GROSS ANATOMY

Detailed explanation-1: -Ventricular depolarization occurs in part via an accessory pathway (AP) directly connecting the atrium and ventricle and thus capable of conducting electrical impulses into the ventricle bypassing the AV-His Purkinje conduction system.

Detailed explanation-2: -During ventricular activation, impulses are first conducted down the left and right bundle branches on either side of the septum. This causes the septum to depolarize from left-to-right, as depicted by vector 1 (Panel A).

Detailed explanation-3: -Repolarization therefore begins in the base and epicardium, followed by the apex and endocardium. Depolarization on the other hand spreads from apex and endocardium to base and epicardium (see Figure 4.4). Thus repolarization occurs in reverse sequence to depolarization, producing the upright T wave.

Detailed explanation-4: -Answer and Explanation: Ventricular contraction begins at the apex of the heart. As the electrical activity passes from top to bottom in the atrium, it then passes directly through the septum in the Bundle of His.