The Dynamic Behavior of the Diastolic Slope of Monophasic Action Potential Can be Related to the Occurrence and Maintenance of Delayed Afterdepolarization Dependent Arrhythmias

We have described the value of the diastolic slope of the MAP recording at the end of a pacing train as a qualifying marker for the induction of delayed afterdepolarization (DAD) dependent arrhythmias. In the present study (1) the behavior of the slope at different time points during a pacing train was quantified and related to the arrhythmogenic outcome (group A) and (2) termination of DAD dependent VT was related to changes in the slope steepness (group B). In dogs with chronic complete AV block, a MAP was recorded during (1) ventricular pacing, before and after ouabain administration (group A) and (2) 6 spontaneous and 6 lidocaine induced VT terminations (group B). During control (group A), the slope at the end of pacing train was 5 +/- 3 m V/s (mean +/- SD), independent of the pacing duration. During ouabain, this increased to 20 +/- 15 mV/s (P < 0.05), varying with the duration of pacing. The slope was steeper after pacing for 4 seconds, compared to 20 seconds (26 +/- 12 mV/s vs 16 +/- 13 mV/s, P < 0.05) which corresponded with more frequent VT induction. In spontaneously terminating VTs (group B), CL increased from 353 +/- 54 ms at the start to 434 +/- 78 ms (P < 0.05) before VT termination. This corresponded with a decreasing steepness of the slope from 19 +/- 10 mV/s to 6 +/- 5 mV/s (P < 0.05). In lidocaine induced VT termination, the CL and the steepness of the slope showed an identical behavior. There is a dynamic variation in the steepness of the diastolic slope during pacing, which depends on the duration of pacing and predicts arrhythmogenic outcome. Furthermore, a decrease in steepness of the slope during DAD dependent VT can be used to predict VT termination.