同济大学：《生理学》课程电子教案（PPT课件）03 Basics of the ElectroCardioGram（ECG）

0 +++++++++ Depolarization 白 wave 行行行用 B Figure 11-2 from Guyton Text

Extracellular voltages recorded from cells. 1.No activity...no potentials Voltmeter ++++++++++++ 十 ■ ■一■■■■■■ +++++++++++++ Cardiac cell in resting state.No Action Potential. No extracellular voltage differences

Extracellular voltages recorded from cells. 2.Advance of an Action Potential...extracellular voltage is detected ▣===+十十+十十 十++++十+■一==▣▣ 十十十十十十十====== ■-■■■一■十++十+十 Action potential is here No AP here Action potential reaches half way along the cell. There is an extracellular voltage between the ends of the cell. There is a positive voltage in the direction of the Action Potential

Extracellular voltages recorded from cells. 3.Plateau of the Action Potential...isopotential. Voltmeter 0 ■=■=一■■==■■一 ++十++++++++++ +++++++十+++++ Action potential covers entire cell. No extracellular voltage differences

The standard way of representing extracellular voltages caused by action potentials: ▣=一=▣■▣++十+十十 十++十十+十=一一一一▣ 十++十十十+▣-■✉= ■■■■=■+十++十十 1.Here is a cell with an action potential. X 2.Represent the cell as a dipole 3.Use an arrow to denote the polarity of the dipole

Represent the activity of many cells as a Net Dipole +++++t+特 ■一■■=■+十十+++ ==■=■■++十+++ +++++++一一一一一▣ +++++++ ±共++±+中++++ ■=+十十++十 +++++干+合 ■■=■■■+十十+十十 The sum of the individual A sheet of cells with APs Represent each dipoles a Net Dipole cell as a dipole

Relationship between the direction of the dipole and the orientation of the recording axis

0 Figure 11-4 from Guyton.The arrows represent the net dipoles for 2 regions

Depolarized RA LA cells SA Wavefront of node electrical activity Net dipole Atria Ventricles L Action potentials propagating through the heart create a net dipole that projects onto each lead

SA node 0 Sequence of activation of heart. Cells activated by action potentials are depicted in yellow. 2 The first cells to reach threshold are in the SA node APs are conducted to the AV node through atrial myocytes. anter Conduction is slow through the AV node. From the AV node APs are conducted through Purkinje fibers(Bundle of His)to the bottom of the ventricles. myocard,froe The bundle splits into right and left branches and activates myocytes in the right and left ventricles