Last reviewed: 30 Oct 2021
Last updated: 10 Jun 2021



History and exam

Key diagnostic factors

  • history of known gene mutation
  • use of drugs or circumstances known to increase the QT interval
  • syncope during heightened adrenergic tone
  • syncope during arousal or surprise
  • arrhythmic symptoms post partum
  • syncope at rest and during bradycardia
  • cardiac syncope
  • palpitations
  • periodic paralysis
  • dysmorphic features
  • sensorineural deafness

Other diagnostic factors

  • dizziness
  • angina
  • fatigue
  • oliguria
  • muscle weakness
  • tetany
  • numbness
  • Chvostek's sign
  • Trousseau's sign
  • cold and pale extremities
  • hypotension
  • confusion

Risk factors

  • KCNQ1 gene mutations
  • KCNH2 gene mutations
  • SCN5A gene mutations
  • QT interval-prolonging drugs
  • hypokalaemia
  • hypomagnesaemia
  • hypocalcaemia
  • bradyarrhythmias
  • central nervous system lesions
  • female sex
  • malnutrition

Diagnostic investigations

1st investigations to order

  • ECG for LQT1
  • ECG for LQT2
  • ECG for LQT3
  • ECG for hypokalaemia and hypomagnesaemia
  • ECG for hypocalcaemia
  • ECG for complete atrioventricular (AV) block
  • serum potassium
  • serum magnesium
  • serum calcium

Investigations to consider

  • Holter monitor
  • exercise tolerance test
  • echocardiography
  • genetic testing
  • adrenaline (epinephrine) test

Treatment algorithm



Mehmet K. Aktas, MD, MBA

Associate Professor of Medicine

University of Rochester Medical Center




MKA declares that he has received research support from Medtronic and Biosense Webster. He is the author of a reference cited in this topic.

James P. Daubert, MD

Professor of Medicine

Duke University Medical Center

Duke Clinical Research Institute




JPD declares that he has received honoraria for advisory boards, data safety monitoring boards, events committees, or lecture fees from Abbott, Biosense Webster, Biotronik, Boston Scientific, Farapulse, Gilead Sciences Inc., Medtronic, Microport, Phillips, Vytronus, and ZOLL; and research grants from Abbott and Medtronic. JPD declares that he has no stock, stock options, or other forms of ownership. He is the author of a reference cited in this topic.

Peer reviewers

Sami Viskin, MD

Director of Cardiac Hospitalization

Department of Cardiology

Tel Aviv Medical Center

Tel Aviv



SV declares that he has no competing interests.

Elizabeth S. Kaufman, MD

Associate Professor

Heart and Vascular Center

MetroHealth Campus

Case Western Reserve University




ESK declares that she has no competing interests.

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