Myocardial performance index and its association with late onset neonatal sepsis : a prospective observational study

The role of targeted neonatal echocardiography (TnECHO) for the evaluation of hemodynamic status in stable as well as sick infants has been well established over the last few years. Its impact in the clinical setting is less well understood. Early recognition of cardiovascular compromise in sick infants enables the physician to take timely therapeutic decisions and monitor response to treatment more objectively.

Neonatal sepsis is a clinical syndrome characterized by systemic signs of infection and accompanied by bacteremia in the first month of life. It has been classified as either early onset sepsis (EOS) (0-72 hours of life) or late onset sepsis (LOS) (72 hours-28 days of age). Neonatal sepsis is a cause of significant short term as well as long term morbidity and mortality among term and preterm infants.

Cardiac dysfunction is a well-recognized complication of neonatal sepsis and is a major contributor to morbidity and mortality in patients with sepsis. Hemodynamic response to sepsis has been less well-characterized in neonates compared with children and adults. Clinical variables to assess hemodynamic status of sick newborn infants such as heart rate, blood pressure and capillary refill time have been demonstrated to be misleading in their accuracy.  It has been demonstrated in several studies that real time objective physiologic data obtained by targeted echocardiography such as cardiac contractility, cardiac output and diastolic functions of heart provide hemodynamic information, which may be different from the assumed underlying physiology.

Cardiac parameters using conventional echocardiography such as superior vena cava flow and cardiac output in neonatal sepsis exist in literature. Systolic and diastolic dysfunction are known to coexist in neonatal sepsis, therefore, an echocardiographic doppler index that combines measures of systolic and diastolic dysfunction is needed.The evaluation of myocardial performance in septic neonates is of critical importance to identify the haemodynamic instability and to predict prognosis. However traditional indices of myocardial function, including cardiac index, stroke volume index, and ejection fraction, may be inaccurate because a significant decline in contractility can be masked by changes in heart rate, preload, and afterload. Tissue doppler imaging (TDI) is an emerging echocardiographic technique that is useful for quantifying myocardial tissue motion. It is easily reproducible and less preload and afterload dependent than conventional doppler techniques. Myocardial performance index (MPI) by using TDI is a powerful quantitative parameter that measures both systolic and diastolic cardiac functions and is independent of heart rate and blood pressure. Indian data on use of tissue doppler imaging for assessment of myocardial dysfunction in sepsis is scarce.

In this study, we aim to measure myocardial performance index using targeted echocardiography in neonates with clinically suspected late onset sepsis, and determine its association with laboratory proven sepsis. We have selected patients with late onset sepsis, as in the first 24-72 hours, newborn infants may be in transitional phase of circulation which may confound echocardiographic findings. Also in our unit, majority of neonates with early onset sepsis have culture negative sepsis, likely due to maternal antibiotics. We expect that the results of our study may help us to understand the value of MPI in neonatal sepsis and to determine whether it has any role in prediction or prognostication of sepsis.