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Channelopathies: Recognition & Referral

Learning Objectives

By the end of this rotation, you should be able to:

  1. Recognize prolonged QTc on ECG and know when to refer
  2. Identify red flag history suggesting channelopathy
  3. Avoid prescribing QT-prolonging medications to at-risk patients
  4. Know when to urgently refer to pediatric cardiology

What Are Channelopathies?

Channelopathies are inherited arrhythmia syndromes caused by ion channel mutations that can cause sudden cardiac death in structurally normal hearts. The most common are:

  • Long QT Syndrome (LQTS) - most common
  • Catecholaminergic Polymorphic VT (CPVT)
  • Brugada Syndrome - rare in children

Key point for residents: These conditions cause sudden death in young, apparently healthy patients. Your job is to recognize warning signs and refer.

Red Flags - When to Refer to Cardiology

Immediate/Urgent Referral

Finding Why It Matters
Syncope with exercise May indicate LQTS, CPVT, or HCM
Syncope with startle/swimming Classic for LQT1
Syncope with auditory trigger (alarm, doorbell) Classic for LQT2
Family history of sudden death <40 years Suggests inherited arrhythmia
Family history of drowning May be undiagnosed LQTS
QTc >470 ms (male) or >480 ms (female) Prolonged QT
Seizures that don't respond to anti-epileptics May be arrhythmia, not epilepsy

ECG Findings That Need Referral

  • Prolonged QTc (see below)
  • Bizarre T-wave morphology (notched, bifid)
  • Brugada pattern (coved ST elevation V1-V2)
  • Epsilon waves (ARVC)

QTc: The One Measurement You Need to Know

How to Measure

  1. Use lead II or V5
  2. Measure from Q wave start to T wave end
  3. Apply Bazett correction: QTc = QT / √RR
  4. Most ECG machines calculate this automatically

Interpretation

QTc Interpretation
<440 ms Normal
440-460 ms Borderline - consider repeat, family history
>460 ms (male) Prolonged - refer
>470 ms (female) Prolonged - refer
>500 ms High risk - urgent referral

Tip: If QTc is borderline, ask about family history of sudden death or syncope. If positive, refer.

Medications to Avoid

Many common medications prolong the QT interval. Before prescribing to any patient with: - Known or suspected LQTS - Family history of sudden death - Prolonged QTc on ECG

Check CredibleMeds.org or avoid these common culprits:

Drug Class Examples
Antibiotics Azithromycin, fluoroquinolones, erythromycin
Antiemetics Ondansetron (especially IV)
Antipsychotics Haloperidol, many others
Antihistamines Diphenhydramine (high doses)

When in doubt: Check CredibleMeds.org before prescribing any medication to a patient with prolonged QT.

What Happens After Referral

Cardiology will: - Obtain detailed family pedigree - Perform exercise stress testing - Consider genetic testing - Start beta-blockers if diagnosed - Discuss ICD if high-risk - Provide school/activity guidance

Your role after referral: Ensure the patient avoids QT-prolonging medications and understands the importance of follow-up.

Key Teaching Points for Residents

  1. Syncope + exercise = cardiology referral - don't assume vasovagal
  2. Family history of sudden death <40 = ECG screening
  3. QTc >460-470 ms = needs evaluation
  4. Check CredibleMeds before prescribing to at-risk patients
  5. "Seizures" unresponsive to therapy may be arrhythmias
  6. Drowning may be undiagnosed LQTS

Key Guidelines

2022 ESC Guidelines for Management of Patients with Ventricular Arrhythmias and Prevention of Sudden Cardiac Death Eur Heart J. 2022;43(40):3997-4126 PMID: 36017572

2017 HRS/EHRA/APHRS Expert Consensus Statement on the Diagnosis and Management of Patients with Inherited Primary Arrhythmia Syndromes Heart Rhythm. 2017;14(12):e555-e607 PMID: 28974073

Board Pearls

Pearl: QTc >500 ms = HIGH risk for sudden death

These patients need urgent cardiology referral, beta-blocker therapy, and often ICD discussion. Avoid ALL QT-prolonging medications.

Pearl: Exertional syncope is NOT vasovagal

Any syncope occurring DURING exercise (not after) suggests cardiac etiology - channelopathy, HCM, or coronary anomaly. Always refer.

Pearl: CredibleMeds.org is your friend

Before prescribing ANY medication to a patient with prolonged QT or family history of sudden death, check this free resource.

Self-Assessment

Question 1

A 12-year-old boy has syncope while swimming. ECG shows QTc of 490 ms. Which is the most likely diagnosis?

Answer **Long QT Syndrome Type 1 (LQT1)** LQT1 is associated with syncope triggered by exercise, especially swimming. Swimming is particularly high-risk because it combines exertion with vagal stimulation (cold water, breath-holding).

Question 2

Which medication should be AVOIDED in a patient with known LQTS?

Answer **Ondansetron** (especially IV) Many common medications prolong QT. Before prescribing any medication to a LQTS patient, check **CredibleMeds.org**. Other common culprits include azithromycin, fluoroquinolones, and many antipsychotics.

Question 3

A 15-year-old presents with syncope during a basketball game. ECG shows QTc of 445 ms. What is the next best step?

Answer **Refer to cardiology for further evaluation** Exertional syncope is NEVER vasovagal. Even with a borderline QTc (440-460 ms), syncope during exercise requires full cardiac evaluation including stress testing and consideration of genetic testing. Ask about family history of sudden death.