Case 5: A 75 year old woman is seen in the emergency room because of progressive dyspnea over a period of three days...
A 75 year old woman is seen in the emergency room because of progressive dyspnea over a period of three days. Her examination confirms the presence of congestive heart failure with bilateral crackles, elevated jugular venous pressure and bilateral 1+ edema.
1. What is the basic rhythm in this patient?
2. Is there evidence of anterior myocardial infarction?
Rhythm in this patient is Atrial Fibrillation and her abnormal ECG pattern is due to a ventricular pacemaker which usually (but not always) obscures the changes of myocardial infarction.
The course oscillations on the baseline as noted to the left are fibrillation waves. They are too rapid and too variable in morphology to qualify for atrial flutter, and no consistent flutter waves are seen in the other leads, particularly leads II, III, and aVF.
Fibrillation waves can be very large as in the case in this patient or so small that they are not identifiable with certainty at all. When atrial fibrillation is chronic and has been present for a long time, there is often a tendency for the fibrillation waves to be smaller and more rapid.
If you look carefully a pacemaker artifact is visible particularly in leads III and aVF but also in V4, V5, and V6 (note the arrows). Pacemaker spikes are often not visible in all leads because their spatial orientation with respect to any particular lead field will vary , making them invisible in certain leads. Notice, however, that the rhythm is absolutely regular which would be most unusual (though not impossible) if this were just atrial fibrillation with no superimposed pacemaker.
The ventricular complexes in I and aVL look for all the world like complete left bundle branch block. This is because the pacemaker catheter is in the right ventricle so activation of that chamber occurs first as would be the case with block of the left bundle branch for whatever reason. Pacing from the right ventricle which is the most common situation, usually produces a left bundle branch pattern. It also produces changes in the chest leads which can be mistaken as anterior myocardial infarction. Note the very small R waves and deep S waves in V3 and V4. These patterns sometimes referred to as "pseudo left bundle branch block" or "pseudo infarction" are caused by the paced rhythm.
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