Which of the following is NOT a known cause of PACs?

Coronary artery bypass grafting (CABG) is a surgical procedure used to improve blood flow to the heart. While this procedure may be associated with various complications and changes in cardiac rhythm, it is not directly recognized as a cause of premature atrial contractions (PACs). PACs are early heartbeats originating in the atria, and their common causes include factors that stimulate increased atrial activity, such as excessive caffeine, hypokalemia (low potassium levels), and digitalis toxicity.

Excessive caffeine stimulates the central nervous system and can lead to increased heart rate and atrial irritability. Hypokalemia affects the electrical conductance of the heart, predisposing individuals to various arrhythmias, including PACs. Digitalis, a medication used to strengthen heart contractions, can lead to toxicity which may manifest as various rhythm disturbances, further including PACs.

In contrast, while CABG may alter the heart's electrical conduction or rhythm post-operatively, it is not inherently a primary cause of PACs in the same way the other options can directly lead to increased atrial activity.