What Causes Fatigue, Shortness Of Breath And Dizziness While On A Pacemaker?

I have had a pacemaker for almost 15 years (on 2nd one)…..have recently experienced fatigue, light headedness and shortness of breath on a daily basis and some edema in hands and feet…am 69 yo…originally had random irregular a-fib…..did not respond to meds …..a-fib was out of control so 15 years ago did heart block and gave me a pacemaker…..6 weeks ago went thru complete cardiac workup….chemical stress.echo cardiogram…blood work…all good…adjusted my sensors twice…..and was told it appeared as if I had a lazy heart…..was no longer assisting my pacer the way it has in the past……(pacer was checked twice)….have a year battery left so will be monitored closely…oh and when originally checking pacer my strip showed that my heart rare had not gone over 80bpm in the last two months…..was slightly better when adjustment was made ( set at 140)…..so what can I do ?????