SUMMARY Left ventricular (LV) size and function were studied by echocardiography in 145 normal children. The LV end-diastolic diameter (EDD) and its percentage change with systole (%ALVD) were measured and mean velocity of circumferential fiber shortening (Vcf) calculated. The LV pre-ejection period (PEP) and ejection time (LVET) were determined from recordings of aortic valve motion.The EDD increased by approximately threefold during childhood and was best correlated with the log of body weight (r = 0. the log of body surface area (r = 0.96). The mean %lALVD was 36 ± 4 (SD), and this index of LV function was independent of age and heart rate. Mean Vcf was higher, and the absolute values of PEP and LVET shorter, in younger children with a faster heart rate. The mean ratio of PEP/LVET was 0.31 ± 0.003, and was relatively independent of age (r = -0.41) and heart rate (r = 0.37). The %ZALVD and PEP/LVET appear to be particularly useful indices of LV function because they remain constant during the course of childhood.casionally a shallow left lateral decubitus position was required to record the ventricular septum clearly. Left ventricular dimensions were measured in the standard manner ( fig. 1). End-diastolic diameter (EDD) was measured at the start of the QRS complex. End-systolic diameter (ESD) was measured at the point in late systole where the septum and LV posterior wall were in closest apposition. These measurements were made with the transducer angled slightly inferiorly and laterally from the point of maximal excursion of the mitral valve in subjects over one year of age. In younger children, as previously noted by Sahn et al.,7 the mitral leaflets appear to extend farther toward the apex, and the LV diameter decreases rapidly as the transducer is directed below the mitral valve. Therefore, in infants under one year of age the LV dimensions were measured at the point of maximal excursion of the mitral valve, from a position from which both leaflets could be visualized. Recordings satisfactory for determination of LV dimensions were obtained in 143 of the 145 subjects (99%).Left ventricular systolic time intervals were determined from recordings of the aortic valve at 100 mm/sec paper speed ( fig. 2)

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Background-Long-QT syndrome (LQTS) is an inherited cardiac arrhythmia that causes sudden death in young, otherwise healthy people. Four genes for LQTS have been mapped to chromosome 11p15.5 (LQT1), 7q35-36 (LQT2), 3p21-24 (LQT3), and 4q25-27 (LQT4). Genes responsible for LQT1, LQT2, and LQT3 have been identified as cardiac potassium channel genes (KVLQT1, HERG) and the cardiac sodium channel gene (SCN5A). Methods and Results-After studying 115 families with LQTS, we used single-strand conformation polymorphism (SSCP) and DNA sequence analysis to identify mutations in the cardiac potassium channel gene, KVLQT1. Affected members of seven LQTS families were found to have new, previously unidentified mutations, including two identical missense mutations, four identical splicing mutations, and one 3-bp deletion. An identical splicing mutation was identified in affected members of four unrelated families (one Italian, one Irish, and two American), leading to an alternatively spliced form of KVLQT1. The 3-bp deletion arose de novo and occurs at an exon-intron boundary. This results in a single base deletion in the KVLQT1 cDNA sequence and alters splicing, leading to the truncation of KVLQT1 protein. Conclusions-We have identified LQTS-causing mutations of KVLQT1 in seven families. Five KVLQT1 mutations cause the truncation of KVLQT1 protein. These data further confirm that KVLQT1 mutations cause LQTS. The location and character of these mutations expand the types of mutation, confirm a mutational hot spot, and suggest that they act through a loss-of-function mechanism or a dominant-negative mechanism. (Circulation. 1998;97:1264-1269.)