This is an interesting teaching ECG on many levels. It is obtained from a man with chest pain. No other history or follow up is available.
Acute M.I. Most striking is probably the clearly-seen anterior-septal wall M.I. There is ST segment elevation in Leads V1, V2, and V3, with ST depression in the low-lateral leads, V5 and V6. There is also ST depression in the inferior Leads II, III, and aVF. The ST elevations have a coved-upward (frown) shape in V1 and a straight shape in V2 and V3. Both of these ST shapes are abnormal and reflect injury. The depressions are presumed to be due to reciprocal changes, since there is no other ST-depression producing condition apparent. There are abnormal Q waves in V1, which could herald the onset of pathological Q waves, a sign of necrosis, in the anterior-septal wall.
Atrial Fibrillation Another very noticeable feature of this ECG is the irregularly-irregular rhythm, with an absence of P waves. This is atrial fibrillation with a controlled ventricular response. This rate of 72 bpm suggests that the rate has been controlled with medication or that the M.I. has slowed the conduction through the AV node. A fib is significant for this patient because the absence of P waves lowers cardiac output. It is more important than ever to keep this patient’s rate controlled, as a fast rate would combine with loss of atrial kick to lower cardiac output and increase myocardial demand – not a good situation for an M.I. patient.
Incomplete Right Bundle Branch Block The shape of the QRS in V1 and V2 is not typical. Those leads should have an rS pattern. The qR in V1 and rSR’ in V2 remind one of the right bundle branch block pattern, but the QRS is not wide. Leads I and V6 have narrow s waves, as well. This is called “incomplete right bundle branch block”.
FLB (Funny-looking Beat) The seventh beat in the strip, marked with an arrow, is different in appearance from all the others. This probably represents aberrant conduction. Usually aberrantly-conducted beats have wide QRS complexes, and this one does not. This different beat ends a short R-to-R cycle which followed a long R-to-R cycle. The refractory period is proportional to the R-to-R interval, becoming longer after a long cycle and shorter after a short cycle. When a long R-to-R interval occurs, the refractory period is lengthened in the next cycle. If that cycle has a short R-to-R, the beat ending the short cycle is more likely to fall into the refractory or relative refractory period. It is interesting, but probably not clinically significant.
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