Long-QT syndrome.

Long QT syndrome (LQTS) is caused by malfunction of cardiac ion channels impairing ventricular repolarization. This predisposes to the development of the polymorphic ventricular tachycardia torsade de pointes (‘twisting of the points’) (Fig. 1). This may either revert spontaneously back to sinus rhythm causing syncope or degenerate to ventricular fibrillation causing sudden death. LQTS can be congenital, in which there are mutations in the genes encoding for the cardiac ion channels, or acquired in which malfunction of the ion channels is caused by drugs or metabolic abnormalities. It is likely that many of those with acquired LQTS have a genetic basis in which common polymorphisms cause subtle alterations in the cardiac ion channels responsible for repolarization. The increase in sympathetic tone associated with the stress of anaesthesia and surgery can provoke torsade de pointes in those with LQTS, and some drugs used during anaesthesia can prolong the QT interval.