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Biological Sciences
Peter A.Bowler

e109 lecture 11/2/12 The Conducting system of the heart -these involve the non-contractile cells -All cells of the SAnode, AV node, and intermodal pathways are authorhythmic, so another part can “take over” if the SAnode cells are not function -Atria are connected to the ventricles by theAV node How does an ECG (EKG) work? -Established correlation between electrical pattern measured on skin and heart electrical activity -non-invasive (attaches electrodes to outside of body to monitor electrical activity inside of body) -Each red line represents a pair of electrodes -called Weingtopin’s triangle -ECG measurement represents sum of all electrical activity (indirect measurement and complicated to interpret) +depending on where you put the leads, you get a different pattern +different from voltage measurements: measure of inside the cell vs. outside the cell -a Lead consists of two electrodes, one positive and one negative -our bodies are not perfectly electrically insulated -see graph of Temperature vs. time in presentation -Heart is not centrally-located, and is tilted; if position and electrical activity was perfectly symmetrical, ECG would be flat! +there would be no measured difference in electrical activity between the left and right heart -qualitative gross measure -pattern repeated over and over again within an ECG (each represents on cardiac cycle) -x axis (time) and y-axis (Temperature) +PQRST Cardiac cycle: Electrical events of the heart 1. Pwave: Depolarization of the SAnode; “Pwave” associated with atrial depolarization 2. PQ or PR segment: conduction throughAV node andA-V bundle 3. “QRS” wave: correlated with ventricular depolarization 4. T wave: correlated with ventricular repolarization ECG vs. single cardiac cell -ECG is the summed electrical acitivity of all cells recorded from the surface of the body -amplitude of only 1 mV single cardiac cell: -the ventricular action potential is recorded from a single cell using an intracellular electrode. Notice that the voltage change is much grader when recorded intracellularly -amplitude of 110 mV Third-degree block -More atrial contractions than ventricular (P’s are correlated with atrial depolarizations, and R’s with ventricular depolarizations)= atrial contraction is happening faster than ventricular contraction -abnormal ECG Atrial fibrillation -Too-frequent atrial depolarizations (“P”s are correlated with atrial depolarizations, and “R”s with ventric
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