Monday, February 28, 2011

Highlighting Atrial Activity on an ECG: The S5 Lead

Kelly Grayson, of A Day in the Life of an Ambulance Driver fame, posted an article on over a year ago entitled The Leads Less Traveled. In this he touched on modified chest leads (MCL1 through MCL6), right precordial leads (V4R), and the S5 Lead.

Update: after posting this I have since learned it is also known as the Lewis Lead, after Sir Thomas Lewis1, and have included a link to an article detailing how it was derived.

I had never heard of the S5 Lead before and promptly forgot about it until yesterday, when I finished acquiring 12-Leads for my limb lead reversal project. I went ahead and captured a rhythm strip from myself using the S5 lead placement.
S5 Leads: monitoring Leads I and II.
Before we cover the S5 Leads, let's recap normal lead placement and our friend, Einthoven's Triangle. This produces convenient ECGs with positive waveforms along the usual mean vector of the heart. Lead I points to 0°, Lead II points to 60°, and Lead III points to 120°.
Our friend, Einthoven's Triangle.
Additionally, the electrodes themselves are placed out on the limbs which generally results in waveforms proportional to the myocardium involved. Atrial activity is shown as well, but considering the proportion of myocardium involved in atrial depolarization, this configuration is not always useful in finding P-waves.
Normal Placement: Leads I and II from the same patient.
Now let's introduce the S5 Lead. You can produce this using many variations of the electrodes, however, for simplicity's sake we will stick with Kelly's description:
  1. Place the Right Arm electrode on the patient's manubrium.
  2. Place the Left Arm electrode on the 5th intercostal space, right sternal border.
  3. Place the Left Leg electrode on the right lower costal margin.
  4. Monitor Lead I.
Maximal atrial activity monitoring Lead I, S5 Lead configuration.
Notice the change in the direction of each lead. Lead I now points to the usual mean vector of atrial depolarization. Lead II and lead III are nearly perpendicular to the usual mean vector of ventricular depolarization. What does this mean for the electrocardiographer? If you remember that a vector which travels towards a lead is positive and perpendicular to a lead is isoelectric the answer is easy: atrial activity is highlighted, ventricular activity is diminished. 
S5: Lead I
S5: Lead II
The new direction Lead I points in is not quite perpendicular to the mean vector and it is also closer to the ventricular depolarization, hence we still have clear ventricular activity. However, the direction and location of Lead I is right in front of the atrial depolarization wavefront, giving clear P-waves. Lead II shows a large P-wave and small, nearly isoelectric ventricular activity.

If I can remember, I will try and acquire S5 Leads in the field. Has anyone else used the S5 Lead? Are there any other interesting lead configurations we should use?
  1. Bakker, ALM, et al. The Lewis Lead: Making Recognition of P Waves Easy During Wide QRS Complex Tachycardia. Circ (2009); 119:e592-e593. [Free Full Text]


The Jarvik 7 said...

Tremendously interesting post! Thank you for introducing me to this. In several cases I have noted that a-flutter is only readily distinguishable in one lead; I am eager to apply this new approach to such situations as well as others! Excellent post!

Cliff Reid said...

Nice post and great blog. Good to meet and drink beer with you in Baltimore. Keep up the great work!

Christopher said...

Thank you Jarvik7, big fan of your blog (I've learned a lot from it), glad I could reciprocate.

And Cliff, crazy that a week or so after hearing you on Dr. Weingart's podcast I'd catch up with you at an airway class! Was fun for certain. Keep up the good work on your blog as well.

The Jarvik 7 said...

Thank you for your kind words, Christopher! I really appreciate your support!

I recently came across this discussion of "high" and low" chest leads placed in the usual distribution but translated up or down one intercostal space-- used to highlight low visibility regions such as in high lateral wall MI. Here is the link:

Not exactly directly on topic, but I thought I would pass it along. Of course, when considering the options, one can always just go for the 80-lead Prime EKG.

Thanks again for the great blog and excellent posts! Keep up the good work!

Christopher said...

I enjoy the Cardiophile blog as well and found that post interesting. All of these good 12-Lead blogs online make it hard to get work done!

Dawn Altman said...

Thanks, Christopher, for commenting on my website. Your interesting comments prompted me to check out your blog, and I'm glad I did. For years, I have "made up" leads to try to highlight atrial activity, especially when looking for flutter waves. I never heard of this lead, and I'm looking forward to trying it out!

I hope you will frequently comment on the content on the ECG Guru, as your comments will be very useful to my visitors. I wlll place a link to your blog on the Guru.



Unknown said...

I've used the S5 lead for years, from the days when my monitor was a LP 5. It's a great lead when you can't see anything in the standard leads. Too bad it isn't regularly taught.

Christopher Wild said...

What a fantastic post! I'm a student cardiac scientist with a specialism in ECG/Echo and this is something that hasn't even been mentioned in lectures, labs or rotation. I'm going to research this until my eyes hurt. Cheers!

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