Potentially something wrong with your lungs (pulmonary disease). When you look at an EKG, you have different waves: P (first bump), QRS (the different parts of the highest peaking wave), and T waves (right after the QRS). Right before the P wave happens, the atria contract due to the sinoatrial node ("pacemaker") in your heart, which is a bundle of nerves stimulating the heart to beat. It's potentially something going on with that as well. I'd discuss this with your doctor to find out exactly what is going on and what to be concerned about.
Sounds like something abnormal with your lungs.