The Cardiac Cycle
Cardiac Cycle: A coordinated sequence of electrical and mechanical events occurring from the start of one heartbeat to the start of the next. A single cardiac cycle includes a complete relaxation and contraction of both atria and ventricles. Relaxation is Diastole and Contraction is Systole
Changes in pressure and volume: A series of pressure changes take place within the heart during the cardiac cycle resulting in the movement of blood. Valves within the heart's direct movement of blood and pressure changes are brought about by conductive electrochemical changes within the myocardium that result in the contraction of cardiac muscle.
Phases:
ECG:
\n \n
Electrophysiology
Cardiac Pacemakers: The cells of the SAN depolarise over time, with the movement of ions causing the resting membrane potential to gradually decrease (pacemaker potential), once the membrane potential exceeds a threshold, an action potential is triggered (this happens automatically about every 0.8 seconds at rest). The cells of the AVN do the same, but more slowly; the result of this is that an action potential is triggered in the AVN before they depolarise enough to trigger their own.
Pacemaker Potentials:
\n
Conduction and ECG
\