1/20. prenatal diagnosis of QT prolongation by fetal magnetocardiogram--use of QRS and T-wave current-arrow maps.To determine the T wave of a fetal magnetocardiogram (FMCG), we have evaluated the T/QRS ratio and obtained current-arrow maps that indicate weak currents. We measured FMCG signals for 52 normal fetuses and two abnormal fetuses with prolonged QT waves by using three superconducting quantum interference device (SQUID) systems: a nine-channel system, a 12-channel vector system and a 64-channel system. The T/QRS ratio was calculated for all the normal fetuses from the maximum magnitudes of the QRS complex and the T wave. Current-arrow maps of the QRS complex (R wave) and T wave were obtained by using the 64-channel system, and the phase differences of the total-current vectors were calculated by using the current-arrow maps. The results showed that the T/QRS ratio had a wide variability of 0.35 for the normal fetuses. However, the magnitude of the prolonged T wave was as weak as the detection limit of the SQUID magnetometer. Although the T/QRS ratios for the fetuses with QT prolongation were within the normal range (< 0.35), the weak magnitude of the prolonged T wave could be evaluated. On the other hand, by comparing the current-arrow maps of the R and T waves for the normal fetuses, we found that the maximum-current arrows were indicated as either in the same direction or in opposite directions. These patterns could be identified clearly by the phase differences. Very weak prolonged T waves for the two abnormal fetuses could be determined by using these current-arrow maps and phase differences. Consequently, although the T/QRS ratios of FMCG signals have a wide distribution, we have concluded that the current-arrow map and phase difference can be used to determine the T wave of an FMCG signal.- - - - - - - - - - ranking = 1keywords = complex (Clic here for more details about this article) |
2/20. cocaine-induced torsades de pointes in idiopathic long Q-T syndrome.torsades de pointes is a ventricular tachycardia characterized by the QRS complexes of changing amplitude that appear to twist around an isoelectric line. It usually precipitates in the setting of underlying Q-T interval prolongation, which has both congenital and acquired causes. The common acquired causes of torsades precipitation are medications, electrolyte imbalance, and severe bradycardia. This report presents a case of torsades de pointes that was precipitated by substance abuse in a patient with idiopathic long Q-T syndrome and required several treatment modalities.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
3/20. Torsade de pointes induced by ajmaline.ajmaline, a reserpine derivative, is an effective class I antiarrhythmic agent. Herein we report two cases of ajmaline-induced abnormal QT prolongation accompanied by polymorphic ventricular tachycardia of the torsade de pointes type. Since ajmaline is increasingly used for the acute termination of wide complex tachycardia and as a diagnostic tool after syncope and in patients with idiopathic ventricular tachyarrhythmias, our observations suggest that caution should be exercised with regard to the effects of the drug on the QT interval and its potency to induce proarrhythmia of the torsade de pointes type.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
4/20. Evidence for a single nucleotide polymorphism in the kcnq1 potassium channel that underlies susceptibility to life-threatening arrhythmias.INTRODUCTION: Congenital long qt syndrome (LQTS) is a genetically heterogeneous arrhythmogenic disorder caused by mutations in at least five different genes encoding cardiac ion channels. It was suggested recently that common polymorphisms of LQTS-associated genes might modify arrhythmia susceptibility in potential gene carriers. methods AND RESULTS: We examined the known LQTS genes in 95 patients with definitive or suspected LQTS. Exon-specific polymerase chain reaction single-strand conformation polymorphism and direct sequence analyses identified six patients who carried only a single nucleotide polymorphism in KCNQ1 that is found in approximately 11% of the Japanese population. This 1727G>A substitution that changes the sense of its coding sequence from glycine to serine at position 643 (G643S) was mostly associated with a milder phenotype, often precipitated by hypokalemia and bradyarrhythmias. When heterologously examined by voltage-clamp experiments, the in vitro cellular phenotype caused by the single nucleotide polymorphism revealed that G643S-KCNQ1 forms functional homomultimeric channels, producing a significantly smaller current than that of the wild-type (WT) channels. Coexpression of WT-KCNQ1 and G643S-KCNQ1 with KCNE1 resulted in approximately 30% reduction in the slow delayed rectifier K current I(Ks) without much alteration in the kinetic properties except its deactivation process, suggesting that the G643S substitution had a weaker dominant-negative effect on the heteromultimeric channel complexes. CONCLUSION: We demonstrate that a common polymorphism in the kcnq1 potassium channel could be a molecular basis for mild I(Ks) dysfunction that, in the presence of appropriate precipitating factors, might predispose potential gene carriers to life-threatening arrhythmias in a specific population.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
5/20. Benefit of pacing and beta-blockers in idiopathic repetitive polymorphic ventricular tachycardia.An 18-year-old woman presented with recurrent exercise-induced syncopal episodes and severe systolic dysfunction. ECG monitoring disclosed repetitive polymorphic ventricular complexes, paroxysms of bidirectional ventricular tachycardia, and nonsustained bursts of slow polymorphic ventricular tachycardia that increased in length and rate during exercise. Ventricular arrhythmias were refractory to medical treatment, which included verapamil and beta-blockers. Addition of permanent atrial pacing to beta-blocker therapy suppressed the arrhythmias and reversed systolic impairment in the following months.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
