An electrocardiogram (ECG) records the heart’s electrical activity. This non-invasive test helps medical professionals assess heart function, identify irregular heartbeats, and detect heart conditions. The ECG machine records tiny electrical changes as the heart muscle depolarizes and repolarizes during each heartbeat. Electrodes are placed on the chest, arms, and legs to detect these signals.
Understanding ECG Leads
ECG leads function as various viewpoints, each offering a distinct perspective on the heart’s electrical currents. Electrodes are placed on the body’s surface, and the electrical potential difference between two or more electrodes creates a “lead”. This allows for a comprehensive assessment of the heart’s electrical pathways.
Lead II’s Unique Perspective
Lead II is one of the standard limb leads, recording the electrical activity between the right arm and the left leg. This specific orientation aligns closely with the heart’s main electrical axis, which generally flows from the upper right to the lower left of the body. Because of this alignment, Lead II provides a clear and representative view of the overall electrical impulse as it travels through the atria to the ventricles. The positive electrode for Lead II is on the left leg, and the negative electrode is on the right arm, ensuring that a depolarization wave moving towards the left leg produces a positive deflection.
Key Information Revealed by Lead II
Lead II is particularly valuable for assessing heart rhythm because it provides clear views of the P waves, QRS complexes, and T waves. The P wave represents the electrical activity of the atria, while the QRS complex signifies ventricular electrical activity, and the T wave indicates ventricular repolarization. Analyzing these waveforms in Lead II helps identify various rhythm disturbances, such as normal sinus rhythm, abnormally fast heart rates (tachycardia), slow heart rates (bradycardia), or irregular rhythms like atrial fibrillation. For instance, a P wave is consistently positive in Lead II during normal sinus rhythm.
Diagnosing Inferior Wall Myocardial Infarction
Lead II, along with Leads III and aVF, also provides a view of the inferior wall of the left ventricle, which can be important for diagnosing conditions like inferior wall myocardial infarction. When an inferior infarction occurs, these leads may show specific changes like ST-segment elevation, pathological Q waves, and T-wave inversions.
Why Lead II is Often Preferred
Lead II is preferred for rhythm assessment and monitoring due to its alignment with the heart’s natural electrical axis. This alignment results in the most positive and distinct deflections for primary electrical events, making waveforms easy to interpret. Its clarity allows for quick and reliable heart rate calculations by measuring the distance between R waves. A prolonged recording from Lead II, known as a rhythm strip, is commonly used to assess cardiac rhythm over time. This consistent and clear view makes Lead II a preferred choice for monitoring heart activity in various clinical settings.