What is a Premature Atrial Contraction (PAC)?
A PAC is an extra heartbeat that starts too early in the upper chambers of your heart (the atria), disrupting your normal heart rhythm and often causing a sensation of a skipped beat or a strong thump in your chest. 1
How Your Heart Normally Works
Your heart has a natural pacemaker called the sinus node that sends electrical signals in a coordinated pattern, making your heart beat regularly. 1 Think of it like a conductor leading an orchestra—everything happens in perfect timing.
What Happens During a PAC
- An electrical signal fires too early from somewhere in the upper chambers of your heart (atria) before the next normal heartbeat is supposed to occur. 1
- This creates an extra, premature beat that interrupts your regular rhythm. 1
- You might feel a pause followed by a stronger-than-normal heartbeat, or you might notice your heart rhythm feels irregular. 1
- The medical abbreviation "PAC" stands for Premature Atrial Contraction—"premature" because it comes early, "atrial" because it starts in the atria (upper chambers), and "contraction" because it causes your heart to squeeze. 1
What You Might Experience
- Most people feel nothing at all—PACs occur in nearly everyone and are often completely asymptomatic. 2
- When symptoms do occur, you might notice palpitations (awareness of your heartbeat), fatigue, lightheadedness, chest discomfort, or shortness of breath. 1, 3
- Some people describe it as feeling like their heart skipped a beat or experiencing irregularities in their heart rhythm. 1
Are PACs Dangerous?
- In healthy people with structurally normal hearts, isolated PACs are generally benign and require no treatment. 3, 2
- However, frequent PACs (more than 2,000 in 24 hours) are associated with increased risk of developing atrial fibrillation (an irregular heart rhythm), stroke, and adverse changes to the heart's structure. 3, 4, 5
- PACs were previously considered completely harmless, but recent evidence shows they can signal underlying heart problems or predict future complications, particularly when they occur frequently. 2, 4, 5
Common Triggers
- Stimulants like caffeine, alcohol, or certain medications (theophylline, adenosine, some chemotherapy drugs). 3
- Electrolyte imbalances or thyroid problems. 2
- Underlying structural heart disease, especially in patients with prior heart surgery or significant heart abnormalities. 3
- Stress and lack of sleep. 2
When to Seek Medical Attention
Any PAC causing symptoms like dizziness warrants evaluation, regardless of how often they occur. 3 Your doctor may recommend a 24-hour heart monitor (Holter monitor) to count how many PACs you're having and determine if they correlate with your symptoms. 3