Echocardiographic evaluation of the failing heart

Current Cardiac Imaging Approaches in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular condition caused by mutations in the dystrophin gene leading to skeletal muscle weakness and dilated cardiomyopathy. The prevalence of DMD-related cardiomyopathy increases with age and is almost universal by the third decade of life. Myocardial fibrosis and progressive left ventricular dysfunction lead to the development of heart failure and premature death. With modern advances in medical and surgical management for patients with DMD increasing their life expectancy, cardiac dysfunction represents an increasing cause of morbidity and mortality in these patients. Early diagnosis of dilated cardiomyopathy before symptom development enables the initiation of potentially disease-modifying therapies, but requires regular dedicated imaging surveillance with sufficient sensitivity to detect subclinical changes in cardiac structure and function. Currently, transthoracic echocardiography (TTE) and cardiac magnetic resonance imaging (CMR) are commonly used and have complementary roles. TTE is rapid and readily available, whereas CMR is the gold standard for the quantification of ventricular structure and function and can detect the presence and extent of myocardial fibrosis, an increasingly appreciated marker for early disease. This review describes the clinical applications, advantages, and disadvantages of cardiac imaging screening and surveillance for the myocardial manifestations of DMD, with a particular focus on TTE and CMR.

Long-term consequences of disrupting adenosine signaling during embryonic development

There is growing evidence that disruption in the prenatal environment can have long-lasting effects on an individual's health in adulthood. Research on the fetal programming of adult diseases, including cardiovascular disease, focuses on epi-mutations, which alter the normal pattern of epigenetic factors such as DNA methylation, miRNA expression, or chromatin modification, rather than traditional genetic alteration. Thus, understanding how in utero chemical exposures alter epigenetics and lead to adult disease is of considerable public health concern. Few signaling molecules have the potential to influence the developing mammal as the nucleoside adenosine. Adenosine levels increase rapidly with tissue hypoxia and inflammation. Adenosine antagonists including the methlyxanthines caffeine and theophylline are widely consumed during pregnancy. The receptors that transduce adenosine action are the A1, A2a, A2b, and A3 adenosine receptors (ARs). We examined the long-term effects of in utero disruption of adenosine signaling on cardiac gene expression, morphology, and function in adult offspring. One substance that fetuses are frequently exposed to is caffeine, which is a non-selective adenosine receptor antagonist. Over the past several years, we examined the role of adenosine signaling during embryogenesis and cardiac development. We discovered that in utero alteration in adenosine action leads to adverse effects on embryonic and adult murine hearts. We find that cardiac A1ARs protect the embryo from in utero hypoxic stress, a condition that causes an increase in adenosine levels. After birth in mice, we observed that in utero caffeine exposure leads to abnormal cardiac function and morphology in adults, including an impaired response to β-adrenergic stimulation. Recently, we observed that in utero caffeine exposure induces transgenerational effects on cardiac morphology, function, and gene expression. Our findings indicate that the effects of altered adenosine signaling are dependent on signaling through the A1ARs and timing of disruption. In addition, the long-term effects of altered adenosine signaling appear to be mediated by alterations in DNA methylation, an epigenetic process critical for normal development.

In Utero Caffeine Exposure Induces Transgenerational Effects on the Adult Heart

Each year millions of pregnant woman are exposed to caffeine, which acts to antagonize adenosine action. The long-term consequences of this exposure on the developing fetus are largely unknown, although in animal models we have found adverse effects on cardiac function. To assess if these effects are transmitted transgenerationally, we exposed pregnant mice to caffeine equivalent to 2–4 cups of coffee at two embryonic stages. Embryos (F1 generation) exposed to caffeine early from embryonic (E) day 6.5–9.5 developed a phenotype similar to dilated cardiomyopathy by 1 year of age. Embryos exposed to caffeine later (E10.5–13.5) were not affected. We next examined the F2 generation and F3 generation of mice exposed to caffeine from E10.5–13.5, as this coincides with germ cell development. These F2 generation adult mice developed a cardiac phenotype similar to hypertrophic cardiomyopathy. The F3 generation exhibited morphological changes in adult hearts, including increased mass. This report shows that in utero caffeine exposure has long-term effects into adulthood and that prenatal caffeine exposure can exert adverse transgenerational effects on adult cardiac function.