Long QT Syndrome - Diagnosis

Diagnosis

The diagnosis of LQTS is not easy since 2.5% of the healthy population have prolonged QT interval, and 10–15% of LQTS patients have a normal QT interval. A commonly used criterion to diagnose LQTS is the LQTS "diagnostic score". The score is calculated by assigning different points to various criteria (listed below). With four or more points, the probability is high for LQTS; with one point or less, the probability is low. A score of two or three points indicates intermediate probability.

• QTc (Defined as QT interval / square root of RR interval)
  • >= 480 msec - 3 points
  • 460-470 msec - 2 points
  • 450 msec and male gender - 1 point
• Torsades de pointes ventricular tachycardia - 2 points
• T wave alternans - 1 point
• Notched T wave in at least 3 leads - 1 point
• Low heart rate for age (children) - 0.5 points
• Syncope (one cannot receive points both for syncope and torsades de pointes)
  • With stress - 2 points
  • Without stress - 1 point
• Congenital deafness - 0.5 points
• Family history (the same family member cannot be counted for LQTS and sudden death)
  • Other family members with definite LQTS - 1 point
  • Sudden death in immediate family members (before age 30) - 0.5 points