Temporal frequency requirements for tissue velocity imaging of the fetal heart

Frame rate required for speckle tracking echocardiography: A quantitative clinical study with open-source, vendor-independent software

OBJECTIVES

To determine the optimal frame rate at which reliable heart walls velocities can be assessed by speckle tracking.

BACKGROUND

Assessing left ventricular function with speckle tracking is useful in patient diagnosis but requires a temporal resolution that can follow myocardial motion. In this study we investigated the effect of different frame rates on the accuracy of speckle tracking results, highlighting the temporal resolution where reliable results can be obtained.

MATERIAL AND METHODS

27 patients were scanned at two different frame rates at their resting heart rate. From all acquired loops, lower temporal resolution image sequences were generated by dropping frames, decreasing the frame rate by up to 10-fold.

RESULTS

Tissue velocities were estimated by automated speckle tracking. Above 40 frames/s the peak velocity was reliably measured. When frame rate was lower, the inter-frame interval containing the instant of highest velocity also contained lower velocities, and therefore the average velocity in that interval was an underestimate of the clinically desired instantaneous maximum velocity.

CONCLUSIONS

The higher the frame rate, the more accurately maximum velocities are identified by speckle tracking, until the frame rate drops below 40 frames/s, beyond which there is little increase in peak velocity. We provide in an online supplement the vendor-independent software we used for automatic speckle-tracked velocity assessment to help others working in this field.

Maternal obesity affects fetal myocardial function as early as in the first trimester

OBJECTIVE

To investigate cardiac function from 14 weeks' gestation in fetuses of obese pregnant women (FOW). Animal studies have shown that maternal obesity induces fibrosis in fetal myocardium. We hypothesized that fetal cardiac function would be impaired among FOW.

METHODS

A case-control study with longitudinal follow-up was performed at Trondheim University Hospital, Norway. In total, 80 pregnant women were included and the final population comprised 52 obese and 24 of normal weight (mean body mass index before pregnancy, 34.8 ± 4.1 vs 21.0 ± 2.2 kg/m(2) ; P < 0.001). The main outcome measures were global strain rate (GSR) and strain by tissue Doppler imaging, tissue Doppler velocities (TDVs) and interventricular septal thickness assessed by fetal echocardiography at gestational ages of 14, 20 and 32 weeks.

RESULTS

In FOW, fetal left ventricle (LV) and right ventricle (RV) GSR and strain were significantly lower than in fetuses of normal-weight pregnant women: LV GSR was 33.3% lower at 14 weeks, 22.4% lower at 20 weeks and 22.8% lower at 32 weeks of gestation (P < 0.001) with no difference in fetal heart rate. Systolic and late diastolic TDVs for LV were significantly lower from 20 weeks' gestation and remained lower throughout pregnancy. Fetal interventricular septum was 26.6% (P < 0.001) thicker in late pregnancy in FOW compared with normal-weight pregnancies.

CONCLUSIONS

At 14 weeks of gestation, we detected fetal myocardial dysfunction with reduced LV and RV GSR and strain in FOW compared with fetuses of women with normal weight. Our finding is alarming considering the high prevalence of obesity and may partly explain the predisposition of offspring to cardiovascular disease later in life.

Ultrafast cardiac ultrasound imaging: technical principles, applications, and clinical benefits

Several recent technical advances in cardiac ultrasound allow data to be acquired at a very high frame rate. Retrospective gating, plane/diverging wave imaging, and multiline transmit imaging all improve the temporal resolution of the conventional ultrasound system. The main drawback of such high frame rate data acquisition is that it typically has reduced image quality. However, for given clinical applications, the acquisition of temporally-resolved data might outweigh the reduction in image quality. It is the aim of this paper to provide an overview of the technical principles behind these new ultrasound imaging modalities, to review the current evidence of their potential clinical added value, and to forecast how they might influence daily clinical practice.

The cardiac state diagram as a novel approach for the evaluation of pre- and post-ejection phases of the cardiac cycle in asphyxiated fetal lambs

The aim of this study was to investigate myocardial wall motion using echocardiography and color-coded tissue velocity imaging and to generate a cardiac state diagram for evaluation of the duration of the pre- and post-ejection phases in asphyxiated fetal lambs. Six near-term lambs were partly exteriorized and brought to cardiac arrest through asphyxia. Echocardiography measurements were recorded simultaneously with arterial blood sampling for lactate and blood gases. All fetal lambs exhibited prolongation of the pre- and post-ejection phases at the time when the most pronounced changes in lactate concentration and pH occurred. The mean change in duration of the pre- and post-ejection phases for all fetal lambs was 36 ± 7 ms (p < 0.002) and 77 ± 17 ms (p < 0.019), respectively, and the percentage change was 50% (p < 0.001) and 38% (p < 0.049), respectively. As asphyxia progressed in fetal lambs, the duration of the pre- and post-ejection phases increased. The cardiac state diagram has the potential to be a comprehensible tool for detecting fetal asphyxia.

Reference values for fetal tissue velocity imaging and a new approach to evaluate fetal myocardial function

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.

Fetal cardiac muscle contractility decreases with gestational age: a color-coded tissue velocity imaging study

Background

Present data regarding how the fetal heart works and develops throughout gestation is limited. However, the possibility to analyze the myocardial velocity profile provides new possibilities to gain further knowledge in this area. Thus, the objective of this study was to evaluate human fetal myocardial characteristics and deformation properties using color-coded tissue velocity imaging (TVI).

Methods

TVI recordings from 55 healthy fetuses, at 18 to 42 weeks of gestation, were acquired at a frame rate of 201–273 frames/s for offline analysis using software enabling retrieval of the myocardial velocity curve and 2D anatomical information. The measurements were taken from an apical four-chamber view, and the acquired data was correlated using regression analysis.

Results

Left ventricular length and width increased uniformly with gestational age. Atrioventricular plane displacement and the E’/A’ ratio also increased with gestational age, while a longitudinal shortening was demonstrated.

Conclusions

Fetal cardiac muscle contractility decreases with gestational age. As numerous fetal- and pregnancy-associated conditions directly influence the pumping function of the fetal heart, we believe that this new insight into the physiology of the human fetal cardiovascular system could contribute to make diagnosis and risk assessment easier and more accurate.