Premature Atrial Contractions
Premature Atrial Contractions, or PACs are also known as atrial premature beats or APBs. They result from abnormal electrical signals arising from somewhere in the atria. A PAC disturbs the rhythm of the heart, and it is often felt as a "flutter" in the chest. The sinus node usually gets "reset" after a PAC, so the heart has to wait a second or so until the sinus node fires again. This often results in a slight pause in the heart rhythm. Since the heart is filling in between beats, a pause results in an increase in filling of the ventricles, and that extra blood that enters the heart is generally ejected with the next beat, so the heart beat following the pause is generally stronger than normal. This often causes symptoms of a "heavy beat" (like the heart is going to jump out of the chest) following the pause.
There is a wide variation in people's perception of irregularities of the heart rhythm. Some people can have thousands of premature beats all day long and never feel a thing, while other people are exquisitely sensitive to the inner workings of their body and feel every single premature beat. The people who do not notice arrhythmias may in fact be blessed, since benign arrhythmias like PACs can be a tremendous source of anxiety to those who feel them. Most normal people have a few PACs, but they occur more frequently in older people.
PACs are benign, and can occur in the absence of any other heart problems. They can occur in the setting of coronary blockages, valvular heart disease, or cardiomyopathy, but they are not necessarily a sign of a bad prognosis. Treatment is only necessary if the symptoms are intolerable. Caffeine, cigarettes, alcohol, and stress may increase PACs, so people with palpitations should avoid these. If the palpitations are severe, medications can be used to decrease the frequency of the PACs. However, since PACs are totally benign, most electrophysiologists prefer not to prescribe medications to treat this condition.