**Core Concept**
Ventricular tachycardia (VT) is a life-threatening arrhythmia characterized by a rapid heart rate originating from the ventricles. It often presents as a broad-complex tachycardia, which is a key feature used in electrocardiogram (ECG) interpretation. The correct identification of VT is crucial for timely management, as it may require urgent electrical cardioversion or other interventions.

**Why the Correct Answer is Right**
The correct answer, **C. Very broad QRS complexes**, is incorrect because VT typically presents with a broad QRS complex, but not always very broad. The QRS duration in VT is usually greater than 120 milliseconds but not excessively broad. This is in contrast to polymorphic VT, where the QRS complexes are often very broad and irregular. **Option C** suggests a feature that is characteristic of VT, but not exclusive to it.

**Why Each Wrong Option is Incorrect**
**Option A:** Fusion beats are actually a feature of ventricular tachycardia, particularly in the context of a reentrant circuit. They occur when the ventricular and supraventricular impulses collide, resulting in a beat that is a mixture of both. Fusion beats are a key diagnostic feature of VT.
**Option B:** Extreme left axis deviation can be seen in various conditions, including ventricular tachycardia. This feature is not exclusive to VT and can be found in other arrhythmias or structural heart diseases.
**Option D:** Response to carotid sinus massage is a feature of VT, as it can sometimes terminate the arrhythmia.

**Clinical Pearl / High-Yield Fact**
VT often masquerades as supraventricular tachycardia (SVT) in the early stages, making it essential to perform a thorough ECG analysis, including the assessment of QRS duration, morphology, and the presence of fusion beats. A high index of suspicion and prompt recognition are critical in the management of VT.

**✓ Correct Answer: C. Very broad QRS complexes**