Prevalence of the congenital long-QT syndrome.

BACKGROUND: The prevalence of genetic arrhythmogenic diseases is unknown. For the long-QT syndrome (LQTS), figures ranging from 1:20 000 to 1:5000 were published, but none was based on actual data. Our objective was to define the prevalence of LQTS. METHODS AND RESULTS: In 18 maternity hospitals, an ECG was performed in 44 596 infants 15 to 25 days old (43 080 whites). In infants with a corrected QT interval (QTc) >450 ms, the ECG was repeated within 1 to 2 weeks. Genetic analysis, by screening 7 LQTS genes, was performed in 28 of 31 (90%) and in 14 of 28 infants (50%) with, respectively, a QTc >470 ms or between 461 and 470 ms. A QTc of 451 to 460, 461 to 470, and >470 ms was observed in 177 (0.41%), 28 (0.06%), and 31 infants (0.07%). Among genotyped infants, disease-causing mutations were found in 12 of 28 (43%) with a QTc >470 ms and in 4 of 14 (29%) with a QTc of 461 to 470 ms. One genotype-negative infant (QTc 482 ms) was diagnosed as affected by LQTS on clinical grounds. Among family members of genotype-positive infants, 51% were found to carry disease-causing mutations. In total, 17 of 43 080 white infants were affected by LQTS, demonstrating a prevalence of at least 1:2534 apparently healthy live births (95% confidence interval, 1:1583 to 1:4350). CONCLUSIONS: This study provides the first data-based estimate of the prevalence of LQTS among whites. On the basis of the nongenotyped infants with QTc between 451 and 470 ms, we advance the hypothesis that this prevalence might be close to 1:2000. ECG-guided molecular screening can identify most infants affected by LQTS and unmask affected relatives, thus allowing effective preventive measures.

A novel form of short QT syndrome (SQT3) is caused by a mutation in the KCNJ2 gene.

Short QT syndrome (SQTS) leads to an abbreviated QTc interval and predisposes patients to life-threatening arrhythmias. To date, two forms of the disease have been identified: SQT1, caused by a gain of function substitution in the HERG (I(Kr)) channel, and SQT2, caused by a gain of function substitution in the KvLQT1 (I(Ks)) channel. Here we identify a new variant, "SQT3", which has a unique ECG phenotype characterized by asymmetrical T waves, and a defect in the gene coding for the inwardly rectifying Kir2.1 (I(K1)) channel. The affected members of a single family had a G514A substitution in the KCNJ2 gene that resulted in a change from aspartic acid to asparagine at position 172 (D172N). Whole-cell patch-clamp studies of the heterologously expressed human D172N channel demonstrated a larger outward I(K1) than the wild-type (P<0.05) at potentials between -75 mV and -45 mV, with the peak current being shifted in the former with respect to the latter (WT, -75 mV; D172N, -65 mV). Coexpression of WT and mutant channels to mimic the heterozygous condition of the proband yielded an outward current that was intermediate between WT and D172N. In computer simulations using a human ventricular myocyte model the increased outward I(K1) greatly accelerated the final phase of repolarization, and shortened the action potential duration. Hence, unlike the known mutations in the two other SQTS forms (N588K in HERG and V307L in KvLQT1), simulations using the D172N and WT/D172N mutations fully accounted for the ECG phenotype of tall and asymmetrically shaped T waves. Although we were unable to test for inducibility of arrhythmia susceptibility due to lack of patients' consent, our computer simulations predict a steeper steady-state restitution curve for the D172N and WT/D172N mutation, compared with WT or to HERG or KvLQT1 mutations, which may predispose SQT3 patients to a greater risk of reentrant arrhythmias.

Temporal variability in birth prevalence of congenital heart defects as recorded by a general birth defects registry.

