The Heart

Location of Heart

• Surrounded by pericardium

• 1.5cm left from center

• Size of a fist• 250-300g

흉골 (胸骨 )

iPad mini: 308g

심낭 , 심막

Anatomy of the Heart

• 4 Chambers• 4 Valves• Aorta– Pulmonary artery

• Veins– Superior vena cava– Inferior vena cava

• Septum– Thicker than RV

walls

Cardiac Muscles

• Myocardium– Striated like skeletal mus-

cles– Divided into 4 groups

• Spirally oriented– 2 groups outside of RV &

LV– 3rd group around RV & LV

• Inside of 1st & 2nd group

– 4th group around LV only– Lower resistance in muscle

fiber direction

Cardiac Muscle Cells• Myocytes• Same activa-

tion like neu-rons– AP about 100mV– But, longer dura-

tion 300ms– Plateau phase

Contraction

• Propagation of AP – From cell to cell

• In any direction

– Rather complex wave-form

– Contraction within plateau

• Conduction barrier– Btw atria & ventricles– Conduction only

through conduction pathway

frog sartorius muscle cell

frog cardiac muscle cell

rat uterus wall smooth muscle cell

Generation of Pulses

• SinoAtrial node on RA– Special muscle cells– Shape of crescent– 15mm long, 5mm wide– Self excitatory– Pacemaker cells

• 70 pulses/min

– Activation start to propagate throughout the atria rather slowly

Conduction to Ventricles

• AtrioVentricular node – Only conducting path – Btw atria and ventricles– Intrinsic frequency

• 50 pulses/min

– Follow higher trigger frequency

Propagation from AV Node

• Bundle of His– Fast conduction– Common bundle– Separate into 2 bundle

branches• Right bundle branch• Left bundle branch

– Purkinje fibers• Diverge to inner side of

ventricles

Propagating Ventricle Walls

• Formation of activa-tion wavefront– Propagation through ven-

tricular mass– Cell to cell activation– From inner to outer side

• Shorter AP impulse in epicardium(outside)– Earlier repolarization than

endocardium(inside)

Electric Events in HeartLocation inthe heart

Event Time [ms]ECG-wave

Conductionvelocity [m/s]

Intrinsicfrequency

[1/min]SA node

Atrium, Right          LeftAV node

Bundle of HisBundle branchesPurkinje fibersEndocardium

  Septum  Left ventricle Epicardium

  Left ventricle  Right ventricle

Epicardium  Left ventricle

  Right ventricle Endocardium  Left ventricle

impulse generateddepolarization depolarization

arrival of impulsedeparture of im-

pulseactivatedactivatedactivated

depolarizationdepolarization

depolarizationdepolarization

  repolarizationrepolarization

 repolarization

05

8550

125130145150

175190

 225250

  400

 600

 PP

P-Qinterval

      

QRS     T

0.050.8-1.00.8-1.0

0.02-0.05

1.0-1.51.0-1.53.0-3.5

0.3 (axial)-

0.8(transverse)

   

0.5

 70-80    

50           

 20-40

Electric Potential Wave-forms

• Intracellular recording– Microelectrodes

inside cardiac cells

Isochronic Ventricle Activation

• By experiment with human heart – Within 30 min post mortem– 870 electrodes

• Initial phase– Radial propagation

• From inside to outside

• In terminal phase– Tangential propagation

Electrocardiogram: ECG

• Recording of electrical activity – Generated by electric activity of the heart– On the surface of thorax– Extracellular electric behavior

• Properties in cardiac cells– Propagation through low resistance gap junc-

tion• Current freely into following cells

– Very restrictive extracellular space• 25% of total volume, ro ri 0

– Linear core conductor model

Linear Core Conductor Model

• Ii=- Io– = - Iiri= Iori, = - Ioro

– =ridx, =-rodx

– Vm= - = (ridx

– dx= Vm /(ri

• = Vm , =- Vm

• “Voltage divider” condition– Relationship of extracellular potential to mem-

brane potential

Depolarization• Wavefront from right to left• Negative during activation

– =- Vm =-(0.5)40mV=-20mV

– Increased Vm during plateau

• Local im in depolarizing re-gion– im =

• Positive VECG potential– Equivalent with potential by

dipole pointing depolarization di-rection

Repolarization

• Different from depolarization– Not propagating activity– Repolarize after certain time after

• Approximate with propagat-ing wavefront– On equal duration of action pulses– Slow recovery: 100ms

• Wide recovery interval

• Negative VECG potential– Equivalent with potential by dipole

pointing reverse direction

Dipole Orientation

• In the example:– Opposite during depolarization and repolarization– Different VECG polarity during depolarization and

repolarization

• In real situation– AP pulse durations are not same

• Actually shorter AP in epicardium than endocardium• Earlier repolarization in epicardium• Same direction of dipole during depolarization and repo-

larization

– Same VECG polarity during de/repolarization

Dipole Orientation

In the example:

In real situation

depolarizationrepolarization