E C G Electro Cardio Graphy Sandipan Dasgupta

E C G Electro Cardio Graphy Sandipan Dasgupta (10 MS 12) 3 rd year UG, Department of Biological Sciences Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

In this presentation. . • • • ECG – A thumbnail account. Brief history of ECG. Underlying principle of ECG – Physics Description of the device – Engineering Clinical significance – Physiology Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

ECG – A thumbnail account German: “Electro” + “kardia” + “graphia” Also, called “Electro-kardio-graphy (EKG)” A procedure for recording the electrical activity of heart in the form of a graphical representation. Note: q. Electrocardiography: The procedure q. Electrocardiogram: The recording Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

A brief history: 1872: Alexandar Muirhead attached wires to the wrist of patients to measure the electrical activity. 1877: Augustus Waller measured heart rate in real time using the Lippman‘s capillary electrometer. 1901: Willem Einthoven discovered the string galvanometer, which was thousands of time more sensitive than capillary electrometer. 1924: Nobel Prize in Medicine. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Basic principle Moving coil Galvanometer q Conversion of Electrical energy to Mechanical energy. q Moving charges experience a force in a magnetic field. q Current carrying coil undergoes rotation (by torque due to magnetic field) , proportional to the current in the coil. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Einthoven’s Galvanometer Willem Einthoven invented this device which consists of a filament placed within strong electro magnetic field. The filament moved sideways in proportion to the current through the filament. The current from the human body was conducted to the filament by salt solution Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Einthoven’s Galvanometer Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

The Cardiac Cycle: the electrical, pressure and volume changes that occur in a functional heart between successive heart beats. • Phase of the cardiac cycle when myocardium is relaxed is termed diastole. • Phase of the cardiac cycle when the myocardium contracts is termed systole. • Atrial systole: when atria contract. • Ventricular systole: when ventricles contract. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Mechanical Changes 1. Ventricular Filling Period [ventricular diastole, atrial systole] 2. Isovolumetric Contraction Period [ventricular systole] 3. Ventricular Ejection Period [ventricular systole] 4. Isovolumetric Relaxation Period [ventricular diastole, atrial diastole] Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

What does ECG record? q These mechanical changes in the heart can be detected by the monitoring the changes in the electrical impulses from the heart. q Situated in the right atrium, is a group of cells (the ‘SA node’) which generate the electrical impulses by complex change in ionic concentration. q A cell-to-cell propagation of these signals take place throughout the myocardium to bring about the mechanical changes, assisted by AV Node and His-Purkinje fibres. q Since body acts as a resistive medium, these impulses move to the body surface, which can be accurately recorded by ECG. q The strength of the ECG signal is thus, dependent on the mass of tissue excited by the signal. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Modern ECG Recorder q In a standard ECG, 9 electrodes are stationed at various parts of the body. q The differential reading between 2 points of the body is called a “Lead”. q Most commonly, 12 such leads are taken into consideration and hence called “ 12 -lead standard ECG”. q Out of these 12, : Ø 3 are limb leads ( I, III) Ø 3 are augmented leads ( a. VR, a. VL, a. VF) Ø 6 are chest leads (V 1, V 2, V 3, V 4, V 5, V 6) q The first six monitors heart’s activity in frontal plane, whilst the last six monitors the heart’s activity in horizontal plane. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

The Electrodes positioning § The first three electrodes are places in right arm (RA), left arm (LA), and the left leg (LL). § There also six chest electrodes positioned horizontally around the left anterior hemi-thorax between the 4 th and 5 th interspaces. Leads from electrodes RA, LL span the entire frontal plane of the body Lead Coordinate ( °) I 0 II 60 III 120 a. VR -150 a. VL -30 a. VF 90 Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata Lead Position V 1, V 2 Right ventricle V 3, V 4 Ventricular septum; Anterior wall of the left ventricle V 5, V 6 Leftt Ventricle

ECG limb and augmented leads Leads I, III are bipolar while others are unipolar. o Limb I, III are measured by differential reading between three electrodes. o Leads a. VR, a. VF, a. VL uses the same electrode but a different reference potential called Wilson’s Composite terminal (WCT) (which approximates to zero) o Note: 1. I + (-II) + III = 0 (Einthoven’s relation) 2. Lead I, III forms a network (Einthoven’s triangle) Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

The Chest leads § Each of the chest leads, are unipolar, measured w. r. t to Wilson Composite Terminal (WCT). § Together with the limb leads and augmented leads, the chest leads form two orthogonal planes which monitors the electrical signal. Note: The 12 -lead data are NOT orthogonal. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Modern ECG measurements NOTE: Both the amplitude and the direction of signal is essential for ECG signal Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

ECG output layout The ECG Graph paper is a heat-sensitive substance coated paper in which the data is recorded by heated stylus. Note: Usual rate of recording: 25 mm/s, but it is customisable. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

A 12 -lead ECG strip Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

A resting state ECG Key durations: 1. Ventricular systole: 0. 3 s 2. Ventricular diastole: 0. 5 s 3. Entire cardiac cycle: 0. 8 s Isopotential line Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Interpretation of ECG data 1. P wave: During normal atrial depolarization, the main electrical impulse from SA Node spreads from the right atrium to the left atrium, thus forming the P wave. (80 ms) 2. PR Interval: Measured from the beginning of the P wave to the beginning of the QRS complex. It reflects the time the electrical impulse takes to travel from the sinus node through the AV node and entering the ventricles. (120 -200 ms). Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Interpretation of ECG data 3. QRS Complex: Rapid depolarization of the right and left ventricles. Much larger amplitude than P wave, due to large muscle mass of ventricles. ( 80 -120 ms). 4. ST Segment: The ST segment connects the QRS complex and the T wave. The ST segment represents the period when the ventricles are depolarized. It is isoelectric. (80 – 120 ms) Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Interpretation of ECG data 5. T wave: Represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. (160 ms) Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

ECG are useful… To detect abnormal characteristics of the cardiac cycle , like: 1. Bradycardia. 2. Tachycardia. 3. Ischemia. 4. Arythmmia. 5. Heart Blockage. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

ECG: My Summary Classical electricity and magnetism Physiology Modern Hi-end electronics engineering Einthoven’s brilliance Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Before concluding… Why Einthoven was a genius? Modern 12 lead-ECG’s are more sophisticated, compact, easy-to-use…. BUT They are only as much sensitive, if not more as the Einthoven’s 3 lead string galvanometer, with salt solution electrodes. Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata

Thank you Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata