I get that on rare occasions. I've never caught it on a monitor but I would guess it is just bursts of tachy. I call mine "wacky tachy." You're right though - it's very uncomfortable.
I had the same thing the otehr day at work, it was like pvc's and tach at the same time and I coughed for like almost 30 seconds before it would even try to stop, it was scary.
PVC's are quite often the triggering mechanism for tachycardia. It's all about timing with electrical pulse setting up at precisly the right moment to trigger the tachycardia. On a monitor, my SVT was always triggered by a PVC.