Effects of sudden changes in cycle length and pacing site on canine cardiac surface QRST isoarea maps

The effects of changes in paced cycle length alone and changes in both paced cycle length and site of pacing on canine cardiac surface QRST isoarea maps were studied. The correlations between QRST isoarea maps acquired during right ventricular pacing at 900 ms and 700 ms averaged 0.97. The correlations between maps acquired during RV pacing at 900 ms and 500 ms averaged 0.94. The root mean square value of QRST areas progressively decreased as cycle length was decreased from 900 ms to 700 ms and then to 500 ms. This suggests that the pattern of distribution of repolarization properties remained the same and the magnitude of difference in repolarization properties decreased as cycle length was decreased. The correlation coefficients of QRST isoarea maps acquired during RV pacing at 900 ms and those acquired during left ventricular pacing at 700 ms and 500 ms averaged 0.74 +/- 0.01 and 0.68 +/- 0.03, respectively. These correlations were lower than those associated with a change in pacing cycle length alone. Root mean square differences in QRST areas recorded during changes in both pacing site and pacing cycle length were greater than the differences associated with change in cycle length alone. This suggests that changes in activation sequence altered repolarization properties more than they were altered by changes in cycle length alone. QRST isoarea maps have been proposed for assessing arrhythmia vulnerability. The results of this study provide a framework for interpreting QRST isoarea maps acquired during supraventricular tachycardias, premature ventricular complexes, and sustained ventricular tachycardias.