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33 Cards in this Set
- Front
- Back
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Cardiac action potential
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sequential change in electrial potential that occurs across a cell membrane when excitation occurs
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Resting membrane potential
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Electrial gradient just prior to exictation
Ranges from -80 to -90mV Inside of cell is negatively charged in relation to outside |
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Phase 0
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Rapid depolarizaton(contraction) of atrial and ventricular
Rapid influx of Na |
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Phase 1
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Brief repolarization(relax)
Inactivation of Na channels Cl influx and/or K efflux |
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Phase 2
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Plateau(no change)
Ca influx, K efflux Stays constant |
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Phase 3
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Rapid ventricular repolarization
K efflux |
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Phase 4
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Resting membrane potential
Na efflx, K influx Leads to Phase 0 |
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Absoulte refractory period
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Cardiac tissue cannot be excited, stimulated or depolarized at all
Phase 0, 1, 2 and part of 3 |
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Relative refractory period
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Cardiac tissue is more difficult to excite but can still be stimulated
Some part of phase 3 |
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Electrocardigraphic waves & intervals
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P wave: atrial depolarization
PR interval:time b/w atrial contraction & ventricular contraction QRS complex: ventricular depolarization(phase 0) ST segment:plateau(phase 2) T wave: ventricular repolarization(phase 3) QT interval: ventriculaer refractoriness, beginning of QRS complex to end of T wave |
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Mechansim of arrythmia formation
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Errors in impulse generation: abnormal automaticity & triggered activities
Errors in impulse conduction: Reentry |
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Abnormal automaticity
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SA node is a pacemaker
Occurs when impulse generation occurs in tissues other than SA node |
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Causes of abnormal automaticity
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1.Digoxin toxicity
2. ^ sympathetic tone(too much epinephrine, surgery) 3.Hypoxemia 4.dec K 5.Cardiac dilatation (HF) 6.Severe pulmonary disease |
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Reentry
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Arrythmia circuit forms
Can occur anywhere Common in HF, heard disease |
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Requirements of reentry
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1.Premature beat
2.Area of unidirectional block(prolonged refractoriness): can't go forward 3.Slow conduction in other pathway(shorter refractory period):Antergrade pathway:forward contraction but slow 4.Reenters area of unidirectional block(Retrograde pathway) 5.Previously refractory tissue now excitable(due to slow conduction antegrade pathway) |
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AF vs AFL
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AF: multiple reentry circuits
AFL:single reentry circuit |
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AF VS AFL rates
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AF : Atrial rate 400-600 bpm
Ventricular rate:120-180 AFL: Atrial rate: 270-330 Ventricular rate: 1:1(life-threatning) 2:1, 3:1 |
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Epidemiologoy
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Associated with ^ risk of mortality
1.Stroke 2.HF 3.proarrhytmia |
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Increased atrial stretch
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1.HTN
2.Ischemic HD 3.Valvular d/o(mitral stenosis, regurgitation) 4.HF 5.Pulmonary disease(COPD, pulmonary embolus) 6.Obesity |
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Increased sympathetic tone
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1.Hyperthyroidism
2.Alcohol intoxication/withdrawal(Holiday heart) 3.Sepsis/infection 4.Surgery |
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Electrolyte abnormalities
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dec K, Mg, Ca
Lone AF: < 5%, absence of HD, pts <60 yrs |
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Hemodynamic consequences
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Rapid, irregular heart rate:hypotension, angina, syncope
Loss of atrial kick(dec SV, CO) dec ventricular diastole filling time(dec SV, CO) Tachycardia-induced cardiomyopathy |
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Thromboembolic consequences
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Loss of organized mechanical contraction in atrial-pooling of blood in atria(clots)-mitral thrombi
Thrombi can break off(Thrombo stroke) |
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Paroxysmal AF
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Duration < 7 days(often <24 hrs)
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Persistent AF
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Duration > 7 days
requires cardioversion to restore sinus rhythm(electrical or pharm) |
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Recurrent AF
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>2 episodes of paroxysmal or persistent AF
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Permanent AF
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Persistent AF that can't be converted to sinus rhythm or pt isn't a candidate for cardioversion
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Medical history
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Duration of arrythmia(> or < 48 hrs)
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Symptoms
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1.Palpitations
2.Dizziness 3.Fatigue 4.Dyspnea 5.Weakness 6.dec exercise tolerance 7.Syncope 8.HF exacerbation 9.Angina |
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Physical exam
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Irregulary, irregular ventricular rhythm, pulse deficit
AF: Irregular, absence of P waves, F waves insead AFL: Regular |
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Lab tests
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EKG confirms AF
Thrombus formation Valvular disease Size of atria(how long) clots Left ventricualr size & function Electrolytes, Thyroid function tests(hyperthyroidsim) |
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CHADS2
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Congestive HF
HTN Age (>75) Diabetes Stroke or TIA 1 point(CHF, HTN, age>75, diabetes) 2 points(Stroke or TIA) |
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Stroke risk
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Low risk( score=0)
Intermediate risk(score=1) High risk(score > or = 2) |
