Health & Medical Cardiovascular Health

A New Approach to Evaluate Fetal Myocardial Function

A New Approach to Evaluate Fetal Myocardial Function

Abstract and Introduction

Abstract


Objectives: Myocardial function can be evaluated using color-coded tissue velocity imaging (TVI) to analyze the longitudinal myocardial velocity profile, and by expressing the motion of the atrioventricular plane during a cardiac cycle as coordinated events in the cardiac state diagram (CSD). The objective of this study was to establish gestational age specific reference values for fetal TVI measurements and to introduce the CSD as a potential aid in fetal myocardial evaluation.

Methods: TVI recordings from 125 healthy fetuses, at 18 to 42 weeks of gestation, were performed with the transducer perpendicular to the apex to provide a four-chamber view. The myocardial velocity data was extracted from the basal segment of septum as well as the left and right ventricular free wall for subsequent offline analysis.

Results: During a cardiac cycle the longitudinal peak velocities of septum increased with gestational age, as did the peak velocities of the left and right ventricular free wall, except for the peak velocity of post ejection. The duration of rapid filling and atrial contraction increased during pregnancy while the duration of post ejection decreased. The duration of pre ejection and ventricular ejection did not change significantly with gestational age.

Conclusion: Evaluating fetal systolic and diastolic performance using TVI together with CSD could contribute to increase the knowledge and understanding of fetal myocardial function and dysfunction. The pre and post ejection phases are the variables most likely to indicate fetuses with abnormal myocardial function.

Introduction


In the progression of fetal hemodynamic adaptation, the assessment of fetal myocardial function could be of crucial importance when evaluating fetuses at risk or suffering from intrauterine hypoxia. Although this has been common knowledge since many years, myocardial performance is typically evaluated by specialists in fetal cardiology, and methods to perform these evaluations are regarded as rather cumbersome and have consequently not been introduced in clinical practice. Furthermore, most studies on myocardial performance have until now been based on conventional Doppler, which measures global cardiac function restricted to flow measurements. Color-coded tissue velocity imaging (TVI) offers quantitative measurements of regional myocardial function, and can potentially provide more sensitive and thus earlier indications of myocardial dysfunction. TVI enables adequate temporal resolution (>200 frames/s) unlike speckle tracking (<80 frames/s) and doesn't overestimate true motion or alter offline gain settings in contrast to spectral Doppler. Velocity can also be measured simultaneously in the different myocardial walls during the same cardiac cycle.

The cardiac state diagram (CSD) is a new visualization tool for the pumping and regulating function of the heart that provides quantitative analysis of the timing of mechanical events in the cardiac cycle without the need of a concurrent ECG signal. Based on the hypothesis that the heart's pumping and regulating function acts according to the Dynamic Adaptive Piston Pump (DAPP), this tool presents comparative data of systolic and diastolic performance and improve separate assessment thereof - providing a more complete overview of the cardiac function. The different time intervals during a cardiac cycle are displayed in a circular diagram, a visual interpretation of which can be seen in Figure 1. To be able to understand fetal cardiac physiology it is essential to understand fetal myocardial function and development throughout gestation. Thus, the general objective of this study was to establish normal reference ranges and gestational age related changes of fetal TVI measurements and to introduce the CSD as a potential aid in fetal myocardial evaluation.



(Enlarge Image)



Figure 1.



The cardiac state diagram (CSD). Example displaying (a) a cardiac state diagram CSD of septum from a healthy fetus at 36 weeks of gestation, and (b) the extracted myocardial velocity (thick curve) and acceleration (thin curve) from which the CSD was generated.





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