1. Cardiac Cycle and Conduction System of the Heart

2. The Cardiac Cycle The mechanical events that take place in one heartbeat.

3. The Cardiac Cycle Contraction of a chamber - systole Relaxation of a chamber - diastole 1 full contraction and relaxation - cardiac cycle

6. Physiology of Contraction (Atrial diastole) AV valves are open, Semilunar closed Blood draining into atria Blood draining into ventricles (gravity/pressure gradient) SA node fires ending atrial diastole AV valves open further. Atria push remaining blood to ventricles then go into diastole

7. Cont...... Increased pressure in ventricles Pressure depends on volume and chamber size Isometric contraction of ventricles (why?) Semi lunar valves open AV valves close due to back pressure Ventricles contract and force blood out

8. Cont...... Ventricles relax - decreased pressure causes semilunar valves to close cycle repeats intra-atrial pressures intra-ventricular pressure

9. Systole and Diastole Peak pressure of a chamber or vessel Stroke volume amount of blood ejected by the heart (LV) in one contraction aprox. 70 cc (60-100 cc) Relaxation of a chamber Pressure at its lowest

10. Cardiac Output amount of blood ejected every minute aprox. 5-6L SV X HR = CO The strength of contraction is directly related to venous return

11. Starling’s Law The more a muscle is stretched the harder it will contract (up to a certain point) Similar to a spring Muscle fibers will stretch and contract harder when there is a increased blood return

12. Blood Pressure The pressure exerted by blood against the walls of a given artery.

13. Factors Affecting Blood Pressure 1.Blood Volume 2.Strength of heart contractions 3.Heart rate 4.Blood viscosity – thickness of blood

14. Electrophysiology Before the heart can contract it must be stimulated. This is accomplished through a specialized network of cells called the conduction system. There are numerous “pacemaker” cells to stimulate the heart to contract.

15. Sinoatrial Node (SA) Located in high RA Main pacemaker of heart Sends out regular impulses at 60- 100 times per minute Regulated by the Autonomic Nervous System (vagus nerve)

17. Atrioventricular Node (AV) Located on floor of TA next to septum and behind CS os Has 2 main jobs Delay the impulse from the SA node long enough so the ventricles can fill with blood Protect the ventricles from rapid atrial rates Inherent rate of 40-70 bpm

18. Bundle of His (HB) A fibrous ring around the 4 valves Only muscular connection between the atria and ventricles AV node and HB collectively are called the AV junction The AV junction can pace the heart at rate of 40-60 bpm

19. Bundle Branches HB branches into rt.... And lt.. Branches Lt.. Bundle branch (LBB) then divides into anterior and posterior sections

21. Purkinje Fibers Terminal portion of the conduction system Located in ventricular muscle Can pace the heart at 20-40 bpm

23. Electrical Properties of Cardiac Muscle

24. Automaticity Property by which a cell can reach threshold potential (depolarize) and send an impulse without help from an external source Excitability Ability of cell to reach threshold potential in response to an outside stimulus Conductivity The propagation of an impulse form cell to cell through intercalated disks Contractility Ability of a muscle to shorten (contract) when stimulated Electrophysiology cont.....

25. Electrophysiology Cont..... The end result of contraction of the heart is electrochemical in nature. The impulse is sent along the conduction system because of changes in cellular polarity.

33. Cardiac Emergencies A thrombosis or embolism may plug the arteries causing a myocardial infarction or “heart attack” Angina pectoris is used to describe the severe chest pain

34. infarct