ASSESSMENT OF SPATIAL AND TEMPORAL CHARACTERISTICS OF VENTRICULAR REPOLARIZATION

Measurement of dynamics and spatial characteristics of ventricular rep olarization is of interest in assessing patients with ischemic heart d isease, particularly in relation to the detection and characterization of ischemic events, identification of patients at risk of ventricular arrhythmias, or determination of the efficacy of drugs intended to al ter repolarization. The QT interval (QTI) has been the index of choice for assessing repolarization abnormalities. It is a general measure o f repolarization duration but lacks the power to assess the spatial as pects of repolarization and the ability to detect localized shortening in the setting of global prolongation. For direct cardiac surface mea surement, QRST integrals and activation recovery intervals (ARIs) were used to assess repolarization and its disparity. The use of similar m easurements from the body surface was proposed to provide better chara cterization of repolarization, its disparity, and its dynamics than is possible using the QTI. In one open-chest experiment using an intact canine heart and two experiments using isolated canine hearts suspende d in a torso-shaped electrolytic tank, 64 epicardial electrograms and 192 torso surface electrocardiograms were measured simultaneously. Ven tricular repolarization was globally altered by varying pacing cycle l engths or tank temperature. Atrial and ventricular pacing were used to assess sensitivity of repolarization indices to activation sequence. At the cardiac surface, (1) QTI tracks global repolarization changes b ut is affected by activation sequence and insensitive to localized sho rtening of repolarization; (2) distribution of QRST integrals reflects disparity of repolarization and is largely independent of activation sequence; and (3) ARI measures local repolarization duration and is on ly weakly affected by activation sequence. At the body surface, findin gs suggest that QRST integrals reflect repolarization disparity and ar e largely unaffected by activation sequence, and ARIs measured at prox imal locations are likely to correlate with direct cardiac measures of repolarization. Thus, body surface QRST and ARIs appear to provide a potentially important means of assessing repolarization, its disparity , and its dynamics, even in the presence of conduction defects.