(CATBR)

  • Genetic basis of short QT syndrome-
    • Due to gain of function mutations of K+ channels.
    • Genes mutated-
      • SQT1- KCNH2
      • SQT2- KCNQ1
      • SQT3- KCNJ2
    • For each gene, loss of function would have produced a long QT syndrome (2, 1 and Anderson-Tawil syndrome respectively).
  • Clinical features of short QT syndrome –
    • Increased risk of both atrial and ventricular fibrillation.
    • Increased risk of cardiac arrest, SCD and SIDS.
  • ECG in short QT syndrome –
    • ST segment is absent.
    • In SQT3, T wave has normal upstroke and extremely rapid downstroke.
    • QT interval below 300 to 320 ms at heart rate below 80/min.
    • QT adaptation to tachycardia is impaired.
    • Other causes of short QT should be excluded-
      • Hypercalcemia
      • Hyperkalemia
      • Hyperthermia
      • Acidosis and
      • Digitalis.
  • EP study of short QT syndrome –
    • Atrial and ventricular effective refractory periods are short.
    • Always inducible ventricular flutter or fibrillation is present.
  • Treatment of short QT syndrome –
    • ICD is indicated for secondary prevention of VF.
    • When to consider ICD for primary prevention of VF is not clear.
    • With ICDs, T wave oversensing can cause inappropriate shocks.
    • Quinidine can normalize QT interval and ventricular refractory period. Whether this can be used for treatment is not clear.