A downward or negative wave of an electrocardiogram following the P wave is known as what?

A downward or negative wave following the P wave in an electrocardiogram is indeed referred to as the Q wave. The Q wave is the first negative deflection that appears after the P wave in the normal electrocardiogram sequence. It represents the initial phase of ventricular depolarization, which is crucial for the heart's electrical activity.

In a typical ECG, the P wave indicates atrial depolarization. After this, the Q wave comes as part of the QRS complex. Its negative nature is significant because it signifies the electrical activity spreading through the ventricles, specifically as the septum depolarizes from left to right. Understanding the role of the Q wave is vital for interpreting heart health and function through ECG readings, as changes in the Q wave can indicate various cardiac conditions.

The other options do not correctly match the description given in the question. The P wave, for instance, relates to atrial depolarization, the R wave is a positive deflection following the Q wave, and the T wave represents ventricular repolarization. Each of these has distinct characteristics and physiological significance within the electrocardiographic tracing.