Schneid Guide to the QRS Vectorcardiogram Loop.
The QRS complex represents ventricular depolarization. In the normal heart, ventricular excitation originates in the middle part of the septum and disperses throughout the septum from left to right (see Figure 5). It is possible that the QRS complex is an RS-complex, a QS-complex, or an R wave, depending on the direction of the vectors and the location of the ECG’s limb and precordial leads.
Vector 1 of Heart
Vector 1 represents the septal vector (q) and the beginning of the normal ventricular impulse. It travels anteriorly from the center of the septum, directed to the right with a slightly downwards projection (impulses traveling through the septal conduction cells). Vector 1 is depicted by the small Q waves in lead 1, V5, and V6.
Vector 2 represents depolarization of the distal left ventricle and the subsequent instantaneous excitation of the main segments of the left and right ventricle. The impulses of vector 2 occur after the impulses mapped by vector 1.
Vector 2 is generally directed to the left, inferiorly, and posteriorly. This vector is represented by the tall R waves in leads I and leads V5 and V6 and by deep S waves in leads V2 and V3.
Vector 2a represents right ventricular depolarization. It is often not appreciated on the ECG unless a medical condition has caused the right ventricle to increase in mass. If the patient has hypertrophy of the right ventricle (e.g., caused by COPD or end-stage liver disease) or a RBBB, vector 2a is significantly increased.
The left ventricular mass represented by vector 2 is normally five times larger than the right ventricular mass represented by vector 2a.
Vector 3 represents the excitation of the superior aspect of the remaining ventricular parts and appears last. The vector travels superiorly toward the right and posteriorly. The ECG tracing reflecting vector 3 shows a small S wave in leads I, V2, V3, and V6.