6/20. Spontaneous onset of torsade de pointes in long-QT syndrome and the role of sympathovagal imbalance.The net effects of sympathetic and vagal activity on the QT interval and the mode of spontaneous onset of torsade de pointes (TdP) are still unclear in long-QT syndrome. Two patients with long-QT syndrome had syncope while undergoing Holter ECG investigation. The spontaneous onset of TdP in these patients was analyzed with respect to the relation between the RR and QT intervals. Both patients were high-school students (16- and 17-year-old boys) who had been diagnosed as long-QT syndrome and followed up without medical treatment because they had had neither a history of syncope nor arrhythmia induction by treadmill exercise tests. The first episode of syncope in both patients occurred during ordinary daily life and was not related to exercise or psychological stress. The dynamic changes between the RR and QT intervals associated with the spontaneous onset of TdP were analyzed by Holter ECG. Both patients showed sinus tachycardia followed by abrupt sinus bradycardia immediately before the onset of TdP. The enhanced rate of the adaptive response of the QT interval that occurred during the deceleration of the heart rate preceded the onset of TdP. These observations suggest that the complex situation that follows sympathovagal imbalance may have an important role in the dynamic change in the QT interval and initiation of TdP in patients with long-QT syndrome.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
7/20. Mechanism of sudden cardiac arrest while swimming in a child with the prolonged QT syndrome.We describe the abrupt sequence of events resulting in cardiac arrest while swimming in a 12-year-old with long qt syndrome. diving into cold water resulted in an irregular cardiac rhythm and further prolongation of the QT interval, followed by a premature ventricular complex, which initiated pulseless ventricular tachycardia (rate >300/minute). The transition from sinus rhythm to ventricular tachycardia occurred in <5 seconds and was followed by a successful implantable cardioverter-defibrillator rescue shock.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
8/20. Sudden arrhythmia death syndrome: importance of the long qt syndrome.In approximately 5 percent of sudden cardiac deaths, no demonstrable anatomic abnormality is found. Some cases are caused by sudden arrhythmia death syndrome. A prolonged QT interval is a common thread among the various entities associated with sudden arrhythmia death syndrome. A number of drugs are known to cause QT prolongation (e.g., terfenadine), as are hypokalemia, hypomagnesemia, myocarditis, and endocrine and nutritional disorders. Recently, attention has focused on a group of inherited gene mutations in cardiac ion channels that cause long qt syndrome and carry an increased risk for sudden death. Some of the highest rates of inherited long qt syndrome occur in Southeast Asian and Pacific Rim countries. The median age of persons who die of long qt syndrome is 32 years; men are predominately affected. In addition to a prolonged QT interval, which occurs in some but not all persons with long qt syndrome, another characteristic electrocardiographic abnormality is the so-called Brugada sign (an upward deflection of the terminal portion of the QRS complex). Most cardiac events are precipitated by vigorous exercise or emotional stress, but they also can occur during sleep. torsades de pointes and ventricular fibrillation are the usual fatal arrhythmias. long qt syndrome should be suspected in patients with recurrent syncope during exertion and those with family histories of sudden, unexpected death. Unfortunately, not all persons with long qt syndrome have premonitory symptoms or identifiable electrocardiographic abnormalities, and they may first present with sudden death. Beta blockers, potassium supplements, and implantable defibrillators have been used for treatment of long qt syndrome. Identifying the specific gene mutation in a given patient with long qt syndrome can help guide prophylactic therapy.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
9/20. Giant J wave on 12-lead electrocardiogram in hypothermia.Findings on standard 12-lead electrocardiogram in patients with hypothermia include sinus bradycardia, prolonged QT and PR interval, wide QRS complex, supraventricular and ventricular arrhythmia, and the most striking electrocardiographic abnormality, the J wave. Although characteristic of hypothermia, J wave also occurs in other conditions. The electro-physiologic basis of J wave in hypothermia has been recently elucidated. We present a case of giant J wave due to accidental hypothermia and in addition discuss the features, mechanism, and significance of J wave in hypothermia.- - - - - - - - - - ranking = 0.5keywords = complex (Clic here for more details about this article) |
10/20. Electrical alternans in long qt syndrome resembling a brugada syndrome pattern.Isolated T wave alternans (repolarization alternans) is frequently associated with long qt syndrome. However, electrical alternans involving the P wave, QRS complex, ST segment (depolarization alternans), and the T wave is a rare finding. This report describes a 62-year-old woman with long qt syndrome and an electrical alternans occurring after previous syncope. Alternating QRS complexes showed a prolonged PR interval, a brugada syndrome resembling pattern of the QRS complexes (elevation and downslope of the ST segments), and a T wave alternans. A genetic basis for the long qt syndrome has been ruled out by sequencing of all coding areas of the LQT genes. Potential mechanisms for the electrical alternans are discussed.- - - - - - - - - - ranking = 1.5keywords = complex (Clic here for more details about this article) |
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