Introduction to CVS and ECG PDF

Introduction to CVS and ECG Dr.Rasha Eldeeb Associate Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Introduction to CVS and ECG Learning Objectives: Describe the chambers of the hear...

Introduction to CVS and ECG Dr.Rasha Eldeeb Associate Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Introduction to CVS and ECG Learning Objectives: Describe the chambers of the heart, valves in the heart, and direction of blood flow Describe the organization of systemic and pulmonary circulations Define ECG Describe the Einthoven triangle Enumerate the leads used in ECG recording Describe the components of ECG waves and their relation to the Cardiac cycle Interpretation of ECG findings Discuss the Applications of the ECG  To Start with … The cardiovascular system is composed of the heart, which is principally a pressure pump, and a group of blood vessels, which comprise arteries, arterioles, capillaries, venules, and veins. The heart is made up of two halves right and left. Each half is made up of an atrium and a ventricle with an atrioventricular (AV) valve in between allowing the blood to pass only in one direction; from the atrium to the ventricle. The ventricles act as a pump, Left ventricle ( pressure pump ) pumps the blood at a high pressure into the greater ( systemic) circulation. The right ventricle ( volume pump ) pumps the same volume of blood as the Left Ventricle (but at lower pressure) to the pulmonary circulation. Semilunar valves control the direction of blood between the ventricles and the aortic and pulmonary blood vessels  Circulation Systemic ( General) Circulation: Carries oxygenated blood to all parts of the body from Left Ventricle to aorta to arteries to arterioles to capillaries (for gas exchange) to venules to veins to SVC & IVC then to Right Atrium Pulmonary (lesser) Circulation carries deoxygenated blood to the lungs from Right Ventricles to pulmonary artery to arterioles to pulmonary caps (for gas exchange) 4 pulmonary veins then to Left Atrium  Blood Vessels Form a closed delivery system that begins and ends at the heart. There are three types of blood vessels: ▪ Arteries - carry blood away from the heart. ▪ Veins- carry blood towards the heart. ▪ Capillaries- carry blood from the arterioles to the venules Arteries (big) —> smaller arteries —> Arterioles—>Capillaries—> (In capillary bed)—>Venules—> small veins—>large veins—> Heart called Resistance vessels So, … What Is The Function of CVS?  Transport and distribute essential substances to the tissue Remove metabolic byproducts Adjustment of oxygen and nutrient supply in different physiological states Regulation of body temperature Humoral communication Now, … How Does The Heart Function?  The parts of the heart normally beat in orderly sequence: Contraction of the atria (atrial systole) is followed by contraction of the ventricles (ventricular systole), and during diastole all four chambers are relaxed. Contraction of the heart is preceded by electrical stimulation (action Potential) The heartbeat originates in a specialized cardiac conduction system and spreads to all parts of the myocardium. To Understand How Does The Heart Function As a Pump You Should Know :  The Properties of Cardiac Muscle Excitability Rhythmicity Conductivity Contractility  Excitability: The cardiac muscle can respond to an adequate stimulus by generating an action potential. Rhythmicity ( automaticity) : The cardiac muscle can initiate its beats regularly and continuously. Cardiac rhythm is myogenic in origin independent of nerve supply. The peacemaker of the heart is the SAN. Conductivity: it’s the ability to spread the cardiac electrical impulse through the conductive system all over the cardiac tissue. Contractility: it is the ability to translate the electrical stimulation (Action potential) into mechanical work ( muscle contraction in the form of systole and diastole) So, … What Is Pumped Out Of The Heart?  Stroke Volume: (SV): It is the volume of blood pumped by each ventricle per beat. Usually it equals 70-80 ml/beat during rest. ▪ SV = EDV –ESV ▪ EDV: Volume of blood remaining in the ventricle at end of diastole = 135 ml. ▪ ESV: Volume of blood remaining in the ventricle at end of systole = 65-70 ml during rest.  Cont.,. Cardiac Output: (CO) : It is the volume of blood pumped by each ventricle per minute. Normally it equals the venous return, and this is called the steady state 5-5.5 L/ min during rest. ▪ CO = Heart Rate (HR) X stroke volume (SV) Cardiac Index = CO/surface area Ejection Fraction: % of EDV that is ejected by the left ventricle per beat = SV / EDV. ▪ Normally lies between 55-80% (average 67 %)  Important Terms Preload: Load acting on the ventricle before its contraction. Venous return or End diastolic Volume (EDV) represents preload to the heart. Afterload: Load acting on the ventricle during its contraction. Arterial resistance or TPR represents afterload to the heart Now, … What Is ECG?  Electrocardiography (ECG) It is the algebraic summation of the electrical activity occurring in the cardiac muscle during the cardiac cycle. It is a recording of the electrical activity (depolarization & repolarization) generated by the cardiac muscle during the cardiac cycle The Electrical activity is either Depolarization (due to Na+ influx) or Repolarization (due to K+ efflux) The Electrical activity precedes cardiac contraction The parts of the heart normally beat in an orderly sequence: Contraction of the atria (atrial systole) is followed by contraction of the ventricles (ventricular systole) and during diastole all four chambers are relaxed  ECG Recording Because the body fluids are good conductors (volume conductors), fluctuations in the potential that represent the algebraic sum of the action potentials of myocardial fibers can be recorded extracellularly The signals are detected using metal electrodes attached to the extremities