ECG Interpretation Review - #24 (Wide Tachycardia - WCT - VT vs SVT vs Flutter)

The lead II rhythm strip shown below was obtained from a patient admitted to the Emergency Department. Interpret the rhythm. How certain are you of your answer?  What would you do?

• Scenario #1:  The patient is unresponsive with a BP = 60 palpable.
• Scenario #2:  The patient is alert and asymptomatic.  BP = 120/80 mmHg.

Figure 1 – Lead II rhythm strip showing tachycardia. What to do?

INTERPRETATION:  The rhythm is fast and fairly (but not completely) regular. The QRS looks to be wide (ie, more than half a large box) and there are no definite P waves.  Thus, this appears to be a WCT (Wide Complex Tachycardia) of uncertain etiology.  As to the question of What To Do? — the answer depends on the clinical scenario. 

• IF the patient is unstable (Scenario #1) — immediately cardiovert.  Regardless of whether the rhythm is VT or SVT with bundle branch block or aberrant conduction — hemodynamic instability is an indication for immediate cardioversion.  
• On the other hand — IF the patient is stable (Scenario #2) — then by definition, you have at least some time to contemplate treatment (while you work to determine the rhythm). We would obtain more history (previous episodes of WCT?) — look for prior tracings on the patient (either on telemetry or from the patient’s chart) — and get a 12‑lead ECG during tachycardia (Figure 2). 

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The 12-lead ECG during tachycardia is shown below (Figure 2):

Figure 2 – 12-lead ECG obtained during tachycardia. Does this help with your answer?  

12-Lead Analysis:  The rhythm is rapid and looks to be regular (albeit with occasional minor variation in the R-R interval).  The rate is ~150/minute (the R-R is ~2 large boxes in duration).

• The QRS is wide (clearly more than half a large box in leads II,III,V3,V4).  That said — overall QRS morphology looks to be supraventricular (in the form of LAHB with LVH and “strain”).
• “Normal atrial activity” is absent in Figure 2 (RED arrow showing no upright P in lead II). 
  

Beyond-the-Core:  One wonders if the RED arrow and negative deflections before the QRS in the inferior leads might represent some form of atrial activity … (Figure 3):

Figure 3 – Short vertical lines have been added to Figure 2 highlighting what might represent underlying atrial activity (See Figure 4).

IMPRESSION (What to do?): This case illustrates the importance of the clinical situation in the approach to this patient.  Whereas immediate cardioversion would be indicated if the rhythm in Figure 1 was associated with hemodynamic instability — additional diagnostic assessment would be appropriate IF the patient is stable (Scenario #2).  Clearly — sometimes “ya just gotta be there” to know which approach is best for an individual patient.  Our Hunch (based on Figures 1,2,3) — is that the rhythm is supraventricular.

• Slight QRS widening (~0.1-0.2 msec) may be seen with both LVH (it takes longer to get through a thicker ventricle) and with LAHB (conduction is delayed through the left hemifascicle).  Thus — QRS widening (as seen in Figure 2) may occur IF there is both LVH and LAHB. 

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To PROVE Our Hunch:

• Find a prior ECG on this patient.  See IF QRS morphology in the past (during sinus rhythm) is the same as on the Figure 2 12-lead obtained during tachycardia (which shows LAHB; LVH with strain). 
• Get more History (prior episodes of WCT that look like Figure 2? ) 
• Consider a vagal maneuver or “chemical Valsalva” (ie, administration of IV adenosine, which may produce similar effect as carotid massage). 
• Treatment will clearly be more effective IF we can be sure of the diagnosis — BUT — IF at any time during the process the patient becomes unstable — Be ready to immediately cardiovert! 
  

Chemical Valsalva in the form of an IV bolus of adenosine was attempted.  The result is shown below (Figure 4).

Figure 4 – Result of “chemical Valsalva”. What does this prove?

Result of “Chemical Valsalva”:  Administration of IV adenosine results in reduced AV conduction with slowing of the ventricular response (RED arrow).  This reveals underlying flutter activity at an atrial rate of ~300/minute (sawtooth flutter waves occurring approximately each large box).  

• Retrospective review of the 12-lead ECG during tachycardia suggests that the negative deflections previously noted in the inferior leads (and to a lesser extent in lead aVR) were in fact flutter waves (short vertical RED lines in Figure 3).
  

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KEY Points in this Case:

The 2 scenarios proposed in this case illustrate how to clinically work though assessment and management of a patient with WCT of uncertain etiology.

• Always presume VT until proven otherwise.  Immediate cardioversion is indicated if the patient is unstable.  BUT — IF the patient is stable, there is at least some time to work through the diagnosis.
• Treatment will be much more effective (and you as clinician will be more confident) — IF you are able to determine what the WCT actually is.  In this case — Knowing that the rhythm in Figure 1 is atrial flutter with 2:1 AV conduction and QRS widening from LVH/LAHB allows us to treat the patient with IV diltiazem (bolus and drip) — whereas diltiazem would be contraindicated if the rhythm was an ischemic form of VT.
• BOTTOM Line: You will not always know the etiology of a tachycardia at the time you first encounter the patient.  No matter — as you can still proceed with an appropriate clinical approach as outlined above.  

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  - See also ECG Blog #23 - 

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