Channelopathies

Long QT Syndrome Overview

  • Long QT syndrome (LQTS) is associated with a prolonged QT interval on ECG, which can lead to torsades de pointes and sudden cardiac death

  • Diagnostics involve identifying mutations and measuring QT intervals

Causes

  • Genetic factors, medications, electrolyte abnormalities

Diagnosis

  • QT Interval Measurements:

    • Traditional cutoff for diagnosing LQTS is a corrected QT (QTc) greater than 440 ms

    • Symptoms often develop with a QTc greater than 470 ms

    • Values over 500 ms usually indicate therapy effects (e.g., beta-blockers)

  • Stress ECG Guidelines:

    • Perform ECG at 4 minutes post-treadmill, not immediately after cessation of exercise

    • Use the tangent method for analysis

ECG Interpretation

  • Importance of ignoring small T waves and U waves when analyzing the ECG

  • Bundle Branch Blocks:

    • Use QT interval correction formulas when QRS duration exceeds 110 ms

    • Subtract extra QRS time from QT interval

Genetic Factors

  • Genetic testing is crucial for managing LQTS

  • Familial Patterns: Patients with a history of familial mutations

Type of Long QT Syndrome

  • LQT1, LQT2, LQT3 distinctions based on triggers and symptoms:

    • LQT1: Triggered by exercise, particularly swimming

    • LQT2: Triggered by emotional stress or loud noises

    • LQT3: Events often occur during sleep without arousal

  • Long Isometric Intervals: A long isoelectric interval in the T wave indicates a potassium current imbalance.

  • Symptomatic Management:

    • Beta-blockers like nadolol and propranolol are utilized

    • IC devices are indicated for those with cardiac arrest history

Treatment Options

  • Left Cardiac Sympathetic Denervation: Effective for LQT management but requires skilled surgical intervention

  • Genotype Specific Therapy:

    • New options include mexiletine for specific genotypes (e.g., KCNH2)

    • Mexiletine shown to reduce risk of cardiac events significantly

Risk Assessment

  • Increased QTc correlates to higher risks:

    • e.g., QTc of 520 ms shows a 6% risk of sudden death from age 19

  • Genetic background informs prognosis but may complicate treatment decisions

Complications from Sudden Cardiac Events

  • Electrical storms in LQT3 can be triggered by exercise or emotional stress

  • Increased mortality risk associated with higher shocks from defibrillators

Catecholaminergic Polymorphic VT Overview

  • CPVT Mechanism:

Catecholaminergic Polymorphic VT Management

  • Flecainide can reduce the amount of exercise-induced ventricular arrhythmias in CPVT; it can reduce leaky calcium

  • BB like propranolol also blocks sodium

Brugada Syndrome Overview

  • Characterized by ST segment elevation in leads V1 and V2, leading to ventricular arrhythmias

  • Genetic abnormalities found in only 20% of cases

    • Most have functional sodium channel disturbances

  • ECG Pattern Recognition:

    • QRS and PR interval prolongation correlates with increased risk for sudden cardiac death

Management of Brugada Syndrome

  • Emphasis on ECG evaluation rather than routine genetic testing

  • Use of ICD in patients with symptomatic bradycardia

  • RVOT ablation for persistent ventricular arrhythmias with Brugada

  • Careful attention to electrolyte and sodium channel behavior in treatment

Conclusion

  • Understanding ECG patterns and patient genetics is crucial for managing long QT syndromes and Brugada syndrome effectively

  • Future guidelines recommend more specific treatments and risk stratifications based on continual research and findings.