1. The Conduction System of the Heart
Anatomy
The Circulatory System

2. Cardiac Physiology
In a single cardiac contraction, or heartbeat, the entire heart contracts in series – first the atria and then the ventricles
Specialized muscle cells of the conducting system control and coordinate the heartbeat
Contractile cells produce the powerful contractions that propel blood

3. The Conduction System
The heart is controlled by the ANS (autonomic nervous system) – it contracts on its own, without neural or hormonal stimulation
The heart has its own regulating system = conduction system
The conduction system is composed of specialized muscle cells/tissue that initiates and distributes electrical impulses (the action potential).

4. Components of the conducting system
SA Node - Located in the right atrial wall below the opening to the superior vena cava
AV Node - Located in the interatrial septum (floor of the right atrium)
Conducting cells – interconnect the two nodes and distribute the stimulus throughout the myocardium

5. Components of the Conduction System
1. SA NODE
Contains pacemaker cells, which initiates and establishes heartbeat
Known as the natural pacemaker
Average = 75 beats/minute
2. AV NODE
Receives the action potential from the SA node
Action potential slows considerably  allows time for the atria to empty into the ventricles

6. Components of the Conduction System
3. AV BUNDLE
Receives impulse from the AV node
Located at the interventricular septum
Passes impulse onto the bundle branches
4. BUNDLE BRANCHES
Located below the AV bundle
Passes impulse onto the conduction myofibers
5. CONDUCTION MYOFIBERS (Purkinje Fibers)
Located in the ventricular myocardium
Receives action potential/impulse from bundle branches and passes it onto ventricular myocardial cells to complete ventricle contraction

7. ECG or EKG
Impulses can be detected on the body surface and recorded with an electrocardiograph.
The recording that is made, the electrocardiogram (ECG/EKG), traces the flow of current through the heart.
Each time the heart beats, a wave of depolarization radiates through the atria, pauses at the AV node, then travels down the interventricular septum to the apex, turns, and spreads through the ventricular myocardium toward the base
An ECG integrates electrical information obtained by placing electrodes at different locations on the body surface
The typical ECG has three recognizable waves:
1st Wave: P wave (depolarization of the atria)
2nd Wave: QRS complex (ventricular depolarization)
3rd Wave: T wave (ventricular repolarization)

8. Clinicians can use an ECG to access the performance of specific nodal, conducting, and contractile components.
Abnormalities in the shape of the wave and changes in the timing could indicate something is wrong.
Examples: An excessively large QRS complex often indicates that the heart has become enlarged. When a portion of the heart has been damaged by a heart attack the ECG reveals an abnormal pattern of impulse conduction.

9. The Cardiac Cycle
Each heartbeat is followed by a brief resting phase, allowing time for the chambers to relax and prepare for the next heartbeat
The period between the start of one heartbeat and the beginning of the next is a single cardiac cycle
Includes alternating periods of contraction and relaxation

10. The Cardiac Cycle Phases
Systole: the phase of contraction of a chamber (the chamber contracts and pushes blood into an adjacent chamber or into an arterial trunk)
Diastole: the phase of relaxation (the chamber fills with blood and prepares for the next cardiac cycle)

11. Blood Pressure
Pressure that blood exerts against the inner walls of the blood vessels
Systolic Number – This is the TOP number in your blood pressure…related to the pressure of contraction in the heart that is placed on the inside of the vessels
Diastolic Number – This is the BOTTOM number in your blood pressure…related to the relaxed phase of your heart that is then transferred to your vessels
Normal blood pressure is 120/80

12. Cardiac Output
For the body to function properly, the heart needs to pump blood at a sufficient rate to maintain an adequate and continuous supply of oxygen and other nutrients to the brain and other vital organs
Cardiac output = describes the amount of blood your heart pumps each minute
A healthy heart pumps about 5-6 liters of blood every minute when a person is resting

13. Cardiac Output Cardiac Output: It is determined by:
1. The amount of blood pumped by the left ventricle during each beat (stroke volume)
2. The number of heart beats per minute
The amount of blood ejected by a ventricle during each contraction (single beat) is called stroke volume
Cardiac output is an indication of the blood flow through peripheral tissues; without adequate blood flow, homeostasis cannot be maintained; helps keep blood pressure at the levels needed to supply oxygen-rich blood to your organs

14. Cardiac Output For an adult at rest… Stroke volume = 80 mL (average)
Heart rate = 75 beats per minute (average)
Therefore, Cardiac Output (CO) = Stroke Volume x Beats per Minute
CO = 80 mL/beat x 75bpm
CO = 6000mL/min (6L/min)

15. Arrhythmia
Abnormal heart rhythm (irregular heartbeats and heart rates)
Bradyarrhythmia (Bradycardia) – heart rates that are slow (less than 50bpm)
Tachyarrhythmia (Tachycardia) – rapid heart rates (faster than 100 bpm)
About 5% of healthy individuals experience a few abnormal heartbeats each day

16. Causes of Arrhythmia
Coronary artery disease (partial or complete blockage of coronary circulation)
Electrolyte imbalances in your blood
Injury from a heart attack
Healing process after heart surgery
Example: Fibrillation (atrial or ventricular) – rapid, uncoordinated shuddering of the heart

17. High Blood Pressure/Hypertension (Silent Killer)
Normal bp = 90/60 (birth) and 120/80 (adults)
Top number shows the pressure when the heart beats
Lower number measures pressure at rest between heart beats, when the heart refills with blood
High blood pressure = 140/90 consistently
High blood pressure can threaten healthy arteries and lead to life-threatening conditions (leading cause of stroke and major cause of heart attack)
Significantly increases the workload on the heart, and the left ventricle gradually enlarges
More muscle mass means a greater oxygen demand
Places physical stress on the walls of blood vessels

18. Hypertension
Prehypertension – blood pressure is consistently just above normal ( & 80-89)

19. What causes hypertension?
Smoking
Being overweight or obese
Lack of physical activity
Too much salt in the diet
Too much alcohol consumption
Stress
Genetics
Older age

20. Atherosclerosis Usual cause of heart attacks & strokes
High blood pressure, smoking or high cholesterol damage the endothelium (lines the arteries) & cholesterol plaque forms
The arteries harden and narrow and block blood flow
Plaque behaves in different ways: can stay within the artery wall, cause blockages, or rupture which allows blood to clot in the artery

21. Heart Attack/Myocardial Infarction
Part of the coronary circulation becomes blocked, and cardiac muscle cells die from lack of oxygen
Coronary heart disease causes the arteries to become narrow and blood cannot flow as well
Fatty matter, calcium, proteins, and inflammatory cells build up within the arteries to form plaque

22. Heart attack continued
When the plaque that forms becomes hard, the outer shell cracks, and blood clots form around the plaque
If a blood clot blocks the artery, the heart muscle becomes “starved” for oxygen
Within a short time, death of heart muscle cells occurs, causing permanent damage

23. Risk Factors of a Heart Attack
1. Smoking
2. High blood pressure
3. High blood cholesterol levels
4. Diabetes
5. Obesity
6. Sedentary lifestyle
7. Genetics

24. Pulmonary Edema
An abnormal buildup of fluid in the air sacs of the lungs, which leads to shortness of breath
In most cases heart problems cause pulmonary edema but fluid can accumulate for other reasons
As pressure in the blood vessels increase, fluid is pushed into the air spaces (alveoli) in the lungs
This fluid interrupts normal oxygen movement in the lungs

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