A heart without hormones

The QT interval on the ECG, corrected for heart rate by use of Bazett's formula, represents ventricular depolarisation and repolarisation, a process mediated by the flux of sodium, potassium, calcium, and chloride ions through myocyte cell membrane channels. Hypo thyroidism is known to cause sinus bradycardia and atrio ventricular and intraventricular conduction delay,1 but ECG repolarisation changes such as QT prolongation and torsades de pointes, are also recognised.2 Insights into the possible mechanisms have been gained through murine models, one of which has shown altered transcription of several ion-channel subunits, together with QT prolongation.3 Other hormonal deficiencies might also be implicated; hypogonadism has been associated with QT prolong ation,4 and cardiac arrest due to corticotropin and corticosteroid deficiency has been reported.5 In our patient's case, syncope is likely to have resulted from ventricular arrhythmia due to striking prolongation of the QT interval and torsades de pointes; because the initial history, examination, and blood test results were unremarkable, LQTS was suspected.