Fluid challenge and left ventricular myocardial performance index assessed by transthoracic echocardiography with tissue Doppler imaging in critically ill patients with regular rhythm.

Background: Fluid challenge may increase cardiac index but can also compromise diastolic function. The myocardial performance index, derived from tissue Doppler imaging, integrates systolic and diastolic performance into a single measure that may reflect the balance between the benefits and risks of fluid challenge. We hypothesized that patients with an increase in cardiac index after fluid challenge would demonstrate a reduced myocardial performance index, indicating improved global function, whereas those without an increase in cardiac index would display stable or higher values, suggesting limited or adverse effects. Methods: This secondary analysis of a prospective observational study was conducted in the intensive care unit of Brugmann Hospital, Belgium, between October 2020 and December 2023. Patients with regular rhythm who received a fluid challenge of 4 mL/kg were included. Fluid responsiveness was defined as an increase in cardiac index of at least 15%, and myocardial performance index values below 0.42 were considered normal. The primary endpoint was the change in myocardial performance index during the fluid challenge. Results: Of 59 patients, 24 (41%) were fluid responders. Among the responders, myocardial performance index decreased significantly after fluid challenge (from 0.48 [0.43-0.58] to 0.42 [0.33-0.54]; Conclusion: In critically ill patients with regular cardiac rhythm, the myocardial performance index decreased after fluid challenge in responders but not in non-responders, suggesting improved global myocardial function. These findings support the potential role of the myocardial performance index as a dynamic marker of cardiac response to fluid challenge.