ECG Blog #25 — Regular SVT and ST Depression

Interpret the 12-lead ECG shown below, obtained from a woman with sensation of “rapid heart beat”.  What is your differential diagnosis?  What diagnostic maneuver might help to determine what the rhythm is?

• Additional Questions: 1) Which leads are most helpful to assess for atrial activity?  2) Do you see atrial activity in all leads on this 12-lead tracing?  3) Do you need to be sure of the rhythm diagnosis before initiating treatment?

Figure 1 – 12-lead ECG from a patient with “rapid heart beat”.  What is your differential diagnosis?  What might you do diagnostically? 

INTERPRETATION:  Our preference is to always obtain a lead II Rhythm Strip whenever a question arises as to rhythm diagnosis.  This is shown in Figure 2.

Figure 2 – Lead II rhythm strip from the patient with tachycardia in Figure 1.  What is your differential diagnosis? 

The rhythm is regular at a ventricular rate that is close to 150/minute (the R-R interval is approximately 2 large boxes in duration — and 300 ÷ 2 = 150/minute).  The QRS complex is narrow (ie, not more than half a large box).  Normal atrial activity is absent, since upright P waves are not seen in lead II.  Instead, there is a suggestion of atrial activity having a negative deflection in lead II (as well as in other inferior leads).  There also appears to be a negative notching in the ST segment in each of the inferior leads.  Could this all represent atrial activity?

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Application of a Diagnostic Maneuver: 

The answer to the question of whether atrial activity is embedded within the 12‑lead tracing is forthcoming from application of a vagal maneuver.  Carotid Sinus Pressure (CSP) is applied at the moment marked by the large arrow in Figure 3. 

• Note shortly after application of CSP — there is reduction in the conduction ratio of impulses passing through the AV Node.  This produces a short pause — during which the typical sawtooth pattern of Atrial Flutter can be readily recognized. 

Figure 3 – Lead II rhythm strip showing the result of CSP, which reveals regular sawtooth flutter waves.

DISCUSSION:  A number of important points are brought out by this case.

• We often do not know definitive diagnosis of the rhythm at the time the patient presents.  This need not hinder our approach to treatment.  First priority in the assessment of any tachycardia is to ensure hemodynamic stability.  Although not explicitly stated in this case (we are not told the patient’s blood pressure) — We may presume the patient is stable because the presenting symptom is “rapid heart beat”.  IF the patient was hemodynamically unstable as a result of the rapid rate (ie, with chest pain, shortness of breath, mental confusion, hypotension) — then regardless of what the rhythm turns out to be, immediate synchronized cardioversion would be indicated.
• Given that this patient is stable — We have time to better assess the rhythm.   Use of a 12‑lead ECG during tachycardia is extremely helpful in this regard.  Next to lead II — lead V1 (which lies in proximity anatomically to the right atrium) is usually the next best lead to look at for atrial activity.  After leads II and V1 — we then direct our attention to all 10 of the remaining leads for clues to atrial activity.  Doing so in Figure 1 — we see suggestion of sawtooth activity in leads II, III, aVF, aVR, and V1 — but no sign of atrial activity in most of the other leads.  The 12‑lead tracing also confirms that the QRS complex is truly narrow in all 12 leads.
• The best description of the tachycardia defined by the rhythm in Figures 1 and 2 is that this represents a regular SVT (SupraVentricular Tachycardia) without sign of normal atrial activity.  This description should prompt consideration of the 3 entities shown in Table 1 as the likely cause of the tachycardia:

Table 1 – List of the 3 most common causes of a regular SVT when normal atrial activity is not seen.

• Practically speaking — 90-to-95% of the regular SVTs that primary care clinicians encounter (in and out of the hospital) will be one of the 3 entities on this list.  Clearly — other causes exist (junctional tachycardia, ectopic atrial rhythms, accessory pathway reentry tachycardias, etc.) — but keeping in mind these 3 entities will simplify and facilitate diagnosis in the majority of cases.
• Heart rate may help in distinguishing between the 3 entities in List #1 — IF the rate exceeds 170/minute in an adult.  This is because it is unusual for a nonexercising adult to be in sinus tachycardia at rates above 170/minute.  Atrial flutter with 2:1 AV conduction is also unlikely when the ventricular rate exceeds 170/minute, since the atrial rate of untreated flutter is rarely faster than 340/minute in adults.  However — when the rate of a regular SVT is approximately 150/minute (as it is in Figures 1,2) — any of the 3 entities in Table 1 may be the cause.
• We suspect the rhythm in Figures 1,2 is not sinus tachycardia, because we do not see an upright P wave in lead II.  Application of a vagal maneuver resolves the issue (Figure 3) — as it brings out flutter waves that had been partially hidden within the QRST complex in Figure 1.
• Although not essential for our initial approach to this patient — knowing definitive diagnosis facilitates treatment.  Use of an AV-Nodal-slowing drug (ie, diltiazem, a beta-blocker) now becomes appropriate at this point. Synchronized cardioversion might ultimately be needed if medical treatment does not convert the rhythm.

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  - See also ECG Blogs #23 and #24 -
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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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