How does the cardiac cycle and electrical activity all relate to blood pressure in the heart?
Blood pressure is determined by cardiac output and the total peripheral resistance, where, from Ohm's Law (Q= P/R):

Mean Arterial Pressure (MAP)= Blood flow (Q) x Total Peripheral Resistance (R)

The cardiac cycle and heart activity will essentially control the cardiac output through the FORCE and the FREQUENCY of contraction. 

Cardiac output is determined by the stroke volume, and the heart rate:

CO= Stroke volume x HR

Changes in HR is linked to changes to the SAN and is controlled by sympathetic and parasympathetic inputs. An increase in HR, will cause cardiac output to increase, causing an increasing in blood pressure (simply put, other physiological changes can also influence blood pressure, such as vasoconstriction and vasodilation).

With regards to the AVN, SAN and bundles of His, this allows electrical conductance which causes the contraction of the heart. The contraction of the heart leads to blood being ejected (i.e. blood flow, which is linked to cardia output). This, together with the peripheral resistance of blood vessels will be linked to blood pressure.