This was contributed by one of our fine interns, Aaron Robinson.
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.
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:
A Relatively Narrow Complex Tachycardia at a Rate of 180.
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.
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 |
Learning Points:
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:
Nice case illustrating use of Lewis Leads. That said, I’d emphasize the point brought out by Dr. Smith — namely that, “when you become accustomed to seeing these (retrograde P waves) — you can readily recognize them.” The BEST way to gain experience in doing this is to simply compare the SVT tracing with the post-treatment sinus rhythm tracing. Retrograde P waves during SVT are typically not seen in all leads. As a result, my “go to” leads are: i) the inferior leads (which should show a negative notch if there is retrograde atrial activity); ii) lead aVR (looking for a positive notch); and iii) lead V1 (looking for a positive notch). After looking first in 5 these leads — I’ll then scan remaining leads — but the 5 leads named provide highest yield when seeking out potential retrograde atrial activity. That said, this case is remarkable, because retrograde atrial activity is actually seen in ALL 12 leads during SVT! Comparing the SVT ECG with the subsequent sinus rhythm ECG shows the notching by retrograde atrial activity has disappeared in all 12 leads on the post-treatment tracing — which proves reentry as the mechanism of this SVT. Of note — most cases of AVNRT show a slightly shorter RP’ interval than is seen here (typically <70msec, therefore usually not separate [after] the QRS as the retrograde P wave is here). This may be a clue to a concealed AP (accessory pathway). Although interesting to contemplate — initial management concerns for AVNRT vs orthodromic AVRT are the same. THANKS again to Dr. Smith for presenting this case.
ReplyDeleteHello.. 1)Since RP interval is not typical of AVNRT(Typical/slow fast), can we consider the possibility of atypical AVNRT(Fast slow variety) ?
Delete2)I did not notice a P wave still, but to me looks more like a T wave.
3)Given the rapid rate and low complex voltage and case description, i considered the possibility of pericardial effusion. ☺️
@ M G — Atypical AVNRT ( = “fast-slow” ) has a VERY long RP’ that is more than half of the R-R interval. That is not the case here. Instead, the retrograde activity that I see in all leads of the initial ECG is seen quite early (ie, just after the QRS ends in the beginning part of the ST segment). As to the possibility of pericardial effusion — clinical correlation is needed whenever you see “low voltage”. Although I agree with you that voltage does appear reduced — the initial tracing technically does not even qualify for “low voltage”, since QRS amplitude in all 6 of the limb leads is not ≤5mm (ie, QRS amplitude >5mm in lead II). Remember that if you took ALL patients who have “low voltage” — the overwhelming majority will not have pericardial effusion. Many will have COPD, large body habitus or “just because” — so awareness of when pericardial effusion is likely becomes a key part of your evaluation.
DeleteKenneth Grauer
Delete9:49 PM (10 hours ago)
to me
Hi Steve. I just submitted a reply to MG on your blog.
This is what I wrote:
———
@ M G — Atypical AVNRT ( = “fast-slow” ) has a VERY long RP’ that is more than half of the R-R interval. That is not the case here. Instead, the retrograde activity that I see in all leads of the initial ECG is seen quite early (ie, just after the QRS ends in the beginning part of the ST segment). As to the possibility of pericardial effusion — clinical correlation is needed whenever you see “low voltage”. Although I agree with you that voltage does appear reduced — the initial tracing technically does not even qualify for “low voltage”, since QRS amplitude in all 6 of the limb leads is not ≤5mm (ie, QRS amplitude >5mm in lead II). Remember that if you took ALL patients who have “low voltage” — the overwhelming majority will not have pericardial effusion. Many will have COPD, large body habitus or “just because” — so awareness of when pericardial effusion is likely becomes a key part of your evaluation.
Perhaps this saves you having to answer — :)
Thanks, Ken!
ReplyDeleteWhat is the best position for lewis leads? The one described here, coming from emcrit/Watford cites two articles that actually position leads differently. Right arm lead to second intercostal space, right of sternum. Left arm to 4th ics, right of sternum. So any thoughts about which is the best lead position to enhance visualisation of atrial activity?
ReplyDeleteDominic,
DeleteI really don't know, but the way Christopher does it is what I do and it has worked well for me.
STeve
An excellently written article, if only all blogger offered the same level of content as you, the internet would be a much better place. Please keep it up!. Great tips, I would like to join your blog anyway. Waiting for some more review. Thank you
ReplyDeleteSlow slow avnrt with retrograde p waves in St t segment.
ReplyDelete