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Friday, June 10, 2011
Interesting Information on Long QT Syndrome
The informative and well written piece which follows was obtained from:
It is wholly the educational work of The Texas Arrhythmia Institute,in Houston.
Long QT syndrome (LQTS) has created great interest because of its unique and dramatic manifestation. This familial disorder was recognized more than 100 years ago. In 1856 a deaf girl was reported to have collapsed and died while being publicly admonished at school. Previously two of her brothers had died suddenly during under similar stressful situations.
In 1975 A. Jervell and F. Lange-Nielson provided the first complete description of LQTS, a syndrome of deafness and sudden cardiac death and associated with a characteristic ECG abnormality (prolonged Q-T interval). The cardiac arrest in these victims, mostly children and teenagers is due to ventricular tachyarrhythmia. Most episodes of arrhythmias are usually self-terminating, even when they provoke a transient loss of consciousness (syncope). However, when the episodes are prolonged, circulatory failure due to arrhythmia may result in sudden death.
LQTS was previously classified into a non-familial sporadic form and two hereditary types, with deafness (Jervell and Lange-Nielson syndrome, autosomal recessive) and without deafness (Romano Ward syndrome, autosomal dominant). In 1991 M. T. Keating et al. demonstrated linkage between LQTS and chromosome 11. Subsequent genetic studies showed that different LQTS syndromes were due to mutations of different genes (at least 5) localized on chromosomes 3,4,7 & 11. These genes are responsible for the synthesis (encoding) of membrane channel proteins that play a pivotal role in the cellular metabolism and regulation of the electric activity of cardiac cells. LQTSs have thus been recognized as cardiac membrane channel diseases ("channelopathies") that invite syncope and SCD due to ventricular arrhythmias.
The two criteria for diagnosis of LQTS are unexplained transient loss of consciousness and an abnormal ECG. Ventricular arrhythmias and syncope are often provoked by increases in heart rate in response to exercise or emotion. Because such responses involve changes in the autonomic neural (non-voluntary) regulation of the heart, it was believed that LQTS resulted from some imbalance in sympathetic innervation of the heart. However nerve deafness and other possible neural abnormalities associated with LQTSs remain to be elucidated.
The incidence of fully expressed LQTS is probably rare, although variations of the syndrome may remain unrecognized and actually be frequent. Cases have been reported in every continent and in every race. Four factors are associated with an increased risk of SCD: deafness, history of syncope, males before puberty and episodes of sustained females menarche, and sustained (>30sec) and/or very irregular ("polymorphic", torsade de pointes) ventricular tachycardia.
There may be channel gene mutations which by themselves do not seriously affect cardiac cell electric activity, but that may render the heart susceptible to drugs that prolong the QT interval of the ECG. These drugs include commonly prescribed agents such as antiarrhythmic drugs, certain antibiotics (antifungals), psychotropic drugs, or diuretics causing wasting of potassium in the urine.
Ideally, drug treatments should be guided by new genetic and electrophysiologic insights into the different LQTS's. Until recently, anti-adrenergic therapy (beta-blockers) has been the major treatment for LQTS. However based on current information, new targeted treatments may now be considered. The underlying mechanisms of LQT3 are an increase in sodium current, whereas LQT1 and LQT2 arise from deficient potassium currents. These changes in membrane currents can be influenced with specific drugs that selectively block excess sodium currents (sodium channel blockers) or activate potassium currents (potassium channel openers).
In some patients with life-threatening arrhythmias, an implanted cardioverter defibrillator (ICD) may be an appropriate therapy.
Daniel, This song is appropriate for us to share because although you could not stay on Earth as long as we had hoped and expected, we remain incredibly proud of all you did while you were here, and of the seeds of a legacy you left with your kindness and your actions, with so many people before your departure.