hello your symptoms seem to due to premature contractions either ventricular or atrial. I will explain what it is- premature contractions occur earlier than expected and are followed by a pause. these produce the symptoms of palpitation and skipped best. -since your EKG and echocardiography were normal, heart is structurally fine. -sometimes excess of thyroid hormone might produce premature contractions , monitor your thyroid function. -one question what is your heart rate while you are resting? because that will give us a rough idea about thyroid function. -thanks for asking , hope you find it useful