What indicates a bundle branch block?

• A. Narrow QRS complex
• B. Presence of the P wave
• C. Wide QRS complex
• D. Irregular heart rate

Answer: (C)

A bundle branch block is characterized by a delay or obstruction in the electrical conduction pathways that lead to the ventricles of the heart. This is reflected in an abnormal widening of the QRS complex on an electrocardiogram (ECG). The normal QRS duration is typically less than 120 milliseconds, while in the presence of a bundle branch block, the QRS complex is prolonged, generally exceeding 120 milliseconds.

The widening occurs because the depolarization of the ventricles takes longer than usual, as one of the bundle branches is blocked or delayed. This results in a slower transmission of the electrical impulse through the affected bundle branch, causing the ventricles to contract asynchronously.

This makes the presence of a wide QRS complex a key indicator of a bundle branch block, as it reveals that there is a disruption in the normal electrical conduction pathway in the heart. Other options do not serve as indicators of bundle branch block. A narrow QRS complex would not suggest any conduction delay, while the presence of a P wave indicates atrial activity rather than ventricular conduction issues. An irregular heart rate can arise from various cardiac conditions but is not specific to bundle branch block.