Electrical signals (impulses) excite heart cells causing the heart chambers to contract and pump blood/oxygen into circulation. The network of pathways for impulses are very complex and occasionally may cause early contractions and/or skipped beats. The skipped beat is usually due to an impulse not progressing along the pathway but the impulse is blocked. A good transmission of electrical conduction requires a balance of elctrolytes in the blood stream. Also, an EKG is not conclusive, requires other clinical evidence, supporting symptoms, etc. Your doctor is not concerned so it is apparent there is no other evidence, and no need to worry.