A 40-something male cancer patient presented to clinic for a routine follow up and stated he was feeling “tired.” He was just finishing a course of antibiotics for bacteremia.
His BP was found to be 60 systolic with a heart rate in the 170s. He was moved to the Emergency Department.
He appeared ill, but was not acutely in distress. He showed signs of volume depletion.
His initial ECG is shown below. What do you see?
|Initial ECG: This is a regular narrow complex tachycardia at a rate of 157 BPM.
There is no obvious atrial activity prior to the QRS. There seems to be some perturbation of the T wave (inverted retrograde P-waves, seen in PSVT) in the inferior leads making SVT very likely.
Smith comment: The differential of regular narrow complex tachycardia at a rate of 157 is:
1. sinus tach
2. paroxysmal SVT (PSVT, due to AVNRT or WPW)
3. atrial flutter with 2:1 conduction, and
4. very rarely, junctional tachycardia.
You can see what appear to be small negative waves after nearly every QRS. This would indicate PSVT When you become accustomed to seeing these, you can readily recognized them as retrograde P-waves.
We have seen many instances in which sinus tachycardia was misdiagnosed as SVT. Here is one:
So if you’re uncertain whether these are retrograde P-waves, and are wondering if you are missing sinus tachycardia, and the patient is stable (as here), you can try Lewis leads to see if sinus P-waves appear.
It takes about 30 seconds to align Lewis leads and then switch to lead I to see the result.
Aaron continues: Bedside cardiac US demonstrated a hyperdynamic and tachycardic heart with IVC variation with each breath, suggesting volume depletion, as we initially suspected.
Fluid resuscitation was started but the rate stayed between 160 and 170.
Smith comment: assessing response to volume repletion is a great way to confirm sinus tach. Sinus is an automatic rhythm with varying rate, where re-entrant rhythms such as PSVT are always at a constant rate. If the rate slowly drifts down, this confirms sinus. If the rate does not change, you have not confirmed a non-sinus rhythm, but you have made it far more likely.
Aaron continues: The physicians then re-arranged the limb leads of the 12-lead ECG in the Lewis Leads pattern, in order to better identify P-waves, or lack thereof.
Smith comment: it is much easier to use the monitor leads for Lewis lead placement than to use the 12-lead.
For a quick review on Lewis Lead Placement, check out this post.
- 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.
Aaron continues: The 12-lead ECG using Lewis Leads is below. What do you see? Remember, look at Lead I. In this example, Lead II is helpful too.
|In this ECG, retrograde atrial activity is more obvious in the Lewis Leads. Do you notice anything weird about the P-waves? They are upright, with 2 humps! The Lewis Leads were reversed on this 12-lead EKG, such that retrograde P-waves appeared upright.
Just as importantly, the Lewis leads did not uncover normal upright P-waves in front of the QRS. Thus, Lewis leads did not reveal sinus rhythm; at the same time, they did confirm retrograde P-waves, but because the leads were reversed, it was somewhat confusing!
Regardless, this Lewis Lead ECG helped the physicians confirm the diagnosis of SVT with retrograde P waves.
The patient was given 6mg adenosine and converted to a rate in the 110’s. His post-adenosine ECG is below.
|Normal sinus rhythm
1. The most important takeaway from this case is that you should use Lewis Leads on the monitor, not on the 12-lead EKG (even though limb leads on the 12-lead will suffice). You will be able to have a live view of the appropriate leads on the monitor. You don’t need all 12 leads!
2. Lewis Leads can help to ascertain atrial activity by focusing the electrodes on the atria.
3. Be mindful of lead reversal. If something doesn’t make sense, consider reversed leads. Check out this LITFL page for a quick summary on lead reversal. In our case, it caused the P waves to be upright, not negative like we expected.
Here is another very nice case using Lewis leads: