An electrocardiogram (EKG) records the heart’s electrical activity. This non-invasive procedure involves placing electrodes on the skin to detect electrical changes with each heartbeat. Premature Atrial Contractions (PACs) are extra heartbeats originating in the heart’s upper chambers (atria), disrupting the normal rhythm. This article clarifies the visual characteristics of PACs on an EKG.
Decoding the EKG: Normal Heartbeat
An EKG tracing displays the heart’s electrical activity as a series of waves and segments on a graph. The P wave represents the electrical activation (depolarization) of the atria, leading to their contraction. Following the P wave is the PR interval, a brief pause indicating the time it takes for the electrical signal to travel from the atria to the ventricles.
The QRS complex then appears as a sharp, prominent deflection, signifying the rapid electrical activation (depolarization) of the ventricles, which causes them to contract and pump blood. The ventricles contain more muscle mass than the atria, making the QRS complex considerably larger than the P wave. Finally, the T wave represents the electrical recovery (repolarization) of the ventricles, as they relax. Recognizing these standard components is fundamental to identifying any deviations from a regular heart rhythm.
Spotting a Premature Atrial Contraction
A Premature Atrial Contraction (PAC) is identifiable on an EKG by a beat that occurs earlier than expected, interrupting the regular rhythm. This premature beat originates from an ectopic focus, a site in the atria other than the heart’s natural pacemaker. The P wave associated with a PAC is often premature and has a different appearance (morphology) compared to normal P waves, because it arises from a different location within the atria. This altered P wave might appear inverted, peaked, notched, or occasionally hidden within the preceding T wave.
The P wave of a PAC is usually followed by a narrow QRS complex, similar to the normal QRS complexes. This occurs because the electrical signal generally travels through the heart’s normal conduction pathways to the ventricles.
A pause often follows a PAC, as the heart’s natural pacemaker resets its rhythm. This pause is frequently “non-compensatory,” meaning the interval from the PAC to the next normal beat is shorter than two regular heartbeats, effectively shifting the overall rhythm. The presence of these early, distinctly shaped P waves, followed by a typically normal QRS complex and an irregular pause, are the hallmarks of a PAC on an EKG.
What Causes PACs and When to Be Concerned
Premature Atrial Contractions are very common and often occur without a clear underlying cause, even in healthy individuals. Common triggers for PACs include lifestyle factors such as stress, caffeine or alcohol consumption, and nicotine use. Fatigue and certain medications can also contribute to their occurrence.
While isolated PACs are generally considered benign and do not typically require treatment, their frequency can sometimes be a cause for concern. Medical attention might be appropriate if PACs are frequent, cause noticeable symptoms like heart palpitations, a fluttering sensation, or a feeling of a skipped beat. Other symptoms that warrant evaluation include dizziness or chest discomfort associated with PACs. Additionally, if there is an underlying heart condition, or if PACs are very frequent, they may indicate an increased risk for other heart rhythm disorders, such as atrial fibrillation.