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به نام یکتای جهان آفرین ECG H.R Tohidypour OVERVIEW Cardiac Physiology Electrocardiography Cardiac Physiology Electrocardiography Diagnosis ARTERIES VEINS distributes blood from heart brings blood back to heart Cardiac Physiology Electrocardiography Diagnosis Atria Ventricles Cardiac Physiology Electrocardiography Diagnosis Sinoatrial Node Atrioventricular Node Conduction System of the Heart: A Conceptual Model for Illustration SA Node Inter-nodal Tract Left Bundle Branch AV Node Bundle of HIS James Fibers Right Bundle Branch Bundle of Kent Septal Depolarization Fibers Anterior Superior Fascicle Posterior Inferior Fascicle Basic conduction mechanisms • Sinoatrial node (SA node)- primary pacemaker of the heart • Atrioventricular node (AV node) • His Bundle • Bundle branches • Purkinje fibers Extrinsic Innervation of the Heart • Heart is stimulated by the sympathetic cardioacceleratory center • Heart is inhibited by the parasympathetic cardioinhibitory center Cardiac Cycle • Cardiac cycle refers to all events associated with blood flow through the heart – Systole – contraction of heart muscle – Diastole – relaxation of heart muscle Cardiac Physiology Electrocardiography Diagnosis Introduction to Electrocardiography (ECG, EKG) • • • • • Electrocardiography - graphic recording of the electrical activity (potentials) produced by the conduction system and the myocardium of the heart during its depolarization / re-polarization cycle. During the late 1800's and early 1900's, Dutch physiologist Willem Einthoven developed the early electrocardiogram. He won the Nobel prize for its invention in 1924. Hubert Mann first uses the electrocardiogram to describe electrocardiographic changes associated with a heart attack in 1920. The science of electrocardiography is not exact. The sensitivity and specificity of the tool in relation to various diagnoses are relatively low Electrocardiograms must be viewed in the context of demographics, health histories, and other clinical test correlates. They are especially useful when compared across time to see how the electrical activity of the heart has changed (perhaps as the result of some pathology). Design considerations: differential recordings • ECG recording is differential = recorded as potential difference between two leads. • This is due to presence of significant electric noise. Typically 60 Hz noise is present and equally distributed over the entire body patients body. Noise amplitude ~100mV, ECG signal amplitude ~1-5 mV <<100mV!!! Subtractions of two signals, recorded from two • different locations will eliminate noise. Differential recording of ECG Accessories used Cardiac Physiology R T P Q S Electrocardiography Diagnosis Cardiac Physiology R T P Q S Electrocardiography Diagnosis Electrical Conduction in Heart 1 1 SA node AV node 2 THE CONDUCTING SYSTEM OF THE HEART 1 SA node depolarizes. SA node 3 Internodal pathways 2 Electrical activity goes rapidly to AV node via internodal pathways. 3 Depolarization spreads more slowly across atria. Conduction slows through AV node. AV node A-V bundle Bundle branches 4 Purkinje fibers 5 4 Depolarization moves rapidly through ventricular conducting system to the apex of the heart. 5 Depolarization wave spreads upward from the apex. Purple shading in steps 2–5 represents depolarization. Electrical Activity P wave: atrial depolarization START P The end R PQ or PR segment: conduction through AV node and A-V bundle T P P QS Atria contract. T wave: ventricular Repolarization Repolarization R T P ELECTRICAL EVENTS OF THE CARDIAC CYCLE QS P Q wave Q ST segment R R wave R P QS P R Ventricles contract. Q P S wave QS Cardiac Physiology R 1 sec T P Q S 0.5 Sec Electrocardiography Diagnosis • The normal electrocardiogram is composed of a P wave, a QRS complex, and a T wave. • The QRS complex is often, but not always, three separate waves: the Q wave, the R wave, and the S wave. • The P wave is caused by electrical potentials generated when the atria depolarize before atrial contraction begins. • The QRS complex is caused by potentials generated when the ventricles depolarize before contraction, that is, as the depolarization wave spreads through the ventricles.Therefore, both the P wave and the components of the QRS complex are depolarization waves. Normal Voltages in the Electrocardiogram. • The recorded voltages of the waves in the normal electrocardiogram depend on the manner in which the electrodes are applied to the surface of the body and how close the electrodes are to the heart. • When one electrode is placed directly over the ventricles and a second electrode is placed elsewhere on the body remote from the heart, the voltage of the QRS complex may be as great as 3 to 4 millivolts. • When electrocardiograms are recorded from electrodes on the two arms or on one arm and one leg, the voltage of the QRS complex usually is 1.0 to 1.5 millivolt from the top of the R wave to the bottom of the S wave; the voltage of the P wave is between 0.1 and 0.3 millivolt; and that of the T wave is