ECG Challenge: A 75-year-old man has a history of hypertension associated with left ventricular hypertrophy and also coronary artery disease. He has not undergone any previous intervention but has chronic stable angina. He presents to his cardiologist for a routine follow-up. He has no complaints. His physical examination is normal. As part of his visit an ECG is obtained.
There is a regular rhythm at a rate of 60 beats per minute. The QRS complexes have 2 different morphologies. The first 3 QRS complexes are wide (0.12 sec) and have a right bundle-branch block morphology with an RSR’ complex in lead V1 (←) and a terminal S wave in leads I and V5 (↑). The axis of these QRS complexes is extremely leftward between −30° and −90° (positive QRS complex in lead I and negative QRS complex in leads II and aVF). This left axis may be attributable to either an old inferior wall myocardial infarction in which the negative complex is the result of a deep Q wave in leads II and aVF, or a left anterior fascicular block in which there is an rS morphology in leads II and aVF. Hence this is a left anterior fascicular block. Along with the right bundle-branch block this indicates bifascicular block or disease. The next 6 complexes are also wide (0.12 sec) but they have a left bundle-branch block morphology with a QS complex in lead V1 (→) and a broad R wave in lead V5-V6 (↓). Because there is an underlying sinus rhythm with a stable rhythm and rate, this reflects the presence of conduction abnormalities effecting both bundle branches and it has been termed bibundle-branch block, a manifestation of trifascicular disease. The QT/QTc intervals are normal (400/400 ms). There is a P wave before each QRS complex and it is positive in leads I, II, aVF, and V4–V6. Hence there is a normal sinus rhythm. However, the PR intervals are not constant. The QRS complex with a right bundle-branch block has a longer PR interval (0.24 sec; └┘) compared with the PR interval of 0.20 sec (↔) associated with the QRS complex that has a left bundle-branch block. The likely explanation is that conduction through only the left bundle (which occurs when there is a right bundle-branch block) is slower than conduction through only the right bundle (which occurs when there is a left bundle-branch block).
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- © 2015 American Heart Association, Inc.