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Long QT Syndrome Management Algorithm

flowchart TD
    A[Suspected LQTS<br/>QTc prolonged or symptoms] --> B[Calculate QTc<br/>Bazett: QT/√RR]

    B --> C{QTc Value}
    C -->|<440 ms| D[Normal<br/>Consider other diagnoses]
    C -->|440-470 ms| E[Borderline<br/>Further evaluation]
    C -->|>470 M / >480 F| F[Prolonged<br/>High suspicion]

    E --> G[Risk Score + Family Hx]
    F --> G

    G --> H[Genetic Testing]

    H --> I{Result}
    I -->|Pathogenic variant| J[Confirmed LQTS]
    I -->|VUS| K[Clinical diagnosis based on<br/>phenotype + risk score]
    I -->|Negative| K

    J --> L{Genotype}
    L -->|LQT1| M[Triggers: Exercise<br/>especially swimming]
    L -->|LQT2| N[Triggers: Auditory<br/>emotional stress]
    L -->|LQT3| O[Triggers: Rest/sleep<br/>bradycardia]

    M & N & O --> P[Risk Stratification]

    P --> Q{Symptoms?}
    Q -->|Prior arrest or syncope| R[HIGH RISK<br/>Beta-blocker + ICD]
    Q -->|Asymptomatic| S{QTc and Genotype Risk}

    S -->|QTc >500 or<br/>LQT2 Female or<br/>LQT3| T[HIGHER RISK<br/>Beta-blocker, consider ICD]
    S -->|QTc <500,<br/>LQT1, Male| U[LOWER RISK<br/>Beta-blocker]

    R --> V[Lifestyle Modifications]
    T --> V
    U --> V

    V --> V1[Avoid QT-prolonging drugs]
    V --> V2[Avoid genotype-specific triggers]
    V --> V3[Maintain K/Mg levels]
    V --> V4[Family screening]

    V1 & V2 & V3 & V4 --> W{Breakthrough Events?}
    W -->|Yes - on Beta-blocker| X[Add Mexiletine if LQT3<br/>Consider LCSD<br/>ICD if not present]
    W -->|No| Y[Continue Surveillance]

    style R fill:#ff6b6b
    style X fill:#ff6b6b
📋 Text Version (if diagram doesn't render) **LQTS Management Algorithm** 1. **QTc Evaluation** (Bazett: QT/√RR): - <440 ms → Normal, consider other diagnoses - 440-470 ms → Borderline, further evaluation - >470 M / >480 F → Prolonged, high suspicion 2. **Workup** → Risk Score + Family Hx → Genetic Testing - Pathogenic variant → Confirmed LQTS - VUS/Negative → Clinical diagnosis based on phenotype + risk score 3. **Genotype-Specific Triggers**: - LQT1 → Exercise (especially swimming) - LQT2 → Auditory stimuli, emotional stress - LQT3 → Rest/sleep, bradycardia 4. **Risk Stratification**: - **HIGH RISK** (prior arrest/syncope) → Beta-blocker + ICD - **HIGHER RISK** (QTc >500, LQT2 Female, LQT3) → Beta-blocker, consider ICD - **LOWER RISK** (QTc <500, LQT1, Male) → Beta-blocker 5. **All patients**: Lifestyle modifications: - Avoid QT-prolonging drugs - Avoid genotype-specific triggers - Maintain K/Mg levels - Family screening 6. **Breakthrough events on beta-blocker** → Add Mexiletine if LQT3, consider LCSD, ICD if not present

QTc Interpretation by Age/Sex

Population Normal Borderline Prolonged
Males <430 430-450 >450
Females <450 450-470 >470
Children <440 440-460 >460

Beta-Blocker Selection

Preferred

  • Nadolol (long-acting, once daily)
  • Propranolol (alternative)

Dosing

  • Nadolol: 1-2.5 mg/kg/day
  • Target: Blunted HR response to exercise

Genotype-Specific Considerations

  • LQT3: Beta-blockers less effective; consider mexiletine
  • LQT1: Beta-blockers most effective

ICD Indications

  • Survivors of cardiac arrest
  • Syncope on beta-blocker therapy

Class IIa (Reasonable)

  • QTc >500 ms with additional risk factors
  • LQT2/LQT3 with high-risk features

Concerns

  • Inappropriate shocks (T-wave oversensing)
  • Need careful programming
  • Psychological impact

Genotype-Specific Triggers to Avoid

Genotype Triggers
LQT1 Swimming, diving, competitive sports
LQT2 Alarm clocks, sudden noises, emotional stress
LQT3 (Events occur at rest - less trigger-specific)

QT-Prolonging Drugs (Partial List)

Avoid in LQTS: - Antiarrhythmics: Sotalol, dofetilide, quinidine - Antibiotics: Macrolides, fluoroquinolones - Antipsychotics: Haloperidol, droperidol - Antiemetics: Ondansetron - Others: Methadone

Resource: CredibleMeds.org