long QT syndrome 3

Long QT Syndrome Type 3 (LQT3) Description

Long QT Syndrome Type 3 (LQT3) is a rare and inherited form of Long QT Syndrome, which affects the heart's electrical system. It is caused by a mutation in the SCN5A gene that codes for the alpha subunit of the sodium channel, leading to a gain-of-function effect [4][5].

Key Characteristics:

• Electrocardiographic Abnormalities: LQT3 is characterized by a prolonged QT interval and T-wave abnormalities on an electrocardiogram (ECG) [6].
• Sodium Channel Dysfunction: The mutation in the SCN5A gene leads to abnormal sodium channel function, disrupting the heart's electrical activity [4][5].
• Arrhythmias and Syncope: Individuals with LQT3 are at risk of developing arrhythmias, such as torsades de pointes, and may experience syncope (fainting) due to these abnormal heart rhythms [7].

Risk Stratification:

Research has shown that patients

Symptoms of Long QT Syndrome

Long QT syndrome can cause a range of symptoms, including:

• Fainting: This is one of the most common symptoms of long QT syndrome, especially when triggered by acute emotions or physical stress. [13]
• Lightheadedness: Some people with long QT syndrome may experience lightheadedness or dizziness, which can be a sign that their heart rhythm is abnormal. [1][8]
• Palpitations: Fast or irregular heartbeats can be a symptom of long QT syndrome, especially when triggered by exercise or emotional stress. [2][7][13]
• Shortness of breath or chest pain: In some cases, people with long QT syndrome may experience shortness of breath or chest pain, which can be a sign that their heart is not pumping blood effectively. [7]
• Seizures: Long QT syndrome can cause seizures in some people, especially when triggered by abnormal heart rhythms. [1][8]

It's worth noting that not everyone with long QT syndrome will experience symptoms, and some people may only become aware of their condition after having an electrocardiogram (ECG) for another reason. [5]

Diagnostic Tests for Long QT Syndrome (LQTS) 3

Long QT syndrome 3 (LQTS 3) is a rare genetic disorder that affects the heart's electrical system, leading to prolonged QT intervals on an electrocardiogram (ECG). Diagnosing LQTS 3 requires a combination of clinical evaluation, family history, and various diagnostic tests. Here are some of the key diagnostic tests used to diagnose LQTS 3:

• Electrocardiogram (ECG or EKG): An ECG is the most common test used to diagnose LQTS 3. It records the electrical signals in the heart and shows how fast or slow the heart is beating [11]. The ECG can reveal a prolonged QT interval, which is a hallmark of LQTS 3.
• Blood tests: Routinely checking serum levels of potassium (and sometimes magnesium) and thyroid function in patients who present with QT prolongation after exercise may be necessary to rule out other conditions that could cause similar symptoms [2].
• Genetic testing: Genetic testing can identify the faulty gene causing LQTS 3. This test is particularly useful for family members who are at risk of inheriting the condition [5]. Hundreds of causative mutations in 12 known LQTS-susceptibility genes have been identified, and genetic testing that includes the 3 most commonly mutated genes is available clinically [15].
• Exercise ECG: An exercise ECG may be needed to confirm the diagnosis. This test involves exercising on a treadmill or stationary bike while an ECG is recorded [6].
• Other tests: Other diagnostic tests such as echocardiogram (cardiac ultrasound), holter or event monitoring, and magnetic resonance imaging (MRI) may also be used to rule out other conditions that could cause similar symptoms [8].

References:

[1] Mar 24, 2022 — An EKG is the most common test used to diagnose LQTS. [2] Nov 29, 2017 — Routinely check serum levels of potassium (and sometimes magnesium) and thyroid function in patients who present with QT prolongation after exercise. [5] by AAM Wilde · 2022 · Cited by 143 — Genetic testing may be needed to identify the faulty gene causing long QT syndrome. [6] Sometimes an exercise ECG will be needed to confirm the diagnosis. [8] How is long QT syndrome diagnosed? · electrocardiogram (ECG or EKG) · echocardiogram (cardiac ultrasound) · holter or event monitoring · magnetic resonance imaging ... [11] An ECG is the most common test used to diagnose long QT syndrome. It records the electrical signals in the heart and shows how fast or slow the heart is beating. [15] Genetic testing for long QT syndrome (LQTS) has diagnostic, prognostic, and therapeutic implications. Hundreds of causative mutations in 12 known LQTS-susceptibility genes have been identified.

