My eldest had tachycardia after my waters broke at 28wks. I was being constantly monitored anyway and he arrived at 30+1wks. The Drs said that it was caused by stress as his heart rate was within normal ranges prior to my waters breaking. It's hard to say if it caused any issues as such as he was born with a severe infection and being 10 weeks early needed interventions anyway. I can say that after the first 2 weeks his heart rate did drop back in to normal ranges and he's had no ongoing heart issues (he's 6.5 now). Hope that helps a little, good luck!