A premature atrial contraction, or PAC, is a highly common variation in heart rhythm that occurs when an electrical signal starts early in the heart’s upper chambers, the atria. This extra beat briefly interrupts the heart’s regular pacing. While PACs are often harmless, the sensation can be startling, ranging from a mild flutter to a significant thud in the chest. For many people, these events are entirely asymptomatic.
Describing the Physical Sensation of a PAC
The most frequently reported sensation of a PAC is that the heart has “skipped a beat.” This feeling is not the PAC itself, but the pause that immediately follows the premature event. This momentary interruption in the rhythm is often followed by a more forceful beat that registers as a “thump” or a “thud.”
Some individuals describe the experience as a brief fluttering, a flip-flop, or an irregular pounding in the chest. The sensation may also be felt intensely in the throat or neck, where the powerful subsequent beat registers more strongly against surrounding tissues.
The perceived force of the beat can cause a momentary feeling of anxiety or lightheadedness in some individuals. Factors like heart rate also influence perception, as the beats are often more noticeable when the heart is beating slowly.
The Electrical Mechanism Causing the Sensation
The normal heartbeat is governed by the sinoatrial (SA) node, the heart’s natural pacemaker, which generates a regular electrical impulse. A PAC occurs when a different site within the atria spontaneously generates an electrical impulse sooner than the SA node was scheduled to fire. This premature electrical signal causes the upper chambers to contract early, creating the extra beat.
This early contraction is often inefficient because the ventricles, the heart’s lower pumping chambers, have not had enough time to fully fill with blood. Following this premature beat, the SA node’s rhythm is momentarily reset, resulting in a slightly longer-than-normal pause, often referred to as a compensatory pause.
During this extended pause, the heart’s chambers have extra time to fill with a larger volume of blood. Consequently, the very next beat, which is the heart’s return to its regular rhythm, is significantly more forceful, resulting in the physical “thump” or “pounding.”
Common Triggers and Underlying Causes
While PACs can occur without an identifiable reason, many non-cardiac factors can increase their frequency. Stimulants are a significant factor, with substances like caffeine, nicotine from tobacco products, and certain decongestants or asthma medications known to provoke extra beats. These compounds can heighten the heart muscle’s excitability.
Temporary physical states also play a large role in prompting PACs. Dehydration and imbalances in electrolytes, such as low levels of potassium or magnesium, can disrupt the heart muscle’s electrical stability. Similarly, periods of heightened emotional stress, anxiety, or chronic sleep deprivation can increase the release of stress hormones, which makes the heart more prone to electrical misfires.
Hormonal fluctuations, such as those experienced during pregnancy or the menstrual cycle, can also contribute to an increased frequency of PACs. Although PACs are usually benign, they can occasionally be a manifestation of underlying health conditions, such as thyroid gland overactivity, or hyperthyroidism, which can accelerate the heart rate.
When to Consult a Healthcare Provider
While occasional PACs are extremely common and do not typically require treatment, certain symptoms warrant a discussion with a medical professional. If the skipped beats are occurring very frequently, in long runs, or if they are causing significant distress and interfering with daily life, an evaluation is advisable.
Accompanying symptoms such as persistent shortness of breath, dizziness, chest pain, or episodes of near-fainting (presyncope) or fainting (syncope) should prompt immediate medical attention.
A healthcare provider may use tools like an electrocardiogram (ECG) to capture the heart’s electrical activity at rest, or an ambulatory monitor, such as a Holter monitor, worn for a day or longer to record the frequency of the PACs over time. Identifying and addressing the triggers is often the first step in management, but diagnostic testing helps determine if the frequency of PACs poses any future risk.