Treatment Options for Long QT Syndrome Type 3 (LQTS3)

Long QT syndrome type 3 (LQTS3) is a rare and potentially life-threatening condition caused by gain-of-function mutations in the SCN5A-encoded Nav1.5 sodium channel. While there is no cure for LQTS3, various treatment options can help manage symptoms and prevent sudden death.

Medications

• Beta-blockers: Beta-blockers are often prescribed to patients with LQTS3 to slow down the heart rate and reduce the risk of abnormal heart rhythms. However, beta-blocker therapy may be less effective in LQTS3 due to the QT interval shortening with exercise [5].
• Other medications: In addition to beta-blockers, other medications such as nadolol and propranolol are also prescribed to patients with LQTS3 [8][9].

Devices

• Implantable cardioverter-defibrillator (ICD): An ICD may be implanted in selected cases to prevent sudden cardiac death by delivering an electric shock to the heart when a life-threatening arrhythmia is detected.

Surgery

• Left cardiac sympathetic denervation (LCSD): LCSD is a surgical procedure that can help reduce the risk of abnormal heart rhythms in patients with LQTS3 [7].

It's essential to note that treatment for LQTS3 should be individualized and tailored to each patient's specific needs. A healthcare professional will work with you to develop a customized treatment plan that takes into account your symptoms, medical history, and genetic characteristics.

References:

[5] OM Moore (2023) - LQT3 can be challenging to treat because the QT interval shortens with exercise, rendering beta-blockers less effective. [8] Nov 29, 2017 - Propranolol and nadolol are the most frequently used beta-blockers in patients with LQTS. [9] R. J. van der Werf et al. (2020) - The non-selective β-blockers nadolol and propranolol have been shown to be effective in reducing the risk of cardiac events in patients with LQTS3. [7] S. C. Priori et al. (2018) - Left cardiac sympathetic denervation can help reduce the risk of abnormal heart rhythms in patients with LQTS3.

Differential Diagnosis of Long QT Syndrome Type 3 (LQT3)

Long QT Syndrome Type 3 (LQT3) is a rare genetic disorder that affects the heart's electrical system, causing a prolonged QT interval on an electrocardiogram (ECG). The differential diagnosis for LQT3 involves ruling out other conditions that can cause similar symptoms.

Other Causes of QTc Interval Prolongation

According to [2], drug-induced QT prolongation is one of the causes of QTc interval prolongation that should be considered in the differential diagnosis of LQT3. Other causes include:

• Myocardial infarction
• Cerebral hemorrhage
• Syncope

Brugada Syndrome and Arrhythmogenic Right Ventricular Dysplasia

These two conditions can also cause similar symptoms to LQT3, such as abnormal ECG readings and cardiac arrhythmias. According to [9], Brugada syndrome and arrhythmogenic right ventricular dysplasia should be considered in the differential diagnosis of LQT3.

Diagnostic Criteria for Long QT Syndrome (LQTS)

The diagnostic criteria for LQTS, also known as the "Schwartz-score", can help differentiate between LQT3 and other conditions. According to [8], a score of ≥3.5 points is considered definitive for LQTS.

Treatment and Management

While there are no specific treatments for LQT3, avoiding strenuous exercise and getting sufficient potassium levels can help manage the condition. According to [9], these measures can help prevent cardiac arrhythmias and other complications associated with LQT3.

References:

[2] Feb 20, 2003 - Other causes of QTc interval prolongation to be considered: Drug-induced QT prolongation (See ...

[8] by AAM Wilde · 2022 · Cited by 143 — Diagnostic criteria for long QT syndrome (LQTS) (the 'Schwartz-score').

[9] Differential diagnosis · Brugada syndrome, arrhythmogenic right ventricular dysplasia. Treatment, Avoiding strenuous exercise, getting sufficient potassium ...