ECG Review

Those First 4 Beats

By Ken Grauer, MD

Figure. 12-lead ECG obtained from a 70-year-old woman with heart failure.

Clinical Scenario: The ECG in the Figure was obtained from a 70-year-old woman in heart failure. There are at least 6 findings that we feel are worthy of mention. Can you identify them? Clinically, what is your concern?

Interpretation/Answer: As suggested by the title of this ECG review, the tracing is most interesting in the way it begins. The underlying rhythm is sinus at a rate of about 100/minute [Finding #1 = sinus tachycardia]. There is initial irregularity in the rhythm, which is obvious from the longer R-R interval between beats #1 and 2, but not so obvious at the point of lead change between leads I, II, III and aVR, aVL, and aVF. Without seeing what occurred before, it is impossible to be sure about beat #1. However, we suspect this complex is supraventricular because the QRS is narrow and preceded by a P wave. The P wave preceding this beat looks to be different however, from the P wave preceding beats #2 and 3 in lead II. Slight variation in QRS morphology of beat #1 compared to the QRS morphology of beats #2 and 3 suggests that this first beat looks different because of aberrant conduction. Notching in the early part of the ST segment of beat #1 is probably the result of a blocked PAC (premature atrial contraction), which accounts for the relative pause between beats #1 and 2. Regular sinus P waves are seen for the rest of the tracing. Though partially hidden by the lead change, the PR interval preceding beat #4 is clearly short. We suspect that beat #4 is a fusion beat (near simultaneous occurrence of a PVC [premature ventricular contraction] with a sinus complex).

Additional findings on this 12-lead ECG are leftward axis (of about -20°), persistent S waves across the precordial leads, and non-specific but fairly diffuse ST-T wave flattening/depression. These ST-T wave changes could be from the relatively rapid underlying rate, drug or electrolye effect, left ventricular "strain" (even though voltage for LVH [left ventricular hypertrophy] is lacking), ischemia - or any combination of the above. Given the patient's presentation in heart failure, clinical correlation is essential.