Prolonged if it is more than 450 msec in men or more than 460 msec in women, correcting for heart rate.
The QT interval should be measured from the Q wave to return to baseline of the T wave.
The longest QT interval is the most important value to consider when assessing arrhythmic risk.
A QTcgreater than 500 ms helps in discriminating between patients who are moderate or higher rhythmic risk.
Prolongation most frequently from delayed ventricular repolarization which is mediated by efflux of intracellular potassium.
Prolongation associated with excess risk for coronary artery disease.
Prolongation of the QT interval is accepted as a warning sign of life-threatening arrhythmia.
The duration of the QT interval, naturally varies, inversely with heart rate and a corrected QT (QTc) that adjusted for heart rate is most predictive of proarrhythmic potential.
QTc is widely used in clinical practice.
A QTC greater than 500 ms discriminate between patients who are at moderate or higher rhythmic risk.
Notches on the T wave or accompanied by mechanical alterations ARE a marker of arrhythmic risk related to early after depolarizations.
Arrhythmic events are due to Torsades de pointes ventricular tachycardia, which often to generates into ventricular fibrillation, causing cardiac arrest and sudden death.
The outcome depends on the duration of Torsades de pointes with prolongation of QT the occurrence of short duration, syncope, or vertigo alerts to the possibility of Torsades de pointes, often, a harbinger of life-threatening arrhythmic episodes.
Prolongation can predict for sudden death in chronic ischemic disease, hypertension, sickle cell anemia, and healthy individuals.
Hypokalemia, hypomagnesemia, and hypocalcemia are all associated with prolonged QT interval which may have it increase relation to sudden cardiac death.
Increased variability, or QT dispersion, noted to be present in sudden deaths associated with congestive heart failure, acute myocardial infarction and hypertrophic cardiomyopathy.
Dispersion is an electrocardiographic measure of ventricular repolarization and a marker for ventricular tachyarrhythmias
Increased QT dispersion on an EKG found in hypertensive patients with severe disease and with the greatest left ventricle mass index and blood pressure.
Long QT syndrome is an uncommon disease of genetic origin with a prevalence of one in 2000 live births, but the actual prevalence is probably higher.
The long QT syndrome is characterized by prolongation of the QT interval on ECG obtained when the patient is at rest and has a propensity for life-threatening arrhythmias that occur mostly in the conditions of physical or emotional stress.
Sudden cardiac death is often the first symptom
Hereditary long QT syndrome associated with a prolonged ventricular repolarization and increased risk for ventricular tachyarrhythmias (torsades de pointes) and sudden cardiac death.
In approximately 75% of patients with LQTS have mutations in three major genes encoding ion channel subunits that control the action potential of the heart (Keating MT, Sanguinetti MC).
Long QT syndrome influenced by gender, congenital deafness, previous cardiac events, family history, QT interval length and genotype.
Majority of cases of long QT syndrome inheritance is autosomal dominant, but can be recessive.
Long QT syndrome characterized by abnormal QT-interval prolongation on EKG and increased risk of sudden death, usually related to ventricular fibrillation.
The QT interval is usually markedly prolonged and is often accompanied by bizarre morphologic changes with the guard to ventricular polarization – by phasic and notch T waves, that should arouse sediagnostic suspicion.
Long QT syndrome consists of a number of cardiac channelopathies with delayed repolarization of the myocardium.
Long-QT syndrome is most often related to an inherited potassium channelopathy, and there is an increased likelihood of electroencephalogram abnormalities in long-QT patients vs healthy controls, perhaps pointing toward an important link between the two conditions.
Long QT syndrome occurs in a structurally normal heart and is associated with increased risk of seizures, syncope, and sudden cardiac death, and these manifestations occur after a precipitating event such as extreme exertion, a motion or even an auditory trigger (Rodem DM).
Emotional and physical stress common causes for syncope or sudden death in long QT syndrome.
Cardiovascular events can be precipitated by loud noises or at rest in the long QT interval syndrome.
Cardiovascular events may occur with the congenital long QT syndrome with a familial gene mutation or due to an acquired long QT syndrome secondary to QT prolonging diseases or conditions that include ischemic heart disease, medications, electrolyte disturbances or bradycardia.
Patients with a prolonged QT interval may present with syncope, sudden cardiac death due to polymorphic ventricular tachycardia, also known Torsades de pointes, and ventricular fibrillation.
Long-QT syndrome associated with hundreds of mutations in 10 genes.
Mutations in the potassium channel genes KCNQ1, KCNH2 and SCN5A cause the most frequent forms: variants in types 1 and 2, KCNQ1, KCNH2 are 40 and 50% respectively involved with the long QT syndrome.
These genes encode the potassium channels, conducting the outward currents Iks and ikr and are critically important for cardiac repolarization and the reduction in their currents caused by pathogenic variants prolong the QT interval and cause long QT syndrome.
During adronergic activation, such as physical activity, the Iks current becomes the prevalent, repoolarization current and carries major clinical implications. if the QT interval does not appropriately shorten when the heart rate increases, ventricular fibrillation may ensue.
