ECG Blog #520 — How Certain are You?

You are asked to interpret the ECG in Figure-1. Which of the following choices provides the best answer?

• A) AFib with a rapid ventricular response.
• B) SVT with RBBB aberration.
• C) The rhythm could be VT.
• D) The rhythm is VT. 

Figure-1: Which of the above choices is the best answer?
= = = = = = =
[ Abbreviations: AFib (Atrial Fibrillation) — SVT (SupraVentricular Tachycardia) — RBBB (Right Bundle Branch Block) — VT (Ventricular Tachycardia)].

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MY Approach to Today's Tracing:

As much as we always want at least a brief history (including at least the age of the patient — and the reason why the ECG was recorded) — we are not provided with one. Nevertheless, there is enough information to select the right answer.

• Take another LOOK at today's tracing in Figure-2. For clarity — I've numbered the beats in the long lead II rhythm strip.

Figure-2: I've numbered the beats in today's tracing.

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MY Thoughts:

By the P's, Q's, 3R Approach (See ECG Blog #185) — the rhythm in Figure-2 is a regular WCT (Wide-Complex Tachycardia):

• The overall rhythm appears to be Regular. This is best assessed in simultaneously recorded leads I and III, in which it is easier to see the consistency in the R-R interval (and more difficult to appreciate in lead II — where there is more artifact distortion).
• The Rate of the rhythm is slightly more than 150/minute (ie, with an R-R interval of slightly less than 2 large boxes in duration).
• The QRS is wide (at least 3 small boxes in duration — therefore ≥0.12 second).
• 
  
• Are there P waves?

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What Can We Already Rule Out?

• The fact that the R-R interval in Figure-2 is regular effectively rules out AFib (and if we can confirm that P waves are truly present — this would definitively rule out AFib).

What We Know:

• The rhythm in Figure-2 is a regular WCT (Wide Complex Tachycardia).
• The rate of the rhythm is slightly more than 150/minute. 
• There is no clear sign of sinus P waves (ie, There is no consistent upright P wave with constant PR interval preceding each QRS complex in the long lead II rhythm strip).
• The above said — a number of small upright deflections in the baseline do appear to be present throughout the long lead II. These could be P waves.
• PEARL #1: Assuming today's patient is an adult — by far, the most common cause of a regular WCT rhythm without clear sign of sinus P waves is VT. Therefore — We need to assume VT until proven otherwise!

PEARL #2: We can go 1 step further in our differential diagnosis by looking at QRS morphology. 

• Although the predominantly upright QRS complex in lead V1, in association with wide terminal S waves in lateral lead V6 could be consistent with RBBB conduction — you should virtually never see an all negative QRS complex in lead I with a supraventricular rhythm. 
• Based on QRS morphology then — this strongly suggests that the rhythm in Figure-2 is VT (which means we can effectively rule out SVT with RBBB aberration). 

QUESTION:

• But — Are we 100% certain that today's rhythm is VT?

  

My Next Thoughts:

At this point in my interpretation — I would estimate the statistical likelihood that the rhythm in today’s case is VT at over 95%! (based on the fact that sinus P waves are absent in this regular WCT rhythm — and the finding that QRS morphology in lead I is all negative). That said — I prefer to increase the accuracy of my interpreatation as much as possible — and — there is a way in today's case that we can increase the statistical likelihood of VT to 100%

• To Emphasize: IF we were at the bedside with this patient — the 1st thing we would do is determine if the patient is hemodynamically stable! That's because if the patient is not stable with this rhythm — then it would no longer matter what the rhythm is, because synchronized cardioversion would then be immediately indicated.
• But assuming that this patient is hemodynamically stable — this gives us a moment in time to quickly look a little closer.
• 
  
• Please NOTE: I have described my above thoughts in slow motion. With practice and experience — You should be able to arrive at this point in the process in no more than 10-to-15 seconds!

The Next Step: So — Are there P waves in Today’s ECG?

Take another LOOK at the ECG in Figure-2.

• Is there an EASY way to determine with certainty whether P waves are (or are not) present in today’s ECG?

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ANSWER: Are there P waves in Today’s ECG?

The KEY to optimizing the accuracy of our interpretation — is to determine IF underlying regular sinus P waves are present!

• PEARL #3: As I have often emphasized in this ECG Blog — the simple step of labeling P waves is incredibly helpful for determining the presence and nature of underlying atrial activity.
• In Figure-3 — I’ve labeled with RED arrows those small upright deflections in the long lead II rhythm strip that look like they may represent P waves.
• If these RED arrows in Figure-3 are in fact highlighting the presence of regular underlying P waves — Does this suggest what the P-P interval might be?
• 
  
• PEARL #4: If we can demonstrate that the small upright deflections in Figure-3 remain consistently regular throughout the long lead II — this would prove that these small upright deflections do represent an underlying rhythm of regular atrial activity. 
• To do this — I look to see what the shortest distance between 2 consecutive RED arrows appears to be. Doesn't it look like this shortest distance repeats between the 4th and 5th RED arrows — and between the 7th and 8th RED arrows?

Figure-3: I've highlighted with RED arrows the small upright deflections in the long lead II rhythm strip that I can clearly see.

PEARL #5: To determine within seconds if an underlying rhythm of regular P waves may be present in the long lead II — You have to use calipers!

