The QRST deflection area of electrograms during global alterations of ventricular repolarization.

Changes of refractory period and QRST deflection area in cardiac electrograms due to localized myocardial warming and altered cycle length were determined. Localized myocardial warming consistently resulted in increased QRST deflection area which was highly correlated with reduction of refractory period. Similar reductions of refractory period by decreased cycle length were associated with insignificant changes of small QRST areas and significant reductions of larger QRST areas. The different effect of local thermal alteration of repolarization and global alteration due to cycle length changes is experimental evidence that QRST deflection area depends on differences in duration of ventricular repolarization properties. The finding of decreased deflection area with decreased cycle length is also evidence of decreased disparity of repolarization properties of normal myocardium at rapid heart rates.