between 0.2 and 0.3 millivolt. Comparison of an ECG and a myocardial action potential • P-Q or P-R Interval. The time between the beginning of the P wave and the beginning of the QRS complex is the interval between the beginning of electrical excitation of the atria and the beginning of excitation of the ventricles. This period is called the P-Q interval. The normal P-Q interval is about 0.16 second. (Often this interval is called the P-R interval because the Q wave is likely to be absent.) • Q-T Interval. Contraction of the ventricle lasts almost from the beginning of the Q wave (or R wave, if the Q wave is absent) to the end of the T wave. This interval is called the Q-T interval and ordinarily is about 0.35 second. Rate of Heartbeat as Determined from the Electrocardiogram • The rate of heartbeat can be determined easily from an electrocardiogram because the heart rate is the reciprocal of the time interval between two successive heartbeats. If the interval between two beats as determined from the time calibration lines is 1 second, the heart rate is 60 beats per minute. The normal interval between two successive QRS complexes in the adult person is about 0.83 second. This is a heart rate of 60/0.83 times per minute, or 72 beats per minute. Limb Leads • Standard ECG Leads (The Einthoven limb leads) are defined as follows According to the Einthoven triangle and Kirchhoff’s voltage law, the standard lead voltages have the following relationship: Hence only two of these three leads are independent. Wilson Central Terminal • Unipolar potential definition by Frank Norman Wilson (1890-1952): unipolar potentials should be measured with respect to the central terminal (CT). • To satisfy the conservation law of current, the total current into the CT from the limb leads must add to zero. Thus, we have: Goldberger Augmented Lead • Three additional limb leads, VR, VL, and VF are obtained by measuring the voltage between each limb electrode and the Wilson CT. For instance, the left leg lead is given by: E. Goldberger observed in 1942 that these signals can be augmented by omitting that resistance from the Wilson CT, which is connected to the measurement electrode. In this way, the aforementioned three limb leads, VR, VL, and VF may be replaced with a new set of leads that are called augmented leads. The equation for augmented left leg lead is: Three additional leads can be obtained by comparing each limb lead potential with the central terminal voltage. For example, from (*) we have, for the right arm, If, in creating the CT voltage, the connection to RA is dropped, then in place of (VR) we have: • A comparison of Eq. VR with Eq. aVR shows the augmented signal to be 50% larger than the signal with the Wilson CT chosen as reference. Electrocardiographic Leads • Three Bipolar Limb Leads • Chest Leads (Precordial Leads) • Augmented Unipolar Limb Leads Three Bipolar Limb Leads • Lead I. In recording limb lead I, the negative terminal of the electrocardiograph is connected to the right arm and the positive terminal to the left arm. • Lead II. To record limb lead II, the negative terminal of the electrocardiograph is connected to the right arm and the positive terminal to the left leg. • Lead III. To record limb lead III, the negative terminal of the electrocardiograph is connected to the left arm and the positive terminal to the left leg. Chest Leads (Precordial Leads) • Often electrocardiograms are recorded with one electrode placed on the anterior surface of the chest directly over the heart at one of the points.This electrode is connected to the positive terminal of the electrocardiograph, and the negative electrode, called the indifferent electrode, is connected through equal electrical resistances to the right arm, left arm, and left leg all at the same time, as also shown in the figure. Usually six standard chest leads are recorded, one at a time, from the anterior chest wall, the chest electrode being placed sequentially at the six points shown in the diagram. The different recordings are known as leads V1, V2, V3, V4, V5, and V6. • In leads V1 and V2, the QRS recordings of the normal heart are mainly negative because , the chest electrode in these leads is nearer to the base of the heart than to the apex, and the base of the heart is the direction of electronegativity during most of the ventricular depolarization process. • the QRS complexes in leads V4,V5, and V6 are mainly positive because the chest electrode in these leads is nearer the heart apex, which is the direction of electropositivity during most of depolarization. Augmented Unipolar Limb Leads • Two of the limbs are connected through electrical resistances to the negative terminal of the electrocardiograph, and the third limb is connected to the positive terminal. • When the positive terminal is on the right arm, the lead is known as the aVR lead; when on the left arm, the aVL lead; and when on the left leg, the aVF lead. •Normal recordings of the augmented unipolar limb leads, are all similar to the standard limb lead recordings, •except that the