心电.ppt

The function of circulatory system Transports materials throughout the body Nutrients, water, gases (O2, CO2), hormones, etc Keeps homeostasis of internal environment Regulates body temperature Endocrines atrial diuretic peptide, vascular active substances Transmembrane potential of the cardiomyocyte Resting potential: varies with different cells Maximal diastolic potential: shown only in cells with autorhythmicity Types of the cardiomyocytes Fast response cells: 1. Contractile (working) cells: ventricular myocytes atrial myocytes 2. Autorhythmic cells: His bundle, Purkinje fibers Internodal pathways Slow response cells: 1. Autorhythmic cells: pacemaker cells in sinus node, atrial-nodal zone and nodal-His zone of the AV node 2. Non-autorhythmic cells: cells in AV nodal zone 1. Transmembrane potential of the  cardiac working (contractile) cells Resting potential: ?80 ? ?90 mV, IK1 channel (Kir channel) Action potential: fast response, 4 phases 2. Diastolic depolarization in cardiac autorhythmic cells Purkinje fiber: If, IK P cell in the sinus node: If, ICaT, IKr Physiological characteristics of cardiomyocyte Excitability （兴奋性） Conductivity （传导性） Autothythmicity (or pacemaker activity) （自律性） Contractility （收缩性） Key point: The ECG recorded by each of the six limb leads is the projection of the frontal vector ring on the respective lead axis. (六个肢体导联所记录的心电图是额面向量环在各导联上的投影) Vector rings: 1. P vector ring 2. QRS vector ring 3. T vector ring Normal QRS and T vector rings QRS and T vector rings in cardiac hypertrophy What will happen if heart rate is too fast? 1. Decrease in cardiac output 2. Instability of cardiac electrophysiology, VF 3. Heart failure Epicardiogram HR 333 bpm VF HR 200 bpm Periodic HR 30