What wave has the first downward deflection in a normal ECG tracing?

In a normal ECG tracing, the Q wave is recognized as the first downward deflection after the P wave. The Q wave is part of the QRS complex, which represents the electrical depolarization of the ventricles. The QRS complex typically starts with the Q wave, followed by the R wave, which is the first upward deflection and the most prominent point in the complex.

The presence of the Q wave signifies the initial phase of ventricular depolarization, where the electrical impulse travels through the interventricular septum from the left bundle branch. This downward deflection is an important indicator of the heart's electrical activity and is used by healthcare professionals to assess cardiac health and detect potential abnormalities.

Other options, such as the R wave and S wave, follow after the Q wave; the R wave represents the initial upward deflection, while the S wave is the subsequent downward deflection following the R wave. The T wave, on the other hand, represents the repolarization of the ventricles, occurring later in the ECG cycle. Thus, the Q wave distinctly marks the first downward deflection of the ECG waveform.