OBJECTIVE: Our aim was to examine the temporal variability in congenital heart defect (CHD) birth prevalence from 1980 to 2000 in Emilia-Romagna, Italy. METHODS: The study population consisted of all infants, surveyed by the Emilia-Romagna birth defects registry (Indagine Malformazioni conpenite in Emilia-Romagna [IMER]), who were affected by CHDs. A simplified classification into "simple" and "complex " CHD was adopted. A comparison with another epidemiologic study using different methodology in the same area was performed. RESULTS: From 1980 to 2000, IMER ascertained 2442 live births with CHD of 480,793 infants born, with an average CHD birth prevalence of 5.1% (Range, 3.1% to 7.5%). A significant increase in prevalence of simple CHD during the second decade of the study was demonstrated because of an increased recognition of "minor" cardiac lesions among the simple CHD. The birth prevalence of complex CHD remained stable. CONCLUSIONS: The apparent increase in live births with CHD results mainly from the current widespread availability of color Doppler echocardiography, which allows the early detection of the "minor" cardiac defects. Other differences are the result of the sources of ascertainment, diagnostic criteria, system of classification, and especially the age limit for enrolling infants with suspected CHD.

Complex electrocardiographic findings in a neonate with long QT syndrome.

A case of long QT syndrome diagnosed in the early neonatal period is described. A full-term male baby was delivered by cesarean section at 38 weeks of gestation. The indication to cesarean section was sudden marked fetal bradycardia. At birth, he presented the following rhythm disorders: a) an ectopic atrial rhythm with T wave alternans, and b) atrioventricular conduction disorders. Sinus rhythm, with a prolonged QT interval and T wave alternans, was recovered soon after birth, before starting beta-blocker therapy. The family history was negative for the long QT syndrome: sudden unexpected death and/or syncopal episodes and cases of congenital deafness have not been reported. Molecular screening of the five long QT syndrome-related genes did not reveal the presence of any mutation. At 3 years of follow-up, the child is well and he did not present with symptoms or arrhythmias during this period.

Left ventricular remodeling, systolic function, and diastolic function in young adults with beta-thalassemia intermedia: a Doppler echocardiography study.

BACKGROUND: The aim of this study was to investigate the left ventricular (LV) remodeling and function in 24 asymptomatic young adults affected by beta-thalassemia intermedia (TI), in order to compare the obtained data with that of 80 patients affected by beta-thalassemia major (TM) and 65 healthy subjects. METHODS: LV volumes and shapes, mass index, mass/volume ratio, systolic and diastolic function, stroke volume, and cardiac index were determined by two-dimensional and M-mode echocardiography. RESULTS: In the TM and TI groups, LV volumes, diastolic and systolic shapes were significantly different from the control subjects, but the ejection fraction was slightly reduced only in the TM group. The TI group had larger LV volumes than did the TM group (mean [+/- SD] end-diastolic volume index, 99.4 +/- 21.9 vs 82.7 +/- 21.5 mL/m(2), respectively [p < 0.005]; mean end-systolic volume index, 42.8 +/- 12.2 vs 36.1 +/- 12.9 mL/m(2), respectively [p < 0.05]). Both groups showed an increase of the LV mass index, but the mass/volume ratio did not differ from the control subjects. The systolic volume index and the cardiac index were increased in both groups, but the increase was more pronounced in the TI group. Fractional shortening (FS) and the mean velocity of circumferential shortening (mVCFc) were decreased in the TM group (FS, 33.6 +/- 5.5% vs 36.9 +/- 4.1, respectively [p < 0.001]; mVCFc, 1.06 +/- 0.18 vs 1.17 +/- 0.12 circumference per second, respectively [p < 0.0001]). The LV contractile state was depressed only in the TM group, and the preload index was normal in both. LV filling showed an increase in the total flow velocity integral due to increases in the peak E wave (E) and peak A wave (A) velocities and integrals, with an increase of the E/A ratio in the TM group and a slight decrease in the TI group. The isovolumic relaxation time was prolonged in both groups. There was no major derangement in the pulmonary venous flow. CONCLUSIONS: Asymptomatic young adults with TI show significant increases in LV volumes, LV mass, and cardiac index that are more pronounced than those in TM patients. LV systolic function is preserved in the TI group but is slightly depressed in the TM group due to the increase of afterload and to reduced contractility. The hemodynamic and hematologic factors involved in the etiopathogenesis of these findings are discussed, such as the treatment strategy.