and chest wall and are then amplified and recorded by the electrocardiograph The ECG may be recorded by using an active (exploring electrode) connected to an indifferent electrode at zero potential (unipolar recording) or by using two active electrodes (bipolar recording)  Einthoven's Triangle EINTHOVEN (a Deutch scientist born in 1860 and died in 1927) stated that In a volume conductor, the sum of the potentials at the points of an equilateral triangle with a current source in the center is zero at all times. This triangle was named after him Einthoven Triangle (putting the heart in the middle) Einthoven's triangle can be approximated by placing electrodes on both arms and the left leg. These are the three standard limb leads used in electrocardiography The center of the triangle offers a reference point for the unipolar ECG leads Lead II = Lead I + Lead III  Leads used in ECG Recording (1) STANDARD BIPOLAR LIMB LEADS (using 2 active electrodes) LEAD I : records the potential difference between the LEFT ARM and the RIGHT ARM (LA – RA) LEAD II: records the potential difference between the LEFT LEG and the RIGHT ARM (L.L. – R.A.) LEAD III: records the potential difference between the LEFT LEG and the LEFT ARM (L.L – L.A.) (2) Unipolar Leads (a) Unipolar Limb Leads (aVR, aVL & aVF) aV.R. = When the exploring electrode is put on the right arm aV.L. = When the exploring electrode is put on the left arm aV.F. = When the exploring electrode is put on the left leg  (b) Unipolar Chest Leads There are six unipolar chest leads: V 1 = when the exploring electrode is put in the fourth intercostal space at the right sternal border V2 = When the exploring electrode is put in the fourth intercostal space at the left sternal border V3 = When the exploring electrode is equidistant (in midpoint) between V2 and V4 V4 = When the exploring electrode is at the apex beat in the fifth intercostals space in the left mid-clavicular line V5 = When the exploring electrode is in the left fifth intercostals space in the anterior axillary line V6 = when the exploring electrode is in the left fifth intercostals space in the mid- axillary line ECG Leads Now, … What Is The Importance of The Different ECG Leads?  The value of different ECG leads The leads I, and aVL look at the left lateral surface of the heart. The leads II, III, & aVF look at the inferior surface of the heart. Lead aVR looks at the atria. V1 and V2 look at the right ventricle. V3 and V4 look at the anterior and lateral walls of the left ventricle Now …Everything is ready!! What Do We Have???!!! Normal ECG Now, … What Does It Mean? Now, … How to Interpret An ECG?  Interpretation of ECG Commonly followed sequence of analysis 1. Check voltage calibration 2. Heart rhythm 3. Heart rate 4. Intervals( PR, QRS, QT) 5. Mean QRS axis 6. Abnormalities of the P wave 7. Abnormalities of QRS 8. ST segment and T wave abnormalities  RR interval to determine heart rate Heart rate = 1500 (bpm) number of small boxes between two consecutive beats Heart rate = 300 (bpm) number of Large boxes between two consecutive beats The standard ECG paper speed is 25mm/sec  Cont.,. Determination of voltage and duration in ECG A normal ECG recording shows: o P wave: It is a positive wave. It is caused by atrial depolarization. Its duration is about 0.1 sec. Its amplitude is 0.1 (up to 0.25) mV o QRS : R is positive, and Q and S are negative waves. QRS is due to ventricular depolarization. Its duration is 0.06-0.08 sec, and its amplitude is about 1mV. Q wave is due to depolarization of the interventricular septum and its duration is about 0.02 sec. R wave is due to depolarization of most of the ventricular muscle fibers and its duration equals 0.04 sec. S wave is a small negative wave due to depolarization of the remaining parts of the base of ventricles and its duration equals 0.02 sec. o T wave: It is a positive wave. It is caused by ventricular Repolarization. Its duration is about 0.25 sec, and its amplitude is 0.2 (up to 0.4) mV. o Atrial repolarization is not recorded as it is submerged in QRS complex o U wave: Sometimes a positive U wave is recorded due to the slow repolarization of the papillary muscle or Purkinje fibers  PR interval o It is the duration between the beginning of P wave to the beginning of R wave o Normal duration is 0.16 sec. (0.12-0.2 sec.) It should not exceed 0.2 sec. o PR interval indicates conduction time from atria to the ventricle. Any delayed conduction in the AV node or bundle of His will prolong PR interval and it is seen in I degree heart block. o It is prolonged in cases of : Partial heart block, increased vagal tone, Atrial hypertrophy. o It is shortened in cases of : AV nodal rhythm, increased sympathetic stimulation and Wolf- Parkinson – White syndrome.  Applications of The ECG Study the function of the heart (rate, rhythm, axis) Diagnosis of cardiac dysfunctions as: Arrhythmias Disorders in the activation sequence ―Atrioventricular conduction defects (blocks) ―Bundle-branch block Increase in wall thickness or size of the atria and ventricles (hypertrophy) Myocardial ischemia and infarction Drug effect (Digitalis ,Quinidine ) Electrolyte imbalance (Potassium , Calcium ) Carditis (Pericarditis ,Myocarditis) Pacemaker monitoring Learning Resources: 1. Marieb EN. Human Anatomy and Physiology, 9th Edition, Pearson International Edition; 2014. ISBN-13: 978-1-2920-2649-7 2. Guyton, Arthur C. Textbook of medical physiology / Arthur C. Guyton, John E. Hall.—11th ed. 3. Ganong's Review of Medical Physiology/Kim E. Barrett, Susan M. Barman, Scott Boitano and Heddwen L.Brooks,23rd ed. 4. Instructional Web site 5. Lectures PDF on Moodle 6. https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780702031144000026  DISCLAMER The contents of this presentation, can be used only for the purpose of a Lecture, Scientific meeting or Research presentation at Gulf Medical University, Ajman. www.gmu.ac.ae