Progressive Care Nursing Certification (PCCN) Practice Exam

What condition is indicated by a patient showing a sudden widening of the QRS complex?

1. Myocardial ischemia

2. Electrolyte imbalance

3. Left bundle branch block

4. Ventricular hypertrophy

The correct answer is: Left bundle branch block

A sudden widening of the QRS complex indicates a delay in the conduction of electrical impulses through the ventricles. This widening can be attributed to conditions that impact the normal pathway of conduction, such as left bundle branch block. In left bundle branch block, the electrical impulse cannot travel down the left bundle branch of the heart's conduction system; instead, it must go through the right bundle branch and then spread to the left ventricle through different pathways. This altered conduction creates a prolonged QRS duration and can lead to characteristic changes observable on an electrocardiogram. Understanding that the QRS complex represents ventricular depolarization is key here. The normal QRS duration is typically less than 120 milliseconds. When there is a block in one of the bundle branches, this duration exceeds that threshold, becoming wider. Therefore, the condition typically denoted by a sudden widening of the QRS complex in a clinical assessment is indeed associated with left bundle branch block. Conditions like myocardial ischemia, electrolyte imbalance, and ventricular hypertrophy may also cause changes in the ECG but do not specifically lead to a sudden widening of the QRS complex in the same way that a bundle branch block does.