Long QT

Exam Cram

• Long QT Syndrome (LQTS) is a cardiac arrhythmia with a long pause between the QRS complex and T wave

• PC: exercised induce (pre)syncope, recent new medication

• Diagnosis: ECG

• Management: 1) Betablocker, 2) ICD

Outline

Background 

• QT interval is measured from the beginning of the Q wave (ventricular depolarisation) to the end of the T wave (ventricular repolarisation).

• QT is prolonged due to medications or a genetic defect

• Long QT Syndrome is caused by a defect in K+ channel- alpha subunit

Assessment

Presentation:

• Exercise induced syncope

• Normal examination

Investigations

• ECG: long QTc

Diagnosis

Diagnostic criteria: 

• ECG: QT interval > 460ms (female), > 440 (male)

• QT normogram should be used to accommodate HR

Differentials:

• Brugada Syndrome: not exercise induced, V1-V3 T wave changes

• HOCM: exercise induced, LVH on ECG

Classification (by aetiology)

• Medication induced

• Genetic

Management

1. Betablockers

2. ICD

Med Reg Notes

Management II

• Betablocker selection: Non selective- e.g. Propanolol or Nadalol, avoid cardio-selective e.g. atenolol [2]

• MCQs usually state betablockers first line if presents with palpitations

• If first presentation serious, e.g. cardiac arrest, implant ICD first. 

Drug Causes of Long QT

• Antibiotics- macrolides (clarithromycin),

• Antidepressants- citalopram

• Antipsychotics- typical and atypical

• DMARDS- hydroxychloroquine

• Ondansetron

There is no evidence ciprofloxacin prolongs the QT [3]

Further Reading 

Genetic Causes of Long QT syndrome

Jervell and Lange-Nielsen Syndrom (JLNS)

• Long QTc > 500ms

• Profound bilateral sensorineural hearing loss

• Gene: KCNQ1 or KCNE1

References

1. https://www.ouh.nhs.uk/services/referrals/genetics/genetics-laboratories/rare-disease-genomics/cardiology/R127.aspx

2. Kaufman ES, Eckhardt LL, Ackerman MJ, Aziz PF, Behr ER, Cerrone M, Chung MK, Cutler MJ, Etheridge SP, Krahn AD, Lubitz SA, Perez MV, Priori SG, Roberts JD, Roden DM, Schulze-Bahr E, Schwartz PJ, Shimizu W, Shoemaker MB, Sy RW, Towbin JA, Viskin S, A M Wilde A, Zareba W. Management of Congenital Long-QT Syndrome: Commentary From the Experts. Circ Arrhythm Electrophysiol. 2021 Jul;14(7):e009726. doi: 10.1161/CIRCEP.120.009726. Epub 2021 Jul 9. PMID: 34238011; PMCID: PMC8301722. 

3. Heemskerk C, Woldman E, Pereboom M, Van der Hoeven R, Mantel-Teeuwisse A, Van Gemeren C, Becker ML. Ciprofloxacin does not Prolong the QTc Interval: A Clinical Study in ICU Patients and Review of the Literature. J Pharm Pharm Sci. 2017;20(1):360-364. doi: 10.18433/J3ZD15. PMID: 29145929. 

Written in 2025.