For The Past Year I Have Been Experiencing Palpitations. Sometimes

For the past year I have been experiencing palpitations. Sometimes I actually feel a skipped beat but not always. I notice I often have an increase in heart rate for a short time (20 or 30 seconds) after the palpitations. I do get very anxious when this happens. Some days it is rare, other days it will happen often. I get thirsty, and sometimes feel short of breath, like I have to take a deep breath and sometimes chills. There is no pain with this. I have been under a lot of stress this past couple years plus I had an Open AAA repair 20 months ago. I have had MRI's CT scans, induced stress test, Etc. All negative. I do have High Blood pressure and take meds for that. I'm about 30 pounds over weight. 5'-9" 190 pounds. Doc says my heart is fine but I do have some Atherosclerosis. I am 72 year old male. Any idea as to what this might be.