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    ECG INTERPRETATIONDefinition of terms:1. Electrocardiogram is an essential tool in evaluating the hearts rhythm and signs of

    ischemia.2. Electrocardiography a transthoracic interpretation of the electrical activity of the heart overa period of time, as detected by electrodes attached to the outer space of the skin andrecorded by a device external to the body.

    3. ECG complex waveform representing electrical events of one cardiac cycle- consists of 5 main waveform: P,Q, R,S,T

    4. Rhythm Strip length of ECG paper that shows multiple ECG complexes representing apicture of the hearts electrical activity in a specific lead.5. Electrodes a conductor through which electricity enters/leaves something such as battery/a piece of electrical equipment.

    6. Lead provides a view of the hearts electrical activity between 2 points/poles 7. Plane is a cross section of the heart which provides a different view of the hearts electricalactivity.8. Depolarization response of a myocardial cell to an electrical impulse that causes movementof ions across the cell membrane which triggers myocardial contraction.9. Repolarization recovery of the myocardial cells after depolarization during which the cellmembrane returns to its resting potential.

    ANATOMY AND PHYSIOLOGY

    HEART- a hollow,muscular organ that works like a mechanical pump- delivers oxygenated blood to the body through the arteries- located between the lungs and in front of the spine- the bottom of the heart called the apex

    Heart wall (3 layers)1. Epicardium2. Myocardium

    - thickest later; contracts with each heartbeat3. Endocardium

    - thin layer of the endothelial tissue

    Pericardium- fluid filled sac that envelopes heart and acts as tough protective coating

    2 types:

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    1. fibrous pericardium2. serous pericardium

    2 layers:a. parietal layer

    - envelopes the visceral pericardium

    b. visceral layer- adheres to the pericardium

    Pericardial space- separates the visceral and parietal layer- contains 10-20mL of thin, clear pericardial fluid that lubricates the 2 surfaces.

    Heart chambers- 4 chambers, 2 atria, 2 ventricles

    1. Right atrium- deoxygenated blood

    2. Left atrium- oxygenated blood

    3. Right ventricle4. Left ventricle

    Heart valves- to keep blood flowing through the heart

    2 AV valves1. Tricuspid valve

    - separates the right atrium from right ventricle2. Mitral valve

    - separates the left atrium from the left ventricle

    2 Semilunar valves1. pulmonic valve2. aortic valve

    Coronary blood supply- main coronary arteries lie on the surfaces of the heart

    - the heart receiver its blood supply almost coordinating through the coronary arteries.

    Coronary arteries Right coronary arteries

    - supplies blood to the right atrium, right ventricles the inferior wall of the left ventricle

    Posterior descending artery- supplies blood

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    Left main coronary artery- splits into 2 major branches

    a. left anterior descending artery- supplies blood to the anterior wall

    b. left circumflex artery

    - provides blood to the lateral wall of the left ventricle andleft atrium

    TRANSMISSION OF ELECTRICAL IMPLUSES:

    1. Automaticity- pacemaker- a cells ability to spontaneously initiates on electrical impulse

    2. Excitability- the cells ability to respond to an electrical stimulus

    3. Conductivity- ability of a cell to transmit an electrical impulse from one

    4. Contractility- the cells ab ility to contract after receiving a stimulus by shortening and lengthening its

    muscle fibers.

    Depolarization and Repolarization- cardiac cells at rest are considered polarized, meaning that no electrical activity false

    places.

    Depolarization and Repolarization cycle

    1. Phase 0 RAPID DEPOLARIZATION- the cell receives a stimulus, usually from a neighboring cell.

    2. Phase 1 EARLY REPOLARIZATION- Na channels close and Na stops flowing into the cell.

    3. Phase 2 PLATEAU PHASE- Ca continues

    4. Phase 3 RAPID REPOLARIZATION- cell membrane is impermeable to Na- K more our of the cell

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    - by the end of this phase, the cell is ready for another stimulus

    Cardiac Veins- the heart has its own veins, which remove oxygen depleted blood for the myocardium

    approximately 75% of the total coronary venous blood flow leaves.

    Cardiac Cycle: Ventricular Diastole(relaxation)

    - blood flows from from the atria into the relaxed ventricles.- atrial contraction(atrial kick) contributes to another 25% to ventricularfilling

    Ventricular systole(contraction)- the ventricle contract ad blood is ejected into the pulmonic andsystemic circulation

    PHASES OF THE CARDIAC CYCLE

    1. Isovolumetric ventricular contraction- in response to ventricular depolarization tension in the ventricles increases.

    2. Ventricular ejection- when ventricular pressure falls below the pressures in the aorta and pulmonary artery

    pressure, the aorta and pulmonic valves open and the ventricles eject blood.

    3. Isovolumetric relaxation- when ventricular pressure falls below the pressures in the aorta and pulmonary artery,

    the aortic and pulmonic valves close.- cells valves are closed during this place.

    4. Ventricular filling- atrial pressure exceeds ventricular pressure, which causes the mitral and tricuspid

    valves to open.- blood then flow passively into the ventricles- about 70% of ventricular filling takes.

    5. Atrial systole(atrial kick)- atrial systole(considering the take ventricular diastole) supplies the ventricles with theremaining 30% of the blood.