What does the presence of a narrow QRS indicate?

The presence of a narrow QRS complex indicates normal conduction through the ventricles. This means that the electrical impulse, which originates in the atria and travels through the bundle of His and into the Purkinje fibers, is transmitted efficiently and quickly through the ventricular myocardium. A narrow QRS typically measures less than 0.12 seconds and reflects that the impulse is conducted along the normal pathway, without delays often associated with conduction blocks or other abnormalities.

In contrast, a wide QRS complex would suggest a delay in conduction, typically due to issues such as bundle branch blocks or other forms of ventricular conduction delay. The other options—conduction through bundle branches or cardiac arrest—relate to different pathological conditions where conduction may be disrupted, leading to prolonged QRS or loss of QRS complexes altogether. However, a narrow QRS reinforces the idea of intact and efficient ventricular conduction.