What are the key clinical features to consider when diagnosing congenital Long QT Syndrome in a young patient?

When diagnosing congenital Long QT Syndrome (LQTS) in a young patient, several key clinical features and diagnostic considerations are paramount.

Clinical Presentation:

• The most common symptom is syncope (fainting), which can be triggered by exercise, emotional stress, or auditory stimuli such as an alarm clock NICE CG109, Khan 2002, Ching & Tan 2006, Crotti et al. 2008.
• Patients may also experience palpitations NICE CKS, Khan 2002.
• Seizures are another important feature and can sometimes lead to a misdiagnosis of epilepsy Khan 2002, Ching & Tan 2006.
• In severe cases, the first manifestation might be sudden cardiac arrest or sudden death Khan 2002, Ching & Tan 2006, Crotti et al. 2008.
• It is important to note that some individuals with congenital LQTS can be asymptomatic Ching & Tan 2006.

Diagnostic Considerations:

• A family history is crucial, particularly a history of sudden unexplained death in young family members, or a history of syncope or seizures within the family NICE CG109, Khan 2002, Ching & Tan 2006, Crotti et al. 2008.
• The hallmark diagnostic finding is a prolonged QT interval on an electrocardiogram (ECG), specifically a corrected QT (QTc) interval Khan 2002, Ching & Tan 2006, Crotti et al. 2008. Specific thresholds, such as a QTc greater than 480 ms in children, are significant Khan 2002.
• Other ECG abnormalities may include T-wave alternans or notched T waves Khan 2002, Ching & Tan 2006.
• The Schwartz Score is a diagnostic scoring system that incorporates ECG findings, clinical symptoms, and family history to assess the likelihood of LQTS Khan 2002.
• Genetic testing can confirm the diagnosis by identifying specific mutations in genes encoding cardiac ion channels, with LQT1, LQT2, and LQT3 being the most common types Ching & Tan 2006, Crotti et al. 2008.