Premature Atrial Contractions
Premature atrial contractions (PACs) are beats which are initiated in the atria or upper chambers of the heart, prematurely, which cause the SA node (the natural pacemaker of the heart) to be interrupted. The terms SVEs (supraventricular extrasytoles) and PJCs (premature junctional contractions) are also often used when describing these beats but the distinctions are beyond the scope of this discussion.
PACs are one of the two most common heart rhythm abnormalities observed, the other being PVCs(premature ventricular contractions). They are frequently benign and require no treatment. However, in some cases they may be so frequent (over 15-20/minute) that they may cause the heart to beat inefficiently enough to cause symptoms which may need to be addressed. Occasionally, patients who have PACs may also have atrial fibrillation at other times.
PACs may occur singly, in pairs, in short runs or every other beat (bigeminy) and also may be aberrant or non-conducted. Examples of all of these are shown below. Patients who have these types of rhythm abnormalities may often refer to them as palpitations, skipped beats, hard beats, irregular beats, missing beats or extra beats. They may also complain of feeling dizzy or lightheaded or experience chest pain. Some patients may have no symptoms at all.
Just to reiterate, PACs are premature beats or beats occurring earlier than they should. Many patients describe them as skipped beats, because when they check their pulse, they don’t feel anything for a moment. However, your heart is not actually skipping or missing a beat. What is happening is that when a beat occurs prematurely, the normal volume of blood has not yet returned to your heart from the previous beat. So, even though your heart contracts, not enough blood has returned from the previous beat for it to pump the normal amount of blood. Because of reduced blood being pumped, it may feel like you have skipped a beat, but you have not, although the beat was certainly not as effective as a normal beat.
Patients frequently experience more of these palpitations at night or when they are relaxing. This is because when the natural pacemaker of the heart (the SA node) slows down, as it frequently will when you are relaxed, these ectopic (out of the wrong place) foci (point of origins) do not get reset soon enough to stop them.