Atrial Contraction on ECG

Introduction

Atrial contraction, also called atrial systole, is an essential phase of the cardiac cycle. It is responsible for pushing blood into the ventricles before ventricular contraction occurs. In an electrocardiogram (ECG), atrial contraction is represented by the P wave.

Understanding the P Wave

The P wave reflects the electrical depolarization of the atria. It starts in the sinoatrial (SA) node and spreads through both atria, leading to their contraction. Key characteristics of a normal P wave:

• Shape: Smooth, rounded, and positive in most leads (except aVR, where it may be negative).
• Duration: Typically less than 120 milliseconds (3 small squares on the ECG grid).
• Amplitude: Usually does not exceed 2.5 mm in height.

Clinical Importance of the P Wave

Abnormalities in the P wave may indicate different heart conditions:

• Enlarged P wave (P pulmonale): Right atrial enlargement, possibly due to conditions like pulmonary hypertension.
• Broad/notched P wave (P mitrale): Left atrial enlargement, often associated with mitral valve disease.
• Absent P waves: May occur in atrial fibrillation, where atrial contraction becomes disorganized.
• Ectopic P waves: Originate from an abnormal location in the atria, seen in conditions like atrial tachycardia.

Related Concepts in ECG

• PR Interval: Measures the time from the onset of the P wave to the beginning of the QRS complex. Normal duration is 120-200 milliseconds.
• Atrial Arrhythmias: Abnormalities in the P wave morphology may be seen in atrial flutter or fibrillation.

Understanding atrial contraction on ECG is essential for diagnosing and managing various cardiac disorders.

Conclusion

Recognizing the characteristics of the P wave is vital for assessing atrial activity and diagnosing possible cardiac pathologies. If you ever notice changes in your ECG related to atrial depolarization, consult a cardiologist.

Source recommendations

1. American College of Cardiology/American Heart Association ECG Interpretation Guidelines

1. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191095
2. https://www.acc.org/Guidelines
3. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191098
4. https://pubmed.ncbi.nlm.nih.gov/19281932/
5. https://www.sciencedirect.com/science/article/pii/S073510970700232X

2. European Society of Cardiology Guidelines on the Interpretation of the Electrocardiogram

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Neonatal-Electrocardiogram-Guidelines-for-the-interpretation-of-the
2. https://pubmed.ncbi.nlm.nih.gov/12269267/
3. https://www.escardio.org/static-file/Escardio/Guidelines/publications/NEONATguidelines-neonatal-slides.pdf
4. https://www.jacc.org/doi/10.1016/j.jacc.2017.01.015
5. https://academic.oup.com/eurheartj/article-abstract/39/16/1466/2965923