What it means
On a heart rhythm strip, a PAC is a premature atrial contraction: an early beat that starts in the atria, usually with an odd-shaped P wave, followed by a pause. PACs are common and often harmless but can come before atrial fibrillationAY-tree-ul fib-rih-LAY-shunAn irregular heart rhythm in which the upper chambers of the heart quiver instead of beating in an organized way.atri/o atrium (upper heart chamber)fibrill/o small fibers, quivering-ation processFull entry . In critical care, PAC can mean pulmonary artery catheter, a line threaded through the heart to measure pressures. Read it in context.
Related terms
arrhythmia
A heart rhythm that is not normal: too fast, too slow or irregular.
electrocardiogram
A test that records the heart's electrical activity as waves on paper or a screen.
atrial fibrillation
An irregular heart rhythm in which the upper chambers of the heart quiver instead of beating in an organized way.
pulmonary artery
The large blood vessel that carries blood low in oxygen from the right side of the heart to the lungs.