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.
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.
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.