### Date : 2024-11-01 18:50 ### Topic : Long QT syndrome #cardiology ---- **Long QT Syndrome (LQTS)** is a cardiac condition characterized by a prolonged **QT interval** on the electrocardiogram (ECG), which indicates delayed repolarization of the heart after each beat. This prolonged repolarization increases the risk of developing life-threatening arrhythmias, particularly **torsades de pointes**, which can lead to fainting, seizures, or sudden cardiac death. ### 1. **Mechanism and Pathophysiology** - **QT Interval**: The QT interval on an ECG represents the time taken for the heart's ventricles to depolarize (contract) and then repolarize (relax) after each heartbeat. - **Prolonged QT**: In LQTS, the repolarization phase is abnormally extended, leading to prolonged QT intervals. This delay predisposes the ventricles to early afterdepolarizations, which can trigger dangerous arrhythmias like **torsades de pointes**. - **Genetic Basis**: LQTS can be inherited or acquired. The inherited forms are due to mutations in genes encoding ion channels responsible for the cardiac action potential, particularly potassium and sodium channels. ### 2. **Types of Long QT Syndrome** - **Congenital (Inherited) LQTS**: Due to genetic mutations in ion channel genes, with several subtypes: - **LQT1**: Caused by mutations in the **KCNQ1** gene, affecting potassium channels. It is the most common type and is often triggered by **exercise** or **stress**. - **LQT2**: Caused by mutations in the **KCNH2** gene, also affecting potassium channels. Symptoms are often triggered by **emotional stress** or **loud noises**. - **LQT3**: Caused by mutations in the **SCN5A** gene, affecting sodium channels. Symptoms typically occur during **sleep** or **rest**. - **Acquired (Secondary) LQTS**: Caused by external factors that prolong the QT interval: - **Medications**: Certain drugs, especially those that block potassium channels or affect ion channels, can prolong the QT interval. Examples include: - **Antiarrhythmics**: Amiodarone, sotalol - **Antibiotics**: Macrolides (e.g., erythromycin), fluoroquinolones - **Antipsychotics**: Haloperidol, ziprasidone - **Antidepressants**: Tricyclics, SSRIs (some) - **Electrolyte Imbalances**: Low levels of potassium, magnesium, or calcium can prolong the QT interval. - **Other Factors**: Conditions like bradycardia, hypothyroidism, and structural heart disease can also contribute. ### 3. **Symptoms and Clinical Presentation** - **Syncope (Fainting)**: Often due to arrhythmic episodes, particularly torsades de pointes, which cause a transient drop in cardiac output. - **Seizures**: Due to reduced blood flow to the brain during arrhythmias. - **Palpitations**: Patients may feel fluttering or rapid heartbeats, especially during or after physical activity or emotional stress. - **Sudden Cardiac Arrest**: In severe cases, prolonged arrhythmias can lead to sudden cardiac death. Symptoms may vary based on the type of LQTS, with specific triggers often associated with each type (e.g., exercise for LQT1, auditory triggers for LQT2, sleep for LQT3). ### 4. **Diagnosis of Long QT Syndrome** Diagnosis is based on a combination of ECG findings, family history, and genetic testing. - **ECG Findings**: - **Prolonged QT Interval**: The QT interval is typically prolonged, with a corrected QT (QTc) > 450 ms in men and > 460 ms in women. - **Calculation of QTc**: QT interval should be corrected for heart rate using formulas like Bazett’s formula: - **T-Wave Abnormalities**: Abnormal T-wave morphology may also be seen (e.g., broad, notched, or biphasic T waves). - **Holter Monitor**: Continuous ECG monitoring to detect intermittent QT prolongation or arrhythmias. - **Genetic Testing**: Used to identify mutations in patients suspected of having congenital LQTS or for family screening. - **Family History**: A history of sudden cardiac death, unexplained fainting, or seizures can raise suspicion of LQTS. ### 5. **Management and Treatment** Treatment focuses on preventing arrhythmias and reducing the risk of sudden cardiac death. - **Lifestyle Modifications**: - Avoid triggers specific to the LQTS type (e.g., strenuous exercise for LQT1, avoiding loud noises for LQT2). - Avoid medications known to prolong the QT interval (e.g., certain antiarrhythmics, antibiotics, antipsychotics). - **Medications**: - **Beta Blockers**: Beta blockers like **propranolol** or **nadolol** are the first-line treatment for congenital LQTS, especially effective for LQT1 and LQT2. They reduce the heart’s response to stress and exercise, lowering the risk of arrhythmias. - **Mexiletine**: This sodium channel blocker may help shorten the QT interval in patients with LQT3. - **Implantable Cardioverter-Defibrillator (ICD)**: - An ICD is recommended for patients at high risk of sudden cardiac death, especially those with a history of syncope, cardiac arrest, or ventricular arrhythmias. - The ICD continuously monitors heart rhythms and delivers a shock if it detects a life-threatening arrhythmia. - **Left Cardiac Sympathetic Denervation (LCSD)**: - This surgical procedure removes part of the sympathetic nervous system’s input to the heart and can reduce the risk of arrhythmias. It is typically considered in high-risk patients who are intolerant to beta blockers or who continue to have symptoms despite therapy. ### 6. **Prognosis and Risk Stratification** - **High-Risk Factors**: History of syncope, documented arrhythmias, and specific genetic mutations increase the risk of sudden cardiac death. - **Family Screening**: First-degree relatives of patients with congenital LQTS should undergo ECG screening and, if possible, genetic testing. - **Regular Follow-Up**: Patients with LQTS require regular follow-up with a cardiologist, especially if they have an ICD or are on antiarrhythmic medications. ### Summary - **Long QT Syndrome** is a condition marked by delayed repolarization, increasing the risk of arrhythmias like torsades de pointes. - **Types**: Includes congenital (genetic) LQTS, with types based on genetic mutations, and acquired LQTS, often due to drugs or electrolyte disturbances. - **Diagnosis**: Based on prolonged QT interval on ECG, genetic testing, and family history. - **Management**: Involves avoiding triggers, using beta blockers, and considering an ICD in high-risk patients. ### Reference: - ### Connected Documents: -