QT INTERVAL DISPERSION - DISPERSION OF VENTRICULAR REPOLARIZATION OR DISPERSION OF QT INTERVAL

The QT interval (QTI) has long been useful as a clinical index of the duration of ventricular repolarization, particularly as a marker of pr olonged repolarization and its well-established association with arrhy thmogenic cardiac states. Likewise, inhomogeneity (dispersion) of repo larization has been linked definitively to increased susceptibility to reentrant arrhythmias. Recent studies have reported the use of QTI di spersion as a meaningful clinical index to identify patients at risk, but the interpretation of the measurement has been controversial. A La ngendorff-perfused, isolated canine heart suspended in a torso-shaped. electrolytic tank filled with NaCl-sucrose solution was used to inves tigate the relationship between body surface QTIs and ventricular repo larization measured directly from the cardiac surface by using activat ion-recovery intervals, which have been documented to reflect the dura tion of local action potentials as well as local refractory periods. T he data showed poor correlation between cardiac surface activation-rec overy intervals and QTIs, as well as the insensitivity of QTIs to regi onal repolarization shortening in the presence of prolonged repolariza tion elsewhere. Furthermore, the data confirmed that torso tank QTI di spersion does not reflect directly the full range of measured ventricu lar repolarization inhomogeneity. It is concluded that body surface QT I dispersion is not a reliable index of repolarization dispersion.