Long QT Syndrome (LQTS): ECG Findings and Clinical Significance

Introduction

Long QT Syndrome (LQTS) is a cardiac condition that affects the electrical signaling of the heart. It is characterized by prolonged ventricular repolarization, which increases the risk of life-threatening arrhythmias, such as torsades de pointes.

How Is Long QT Seen on an ECG?

On an electrocardiogram (ECG), LQTS manifests as a prolonged QT interval. The QT interval represents the time from the start of ventricular depolarization to the end of repolarization. It is measured in milliseconds (ms) and is corrected for heart rate (QTc).

Key ECG Findings:

• Prolonged QT interval: Generally, QTc is considered prolonged if:
  • > 450 ms in men
  • > 460 ms in women
• T-wave abnormalities: These may appear as broad or notched T-waves.
• Risk of torsades de pointes: The prolonged QT can lead to a dangerous polymorphic ventricular tachycardia, which can cause syncope or sudden cardiac death.

Causes of Prolonged QT

LQTS can be either congenital or acquired: - Congenital LQTS: Caused by genetic mutations affecting ion channels in the heart. - Acquired LQTS: Induced by medications (e.g., certain antibiotics, antiarrhythmics, or antidepressants), electrolyte imbalances (e.g., hypokalemia, hypomagnesemia), or conditions like bradycardia.

Why Is It Important?

Identifying LQTS on an ECG is crucial because it allows for risk stratification and initiation of preventive measures, such as:
- Avoiding QT-prolonging medications
- Correcting electrolyte imbalances
- Considering beta-blocker therapy or implantable cardioverter-defibrillator (ICD) implantation in high-risk cases

Conclusion

If you or a loved one have a prolonged QT on ECG, consult a cardiologist for risk assessment and management. Early detection and treatment can prevent life-threatening complications.

Source recommendations

1. European Society of Cardiology (ESC) Guidelines on the Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death

1. https://pubmed.ncbi.nlm.nih.gov/36017572/
2. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
3. https://pubmed.ncbi.nlm.nih.gov/26320108/
4. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
5. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549

2. American Heart Association (AHA) Guidelines on the Evaluation and Management of Patients With Syncope

1. https://www.ahajournals.org/doi/10.1161/cir.0000000000000499
2. https://www.jacc.org/doi/10.1016/j.jacc.2017.03.003
3. https://www.ahajournals.org/doi/10.1161/cir.0000000000000498
4. https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2017/03/07/23/36/2017-acc-aha-hrs-guideline-for-syncope
5. https://www.heart.org/en/health-topics/arrhythmia/symptoms-diagnosis--monitoring-of-arrhythmia/syncope-fainting