**Core Concept**
The location of the pacemaker in the heart determines the timing and origin of the electrical impulses that control the heartbeat. In a normal heart, the sinoatrial (SA) node acts as the natural pacemaker, generating electrical impulses that travel through the atria and ventricles to produce a coordinated heartbeat. However, in cases where the SA node is dysfunctional, other regions of the heart can take over as the pacemaker, leading to abnormal ECG patterns.

**Why the Correct Answer is Right**
The absence of a P wave on the ECG suggests that the electrical impulses are not originating from the atria, indicating that the SA node is not functioning properly. The presence of a normal QRS complex and T wave, however, suggests that the ventricles are still receiving and responding to electrical impulses, indicating that the ventricular conduction system is intact. This points to the existence of an ectopic pacemaker located in the ventricles, which is capable of generating electrical impulses that bypass the atria.

**Why Each Wrong Option is Incorrect**
* **Option A:** The absence of a P wave does not necessarily indicate a pacemaker located in the atria, as it could also be due to a block in the AV node or a failure of the atrial depolarization.
* **Option B:** The presence of a normal QRS complex and T wave does not rule out a pacemaker located in the atria, as the ventricles can still respond to electrical impulses originating from the atria.
* **Option D:** The correct location of the pacemaker is not related to the presence of a bundle branch block, which is a separate condition that affects the ventricular conduction system.

**Clinical Pearl / High-Yield Fact**
A pacemaker located in the ventricles, such as the bundle of His or the ventricular septum, is known as an ectopic pacemaker, and can produce a variety of abnormal ECG patterns, including a normal QRS complex and T wave, but no P wave.

**Correct Answer:** C.