Monday, December 20, 2010

ECG Interpretation Review - #6 (Chest Pain, Subtle ECG Changes)

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QUESTION: Interpret the 12-lead ECG below, obtained from a 45 year old man who presented to the ED with new-onset chest discomfort.  He had been previously healthy.  Risk factors include a history of smoking.  No prior ECG available.
  • How would you interpret his ECG?  - Any potentially worrisome ECG findings?
  • Clinically - What would you do?
Figure 1 (ECG reproduced from our Expanded ECG pdf File)
Note - Enlarge by clicking on Figures -
INTERPRETATION:  The rhythm is sinus arrhythmia at a rate between 55-65/minute. All intervals (PR, QRS, QT) are normal.  The mean QRS axis is normal (about +80-85 degrees). There is no chamber enlargement.
  •  Q-R-S-T Changes:  - Small and narrow q waves are seen in a number of leads (II, III, aVF and V6) - and a deep Q wave (QS complex) is seen in lead aVL. Transition occurs normally (between leads V3-to-V4). T waves are somewhat peaked in several leads.  There is a hint of ST segment flattening (in leads II, III, aVF - as well as in lead aVL and V6).  There is isolated symmetric T wave inversion in lead aVL.
CLINICAL IMPRESSION:  Sinus arrhythmia.  Small inferior q waves, and a QS in lead aVL of uncertain significance.  Small q in V6. Isolated symmetric T wave inversion in aVL.  T wave peaking, and subtle ST segment flattening in several leads.  These changes are probably not acute - but strongly suggest clinical correlation (See Comment below).
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COMMENT:  - In view of the worrisome history (this 45-year-old man presents to the ED with new-onset chest discomfort) - there are 4 ECG findings that should at least be noted and addressed:
  1. Small and narrow q waves are seen in a number of leads. Small and narrow q waves are commonly seen as a normal finding in one or more of the lateral leads (I,aVL,V4,V5,V6). This reflects the process of septal activation, which normally moves from left-to-right.  Thus, the q wave in lead V6 is almost certainly a normal septal q wave.  There are also small and narrow inferior q waves (in leads II,III,aVF).  On occasion - inferior q waves may also be a normal finding IF seen in association with a relatively vertical QRS axis (as is the case here) and in the absence of other acute findings.
  2. In lead aVL - there is a deep Q wave (QS complex) and shallow but symmetric T wave inversion.  However, as an isolated finding - neither the deep Q wave nor the symmetric T inversion are necessarily abnormal in this lead (See Figure 4 in ECG Review #9).
  3. T waves are peaked in several leads in Figure 1 (in leads II,III,aVF,V4,V5,V6).  Although some T wave peaking may be a normal finding - this should be noted. The presence of T wave peaking always brings up the possibility of hyperkalemia as a cause - although there is nothing else in the clinical scenario given here to suggest hyperkalemia (no mention of renal disease, acidosis, or potassium-retaining drugs).  T wave peaking may also be due to ischemia on occasion (which could be relevant given the history of chest discomfort in this patient . . . ).
  4. There is subtle but real flattening of the ST segment in several leads in Figure 1 (leads II,III,aVF,aVL,V6).
BOTTOM Line:  The history in this case is worrisome (a 45-year-old man who presents to the ED with new-onset chest discomfort) - and - a number of findings have been noted in our Descriptive Analysis of his initial ECG (above).  That said - we suspect that nothing acute is going on because the changes that are noted are subtle and not necessarily outside the range of normal.  That said - we can not tell for sure that nothing acute is going on based on this single tracing.
  • The clinical reality is that you will often not be able to tell for sure if acute infarction is occurring from assessment of a single ECG.
  • Clinically - A worrisome history by itself is more than enough to justify admission to the hospital to rule out acute infarction.  In the absence of a prior ECG for comparison - we would definitely admit this patient with chest discomfort to the hospital.  Even IF we had a prior ECG that looked identical to this one - IF the history was of concern, that alone would justify admission to the hospital.
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2 comments:

  1. What is the significance of ST segment flattening? I understand it must be clinically coordinated, but theoretically what could this imply?

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  2. Good question Andrew. There are many potential causes of ST-T wave flattening. To me - the principal significance of recognizing that ST-T waves in leads like II,III,aVF and V6 in this tracing are distinctly straight with abrupt transition from ST segment-to-T wave - is that it tells me the ST segments are not "normal". Coronary disease (ischemia) may clearly cause such flattening. Other factors (drugs, electrolyte disturbance, hyperventilation, etc.) may also cause such flattening - however the ST-T wave straightening that we see here occurs in the context of a previously healthy 45 yo who presents with new-onset chest discomfort. In this context - ischemia/coronary disease move to the forefront of conditions that should be excluded.

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