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.|
|Our friend, Einthoven's Triangle.|
|Normal Placement: Leads I and II from the same patient.|
- Place the Right Arm electrode on the patient's manubrium.
- Place the Left Arm electrode on the 5th intercostal space, right sternal border.
- Place the Left Leg electrode on the right lower costal margin.
- 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?
- 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]