Hello! Iv Been Getting Palpitations And Heart Flutters For Passed

Hello! Iv been getting palpitations and heart flutters for passed 6 weeks on and off. Excercising has been fine with no problems or stress on my body. No chest pain or blackouts/fainting. I had ECG and the doctor told me it looked fine but need to go to see cardiologist to get checked out as the beats seemed longer than usual. He said I could still exercise and was just precaution to make sure in future due to the longer beat certain drugs might not agree with me. Tonight after seeing the Dr and initial look at what a longer beat on ecg means I feel very panicky as i read about QT syndrome. Although my family has no history of this, I have not had any blackouts and feel great when excercising. Apart from the palpitations and the ecg I'm quite concerned and feel incredibly anxious as to what this means. Are there many problems or explanations for a longer beat on an ecg? Many thanks Peter (age 34,non smoker.0,non drinker)