please join us in the heart rhythm forum also =)
http://www.medhelp.org/forums/Heart-Rhythm/show/92 you'll find many others there like myself dealing with NSVT and VT =)
also, if you look in my journals, I have alot of info on Pvc's, NVST, VT and VTach
Both conditions have to do with faster than 100 beats per minute and that is classified as ventricular arrhythmia. Non-sustained and verified by an EKG reading 6 beats every 29 sec and that would show on the horizontal axis. Sustained is arrhythmia greater than 30 sec. duration and may require intervention to terminate.
Briefly the difference relates to the time of arrhythmia and number of beats.
Hope this helps and if you have any further questions or comments you are welcome to respond. Thanks for the question, take care.
Ken