Minor movements, beats at times.

Hello Doctors, Last month I woke up from sleep and had fast heart beat, I checked in pulse oximeter and it was around 167bpms. I immediately rushed to hospital and got ECG done. The report came out as sinus tachycardia and non specific St abnormality. Next day I consulted cardiologist and recommended tmt since echo test was done last November. Report says good effort tolerance, added screenshot of it , came out normal and doctor said not to worry about anything. Recently got Spandan hand held ECG device to check for parents and myself. At times the report has variations. Sometimes comes normal ECG, at times it shows ST elevation in V2, tachycardia, left bundle branch block. Should I be worried about the readings taken on the hand held machine? Symptoms: at times I can feel some movements around chest area left side, no pain or discomfort. But I get tensed when I feel it.