An electrocardiogram (EKG or ECG) is a simple, non-invasive test used to measure the heart’s electrical activity. The standard 12-lead EKG uses ten electrodes placed on the limbs and the chest to capture the heart’s function from twelve different perspectives. Six of these electrodes, known as the precordial or V-leads (V1 through V6), are placed directly on the chest wall to view the heart’s electrical activity in the horizontal plane.
Exact Placement of V2
The location of the V2 electrode is determined by identifying a specific anatomical landmark on the chest. V2 is placed in the fourth intercostal space (ICS) immediately to the left of the sternal border. To find the fourth intercostal space, a clinician must first locate the Angle of Louis, the ridge where the manubrium meets the body of the sternum.
This ridge corresponds directly to the second rib, which is the starting point for counting the spaces between the ribs. Counting down from the second rib, the fourth intercostal space is the gap between the fourth and fifth ribs. The V2 electrode is then applied within this space, right at the edge of the breastbone on the left side.
Sequential Placement of the Precordial Leads
The V2 lead’s placement sets the stage for positioning the other five precordial leads. The V1 electrode is placed in the mirror position to V2, meaning it is also in the fourth intercostal space but immediately to the right of the sternal border. Once V1 and V2 are secured, the next step is to locate V4, since V3’s location depends on these two points.
V4 is positioned in the fifth intercostal space, along the mid-clavicular line, an imaginary vertical line running down from the middle of the collarbone. The fifth intercostal space is one space below V1 and V2. After V2 and V4 are placed, the V3 electrode is situated exactly midway between the V2 and V4 positions. Placing V4 before V3 ensures the correct spacing and alignment for the anterior wall view of the heart.
The remaining leads, V5 and V6, are placed along the same horizontal line as V4, following the fifth intercostal space. V5 is placed on the anterior axillary line, which aligns with the front fold of the armpit. V6 is positioned on the mid-axillary line, running vertically from the center of the armpit, maintaining the same horizontal level as V4 and V5.
Diagnostic Significance of Correct Positioning
The correct placement of the V2 lead, along with V1, is important for generating an accurate EKG tracing, as these leads specifically view the septal and anterior walls of the heart. Misplacement, particularly placing V1 and V2 too high (e.g., in the third intercostal space), is a common technical error that can significantly distort the waveform. This upward displacement can decrease the amplitude of the initial R-wave, which may incorrectly suggest a prior anterior heart attack or poor electrical progression.
Such an error can generate false-positive findings, potentially mimicking conditions like an acute anterior ST-segment elevation myocardial infarction (STEMI) or certain types of bundle branch blocks. Incorrect positioning can lead to unnecessary medical interventions, such as activating a cardiac catheterization lab, which wastes resources and exposes the patient to risk. Conversely, misplacement can also mask true signs of myocardial ischemia, preventing a timely diagnosis.