Isochronal difference mapping: an approach for mapping dynamic changes during reentrant ventricular tachycardia

During clinical electrophysiological study for treatment of reentrant ventricular tachycardia, activation maps constructed from the acquired electrophysiological data can be difficult to interpret when the reentrant circuit is changing from one cardiac cycle to the next. Reduction of complexity would be beneficial but has been difficult. A new technical method termed isochronal difference mapping (IDM) was devised to reduce complexity and enhance distinctive conduction patterns present in the data. Electrograms were acquired from 196 sites using a canine model of a reentrant ventricular tachycardia circuit with a figure eight conduction pattern occurring in the epicardial border zone. Activation maps were constructed for all cardiac cycles during episodes of tachycardia in five experiments. IDM maps were then created, which are subtractive comparisons of the activation maps from two different cardiac cycles during a given tachycardia episode. In each map the electrical activation occurring for only one or for both of the cardiac cycles was separately highlighted in distinct spatial areas of the border zone during an isochronal interval. Based on the mappings, areas of conduction velocity change, regions of breakthrough of the wavefront across functional lines of block, regions with coherent activation, and regions with irregular activation became readily apparent. IDM maps showed that when cycle length prolonged due to deceleration of conduction within the reentrant circuit isthmus, conduction velocity increased elsewhere in the circuit. IDM accentuates cycle-to-cycle differences in multi-channel electrophysiological data and can be used to reduce complexity and enhance distinctive conduction patterns.