recording from the aVR lead is inverted. Principles of Vectorial Analysis of Electrocardiograms • heart current flows in a particular direction in the heart at a given instant during the cardiac cycle. • A vector is an arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction. • Also, by convention, the length of the arrow is drawn proportional to the voltage of the potential. The Concept of a “Lead” RA & LA - Augmented Voltage Leads AVR, AVL, and AVF LEAD AVR RA By combining certain limb leads into a central terminal, which serves as the negative electrode, other leads could be formed to "fill in the gaps" in terms of the angles of directional recording. These leads required augmentation of voltage to be read and are thus labeled. LEAD AVL + + - RA & RL LA LL & LA LL + LEAD AVF The Concept of a “Lead” Summary of the “Limb Leads” Each of the limb leads (I, II, III, AVR, AVL, AVF) can be assigned an angle of clockwise or counterclockwise rotation to describe its position in the frontal plane. Downward rotation from 0 is positive and upward rotation from 0 is negative. LEAD AVR LEAD AVL -150o -30o 0o LEAD I 60o 120o LEAD III 90o LEAD AVF LEAD II Hexaxial Array for Axis Determination – Example 1 Lead I If lead I is mostly positive, the axis must lie in the right half of of the coordinate system (the main vector is moving mostly toward the lead’s positive electrode) Hexaxial Array for Axis Determination – Example 1 Lead AVF If lead AVF is mostly positive, the axis must lie in the bottom half of of the coordinate system (again, the main vector is moving mostly toward the lead’s positive electrode Hexaxial Array for Axis Determination – Example 1 I AVF Combining the two plots, we see that the axis must lie in the bottom right hand quadrant Cardiac Physiology Electrocardiography Diagnosis Atrioventricular Block • Ischemia • Nodal Compression • Nodal Inflamation • Extreme Stimulation Cardiac Physiology Electrocardiography Diagnosis Normal ECG ECG with Atrioventricular Block Cardiac Physiology Electrocardiography Diagnosis Preventricular Contractions • Coffee • Cigarettes • Sleep deprivation • Pathology Cardiac Physiology Electrocardiography Diagnosis Normal ECG ECG with Preventricular Contractions Cardiac Physiology Electrocardiography Diagnosis Ventricular Fibrilation • Ischemia • Electric Shock Cardiac Physiology Electrocardiography Diagnosis Normal ECG ECG during Ventricular Fibrillation Abnormal Sinus Rhythms • Tachycardia : means fast heart rate, usually defined in an adult person as faster than 100 beats per minute • Bradycardia : means a slow heart rate, usually defined as fewer than 60 beats per minute. ECG Changes : Ischemia • • • • T-wave inversion ( flipped T) ST segment depression T wave flattening Biphasic T-waves Baseline ECG Changes: Injury • ST segment elevation of greater than 1mm in at least 2 contiguous leads • Heightened or peaked T waves • Directly related to portions of myocardium rendered electrically inactive Baseline Evolving MI and Hallmarks of AMI Q wave ST Elevation 1 year T wave inversion Now…The Circuit • PreAmp • Low Pass Filter • High Pass Filter Noise • Several sources •60Hz power lines – shielding, filtering •Other biopotentials – filtering •Motion artifacts – relaxed subject •Electrode noise – high quality electrodes, good contacts •Circuit noise – good design, good components When measuring biopotentials (say ECG), EVERYTHING else creates noise – power line interference – even other biopotentials (like EEG, EMG, EOG) are noise sources. These have characteristic frequencies. So use Band Pass Filters. Pass only fL to fH attenuate the others. fL fH Frequencies of Biopotentials Signal ECG Frequency range (Hz) 0.01 – 300 Amplitude range(mV) 0.05 – 3 EEG 0.1 – 100 0.001 – 1 EOG 0.1 – 10 0.001 – 0.3 EMG 50 – 3000 0.001 – 100 QRS Detector Components • Why detect QRS Complex? 1. Most Rhythm analysis algorithms are based on QRS complex 2. Used in the diagnosis of Tachycardia 3. Largest amplitude and sharpest waveform the can be extracted from the ECG Preprocessing Stage filters the signal down to the range of 10Hz to 25Hz. Activation Currents in Cardiac Tissue • However, the electrocardiogram (ECG) is a recording of the electric potential, generated by the electric activity of the heart, on the surface of the thorax. The ECG thus represents the extracellular electric behavior of the cardiac muscle tissue. • There are two important properties of cardiac tissue that we shall make use of to analyze the potential and current distribution associated with these propagating waves. First, cells are interconnected by low-resistance pathways (gap junctions), as a result of which currents flowing in the intracellular space of one cell pass freely into the following cell. Second, the space between cells is very restrictive (accounting for less than 25% of the total volume). As a result, both intracellular and extracellular currents are confined to the direction parallel to the propagation of the plane wavefront. Io+Ii=0 Integrating from x = – inf Vm = phi(i) – phi(o) , to +inf x = x gives Thank you