1. Physiology of the Cardiovascular System

2. The Conduction System of the Heart Modified cardiac muscle that specializes in contraction There are four main structures that compose the conduction system of the heart Sinoatrial (SA) node Sinoatrial (SA) node Atrioventricular (AV) node Atrioventricular (AV) node AV bundle AV bundle Purkinje system Purkinje system

3. Sinoatrial (SA) Node Initiates the mechanical contraction of the heart (known as the pacemaker) Located in the right atrium just below the junction of the superior vena cava Possesses an intrinsic rhythm. This means that without any stimulation by nerve impulses from the brain and cord, they themselves initiate impulses at regular intervals.

4. Atrioventricular (AV) Node The impulse generated in the SA node travels swiftly throughout the muscle fibers of each atria. The stimulated atria begin to contract– they will completely contract before the impulse reaches the ventricles The action potential enters the AV node by way of three internodal bundles of conducting fibers

5. AV Bundle and Purkinje Fibers The impulse slowly passes through the AV node then speeds up as the impulse is relayed through the AV bundle (bundle of His) into the ventricles It is the right and left bundle branches and the Purkinje fibers that conduct the impule through the ventricles, causing them to contract simultaneously.

6. Conduction System of the Heart

7. Artificial Pacemakers Devices that electrically stimulate the heart Electrodes sewn directly into the epicardium or directly inserted into the heart chamber Inferior to the heart’s natural pacemaker

8. Electrocardiogram (ECG) Impulse conduction generates tiny electrical currents in the heart that spread through surrounding tissues to the surface of the body. An electrocardiogram (ECG OR EKG) is a graphic record of the hearts electrical activity— the impules that preced the actual contraction Electrodes are attached to a voltmeter and to the limbs and chest of the subject.

10. Theory of Electrocardiography A.At rest (baseline) B.Action potential reaches the first electrode (relatively negative) C.Action potential reaches the second electrode (pen returns to baseline) D.End of action potential passes the first electrode (relatively positive) E.Action potential passes second electrode (returns to baseline)

11. ECG Waves Represent the dynamic events that happen during the contraction of the heart Letters are arbitrary and do not stand for any words

12. P Wave A.Heart wall is completely relaxed—no change in electrical activity B.P wave represents the depolarization of the atria

13. QRS Complex C.Atrial walls are completely depolarized—no change recorded D.QRS Complex occurs as atrial walls repolarize and ventricular walls depolarize (massive depolarization of ventricles overshadows atrial repolarization)

14. T Wave E. Atrial walls are completely repolarized and ventricular walls are completely depolarized F.T wave appears as the ventricular walls replarize

15. Back to Baseline G.Once the ventricles are completely repolarized it is back to the baseline ECG

16. Bradycardia Slow heart rhythm— below 60 beats per minute Slight bradycardia is normal during sleep and in conditioned athletes when awake Can be caused by damage to the SA node

17. Tachycardia Very rapid heart rhythm— more than 100 beats per minute Normal during and after exercise and during the stress response Can result from improper autonomic control of the heart, blood loss, shock and a host of other factors

18. Ventricular Fibrillation Complete disruption of the normal heart rhythm Death may occur within minutes if the heart beat is not corrected by defibrillation or other means