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SA node
normal pacemaker of the heart
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AV node
- regulates impulse transmission to the ventricles
- delays impluse slightly to allow for atrial contraction
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Bundle of His
continues conduction from SA/AV to ventricles
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Perkinje fibers
terminal branches, innervates all aspects of ventricular tissue
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PR interval
- atrial depolarization
- delay to the AV node
- 0.12-0.2 seconds
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QRS
- ventricular depolarization
- contraction
- 0.06-0.1 seconds
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P wave
atrial depolarization
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T wave
- ventricular repolarization
- resting and filling
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QT interval
- ventricular depolarization, then repolarization
- < 0.44 seconds
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Heart rate calculation
- 300 divided by # of large boxes
- or
- 1500 divided by # of small boxes
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Rhythm interpretation
- rate
- rhythm (reg or irreg)
- PR interval
- QRS
- QT
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Second degree AV block, Type I
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Second degree AV block, Type II
- has extra nonconducting P waves
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Complete/third degree heart block
- random P waves
- random QRS complexes
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Torsades de pointes
- prolonged QT interval, followed by polymorphic ventricular tachycardia
- caused by CNS disease, certain meds, or low electrolytes
- tx - correct e- imbalance, isoproterenol IV, or use ventricular pacing
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Class I antiarrhythmics
- block sodium channels
- slow or normalize conduction, depolarization, repolarization
- e.g. dilantin, lidocaine
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Class II antiarrythmics
- decrease sympathetic activity in SA/AV nodes
- prolong refractory period
- treats ST, Afib/flutter
- e.g. propanolol
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Class III antiarrhythmics
- prolong action potention
- used in VT, VF, Afib
- e.g. amiodarone, ibutilide, sotolol
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Class IV antiarrythmics
- calcium channel blockers
- slow AV node conduction
- e.g. verapamil
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Misc. antiarrhythmics
- slows AV conduction
- e.g. adenosine
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ST elevation
- acute MI
- injury: arterial occlusion with ischemia
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ST depression
ischemia: lack of oxygen to the cardiac tissue
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Meds for acute MI
- ASA
- Plavix (ADT blockers/theinopyridine antiplatelet)
- Heparin
- Glycoprotein IIb/IIIa inhibitors (eptifibatide, abciximab)
- Fibrinolytics (Activase - clot busting)
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Stroke volume
the amount of blood ejected with each heartbeat
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Cardiac output
- amount of blood pumped by the ventricles
- liters per minute
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Preload
degree of stretch of the cardiac muscle fibers at the end of diastole
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Contractility
ability of the cardiac muscle to shorten in response to an electrical impulse
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Afterload
the resistance to ejection of blood from the ventricle
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Ejection fraction
the fraction of end-diastolic volume ejected with each heartbeat
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Cardiac index
- cardiac output adjusted to body size
- better parameter than cardiac output
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Meds to increase BP
- epinephrine
- norepinephrine (dysrhythmias, severe HTN, HA)
- dopamine (caution w/ ischemic heart disease)
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Post-op complications for CABG
- dysrhythmias (AF)
- pre + post beta blocker therapy
- heparin for pts in Afib for more than 24 hours
- ventricular disrhythmias w/ electrolyte imbalances
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Cardiac tamponade
- restriction of heart function due to fluid from pericardial effusion (accumulation of fluid in pericardial sac)
- decreased venous return, decreased cardiac output
- falling systolic BP, narrowing pulse pressure, rising venous pressure, SOB, visible neck veins
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Cardiomyopathy
- progressive events that result in impaired cardiac output
- can lead to heart failure, sudden death, dysrhythmias
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