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31 Cards in this Set
- Front
- Back
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vector at 0 degrees is in what orientation
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exactly horizontal and pointing to person's left side
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which direction does the scale of vectors rotate
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clockwise from L horizontal
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average direction on vector during depolarization
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59 degrees
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How to determine an individual lead potential from the average potential of all leads
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draw line perpendicular to lead from tip of average potential vector
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Instantaneous voltage calculation
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length between axis and perpendicular line divided by length of average vector all multiplied by 2 mV
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order of repolarization in ventricles
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epicardium to endocardium (why the T wave is positive)
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Postulated reason why endocardium repolarizes last in ventricles
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high BP inside ventriles reduces coronary blood flow to endocardium, slowing repolarization
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length of ventricular repolarization
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0.15 s
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vectorcardiogram
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shows changes in average direction of electical potential in heart during the cadiac cycle
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normal deviation of mean electrical axis
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59 degrees average, range from 20-100 degrees
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causes of left shift of mean electrical axis
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end of deep expiration; lying down; obese people
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causes of right shift of mean electrical axis
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end of deep inspiration; standing up; tall lanky people
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abnormal reasons of mean electrical axis shift
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hypertrophy (shift toward); bundle branch block
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reasons for L ventricular hypertrophy
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hypertension, aortic valvular stenosis, aoritic valvular regurgitation
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reasons for R ventricular hypertrophy
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congenital pulmonary valve stenosis, tetralogy of Fallot, interventricular septal defect
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bundle branch block
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mean electrical axis shifts toward block; prolonged QRS complex
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Variation in QRS complex voltage of limb leads
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0.5 to 2.0 mV (lead III < lead I < lead II);sum of all leads greater than 4 mV is considered a high-voltage ECG
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Causes of abnormal voltage in QRS complex (peak of R to bottom of S)
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Increases muscle mass (hypertrophy-increases mV); old Mis (decrease mV and prolongs QRS complex); fluid in pericadium (decrease mV); pulmonary emphesema (decrease mV)
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How does fluid in the pericardium affect conduction
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large portion of electricity flows into pericarial fluid and away from heart "short circuiting" the heart (pleural effusion can also cause, although affect smaller)
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Pulmonary emphysema affect on heart conduction
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conduction depressed due to excessive quantity of air in lungs; lungs also insulate heart as they enlarge
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purkinje system block
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AP travels through cardiac muscle - decreases speed by 1/3; QRS complex duration increases
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What is considered an abnormal length of QRS complex
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0.09 s or greater
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what is Current of injury
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occurs when injured area remains partially or totally depolarized ALL the time
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what causes current of injury
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mechanical trauma; infectious process; ischemia (most common)
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What is the J point
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after the QRS complex when everything is depolarized (used as a reference point when there is a current of injury)
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what is indicated by strong negative injury potential in V2
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anterior wall infarction
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What kind of infarction developes a Q wave at the beginning og the QRS complex in lead I
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anterior infarction due to loss of muscle mass in anterior wall of L ventricle
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What kind of infarction developes a Q wave at the beginning of the QRS complex in lead III
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posterior infarction due to loss of muscle mass in posterior apical part of ventricle
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What do you look for in electrocadiogram of patient exercising that shows mild coronary insufficiency
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inverted T wave in ANY lead (or biphasic wave)
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Sign of digitalis toxicity
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inverted or biphasic T wave
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what does digitalis do
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increases strength of cadiac contraction (used during coronary insufficiency)
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