The SCN5A gene encodes the voltage gated sodium channel conducting the major depolarization in which sodium current Ina.
Pathologic variants of SCN5A produce gain of function, prolong repolrization and caused long QT syndrome type 3 approximately 10% of cases.
Persons with long QT syndrome, type 1 or an increased risk when sympathetic activity increases, as during emotional and physical stresses, especially swimming.
Persons with long QT syndrome type 2 are an increased risk when exposed to sudden noises, especially if they are at rest or asleep or awoken abruptly, they are exquisitely sensitive to low plasma potassium levels, and to QT interval prolonging, drugs, and female patients are at high risk during the postpartum period, probably due to sleep disruption causing rebounds of the arrhythrogenenic rapid eye movement sleep.
Persons with long QT syndrome type 3 are at risk primarily at rest or when asleep.
Additional genes linked to long QT syndrome but few have important roles: CACNA1C, CALM 1–3.
Female predominance in long QT syndrome.
Abnormal prolongation and shortening of QT-interval duration are associated with increased risk for ventricular arrhythmias and sudden cardiac death.
Prolongation of the QT interval is a common adverse event associated with many chemotherapeutic agents, and can lead to life-threatening arrhythmias such as Torsades de pointes.
Torsades de pointes often degenerates into ventricular fibrillation, causing cardiac arrest, and sudden death.
In subjects with QT prolongation the occurrence of short duration syncope, or vertigo, suggest the possibility of torsade de pointes, often a harbinger of life-threatening arrhythmic episodes.
The prognosis of the congenital long QT syndrome can be improved if properly and promptly diagnosed and treated.
The mortality associated with acquired long QT syndrome in patients with cardiovascular disease and stroke is high.
Long QT syndrome contributes to sudden death in infancy as up to 10% of infants who died suddenly in the first year of life, or in utero, carry long QT syndrome causing variants.
The acquired long QT syndrome is often observed in patients with drug exposure, and in combination with other risk factors such as female gender, bradycardias, renal dysfunction, and electrolyte abnormalities fatal of ventricular arrhythmias may manifest.
A QT interval of more than 500 ms is used as a threshold for the risk of develping Torsades de pointes.
QTc interval refers to the QT interval corrected for the heart rate.
In a retrospective analysis of a QT alert system 86,107 ECGs on 52,579 patients compared the survival rate of those between those with a QTc interval of 500 ms or greater and those with QTc interval less than 500 ms:all cause mortality rate for patients with QTc interval of 500 ms or greater was 19% compared With 5% in patients with QTc interval less than 500 ms (Haugaa KH et al).
A number perioperative drugs prolonged QT interval and include volatile anesthetics, anti-emetics, muscle relaxants, and some opioids.
Droperidol may be associated with prolonged QT interval.
Diagnosis:
Typical cases, such as syncope with clear QTc prolongation diagnosis is straightforward.
In cases where there is modestQTc prolongation and no symptoms, genetic screening may help as well as a 24 hour Holter recording unmasking typical changes, especially at night.
Prolongation of the QTc interval in the recovery phase of an exercise stress test or the appearance of complete fusion of the T and P waves at peak exercise can contribute to the diagnosis.
Four cornerstones of therapy are beta blockers, mexiletine left cardiacsympathetic denervation, and implantable cardiodefibrillator (ICD:reflect the underlying pathology of long QTsyndrome.
Lifestyle modification, including avoidance of QT prolonging drugs, and use of potassium supplements to maintain adequate plasma potassium can contribute substantially to lowering rhythmic risk.
Beta blockers are effective in the syndrome are propanolol at a dose of 2 to 3.5 mg per kilogram of bodyweight per day, and Nadolol 1 to 1.5 mg per kilogram per day.
Metoproprolol should not be used.
Non adherence to beta blocker of therapy and the use of QT prolonging drugs, cause most life-threatening failures of beta blocker of therapy with the long QT syndrome.
A left, cardiac sympathetic renovation, mostly performed by means of thoracoscopy, involves removal of the lower half of the stellate ganglion to prevent Horner’s syndrome, and of the first four thoracic ganglia, performing left cardiac sympathetic denervation with anti-fibrillatory effect reduces norepinephrine release at the ventricular level, without heart rate reduction, and shows high success rate when performed in response to electrical storms of episodes of ventricular tachycardia-fibrillation, resulting in ICD interventions, and reduces the annual indicence of ICD shocks by 90%.
The procedure clinically significantly shortens QTC in most patients and is associated with long-term protection.
In patients with electrical storms left cardiac sympathetic denervation should replace the use of ICD.
Mexiletine a sodium channel blocker is widely used in the long QT syndrome type 3 and reduces the risk of an arrhythmia by shortening the QTC.
Almost 70% of patients with long QT syndrome type 2 have a reduction in the QTC interval with mexiletine .
A mexiletine trial can indicate the efficacy of the drug before starting on long-term institution.