ECG Review
ECG Review
Premature Ischemia?
By Ken Grauer, MD, Professor, Assistant Director, Family Practice Residency Program, University of Florida. Dr. Grauer reports no financial relationship to this field of study.
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Figure. 12-lead ECG obtained from a 57-year-old man with intermittent episodes of atypical chest discomfort. |
Clinical Scenario: The 12-lead ECG in the Figure was obtained from a 57-year-old man who presented with intermittent episodes of atypical chest pain, most often of short duration. The tracing was interpreted as showing PVCs, but without acute changes. What two amendments to this interpretation should be made?
Interpretation/Answer: Although no single lead rhythm strip is shown, the underlying rhythm in this tracing appears to be of sinus origin, since upright P waves with a constant PR interval are seen for the first 2 beats in lead II. Thereafter, there is obvious irregularity. The third beat in lead II (labeled #3) occurs early and is widened, however it is not a PVC. Instead, a "telltale" notched premature P wave is seen to precede beat #3, identifying this beat as a PAC (premature atrial contraction). QRS widening is the result of aberrant conduction.Consecutive beats have been labeled in the figure under the middle row of complexes (ie, in leads II, aVL, V2, and V5). Following beat #3, the pattern of an early, widened beat is again seen for beats #7 and 11. Although a longer rhythm strip would be needed for confirmation, it appears that a pattern of "quadrigeminy" is present. It is likely that each of the premature, widened complexes (ie, beats #3, 7, and 11) are PACs conducted with aberration. We say this because two of these complexes are clearly preceded by premature P waves (beats #3 and 11), and QRS morphology for each of the widened complexes in the various leads is consistent with a RBBB (right bundle branch block) and LAHB (left anterior hemiblock) pattern. QRS morphology for aberrantly conducted premature beats most often manifests some pattern of bundle branch block, reflecting the fact that a PAC arrives at the AV node at an early enough point in time when a portion of the ventricular conduction system has not yet recovered. Thus, the wide terminal S wave seen in the early beats shown in leads I and V6, in conjunction with the tall widened qR pattern seen in lead V1 is consistent with RBBB morphology; and the deep negative S wave in lead II is consistent with LAHB. The rhythm in this tracing is therefore atrial quadrigeminy (ie, every fourth beat is a PAC), with QRS widening due to aberrant conduction (in which widened beats manifest a bifascicular block pattern of RBBB with LAHB).
The second important finding to note on this tracing is the ST-T wave change seen in the lateral precordial leads. Interpretation of ST-T wave changes is often a challenging task when a 12-lead ECG is marked by frequent ectopy. One needs to avoid using the ST segments not only of the premature widened beats, but also of normally conducted beats that immediately precede widened complexes, since the PACs may distort the ST segments of these normally conducted beats. We therefore focus our attention on the ST segments of beats #1, 4, 5, 8, 9, and 12 in this figure. Subtle but definite shallow symmetric T wave inversion is seen in leads V4-6. In view of the history of chest discomfort, these lateral precordial ST-T wave changes may reflect ischemia.
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