ECG changes in Bundle Branch Blocks and Ventricular Hypertrophy

Posted by e-Medical PPT Saturday, July 17, 2010
Electrical impulse of the heart begins in the SA node and then travels next through the left and right atria and summates at the atrioventricular node. From the AV node the electrical impulse travels down the Bundle of His and divides into the right and left bundle branches. The right bundle branch contains one fascicle. The left bundle branch subdivides into two fascicles: the left anterior fascicle and the left posterior fascicle. Ultimately, the fascicles divide into millions of Purkinje fibres which in turn interdigitise with individual cardiac myocytes, allowing for rapid, coordinated, and synchronous physiologic depolarization of the ventricles.
Bundle branch block can be diagnosed when the duration of the QRS complex is more than 120 ms. A right bundle branch block typically causes prolongation of the last part of the QRS complex, and may shift the heart's electrical axis slightly to the right. The ECG will show a terminal R wave in lead V1 and a slurred S wave in lead I. Left bundle branch block widens the entire QRS, and in most cases shifts the heart's electrical axis to the left. The ECG will show a QS or rS complex in lead V1 and a monophasic R wave in lead I. Another normal finding with bundle branch block is appropriate T wave discordance.

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