Precordial leads provide a window into the heart’s electrical activity from the Anterior-Posterior perspective. This post delves into how these leads are placed and what regions of the heart they examine.
What Are Precordial Leads?
Precordial leads are six chest leads (V1 to V6) placed on the anterior thoracic region. They capture the anteroposterior (front-to-back) flow of electrical impulses, offering a detailed view of the heart’s AP plane.
Precordial leads on a standard EKG
On a standard EKG, there are 6 precordial leads. Proper electrode placement is crucial:
- V1: 4th intercostal space, right of the sternum.
- V2: 4th intercostal space, left of the sternum.
- V3: Midway between V2 and V4.
- V4: 5th intercostal space at the midclavicular line.
- V5: Horizontally aligned with V4 at the anterior axillary line.
- V6: Horizontally aligned with V4 and V5 at the midaxillary line.
Regions Viewed by Precordial Leads
- V1 and V2: Septal leads, focusing on the heart’s septum.
- V3 and V4: Anterior leads, viewing the front wall of the heart.
- V5 and V6: Lateral leads, examining the side wall of the heart.
Notice how none of these leads look at the right side of the heart (Right ventricle and its free wall): So, what do we do if we are concerned about a right sided pathology?
Right Sided Leads
We could simply place the leads in a “mirror image pattern”:
- V1R: 4th intercostal space, left of the sternum.
- V2R: 4th intercostal space, right of the sternum.
- V3R: Midway between V2R and V4R.
- V4R: 5th intercostal space at the midclavicular line on the right
- V5R: Horizontally aligned with V4R at the anterior axillary line on the right.
- V6R: Horizontally aligned with V4R and V5R at the midaxillary line on the right.
Generally, on a EKG, we replace V3, V4, and V5 with V4R, V5R, and V6R when we need to evaluate the RV- This provides the information we need in most cases.
How about if we are concerned about the posterior part of the heart?
Posterior Leads
On a standard EKG, there are no posterior leads. So, we use the anterior leads to evaluate the posterior wall of the heart! For instance, Q waves in the posterior wall imply that the net depolarization wave is moving away from the posterior wall. That means it is moving toward the anterior wall and so, R waves in V1 or V2 may signify the presence of Q waves posteriorly.
We could also place leads on the back to better understand the flow of depolarization.
• Lead V7: Left posterior axillary line, in the same horizontal plane as V6.
• Lead V8: Left mid-scapular line (beneath the tip of the left scapula), same horizontal level as V6.
• Lead V9: Left paraspinal region, same horizontal level as V6.
Finally note that the leads do not capture individual waves of depolarization: Instead they capture the net wave of depolarization. This leads us to the next interesting concept- vectors.
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