These are the most positive deflections when the lead axis and QRS axis are parallel (or most negative if the current flows toward the negative electrode).

These are the most positive deflections when the lead axis and QRS axis are parallel (or most negative if the current flows toward the negative electrode).

• A. Heart complexes
• B. R waves
• C. Q waves
• D. S waves

Answer: (A)

The key idea is ventricular depolarization as it appears on the ECG. The QRS complex represents the whole ventricular depolarization event, and the size and direction (positive or negative) of its deflections in any given lead depend on how the heart’s mean QRS vector aligns with that lead’s axis. When the lead axis runs in the same direction as the QRS axis, the projection is maximal and shows up as a strong positive deflection. If the current vector points toward the negative electrode, the projection is inverted and appears as a prominent negative deflection. So the largest positive deflections you see in a lead correspond to the QRS complexes, i.e., ventricular depolarization. The R wave is the prominent upward part within the QRS, while Q and S waves are other components, but the overall “heart complexes” term here refers to the QRS complex as the principal positive deflection when axes are aligned.

The key idea is ventricular depolarization as it appears on the ECG. The QRS complex represents the whole ventricular depolarization event, and the size and direction (positive or negative) of its deflections in any given lead depend on how the heart’s mean QRS vector aligns with that lead’s axis. When the lead axis runs in the same direction as the QRS axis, the projection is maximal and shows up as a strong positive deflection. If the current vector points toward the negative electrode, the projection is inverted and appears as a prominent negative deflection. So the largest positive deflections you see in a lead correspond to the QRS complexes, i.e., ventricular depolarization. The R wave is the prominent upward part within the QRS, while Q and S waves are other components, but the overall “heart complexes” term here refers to the QRS complex as the principal positive deflection when axes are aligned.