My Wife Has Been Complaining Of Occasional Heartbeat Palpatations. I

My wife has been complaining of occasional heartbeat palpatations. I noticed by listening that every once and a while there is a longer pause before the next beat (skipped beat) by which the following beat is a heavy one sounding as if pushing out excess blood. What particular type of Premature Heartbeat would this be classified as? She doesn't take narcotics, anxiety medicine, or excess caffeine and doesn't have a thyroid issue. Does get little sleep though.