Question: I am 33y.o. w/ a hx of SVT. First episode occurred 5 years ago in 2006, 6 months after having my first child. Was in SVT for 1 hour at 280-290bpm. Had EP study, unable to produce SVT, so unable to ablate. Dx with Inappropriate Sinus Tachycardia. Since that time, I'd have intermittent short runs of SVT. They'd usually last about 20 seconds and stop on their own without vagal maneuvers. Sometimes I would go months without feeling a run of SVT, sometimes I'd feel 2 runs in a week. My past rx for the SVT / IST was Verapamil. But I stopped it when I got pregnant the 2nd time and never went back on it. The SVT and Tachycardia seemed to improve after the pregnancy. The short runs of SVT are more intermittent/rare than ever. But basically, for the last 15 years, I have been completely sedentary with a very poor diet. In October of this year, I hit 200lbs (I am 5'0" tall.) Since October 3rd, I've been working out at Planet Fitness on the treadmill. Sometimes 5 times a week, sometimes 2 times a week. Then in November, I started using an app on my phone called Lose It. I input all of my stats (age, height, weight), I input that I'd like to lose 50lbs by April with an average of 2 lbs loss per week. So, my daily caloric intake was set at approx 1100 calories. I stick to this to the T. I have cut all sweets, I eat a decent sized breakfast and lunch and frequent small snacks throughout the day. Then I usually have a smaller portioned dinner and don't eat after 7p.m. Obviously, this is completely drastic lifestyle change from the last 15 years. So far, in 3 months, I have lost 30lbs. I've never felt SVT while exercising and the short 15-20 second runs of SVT were still rarely occurring. Here is the problem. 3 nights ago, I had a run of SVT that lasted 15 minutes. Numerous vagal maneuvers did not work. I was symptomatic with SOB and slight dizziness. I was alone, and could not even count my HR. Eventually, I did a vagal maneuver of bearing down as long as I could and the SVT stopped. Went to doctor the next day. He scheduled me for an echo. And did an EKG, which he compared to an EKG from May. He noted my PR interval had shortened since May. He also ordered CBC w/diff, CMP, Lipids, Thyroid, Magnesium, & Phosphorus. Should get results today. But my EKG readout looks like this:

Vent Rate: 107bpm
RR Int: 557ms
PR Int: 110ms
QRS Dur: 78ms
QT Int: 338ms
QTc Int: 420ms
QT Dispers: 34ms
P-R-T Axis: 35' 53' 49'

Also reads:
Sinus tachycardia
Anterior T wave changes are non-specific
Borderline ECG

What is your opinion on why the SVT would come back all of a sudden? I have actually decreased my workouts to twice a week in December, so I am not overdoing that. Do you think the changes in my lifestyle have done something to start this up again? I am sticking to my healthy diet, I am not starving myself. What could cause this? Do you think my doc should order anything else? He also wants me to see my EP doctor again.