The Heart Location of Heart Surrounded by pericardium
The Heart
Location of Heart 흉골(胸骨) • Surrounded by pericardium심낭, 심막 • 1. 5 cm left from center • Size of a fist • 250 -300 g i. Pad mini: 308 g
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 muscles – Divided into 4 groups • Spirally oriented – 2 groups outside of RV & LV – 3 rd group around RV & LV • Inside of 1 st & 2 nd group – 4 th group around LV only – Lower resistance in muscle fiber direction
Cardiac Muscle Cells • Myocytes • Same activation like neurons – AP about 100 m. V – But, longer duration 300 ms – Plateau phase
Contraction • Propagation of AP frog sartorius muscle cell – From cell to cell • In any direction – Rather complex waveform – Contraction within plateau frog cardiac muscle cell • Conduction barrier – Btw atria & ventricles – Conduction only through conduction pathway rat uterus wall smooth muscle cell
Generation of Pulses • Sino. Atrial node on RA – – – Special muscle cells Shape of crescent 15 mm long, 5 mm wide Self excitatory Pacemaker cells • 70 pulses/min – Activation start to propagate throughout the atria rather slowly
Conduction to Ventricles • Atrio. Ventricular 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 activation wavefront – Propagation through ventricular mass – Cell to cell activation – From inner to outer side • Shorter AP impulse in epicardium(outside) – Earlier repolarization than endocardium(inside)
Electric Events in Heart Location in the heart SA node Atrium, Right Left AV node Bundle of His Bundle branches Purkinje fibers Endocardium Septum Left ventricle Epicardium Left ventricle Right ventricle Endocardium Left ventricle Event Time [ms] impulse generated depolarization arrival of impulse departure of impulse activated 0 5 85 50 125 130 145 150 depolarization 175 190 depolarization 225 250 repolarization 400 repolarization 600 ECGwave P P P-Q interval QRS T Conduction velocity [m/s] 0. 05 0. 8 -1. 0 0. 02 -0. 05 Intrinsic frequency [1/min] 70 -80 50 1. 0 -1. 5 3. 0 -3. 5 0. 3 (axial) 0. 8 (transverse) 0. 5 20 -40
Electric Potential Waveforms • 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 junction • Current freely into following cells – Very restrictive extracellular space • 25% of total volume, ro ri 0 – Linear core conductor model
Linear Core Conductor Model •
Depolarization •
Repolarization • Different from depolarization – Not propagating activity – Repolarize after certain time after • Approximate with propagating wavefront – On equal duration of action pulses – Slow recovery: 100 ms • 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 repolarization – Same VECG polarity during de/repolarization
Dipole Orientation In the example: depolarization In real situation repolarization
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