Regional myocardial function and response to acute afterload increase in chronically anemic fetal sheep: evaluation by two-dimensional strain echocardiography

Cardiac function and dysfunction in the fetus

Evaluation of fetal cardiac function is one of the most important components of fetal echocardiography. Fetal cardiac dysfunction is closely linked to risk of intrauterine fetal demise, in many, but not all cases is indicative of worse postnatal prognosis and may prompt the use of medications or interventions to optimize outcomes. There may be implications for termination versus continuation of pregnancy, an indication for early delivery, a change in location and even mode of delivery. In extreme cases, fetal cardiac dysfunction may prompt prenatal or early neonatal listing for cardiac transplantation. There are several important differences between the fetal and postnatal circulatory physiology which affect echocardiographic assessment of cardiac dysfunction. In this review, we examine the echocardiographic findings according to their underlying pathophysiology with reference to common causes.

Feasibility of detecting myocardial infarction in the sheep fetus using late gadolinium enhancement CMR imaging

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging has enabled the accurate assessment of myocardial infarction (MI). However, LGE CMR has not been performed successfully in the fetus, where it could be useful for animal studies of interventions to promote cardiac regeneration. We believe that LGE imaging could allow us to document the presence, extent and effect of MI in utero and would thereby expand our capacity for conducting fetal sheep MI research. We therefore aimed to investigate the feasibility of using LGE to detect MI in sheep fetuses.

METHODS

Six sheep fetuses underwent a thoracotomy and ligation of a left anterior descending (LAD) coronary artery branch; while two fetuses underwent a sham surgery. LGE CMR was performed in a subset of fetuses immediately after the surgery and three days later. Early gadolinium enhancement (EGE) CMR was also performed in a subset of fetuses on both days. Cine imaging of the heart was performed to measure ventricular function.

RESULTS

The imaging performed immediately after LAD ligation revealed no evidence of infarct on LGE (n=3). Two of four infarcted fetuses (50%) showed hypoenhancement at the infarct site on the EGE images. Three days after the ligation, LGE images revealed a clear, hyper-enhanced infarct zone in four of the five infarcted fetuses (80%). No hyper-enhanced infarct zone was seen on the one sham fetus that underwent LGE CMR. No hypoenhancement could be seen in the EGE images in either the sham (n=1) or the infarcted fetus (n=1). No regional wall motion abnormalities were apparent in two of the five infarcted fetuses.

CONCLUSION

LGE CMR detected the MI three days after LAD ligation, but not immediately after. Using available methods, EGE imaging was less useful for detecting deficits in perfusion. Our study provides evidence for the ability of a non-invasive tool to monitor the progression of cardiac repair and damage in fetuses with MI. However, further investigation into the optimal timing of LGE and EGE scans and improvement of the sequences should be pursued with the aim of expanding our capacity to monitor cardiac regeneration after MI in fetal sheep.

How to build a healthy heart from scratch

By any of several measures, the health of the American population has been worsening over the last two decades. Obesity, type 2 diabetes and heart failure have risen dramatically. All the while, the average birthweight at all gestational ages has declined. The relationship between robust growth in the womb and lifelong health is now well established. Likewise, babies born at the low end of the birthweight scale are known to have highly elevated risks for ischemic heart disease, hypertension, stroke and metabolic disease. The biological mechanisms by which developmental plasticity becomes a risk for cardiovascular disease are only now being understood. Translating from animal and human studies, low birthweight babies are likely to have endothelial dysfunction, fewer nephrons, fewer pancreatic beta cells, less vascular elastin, fewer cardiomyocytes, increased sympathetic tone and liver-derived dyslipidemias. Only in the past few years, however, has it become known that maternal and placenta phenotypes are associated with adult onset cardiovascular disease. Helsinki Birth Cohort studies have been especially important in the discovery of these relationships. Sudden cardiac death is associated with a thin placenta and heart failure is associated with a small placenta in short mothers. Coronary heart disease is associated with three combinations of maternal-placental phenotypes. Because the diet is important in providing nutrients for the development of the female body before pregnancy and for providing nutrients during pregnancy, there is increasing evidence that the western diet is an underlying cause for the increase in metabolic disease in the American population. A large segment of the American population suffers from high calorie malnutrition. Scientists in this field now have a responsibility to educate the public on the topic of nutrition and health. This chapter honors Lawrence Longo for decades of work in bringing health to pregnant women and their babies.