My Wife Is Experiencing Some On And Off Pricking Sensations

my wife is experiencing some on and off pricking sensations closer to her heart. Once recently it has started from the spine area & then travelled forward to the heart area as per a very recent experience. But the ECG obtained few days back after a day or two after experiencing similar sensations, was in a near perfect healthy situation as per our family physician. But she again felt the same sensation after a day or two also. She has been complaining of this matter within a period of about 06 months to one year by now. This is not a daily occurence, but after a quite some time she has been experiencing this about 03-04 times within a space of 01-1.5 weeks by now. What can this situation be. Her pressure is also normal & choletrol levels are also generally within limits without taking any medication. please advice.