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Assessing QT interval in patients with autoimmune chronic inflammatory diseases: perils and pitfalls
  1. Pietro Enea Lazzerini,
  2. Pier Leopoldo Capecchi and
  3. Franco Laghi-Pasini
  1. Department of Medical Sciences, Surgery and Neurosciences, University of Siena, Siena, Italy
  1. Correspondence to Dr Pietro Enea Lazzerini; lazzerini7{at}unisi.it

https://doi.org/10.1136/lupus-2016-000189

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    The QT interval on the ECG reflects the duration of action potential (AP) in ventricle cardiomyocytes, in turn representing the sum of ventricular depolarisation and repolarisation.1 AP is caused by transmembrane flow of ions, including inward depolarising currents mainly through sodium and calcium channels, that is, the sodium current (INa) and the L(long-lasting)-type calcium current (ICaL), and outward repolarising currents mainly through potassium channels, particularly the transient outward current (Ito), the rapid and the slow component of the delayed rectifier potassium current (rapid component, IKr, and slow component, IKs) and the inward rectifier potassium current (IK1) (figure 1).1

    Figure 1

    QT interval, inflammation and autoimmunity. From the cell to the surface ECG. (i) Inflammatory cytokines prolong APD and QTc by directly modulating the expression and function of potassium or calcium channels in cardiomyocyte, resulting in changes of the related currents: TNF-α inhibits IKr, IKs and IK1 currents, while IL-1 and IL-6 enhance the L-type Ca2+ current. (ii) Anti-Ro/SSA-52kD directly cross-react with the extracellular loop of the hERG-potassium channel pore-forming region, leading to IKr inhibition with APD and QTc prolongation. APD, action potential duration; QTc, heart rate-corrected QT interval; TNF-α, tumour necrosis factor α; IL-1, interleukin-1; IL-6, interleukin-6; Na+, sodium; Ca2+, calcium; K+, potassium; INa, sodium current; Ito, transient outward current; ICaL, L(long-lasting)-type calcium current; IKr, rapid component of the delayed rectifier potassium current; IKs, slow component of the delayed rectifier potassium current; IK1, inward rectifier potassium current; anti-Ro/SSA-52kD, anti-Ro/SSA-52kD antibodies. Modiified from: Lazzerini et al.4

    The long QT syndrome (LQTS) is a multifactorial disorder characterised by a prolonged heart rate-corrected QT interval (QTc), which predisposes to life-threatening ventricular arrhythmias, particularly torsades de pointes (TdP), that can degenerate into ventricular fibrillation and cause sudden cardiac death.2 ,3 Although …

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