• To Emphasize: I am not encouraging the use of calipers if your patient is unstable. A hemodynamically unstable patient in a WCT rhythm should be immediately cardioverted!
• But IF the patient whose rhythm is shown in Figure-3 is hemodynamically stable — it takes no more than seconds using calipers to "walk out" the rhythm that I've highlighted with colored arrows in Figure-4.

Figure-4: I've added WHITE and PINK arrows to Figure-3.

Breaking Down Figure-4: 

All that I've done to get from Figure-3 to Figure-4 — is to set my calipers to the P-P interval suggested by the distance between the 4th and 5th RED arrows in Figure-4 (which equals the distance between the 7th and 8th RED arrows) — and then to "walk out" this presumed P-P interval with your calipers throughout the remainder of the long lead II.

• Although on-time regular wide QRS complexes prevent us from seeing P waves under the WHITE arrows that I've added to Figure-4 — a definite underlying upright deflection can clearly be seen peaking out from the tail end of the QRS of beats #7 and 28 (ie, under each of the 2 PINK arrows).
• This tells us that the colored arrows in Figure-4 represent an underlying rhythm of regular P waves occurring at an atrial rate of ~90/minute!

PEARL #6: The P waves represented by the colored arrows in Figure-4 are unrelated to neighboring QRS complexes. This tells us there is complete AV dissociation occurring throughout the long lead II rhythm strip — which proves that the rhythm is VT!

• In my experience — AV dissociation is very much overdiagnosed! This is because of the tendency to assume there is AV dissociation whenever clinicians see any suggestion of underlying baseline deflections. In my decades of following up on regular WCT rhythms — most cases of WCT rhythms labeled as showing "AV dissociation" do not truly represent this finding.
• It is because true AV dissociation proves that a WCT rhythm is VT — that I feel it best to avoid the diagnosis of AV dissociation unless you can clearly demonstrate the presence of underlying regular P waves throughout a significant portion of the rhythm. Doing so can only be done by use of calipers.
• Unfortunately — the clinical reality is that it is rare to see AV dissociation in faster WCT rhythms. This is because when a WCT occurs at a faster rate — the wide QRS complexes (and accompanying often large-sized ST-T waves) are highly efficient at concealing underlying on-time P waves that are hidden within.
• 
  
• BOTTOM Line: The colored arrows seen in Figure-4 are convincing of AV dissociation — because they consistently occur thoughout the long lead II rhythm strip. This proves beyond doubt that today's WCT rhythm is VT!

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NOTE: For readers wanting more regarding the concepts and clinical use of AV dissociation for assessing the etiology of a regular WCT rhythm — Review of ECG Blog #335 should prove insightful.

• Additional examples of "My Take" on assessing the regular WCT rhythm can be found in ECG Blog #196 — Blog #220 — Blog #263 — and Blog #283 — among many others.

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Today's CASE Continues:

The patient in today's case is a middle-aged man with a history of hypertrophic cardiomyopathy. He was seen for new palpitations that occurred in association with today's presenting rhythm.

• Paramedics on the scene cardioverted the patient. This worked momentarily to restore a normal rhythm — but soon after the WCT rhythm returned.
• IV Amiodarone was started. The patient quickly improved — and vital signs stabilized. 
• At this time — the repeat ECG shown at the bottom of Figure-5 was recorded. 

QUESTIONS:

• How do you interpret the rhythm in the repeat ECG?
• Does ECG #2 support our diagnosis of VT in the initial tracing?

 

Figure-5: The repeat ECG recorded after starting IV Amiodarone. The initial ECG is shown on top (with RED arrows highlighting AV dissociation from the underlying regular sinus P waves). 

The Rhythm in ECG #2:

The repeat ECG ( = the tracing at the bottom of Figure-5) — shows a bigeminal rhythm, in which every-other-beat is a PVC.

• Once again — the KEYs to interpreting the repeat tracing are to: i) Label the P waves in ECG #2; — and, ii) Determine if the P waves in ECG #2 are related to neighboring QRS complexes?

Note the following:

• Regular P waves are seen in the repeat ECG throughout the long lead II rhythm strip ( = RED arrows in the bottom tracing in Figure-6). The rate of these P waves in the repeat tracing is slightly slower than it was in ECG #1.
• Normal sinus rhythm conduction is seen in ECG #2 for all odd-numbered beats — as determined by the fixed PR interval before beats #1,3,5,7,9,11,13,15,17.
• All even-numbered beats in ECG #2 are PVCs. The fact that on-time sinus P waves continue throughout the long lead II rhythm strip in this repeat tracing proves that beats #2,4,6,8,10,12,14,16 are PVCs — as is shown in the laddergram in Figure-7 ( = the only way for on-time sinus P waves to continue uninterrupted in Figure-7 — is for the even-numbered beats to originate from the ventricles, with retrograde conduction of these PVCs not reaching all the way back to the atria).
• Finally — Note that QRS morphology of the premature wide beats in ECG #2 is identical to QRS morphology in each of the 12 leads of the initial ECG (thereby confirming our diagnosis of VT for ECG #1).

Figure-6: I've labeled P waves in the repeat ECG.

 

Figure-7: Laddergram of the repeat ECG.

CASE Conclusion:

• The paramedic team transported the patient to the hospital. Referral was made to EP cardiology for consideration of an ICD (Implantable Cardioverter-Defibrillator).

 

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Acknowledgment: My appreciation to Konstantin Тихонов (from Moscow, Russia) for the case and this tracing.

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