As a medical professional with expertise in cardiology, I can provide you with a detailed explanation of what a bundle branch block looks like on an ECG. A bundle branch block (BBB) on an ECG is characterized by a delay in the electrical conduction through one of the bundle branches in the heart. This delay causes a specific pattern on the ECG that can be identified by certain features: 1. Prolonged QRS complex: The QRS complex represents the depolarization of the ventricles. In a BBB, the QRS complex is wider than normal, typically greater than 120 milliseconds. 2. Right Bundle Branch Block (RBBB): In the case of a right BBB, you would see a terminal R wave in lead V1 and a slurred S wave in lead I. This is because the right ventricle is delayed in depolarizing, which results in a late positive deflection (R wave) in the chest lead V1. 3. Left Bundle Branch Block (LBBB): For a left BBB, the ECG would show a different pattern. The QRS complex would be even more prolonged, and there would be a deep, wide S wave in lead V1 and a tall, narrow R wave in lead V5 or V6. 4. Electrical Axis: A right BBB may cause a slight shift in the heart's electrical axis to the right, which can be determined by analyzing the QRS complex in the limb leads. 5. Other signs: There may also be secondary changes in the ECG such as ST segment and T wave abnormalities, which are often discordant with the QRS complex in LBBB and concordant in RBBB. It's important to note that the presence of a BBB on an ECG does not necessarily indicate a serious condition, but it can be associated with underlying heart disease or other conditions that affect the electrical conduction system of the heart. read more >>

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.read more >>