ECG Interpretation Review - #26 (Regular SVT - Diffuse ST Depression - List #4)

Interpret the ECG below, obtained from an older woman on multiple drugs who presented to the emergency department.  She was complaining of chest pain, and clinically was in heart failure.  How would you interpret her 12-lead tracing?  Why so much ST segment depression?  Clinically — What would you do?

Figure 1 – 12-lead ECG from a patient with chest pain and heart failure.  What is the rhythm?  Why so much ST depression?

INTERPRETATION:  The rhythm is rapid and regular at a rate of ~180/minute.  The QRS complex is narrow in all 12 leads.  This defines the rhythm as a SupraVentricular Tachycardia (SVT ).  No definite P waves are seen.  It is impossible to know IF the small upright deflection midway between QRS complexes in lead II represents a P wave, T wave, or both.  This leaves us with the differential diagnosis of a regular SVT without definite sign of atrial activity (See below).

• Otherwise — the rate is too fast for assessment of the QT interval to be meaningful; voltage criteria for LVH are easily satisfied (very deep S in V1 plus tall R in V5 easily exceeding 35 mm); and there is diffuse ST depression that exceeds 2-3 mm in many leads.

CLINICAL IMPRESSION:    

The RHYTHM:  As discussed in ECG Review #25 — 3 entities should be considered in the differential diagnosis of a regular SVT when atrial activity is uncertain (Table 1):

Table 1 – List of the most common causes of a regular SVT when there is no definite sign of atrial activity.

In this particular case — the rapid rate (ie, ~180/minute) strongly suggests PSVT (Paroxysmal SupraVentricular Tachycardia) as the diagnosis. 

• The most common ventricular response with untreated atrial flutter is with 2:1 AV conduction. Because the atrial rate of flutter is most often very close to 300/minute (250-350/minute range) — the ventricular rate will usually be close to 150/minute (most often between 140-160/minute). The substantially more rapid rate seen in Figure 1 makes atrial flutter unlikely.  
• Similarly — sinus tachycardia in non-exercising adults rarely attains rates in excess of 160-170/minute. By exclusion — PSVT is therefore the likely diagnosis for the regular SVT shown in Figure 1.

Diffuse ST Depression:  Next to the rapid rate — the most remarkable finding in Figure 1 is the deep and diffuse ST segment depression.  Although there are many possible causes of ST depression — we find it helpful to routinely consider the diagnostic entities listed in Table 2:

Table 2 – List of the most common causes of ST segment depression.

It will often not be possible to determine the precise cause(s) of ST depression:

• In the case presented here — the patient has chest pain, heart failure, and is taking multiple medications. The deep and diffuse ST depression seen in Figure 1 may reflect ischemia (she has chest pain); “strain” (increased voltage; history of heart failure); digitalis effect/electrolyte disturbance (diuretics and possibly also digoxin may be among her multiple drugs); tachycardia (PSVT at 180/minute) — or more likely, some combination of all of these factors.

CLINICAL APPROACH:

The first priority in treating this patient is to address her tachycardia.  Clearly — sudden onset of PSVT at 180/minute in an older patient with heart failure may exacerbate her condition.  Chest pain (and ST depression) may result from the associated reduced coronary perfusion or the tachycardia itself.  Both may resolve with conversion to sinus rhythm.  PSVT usually responds promptly to medical treatment (adenosine, diltiazem, a beta-blocker — with or without attempted vagal maneuver).  The patient will undoubtedly be admitted to the hospital to optimize treatment for heart failure.  Follow-up ECGs and serum troponin values after conversion to sinus rhythm will hopefully elucidate whether the deep and diffuse ST depression seen in Figure 1 was the result of a transient phenomenon (associated with her PSVT) or a primary cardiac event.

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  - See also ECG Blog #25.

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