ECG Challenge: A 63-year-old woman without any known heart disease, but with a history of osteoarthritis, diabetes mellitus (using oral hypoglycemic agents), and mild chronic obstructive pulmonary disease, presents to her primary care physician for a follow-up. As part of the examination an ECG is obtained (ECG A). It is compared with her previous ECG obtained 1 month before (ECG B) when she was seen in the emergency department with pneumonia.
ECG A shows a regular rhythm at a rate of 90 bpm. There is a P wave before each QRS complex (+) with a stable PR interval (0.20 s). The P wave is positive in leads I, II, aVF, and V4 through V6. Hence, this is a normal sinus rhythm. The QRS complex duration is increased (0.14 s) and there is a left bundle-branch block morphology with a QS complex in lead V1 (→) and a broad R wave in leads I and V6 (←). The axis is about –30° (positive QRS complex in lead I, negative QRS complex in lead aVF, and biphasic complex in lead II). The QT/QTc intervals are prolonged (400/490 ms) but are normal when the prolonged QRS complex duration is considered (360/440 ms).
ECG B shows a regular rhythm at a rate of 80 bpm. There is a P wave before each QRS complex (+) with a stable PR interval (0.20 s). The P wave is positive in leads I, II, aVF, and V4 through V6. Hence, this is a normal sinus rhythm. The P-wave morphology and PR interval are the same as in ECG A. The QRS complex duration is increased (0.14 s) and the morphology is that of a right bundle-branch block with an RSR′ complex in lead V1 (→) and a broad terminal S wave in leads I, V5, and V6 (←). The axis is rightward between +90° and +180° (negative QRS complex in lead I even when the terminal S wave is considered and positive in lead aVF). There are multiple causes for a rightward axis including:
Right ventricular hypertrophy which cannot be established in the presence of a right bundle-branch block;
R-L arm lead switch in which there are negative P and T waves in leads I and aVL and positive P and T in lead aVR;
Dextrocardia which has the appearance of R-L arm lead switch and also reverse R-wave progression across the precordium;
Wolff-Parkinson-White with a short PR interval and a delta wave;
Old lateral wall myocardial infarction with a deep Q wave in leads I and aVL;
A left posterior fascicular block, which is a diagnosis of exclusion (ie, it is established only if other reasons for a rightward axis are excluded).
In this case, there other causes for a rightward axis that can be excluded and, hence, this is a left posterior fascicular block. Along with the right bundle-branch block, this represents bifascicular disease or block. The second QRS complex (*) is premature, has a different morphology, and is not preceded by a P wave. Hence, this is a premature ventricular complex. The presence of both a left bundle-branch block and a right bundle-branch block (with a left posterior fascicular block) on subsequent ECGs is termed bilateral bundle-branch block and it is a manifestation of trifascicular disease.
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- © 2015 American Heart Association, Inc.