short QTc

see also:

• The basics of reading an ECG
• patterns of ECGs
• torsade de pointes VT
• prolonged QTc

• the normal QTc on the ECG is 360-390msec in males and 370-400msec in females
• most doctors are well aware of the potential lethal effects of prolonged QTc, but few are aware that short QTc with QT < 320ms and a QTc < 340ms can also cause sudden death.
• the main issue is the autosomal dominant genetic channelopathy of “short QT syndrome (SQTS)” discovered in 2000 (thus far there have been 5 genotypes discovered) which is associated with paroxysmal atrial fibrillation and ventricular fibrillation (VF), syncope / near syncope and sudden cardiac death in otherwise well people from infants to 60 yrs of age
• short QTc may also be caused by other conditions such as severe hypercalcaemia

• see also:
  • https://lifeinthefastlane.com/ecg-library/basics/short-qt-syndrome/
  • Arrhythm Electrophysiol Rev. 2014 - review of SQTS
  • https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-9/Short-QT-Syndrome
  • http://www.mdedge.com/ccjm/article/95878/cardiology/short-story-short-qt-syndrome

• QT < 320ms and a QTc < 340ms with short or absent ST segments making the complexes look bunched up
  • as incidence of short QTc is < 0.5% in the general population, males with QTc ≤330 ms and females with QTc ≤340 ms have abnormally short QT and should be considered to have SQTS, even if they are asymptomatic ¹⁾
• peaked T waves, esp. precordia leads
• lack of the normal prolongation of QT with slower heart rate
• potentially, episodes of atrial fibrillation or ventricular fibrillation (VF)

• implantation of an ICD, but this tends to over-sense the tall narrow T waves and give inappropriate shocks
• quinidine may be helpful

• severe hypercalcaemia with corrected calcium > 3.4 mmol/L
  • may also cause Osborne J waves, and with extreme hypercalcaemia, may cause ventricular fibrillation (VF)
• hyperthermia
• drugs which shorten QTc:
  • use of these drugs in patients with SQTS may be life threatening, and it is not inconceivable that even in people without SQTS, but with other genotypes which cause mild shortened QTc such as CC phenotype of K897T (A2690C) which is found in 5% of white Germans, may be at risk when given such medications
  • see Br J Pharmacol. 2010 Drug-induced QT interval shortening: potential harbinger of proarrhythmia and regulatory perspectives
  • ATP-dependent potassium channel openers such as pinacidil, nicorandil and levcromakalim
  • anticonvulsants such as primidone, lamotrigine, rufinamide
    • could some cases of sudden death in epilepsy be caused by undiagnosed SQTS?
• other possible causes being investigated:
  • thyroid disorder
  • chronic fatigue syndrome