ECG Blog #112 (Sinus Rhythm – Lead II – Nonspecific ST-T Wave Abnormalities

The ECG in Figure-1 was obtained from a 43-year old man who presented to his primary care clinician because he “wasn’t feeling well”. His symptoms suggested an influenza-like syndrome. The ECG was ordered because of some associated and atypical chest discomfort.

• Are you concerned about the ST-T wave changes on this tracing?
• Any other findings of note?

Figure-1: 12-lead ECG and lead II rhythm strip obtained from a 43-year old man with influenza-like illness and atypical chest pain. Are you concerned about ST-T wave changes on this tracing? Other findings of note? 

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ANSWER: The reason we selected this tracing was not because of the ST-T wave changes. Instead, our focus was on the cardiac rhythm. If you did not appreciate anything unusual about the rhythm — Take a 2nd look ... 

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The rhythm is fairly regular at a rate slightly less than 100/minute. There is no P wave visible in lead II. We say this based not only on the 3 beats shown for lead II within the 12-lead ECG, but also on complete lack of atrial activity on any of the 15 beats seen in the long lead II rhythm strip at the bottom of the tracing. Therefore — this is not a sinus rhythm.

• Atrial activity is seen in several other limb leads. That is, small-but-definitely-present upright P waves with a fixed PR interval are seen preceding each QRS in leads I and aVL — and, a small negative P wave precedes each QRS in lead III. Thus, this is a low atrial rhythm.
• Tiny upright P waves are also seen in lead V1 and V2. These would be easy to overlook were it not for the presence of definite atrial activity in leads I,III and aVL.

Regarding the other findings on this tracing:

Intervals: Both QRS duration and the QT interval are normal. Since the rhythm is not sinus — we cannot assess the PR interval (other than to say that it does not appear to be prolonged).

• Axis: Normal (approximately +50 degrees).
• Chamber Enlargement: None.
• Q-R-S-T Changes: No consistent Q waves are seen. Transition may occur slightly early (the QRS complex is equiphasic by lead V2 — and definitely positive by lead V3). There is nonspecific ST-T wave flattening in multiple leads — but nothing that appears to be acute.

IMPRESSION: As stated — the reason this ECG was obtained was the patient’s description of atypical chest discomfort. While ultimate decision-making depends on full clinical assessment of the patient — this ECG should be reassuring in that at least there are no acute changes. The presence of nonspecific ST-T wave abnormalities and a non-sinus (low atrial) rhythm are not pathologic per se — and may simply reflect that the patient was not feeling well with an influenza-like illness. Whether or not to repeat the ECG if the patient’s clinical course is otherwise uneventful — is a determination that can be decided in follow-up.

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KEY Point: Assuming there is no dextrocardia or lead misplacement — IF there is no upright P wave in lead II — then the rhythm is not sinus! For this reason, the very 1st Thing To Do when assessing any 12-lead ECG or rhythm strip — is to look at lead II to see if an upright P wave is (or is not) present. In our experience, failure to do so accounts for the main reason that non-sinus rhythms are sometimes overlooked ...

• Although lead II is typically the best lead for visualizing P waves — there are times when other leads may visualize atrial activity not seen in lead II. In general — anatomic proximity of lead V1 (overlying the atria) makes this lead the 2nd-best for visualizing atrial activity. This is especially true when the rhythm is non-sinus. Leads III and aVR are other leads on a 12-lead tracing that often pick up non-sinus activity that might not be seen in lead II. Bottom Line: If no atrial activity is seen in lead II — Be sure to survey each of the other 11 leads before concluding that no atrial activity is present.

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