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K 305 16 May 03 03/05/16 1 Cardiac Excitation Cardiac Action Potential Ionic Basis of Ventricular AP Initiation of Excitation Propagation of Excitation EKG 03/05/16 2 Information garnered from EKG •anatomical orientation of heart •chamber sizes •arrhythmias and conduction problems •ischemia - degree and location •previous MIs 03/05/16 3 03/05/16 4 Action Potentials in Myocardium Superior Vena Cava SA Node Atrium AV Node Purkinje Tricuspid Valve Mitral Valve Ventricle R T ECG P Q S 03/05/16 PR 5 QRS EKG conventions: •currents move from positive to negative •currents moving towards positive (or recording) electrode produce an upward deflection on EKG chart 03/05/16 6 •Bipolar EKG Leads •Standard limb leads •Unipolar leads •augmented aVR = right arm aVL = left arm aVF = foot •precordial 6 chest leads across intercostal spaces (V1-V6) 03/05/16 7 Standard bipolar limb leads (Figures 22-33, 22-34) bipolar (remember the polarity) Einthoven's triangle lead 1: LA+ RA lead 2: LL+ RAlead 3: LL+ LAAnatomic orientation and dimensions of chambers Remember : I + III = II 03/05/16 8 03/05/16 9 03/05/16 10 03/05/16 11 Information garnered from EKG •anatomical orientation of heart •chamber sizes •arrhythmias and conduction problems •ischemia - degree and location •previous MIs 03/05/16 12 03/05/16 13 03/05/16 14 Information garnered from EKG •anatomical orientation of heart •chamber sizes •arrhythmias and conduction problems •ischemia - degree and location •previous MIs 03/05/16 15 arrhythmias and conduction problems •Bundle branch block •Long QT syndrome 03/05/16 16 arrhythmias and conduction problems •Bundle branch block •Long QT syndrome 03/05/16 17 03/05/16 18 Action Potentials in Myocardium Superior Vena Cava SA Node Atrium AV Node Purkinje Tricuspid Valve Mitral Valve Ventricle R T ECG P Q S 03/05/16 PR 19 QRS arrhythmias and conduction problems •Bundle branch block •Long QT syndrome 03/05/16 20 03/05/16 Long QT syndrome - QT > 0.5s 21 HERG Long QT mutations T474I S1 S2 S3 S5 G628S S6 V822M NH2 COOH 03/05/16 22 03/05/16 23 Boy with congenital Long QT syndrome that becomes “torsades de pointes”. Q T QT interval > 0.6 s 03/05/16 24
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