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Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/ min 40-60/ min 30/ min

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Page 1: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Intrinsic Cardiac Conduction SystemApproximately 1% of cardiac muscle cells are

autorhythmic rather than contractile

75/min

40-60/min

30/min

Page 2: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Intrinsic Conduction SystemFunction: initiate & distribute impulses so heart depolarizes & contracts in orderly

manner from atria to ventricles.

SA node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

Page 3: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Waves

(Pacemaker) Atrial repolarization

Page 4: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Waves

1st Degree Heart Block = P-Q interval longer than 0.2 seconds.

60 seconds ÷ 0.8 seconds = resting heart rate of 75 beats/minute

Page 5: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Wave Irregularities

Enlarged QRS =

Hypertrophy of ventricles

Page 6: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Wave Irregularities

Prolonged QT Interval =

Repolarization abnormalities increase chances of ventricular arrhythmias.

Page 7: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Wave Irregularities

Elevated T wave :

Hyperkalemia

Page 8: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Wave Irregularities

Flat T wave :

Hypokalemia or ischemia

Page 9: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Heart Blocks

Normal ECG

3rd Degree Block

No P waves. Rate determined by autorhythmic cells in ventricles

2nd Degree BlockNot a QRS for each P wave

P

QRS

T

Page 10: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Cardiac Cycle• All events associated with a single heart

beat including atrial systole & diastole followed by ventricular systole & diastole.

(V. Systole) (V. Diastole)

Systolic BP

Diastolic BP

Page 11: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

ECG Deflection Waves60 seconds ÷ 0.8 seconds = resting heart rate of 75 beats/minute

Page 12: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Frank Starling Law of the Heart

• The more cardiac muscle is stretched within physiological limits, the more forcibly it will contract.

• Rubber band analogy

• Increasing volumes of blood in ventricles increase the stretch & thus the force generated by ventricular wall contraction.

• Greater stretch means more blood volume is pumped out, up to physical limits.

Page 13: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Frank Starling Law of the Heart

Increased blood volume = increased stretch of myocardium

=

Increased force to pump blood out.

Page 14: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Terms, Definitions & Units• Blood Pressure - force generated against

arterial walls per unit of area in mm Hg.

• Systolic Pressure - peak arterial pressure. Averages about 120 mm Hg in healthy adults.

• Diastolic Pressure - lowest arterial pressure. Averages between 70 - 80 mm Hg in healthy adults.

• Blood Volume - quantity of blood in cardiovascular system. Varies from 4-5 L. in females to 5-6 L. in males.

Page 15: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Terms, Definitions & Units

• Cardiac Output - the amount of blood pumped by a ventricle per minute. Units may be in milliliters or Liters per minute.

• Heart Rate - number of cardiac cycles per minute. Average for males = 64-72/min. Average for females = 72-80/min.

• Stroke Volume - amount of blood pumped out of a ventricle each beat. Average resting stroke volume = 70 ml.

Page 16: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

• Blood volume increases due to increased water retention from increased ADH production, IVs or transfusions = BP

• Blood volume loss due to injuries, hemorrhages, use of diuretics, etc. = BP

Blood Pressure = Blood Volume × Peripheral Resistance

Factors influencing blood pressure

Page 17: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Cardiac Output = circulating blood volume

Blood Pressure = Blood Volume × Peripheral Resistance

Factors influencing blood pressure

Cardiac Output = Heart Rate × Stroke Volume

Increased heart rate caused by the release of epinephrine into blood by the adrenal glands = increased cardiac output, which increases circulating blood volume, to increase blood pressure.

Page 18: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Vasodilation = diameter = resistance = BP

Peripheral Resistance affected by:

•blood viscosity (thickness)

•diameter of vessels (vasoconstriction/vasodilation)

Blood Pressure = Blood Volume × Peripheral Resistance

Factors influencing blood pressure

Vasoconstriction = diameter = resistance = BP

Elastic Arterial Walls = BP

(Polycythemia)

•elasticity of arterial walls

Page 19: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

BP - Stimulates Cardioinhibitory center to heart rate & Vasomotor center to diameter.

Homeostatic Blood Pressure Regulation Mechanisms

• Medullary Reflex Centers:

– Cardioacceleratory - increases heart rate

– Cardioinhibitory - decreases heart rate

– Vasomotor - changes diameter of vessels

BP - Stimulates Cardioacceleratory center to heart rate & Vasomotor center to diameter.

• Baroreceptors in aortic arch & carotid sinuses:

– sensitive to changes in blood pressure.

Page 20: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

in CO2 or in O2 stimulates Vasomotor center to diameter (vasoconstrict) of vessels to BP.

Homeostatic Blood Pressure Regulation Mechanisms

• Medullary Reflex Centers:

– Cardioacceleratory - increases heart rate

– Cardioinhibitory - decreases heart rate

– Vasomotor - changes diameter of vessels

in CO2 stimulates Vasomotor center to diameter (vasodilate) of vessels to BP.

• Chemoreceptors in aortic bodies & carotid bodies:

– sensitive to changes in CO2 & O2 in blood.

Page 21: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Aneurysm• Weakness of the wall of an artery causing

an abnormal enlargment or bulge.

• The aorta or the arteries that supply the heart, brain, legs or kindeys are most commonly affected.

Page 22: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Angina Pectoris

• Medical term for chest pain due to coronary heart disease.

• It occurs when the myocardium doesn’t get as much blood (Oxygen) as it needs.

• Insufficient blood supply is called ischemia.

• May initially occur during physical exercise, stress, or extreme temperatures.

• It is a sign of increased risk of heart attack.

Page 23: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Hypertension

• High blood pressure.• Sustained arterial blood pressure of 140/90

mm Hg or above.• Rising diastolic pressure generally indicative

of progressive hardening of arteries.• Since the heart must work harder to pump

blood against higher pressures, there is increased risk of a cardiovascular accident.

Page 24: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Hypotension

• Abnormally low blood pressure.

• Sustained systolic blood pressure of below 100 mm Hg.

• Generally associated with lower risk of cardiovascular accidents & long life providing that the tissues are adequately perfused..

Page 25: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Circulatory Shock• Blood vessels inadequately filled to enable

normal circulation & supply of O2 & nutrients.

• May result in death of cells & damage to organs.

• Common Types:

• Hypovolemic - severe blood loss

• Cardiogenic - heart (pump) failure

• Vascular - excessive vasodilation

• Septicemic - vasodilation due to bacterial toxins produced during an infection.

Page 26: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Atherosclerosis (Arteriosclerosis)

• Narrowing and hardening of arteries and impairment of blood flow due to the deposition of fatty materials and calcium in their walls.

• Risk factors include:– smoking– inactivity– diabetes– high blood cholesterol– personal or family history of heart disease

Page 27: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

Arteriosclerosis (Atherosclerosis):

All images copyright © Camera M.D. Studios. Special thanks to Gregory Curfman, M.D..

Page 28: Intrinsic Cardiac Conduction System Approximately 1% of cardiac muscle cells are autorhythmic rather than contractile 75/min 40-60/min 30/min

AcknowledgementsMost of the figures used in this presentation came from the Benjamin Cummings Digital Library

Version 2.0 for Human Anatomy & Physiology, Fifth Edition. Other figures came from public domain internet sources and software in the possession of the author.


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