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Typical Heart Rate
- 60-80 bpm
- AV node can't fire more than 230 bpm, so this is the highest possible frequency of ventricular contractions
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Bradycardia
Heart rate is slower than normal
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Tachycardia
Heart rate is faster than normal
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Electrocardiogram (EKG/ECG)
- Recording of all action potentials in nodes and myocardial cells
- Measured with electrodes on arms, legs, and sometimes chest
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P Wave
SA node and atrial depolarization
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QRS Complex
Ventricular depolarization
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ST Segment
Ventricular Systole (plateau)
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T Wave
Ventricular repolarization
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Nodal Rhythm
- SA node not firing at all or not at the correct time
- No P wave (or misplaced or inverted P Wave)
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Heart Block
- Block anywhere in electrical conduction system
- EKG signs depend on location of block
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Premature Ventricular Contraction
Heartbeat initiated by ventricles instead of SA node
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Ventricular Tachycardia
Four or more premature ventricular contractions without normal beats in between
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Ventricular Fibrillation
Uncoordinated ventricular contractions
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Pressure
Causes blood to flow
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Pressure Gradient
- Pressure difference between two chambers
- Fluid flows from high pressure to low pressure
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Cardiac Cycle Phases
- 1. Ventricular Filling
- 2. Isovolumetric Contraction
- 3. Ventricular Ejection
- 4. Isovolumetric Relaxation
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Ventricular Filling
- Ventricles expand during diastole
- Pressure drops below that of atria so blood rushes in
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3 Phases of Ventricular Filling
- Rapid ventricular filling: blood enters quickly
- Diastasis: blood enters slowly
- Astrial Systole: contraction
- End-Diastolic Volume: amount of blood contained in each ventricle at end of filling (130 mL of blood)
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Isovolumetric Contraction
- Ventricles depolarize (QRS complex)
- Cardiocytes begin to contract, which increases pressure in ventricles
- AV valves close
- Isovolumetric because ventricles haven't yet ejected blood
- Pressure is still high in aorta and pulmonary trunk
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Ventricular Ejection
- Contraction of enough cardiocytes causes pressure in ventricle to exceed that of aorta/pulmonary trunk and semilunar valves to open
- Rapid ejection at first
- Reduced ejection follows
- End Systolic Volume: Amount of blood left behind
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Stroke Volume
- Amount of blood ejected
- Normally about 70 mL
- "Ejection Fraction": about 50% but much higher during vigorous exercise
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Isovolumetric Relaxation
- Early phase of ventricular diastole
- Ventricular expansion reduces pressure
- Fluid in aorta/pulmonary trunk begins to flow backwards but this closes semilunar valves
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What does exercise do?
- Primarily changes cardiac output: Amount ejected by each ventricle in one minute)
- Cardiac Output: Heart rate x stroke volume
- 4-6 L/min at rest
- 21 L/min during vigorous exercise
- Cardiac reserve: difference between maximum CO and resting CO
- Increases with fitness
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How does exercise effect CO?
- Proprioceptors signal cardiac center in medulla to increase sympathetic tone
- Heart rate increase
- Increase in volume of blood returning via veins, so increases ventricular pressure
- SV increase
- Increase SV allows heart to beat more slowly at rest
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Heart Sounds
- "lub dub"
- Lub: S1, loudest and longest sound; closure of AV valves
- Dub: S2, softer and shorter sound; closure of semilunar valves
- S3: normally only in youth and athletes; probably blood moving around between walls and vetricle
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Valvular Insufficiency
Valve doesn't prevent reflux
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Valcular Stenosis
- Cusps of valves are stiffened and opening constricted by scar tissue
- Heart murmer
- Sudden fainting or dizziness
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Mitral Regurgitation
Mitral valve cusps bulge into atria during ventricular contraction
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