Week_3_Cardiology

# Week_3_Cardiology - Lec 14 Risk Ratios and Confounding...

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Lec. 14 Risk Ratios and Confounding Incidence vs Prevalence Incidence is how many new events per time period Prevalence is how many people have the condition during any given time Relative Risk Aka risk ratio. Says how many times more likely something will happen if exposed to risk factor Compares incidence or prevalence rate in one population to another Disease + Disease - Total Risk + a b a+b Risk - c d c+d TOTAL a+c b+d RR= ( + ) ( + ) a a b c c d = (% of ppl with disease and risk factor) / (% of ppl w/ disease and no risk factor) Odds Ratio Compares the odds of two factors o Odds are the likelihood an event will happen ex) 6:1-random day is not a Sunday, or 1:1-random person is male Disease + Disease - Total Risk + a b a+b Risk - c d c+d TOTAL a+c b+d Odds ratio = abcd = number can be between 0 and infinite Confounding A confounding variable is an extraneous variable that just happens to correlate positively or negatively with a data set o When a cause and relation are not actually linked Ex) people who drink coffee have ↑ risk for heart disease o Actually people smoke usually drink coffee and the smoking is the cause of the heart disease Can cope with confounding by matching up groups, adjustments in age, multiple linear regressions. .. Lec. 15 Electrocardiography and ECG

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Cardiac Vector Sum of all electric force vectors in the heart at any given moment. Is a 3-D vector Always point in direction of positive current o Same direction as depolarization o Opposite direction as repolarization Vector direction and amplitude change with time Vector planes Heart vectors measures in two planes: Frontal and Transverse o The recordings on an ECG are along the X axis of each plane o I need to know orientation and polarities of the different leads o When vector is in direction of + end of lead then recording is positive
Leads and ECG output 12 leads output 12 plots of vector amplitude vs time o To determine magnitude of a cardiac vector only have to use 2 leads, but common practice uses 12 Horizontal axis is 1mm box for .04sec and vertical is 1mm box for .1mV Normal Basic Patterns of ECG Wave P wave - atrial depolarization QRS complex - ventricle depolarization T wave - ventricle repolarization P Wave Commonly looked at using lead II P wave points left and inferiorly First RA depolarizes and generates first signal then LA depolarizes and generated 2nd signal o Because depolarize in stages vector forms a smooth curve Lead II gives a positive signal while lead aVR gives an inverted reading for the P wave Gap of time between P wave and QRS complex is PR segment Ventricular Depolarization - QRS Complex Nomenclature Different nomenclature for readings of QRS complex from different leads o If initial wave is negative is labeled Q o First positive wave is R o Second positive wave is R' o Wave that follows R and is negative is S o A single negative peak is called QS o Large waves a gives uppercase letters small waves lowercase letters

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Week_3_Cardiology - Lec 14 Risk Ratios and Confounding...

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