Long QT syndrome
Long QT syndrome (LQTS) is a heart rhythm disorder characterized by an extended QT interval, which is visible on an electrocardiogram (ECG). This condition can be either congenital, meaning inherited genetically, or acquired due to factors like certain medications. Individuals with LQTS are at risk for dangerous arrhythmias, such as ventricular tachycardia and torsade de pointes, potentially leading to fainting, cardiac arrest, or even sudden death. Genetic factors play a significant role, with various forms of LQTS linked to abnormalities in ion channel genes. Common variants include Romano-Ward syndrome and Jervell and Lange-Nielsen syndrome, the latter associated with congenital deafness. Symptoms may not always be apparent but can include fainting, abnormal heart rhythms, and in severe cases, sudden death, often triggered by physical exertion or emotional stress. Diagnosis usually involves a detailed medical history, ECG, and sometimes genetic testing. Treatment options range from lifestyle modifications and medication to advanced interventions like implantable defibrillators or surgeries, depending on the severity of the condition. Early diagnosis and appropriate management are crucial to mitigate the risks associated with LQTS.
Long QT syndrome
ALSO KNOWN AS: LQTS; congenital long QT syndrome; Jervell and Lange-Nielsen syndrome; Romano-Ward syndrome
DEFINITION The QT interval, shown on an electrocardiogram (ECG), is the time it takes for the heart’s ventricles to electrically recharge (contract and then recover) between beats. Long QT syndrome (LQTS) is a congenital or acquired heart rhythm disorder in which the QT interval is longer than normal. LQTS may cause abnormally rapid and possibly life-threatening heart rhythms, such as ventricular tachycardia or torsade de pointes, which can lead to syncope (fainting), cardiac arrest, or sudden death in otherwise healthy children and young adults.
Risk Factors
Risk factors for congenital LQTS include a family history of LQTS, syncope, or unexplained sudden death. Deafness at birth is associated with one congenital form of LQTS.
Acquired, drug-induced LQTS is associated with medications that prolong the QT interval. Some patients with acquired LQTS have congenital heart defects that may increase the risk of developing the condition. Low blood levels of potassium, magnesium, or calcium may also increase the risk.
Etiology and Genetics
Inherited forms of LQTS are caused by abnormalities in the structure of the genes that form the potassium, sodium, or calcium ion channels within the heart, interrupting the normal transmission of the heart’s electrical impulses.
There are at least twelve genotypes of LQTS, with classifications based on the ion channel affected. The main forms of inherited LQTS include the autosomal dominant Romano-Ward syndrome, commonly associated with ventricular tachyarrhythmias, and the autosomal recessive Jervell and Lange-Nielsen syndrome (JLNS), associated with deafness at birth. Nearly 50 percent of JLNS patients have a cardiac event by age three, according to 2022 data from the National Library of Medicine.
Two other syndromes include Andersen-Tawil syndrome (LQT7) and Timothy syndrome (LQT8), affecting the heart’s potassium and calcium ion channels, respectively. LQT7 is characterized by muscle weakness and ventricular arrhythmias. LQT8 patients may have certain congenital heart defects and features of autism or similar disorders. Patients with LQT8 have a greater risk of arrhythmias and sudden death.
LQT1, LQT2, LQT5, LQT6, LQT7, and LQT11 affect the heart’s potassium ion channel. LQT1 and LQT2 are the most frequent forms. Most LQT1 patients experience cardiac events during exercise, especially swimming, while LQT2 patients commonly experience cardiac events during emotional stress, particularly auditory stimulation.
LQT3, LQT9, LQT10, and LQT12 affect the sodium ion channel. Many LQT3 patients experience cardiac events despite beta blocker therapy, which increases the risk of life-threatening arrhythmias. Treatment with a defibrillator or pacemaker is recommended for LQT3 patients. LQT4 affects the heart’s potassium, sodium, and calcium ion channels.
Symptoms
Congenital LQTS may not be associated with any symptoms. When present, symptoms may include unexplained syncope or fainting, abnormal heart rate or rhythm, unexplained seizures, unexplained drowning or near drowning, or sudden death. Symptoms are often associated with exercise or exertion, occur at times of emotional excitement, or rarely, during sleep or when awakened suddenly.
Patients with LQTS should wear medical identification and be aware of personal symptoms, and family members should know cardiopulmonary resuscitation (CPR) and how to respond during a syncope episode.
Screening and Diagnosis
The diagnosis of LQTS is based on the patient’s medical and family history, and ECG measurement of the QT interval can confirm the diagnosis. Often, LQTS is discovered during a routine exam for another condition or after a family member has been diagnosed with the condition. Other diagnostic tests include pharmacological stress tests, ambulatory cardiac monitors, and an electroencephalogram to rule out neurological causes.
Genetic testing can identify the specific LQTS gene mutations in about 70 percent of individuals with a confirmed diagnosis. Neonatal ECG screening may aid the diagnosis in patients with a known family history. Researchers say additional gene mutations may be discovered to play a role in some cases.
Treatment and Therapy
Identification of the specific gene mutation can help physicians guide treatment. Changing medications may be the only treatment needed for patients with drug-induced LQTS.
Treatment includes beta blocker and potassium medications, a defibrillator or pacemaker to maintain a normal heart rhythm, and in some cases, surgery. Device therapy and surgical treatment are generally reserved for patients with a high risk of sudden death. Left-sided sympathetic denervation is the surgical treatment for LQTS in which select nerves that regulate the heart rhythm are disconnected.
Physical activity limitations may be advised, such as avoiding strenuous activities and contact sports. Avoiding stressors and other triggers may also be recommended.
Prevention and Outcomes
There is no effective means of preventing congenital forms of LQTS. Avoidance of medications that prolong the QT syndrome may reduce the risk of drug-induced LQTS, as well as help reduce the risk of dangerous heart rhythms in patients with inherited LQTS.
If undiagnosed and untreated, LQTS can be a life-threatening condition, and it is a leading cause of sudden death in otherwise healthy children and young adults. It also contributes to sudden infant death syndrome. A prompt diagnosis and proper treatment can reduce the life-threatening consequences of LQTS.
Bibliography
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