The long QT syndrome and torsade de pointes

The LQTS is a prime example of how molecular biology, ion channel, cellular , and organ physiology, coupled with clinical observations, promise to be t he future paradigm for advancement of medical knowledge. Both the congenita l and acquired LOTS are due to abnormalities (intrinsic and/or acquired) of the ionic currents underlying cardiac repolarization. In this review, the continually unraveling molecular biology of congenital LOTS is discussed. T he various pharmacological agents associated with the acquired LOTS are lis ted. Although it is difficult to predict which patients are at risk for TdP , careful assessment of the risk-benefit ratio is important before prescrib ing drugs known to be able to cause QT prolongation. The in vivo electrophy siological mechanism of TdP in the LOTS is described using, as a paradigm, the anthopleurin-A canine model, a surrogate for LQT3. In the LOTS, prolong ed repolarization is associated with increased spatial dispersion of repola rization. Prolongation of repolarization also acts as a primary step for th e generation of EADs. The focal EAD induced triggered beat(s) can infringe on the underlying substrate of inhomogeneous repolarization to initiate pol ymorphic reentrant VT, sometimes having the characteristic twisting QRS con figuration known as TdP. The review concludes by discussion of the clinical manifestations and current management of both the congenital and acquired LOTS. The initial therapy of choice for the large majority of patients with the congenital LOTS is a beta-blocking drug. This therapy seems to be effe ctive in LQT1 and LQT2 patients, but may not be as effective in LQT3 patien ts. Other therapeutic options in elude pacemakers, cervicothoracic sympathe ctomy, and the implantable cardioverter defibrillator. Recent molecular gen etic studies have suggested several genotype specific therapies; however, l ong-term efficacy data are not available.