The 12 Leads of Christmas: V4

This article is the eighth in our latest series, The 12 Leads of Christmas, where each day we examine a new finding particular to an individual electrocardiographic lead.

Lead V4

Like aVF, V4 is a tough lead to discuss on its own. It’s part of the natural flow of the complexes across the precordium and it is certainly nice to have, but because it’s so closely related to V3 and V5 there isn’t a whole lot that makes it unique. The two topics we’ll discuss today involve, but are not isolated to, V4.

First off, I can’t discuss V4 without mentioning the work of our blog’s good friend and mentor, Dr. Stephen Smith, on differentiating early repolarization from subtle anterior STEMI. The formula he and his team derived uses the R-wave amplitude in V4 as one of the three variables in an equation that can be utilized as a decision-aid in the evaluation of these difficult EKG’s.

  • A series of cases displaying how and when to use the formula can be found here on his site.
  • The article describing the derivation of the formula can be found here (free full text!).
  • A simple form for calculating the value is available on the right-hand sidebar of Dr. Smith’s site.
  • Alternatively, a simple calculator is also available on the MDCalc site.

Earlier this year he was nice enough to feature a case of mine that really shows off the utility of the formula (among other lessons). Here’s a link to the full case description, while the image below is merely a teaser.

01 - 1386 - 75yo F - 01

Early repolarization or subtle anterior STEMI? Check out the link above to find out.


Another time V4 becomes useful is when you see a wide QRS complexes on the EKG but aren’t sure whether they’re due to a paced or native rhythm.

Most of the time you can see pacemaker spikes in several leads but, especially with aggressive filter settings, it’s also not unusual for those pacer spikes to be nearly invisible. Since most ventricular pacing wires are inserted into the RV apex, it turns out that the leads closest to that location are also the ones best suited to capture evidence of it firing.

Due to variability in individual anatomy and positioning of the pacing lead it doesn’t always work out but, in my experience, ventricular pacing spikes are usually best seen in V3–V5 region, so I typically center my scrutinization around V4. Atrial spikes, on the other hand, are usually best seen in V1 and V2, closer to where those wires are placed. Here are some examples of the former:

02 - 0862 - 83yo F - 08

They’re super subtle but V4 is the only lead in which ventricular pacer spikes are visible.

03 - 1314 - 76yo M

Ventricular pacer spikes are visible in V3–V5 but most visible in V4.

04 - 0855 - 66yo M - 03

Subtle ventricular pacer spikes are only visible in V3 and V4.

05 - 0275 - 78yo F

Subtle ventricular pacer spikes only visible in V4–V6. Interestingly, though the computer is usually pretty good at spotting PM’s, in this case it only picks up the atrial spikes.

06 - 0269 - 84yo M

Subtle ventricular pacer spikes in V3–V6, best seen in V4.

07 - 0635 - 82yo M

There’s a decent amount of artifact but there are also ventricular pacing spikes visible in V3 and V4 (in this case V3 > V4).


Another easy way to increase the visibility of pacer spikes is to increase the adjust the filter settings of the electrocardiograph. Depending on the particular machine you’re using this ranges in difficulty from easy to hard but it’s still worth knowing how to do—even is it’s only changed on rare occasions.

09 - 1450 - 75yo F - 01b

This EKG was printed with a filter bandwidth of 0.05–40 Hz. 40 Hz is a more aggressive low-pass filter than most guidelines recommend for diagnostic use (usually 100 or 150 Hz), but in the emergency setting I find the clarity that setting offers outweighs the small effects it has on the size of complexes.

08 - 1450 - 75yo F - 01a

This is the same exact ECG printed with a higher frequency low-pass filter (300 Hz vs 40 Hz). As you can see, there is increased artifact but the pacer spikes are much more visible. Unlike the prior cases, in this instance V3–V5 are not the best leads for seeing the ventricular pacing spikes.


I hope you’re enjoying our 12 Leads of Christmas series. You can check out the rest of the posts below (updated as new posts come out):

12 Leads of Christmas: Lead I
12 Leads of Christmas: Lead II
12 Leads of Christmas: Lead III
12 Leads of Christmas: aVL
12 Leads of Christmas: aVF
12 Leads of Christmas: aVR
12 Leads of Christmas: V1
12 Leads of Christmas: V2
12 Leads of Christmas: V3
12 Leads of Christmas: V5
12 Leads of Christmas: V6


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