CARDIAC DISORDERS

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CARDIAC DISORDERS
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Introduction to Cardiac

• Every year since 1900 (except 1918) cardiac
  disease has been the leading cause of death in
  the US
• 42 of all deaths (1 million) are related to CVD
• Leading cause of death for women
• 1 in 5 people has experienced and are living with
  CVD

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Function of the Heart

• Collects deoxygenated blood coming from the body
• Sends this blood to the lungs for oxygen
• Receives oxygenated blood from lungs
• Pumps oxygenated blood and nutrients to the body
• Does this an average of 70 times a minute
• Pumps 60 mL of blood with each beat or 5 L/min

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Cardiac Anatomy

• 4 chambers
• Right atrium- receives blood from the body by way
  of the superior and inferior vena cava and from
  the coronary sinuses
• Right ventricle- receives blood from the right
  atrium through the tricuspid valve. It then
  contracts (systole), and forces blood through the
  pulmonary valve into the pulmonary artery. The
  pulmonary artery carries the blood to the lungs
  and CO2 is released and O2 picked up and
  transported back to the heart through the
  pulmonary veins

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Cardiac Anatomy, cont.

• Left atrium- oxygenated blood received from the
  lungs and transferred by way of the mitral valve
  into the left ventricle
• Left ventricle- strongest muscular chamber of the
  heart. Pumps blood through the aortic valve into
  the aorta

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Four Cardiac Valves

• Atrioventricular Valves
• Open with diastole, close with systole
• Tricuspid- between the RA and LA- 3 leaflets
• Mitral- between the LA and LV- 2 leaflets
• Semilunar valves
• Open during systole, close with diastole
• Pulmonic- between the RV and the PA
• Aortic- between the LV and the aorta

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Cardiac Muscle

• 3 layers of muscle
• Endocardium-inner layer
• Lines the heart chambers
• Myocardium-middle layer
• Muscle fiber which pumps the blood
• Epicardium-outer layer
• Covering of the heart which contains the coronary
  arteries

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Heart Sounds

• S1
• ventricular contraction
• Systole
• Lub
• S2
• ventricular relaxation
• Dub
• Diastole
• Closure of aortic and pulmonic valves

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Coronary Arteries

• Originate from an area on the aorta beyond the
  aortic valve
• 2 main coronary arteries
• RCA- supplies the right atrium, the right
  ventricle and the inferior of the left ventricle
• Left main artery- divides into 2 branches
• LAD-supplies most of the front of the LV, and
  part of the septum
• LCX-descends around the back of the LV
• Both of these have branches called diagonals and
  obtuse marginals
• Supplied with blood during diastole
• Must maintain a mean arterial blood pressure of
  at least 60 to maintain perfusion of the heart

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Conduction System

• Composed of special nerve fibers which send
  impulses throughout the cardiac muscle and
  initiates a muscle contraction
• Cardiac muscle cells possess characteristics of
• Automaticity-can initiate impulses spontaneously
• Excitability-cells respond to a stimulus by
  initiating an impulse
• Conductivity-transmit an electrical impulse
• Refractoriness cardiac muscle cannot respond to
  a stimulus until it has recovered (repolarized)
  from a pervious stimulus

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Conduction System, cont.

• Sinoatrial node (SA node)
• Major regulator of heart rate
• Called the pacemaker
• Spontaneously initiate impulses at a rate of
  60-100, called a sinus rhythm
• Atrioventricular node (AV node)
• Receives impulse form SA node
• Located at the junctional area
• Can sent impulse of 40-60 beats without SA node
  stimulus

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Conduction, cont.

• Bundle of HIS
• Continuation of AV node
• Located in the intraventricular septum
• Has a right and left branch
• Purkinje fibers
• Join the Bundle
• Terminal branches of system
• Can deliver a rate of 20-40 beats a minute
• When impulse reaches here ventricles contract

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Conduction, cont.

• At rest the inside of the cell is negatively
  charged and outside the cell is positively
  charged
• When an impulse is received from the SA node,
  there is a change in the electrical charge of the
  cells lose their internal negativity and become
  depolarized this goes from cell to cell
• Repolarization is when the resting state returns
• Then the cycle continues

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Other Cardiac Stimulus

• Autonomic Nervous System
• Sympathetic
• Fight or flight - HR, strength of contraction
• Parasympathetic (part of the vagus nerve)
• Found in the SA and AV nodes
• Slows HR
• Decreases strength of contraction

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Mechanical Function

• Phases of Cardiac Cycle
• Diastole 2/3 of cycle, relaxation and filling
  of the atria and ventricles, atrial kick is at
  the end of this cycle
• Systole contraction and emptying of the
  ventricles

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Mechanical Function, cont.

• Stroke volume is amount of blood ejected from
  the ventricle with each heart beat. Normal is
  60-100 mL
• Cardiac output amount of blood in liters,
  ejected by the heart each minute. Normal is 4-6
  liters/min
• To calculate CO HR x SV

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Factors Which Affect Stroke Volume

• Preload determined by the amount of blood
  returning to the heart from the venous system and
  the pulmonary system
• Afterload amount of resistance which the heart
  must overcome to eject blood from the LV into the
  peripheral vascular system
• Contractility the force of contraction of heart
  muscle
• Inotropic term which refers to the contractile
  state of the cell
• Positive inotropic
• Negative inotropic

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O2 Consumption

• Determined by the needs of the myocardium
• O2 is delivered to the heart muscle by the
  coronary arteries
• 2 ways to increase O2 to the myocardium
• Increase coronary blood flow
• Increase O2 in the blood by giving O2 supplement