Normal values and methodologic recommendations for signal-averaged electrocardiography in children and adolescents.

Signal-averaged electrocardiography was performed in 153 normal children and adolescents (1 day to 18.3 years old) to examine the effects of age, sex, and race on different electrocardiographic variables, and to evaluate whether the current methods for analysis of the signal-averaged electrocardiogram are applicable to small children. Tracing with inaccurate automatic determination of the QRS end point or high noise levels were excluded. Filtered QRS duration, root-mean-square voltage, and low-amplitude signal duration were measured using 25, 40, and 80 Hz filters. All variables were significantly different (p <0.01) in infants compared with subjects aged >15 years. These differences gradually resolved with increasing age. Sex differences were present for some variables in adolescents only, and there was no significant race-related difference. Because of the shorter QRS duration, the terminal activities were more accurately reflected at the terminal duration of 30 ms in infants and 35 ms in children aged at least 1 year to <6 years. Normative data for filtered QRS duration, root-mean-square voltage, and low-amplitude signal duration are provided for different age groups.

Cardiac expression of polysialylated NCAM in the chicken embryo: correlation with the ventricular conduction system.

The neural cell adhesion molecule (NCAM) and its polysialic acid moeity (PSA) affect cellular interactions during the development of the nervous system and skeletal muscle. NCAM has also been identified in the embryonic heart of various species including humans. However, knowledge regarding the role of NCAM and its function-modulating PSA in cardiogenesis is limited. The distribution of NCAM and its PSA in the ventricular myocardium of chicken embryos was determined by indirect immunofluorescence staining. The NCAM polypeptide was found throughout the cardiac myocardium. In contrast PSA was located in discrete regions in stage 20 to 44 embryos (during and after septation). Myocardium at the subendocardial regions of the atrioventricular canal and ventricular trabeculae were PSA positive by stage 20. At later stages, transverse sections of the postseptation heart just below the level of the atrioventricular interface revealed a PSA-positive bundle of myocardium in the septum. This bundle was continuous with two branches at a more apical level which in turn were continuous with the PSA-positive subendocardial myocardium lining the left and right ventricles. This pattern of PSA in the myocardium was similar to that of the ventricular conduction system configuration defined in the adult heart. Electron micrographs of the subendocardium of the ventricular septum revealed PSA positivity on myofibril-containing cells with the ultrastructural location of Purkinje fibers. At later stages (35-44) a subset of cells within PSA-positive regions was stained by an antibody against an isoform of the myosin heavy chain found in adult Purkinje fibers. These cells and surrounding tissue lacked PSA in the adult heart. Thus polysialylated NCAM may be modulating cell-cell interactions during the development of the ventricular conduction system.