration of coronary artery circulation and c) the dysfunction of persistence for a limited period, but longer compared to recovery coronaire's flow.

Cardiac surgery with cardiopulmonary bypass is a leading cause of bewilderment myocardique. This technique associated with administering a cardioplegic solution used to stop the heart and myocardial protection on ischemia see myocardique consideration. It typically also secondary to secondary inflammatory condition in the extracorporeal circulation and the ischemia-reperfusion phenomenon (formation of free radicals), also with the important activation coagulation. Myocardial stunning occurs in suites aortic unclamping during cardiopulmonary bypass. Cold ischemia performed by a cardioplegic liquid at 4 °C results in reduced energy demands and thus to maintain some balance between metabolism, perfusion and myocardial function during coronary by-pass. When aortic unclamping, there is usually a pure myocardial stunning (without necrosis). After the coronary by-pass, the myocardial thickening fraction is unchanged in the immediate future, but significantly decreased in the hours before a full recovery between the following hours. In the factors associated with changes in systolic function, autonomic nervous system is responsible for the regulation of blood pressure and heart function in response to the stress of the coronary by-pass and the postoperative state. Reduced variability in heart rate (heart rate variability - HRV) heard how sign of autonomic dysfunction is also associated with myocardial stunning with a rate of cardiaque post-surgery complications high.

So far no group has had the opportunity to study "in vivo" the temporal evolution of myocardial stunning after the coronary by-pass as an example of myocardial stunning "controlled" in order to better understand the pathophysiology of 'event. Indeed, the basis of myocardial function recovery time following coronary by-pass is unknown and the impact of intraoperative procedures on this recovery.

Transesophageal echocardiography, that is the gold standard for assessment of systolic function, has gradually gained popularity and is used daily in the ICU to evaluate the patient's hemodynamic status and evaluation of contractile function of the left ventricle to load. One of its advantages is to measure heart activity at the bedside and assist the physician in intensive care in the management of hemodynamic acute changes. It also allows also to analyze the response to treatment defined above. Among the limitations of transesophageal echocardiography are: the need for intensivists to be relevant to this technique, the discontinuous nature of the procedure ( "one shot" monitoring) and finally semi-invasif character that make it difficult 'prolonged and repeated execution of the various measures.

Recent improvement in electronics has enabled the development of miniaturized sensors for hemodynamic transesophageal echocardiography (ImaCor® ClariTEE®), called hTEE (hemodynamic trans-esophageal echocardiography), which are used to perform an extended hemodynamic monitoring ventilated patients; these prototypes are not yet widespread in Intensive Care Unit; their diagnostic capabilities and therapeutic impacts are currently under clinical research. been studies in the past allowed us to validate the clinical image quality and how the clinical information obtained are useful for clinical management of patient. In particular, these studies have demonstrated the ease with which thanks to the small size of the probe, the feedback of the superior vena cava, the patient's volume status, left ventricular systolic function based on the Fractional Area Change, the size of the right ventricle, and a pericardial effusion and cardiac tamponade during the first test of positioning sonde.

The advantages of continuous Htee of this new technique are related to the small size of the probe, ease of positioning the probe in the esophagus, the diagnostic reliability and the ability to stay up to 72 hours because the risk of pressure sores or lesions are comparable to those of a nasogastric feeding tube (which is the same size). Compared to the conventional trans-esophageal echocardiography, hTEE offers the advantage of performing continuous monitoring rather than a case-by case basis. In particular, for the study of post-operative myocardial stunning, this technique allows for a verification of the time course of myocardial stunning, and thus describe the pathophysiology and the kinetics of recovery of left ventricular contractile function. Furthermore this technique provides the means to identify perioperative factors that can change this recovery (induce or shorten).