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Ecg signal processing for detection and classification of cardiac diseases

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  • 1. International Journal of Electronics and CommunicationTechnology (IJECET),International Journal of Electronics and Communication Engineering &ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEMEEngineering & Technology (IJECET)ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) IJECETVolume 1, Number 1, Sep - Oct (2010), pp. 33-43 ©IAEME© IAEME, http://www.iaeme.com/ijecet.html ECG SIGNAL PROCESSING FOR DETECTION AND CLASSIFICATION OF CARDIAC DISEASES Ms Kavita L.Awade Dr Babasaheb Ambedkar Technological University, Raigad E-Mail: Kavitaawade@hotmail.comABSTRACT: This paper contains brief introduction of the conduction of the heart, itsperiodicity and stability for the normal sinus rhythm. Any disorder in the cardiac rhythmmay cause heart failure .In this classification of different cardiac disease like ventricularand super ventricular fibrillation [SVF], arterial flutter/Fibrillation [AF], ventricularfibrillation, [VF], Premature ventricular contraction [PVC], is chemia, MayocardialInfraction [MI] etc. is covered This work presents the approach followed for theassessment of cardiac arrhythmias, with clinical relevance for heart failure prevention.The results figures are produced for the detection of the arrhythmia using Pan Tompkinsalgorithm .MIT BHI database is use for the detection of arrhythmia and the verified withthe physionet.org ATM.INTRODUCTION: More than 35 % of all deaths in Asia are due to cardiovascular disease (CVD) andmore than 20% of all asian citizens suffer from a chronic CVD, such as myocardialinfarction, arrhythmias and congestive heart failure. Despite the advances in the treatmentof heart failure (HF), it is observed that the mortality rate continues to be high. Now adays, close to 40% of deaths in HF are thought to occur suddenly. The principal cause ofmortality in HF is not absolutely clear, but the presence of cardiac arrhythmias suggests areserved prognosis. Atrial fibrillation (AF) and ventricular tachyarrhythmia (VA) are themost significant rhythm disturbances found in ventricular dysfunction (decompensation)both in terms of the number of patients affected and the associated mortality andmorbidity 33
  • 2. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME Although several cardiac arrhythmias classification methods have been proposed,it is observed that usually they focus on one specific problem, i.e. AF, PVC, VT or VFdetection, and only few methods consider the problem of ECG analysis as aglobal/integrated procedure.1 ANATOMY OF THE HEART The heart consists of four compartments: the right and left atria and ventricles. Itserves as a four-chambered pump for the circulatory system, as shown in Figure 1. Themain pumping function is supplied by the ventricles, and atria are merely used to storeblood when the ventricles are pumping. The walls of the heart are composed of cardiacmuscle, called myocardium. The heart has four valves: the tricuspid valve, mitral valve,pulmonary valve, and the aortic valve (see Figure 1), which determine the direction ofblood flow within the heart. Opening and closing of the valves is controlled by thepressures exerted on both sides of the valves. Figure 1 The anatomy of the heart A cardiac cycle takes around 1 second, which can be divided into four phases:contraction phase, ejection phase, resting phase, and ¯ lling phase. The resting and¯ falling phase is called diastole; the pumping phase (contraction and ejection) is calledsystole. The atria systole is followed by ventricular systole, and then ventricular diastole. 34
  • 3. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME Figure 2 (Left) The conduction system of the heart; (Right) Different waveforms representing action potentials from each of the specialized cells found in the heart; (Bottom) normal scalar ECG.2 THE CONDUCTION SYSTEM OF THE HEART: The electrical activation patterns in the walls of the atria and ventricle are initiatedby a coordinated series of events taking place in the specialized conduction system ofthe heart, which merely constitutes a small portion in relation to the whole heart The system mainly consists of the sinus node (SA node), atrioventricular node(AV node), intermodal atrial pathways between the SA and AV nodes, a common bundlecalled the bundle of His, and its branches, Purkinje ¯ bers, as shown in Figure 2. Cardiaccontraction is stimulated by impulses generated in pacemaker cells in the SA node, whichare self-excitatory and generate an action potential at a rate of about 70/min. Theimpulses are conducted through the atria to the AV node, which has an intrinsicfrequency of about 50 pulses/min. There the passage of the impulses are delayed. Thenthe propagation goes through the bundle of His, the left and right bundle branches and thePurkinje ¯ bers, which further transmit the impulses to the ventricular myocardium. Thus,via the the cardiac conduction system, the heartbeats are spread to all parts of themyocardium. 35
  • 4. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME3 PROPERTIES OF CARDIAC MUSCLE CELLS In the heart muscle cell, or myocyte, electric activation takes place due to thein°ow of sodium ions (Na+) across the cell membrane. Myocardial ¯ bers have a restingmembrane potential of approximately -90 mV. As shown in Figure 3, the transmembraneaction potential of single cardiac muscle cells are characterized by a rapid depolarization,a plateau phase, and a slow repolarization procedure. Figure 3 Phases of the action potential of a cardiac muscle The initial depolarization is due to Na+in°ow through rapid opening of Na+channels. The plateau phase is produced by more slowly Ca2+ in flow, and therepolarisation is due to net K+ out flow. The waveforms of action potential observed inrepresentative cells of different cardiac tissues show different characteristics, as we cansee in Figure 2 (right part). For example, cells within the SA node are called primarypacemaker, which do not have a constant resting potential. Instead, they generate regular,spontaneous action potentials. The depolarizing current is carried primarily by relativelyslow, inward Ca2+ currents instead of by fast Na+ currents. The bottom trace of Figure 2also shows the sum of electrical activity of all the cardiac muscle, which is theElectrocardiogram (ECG).4. ECG MEASUREMENTS The most commonly used clinical ECG-system is the 12-lead ECG system,providing different views of the same electrical activity within the heart in a three-dimensional view. 36
  • 5. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME5 ECG DIAGNOSIS OF CARDIAC DISEASES Since many parts of the heart have an inherent rhythm, any part under abnormalconditions can become the dominant cardiac pacemaker. This can happen when the SAnode activity is depressed, when the bundle of His is interrupted or damaged, or when anectopic focus in the atria or in specialized conduction system tissue in the ventriclesdischarges at a rate faster than the SA node. These abnormal rhythms are normally berejected on ECG.The symptoms of most common diseases can be categorized below.5.1 DISTURBANCES OF IMPULSE CONDUCTION 1. AV Block: On the ECG of a heart block associated with AV node, the PQinterval is progressively prolonged until the arterial impulse fails to conduct to theventricle. The lengthened but otherwise normal impulse conduction in the AV node iscalled ¯ rst-degree AV block (PQ interval >200ms). Second-degree AV block is whenevery second or third impulse is conducted. A complete block of signals from the atria tothe ventricles is called third-degree AV block. There is total disjunction .between theQRS complex and P waves: the P wave is at a normal sinus rate, while the QRSs is eitherin a AV rhythm (40-55/min) or a ventricular rhythm (25-40/min). Artificial pacemakershould then be used. (See Figure 4).Figure 4 (A) First-degree AV block; (B) Second-degree AV block; (C) Third-degree AV block. 37
  • 6. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME 2. Bundle Branch: Block Disturbance of conduction in a branch of the bundle ofHis. If the two bundle-branches are blocked simultaneously, the activation from the atriato the ventricles is completely prohibited. Bizarrely shaped QRS complexes ofabnormally long duration occur on the ECG.5.2 ISCHEMIA Ischemia is an inadequate flow of blood to the cardiac muscle caused byocclusion of coronary arteries. It is most likely to occur when the heart demands extraoxygen. Ischemia can present symptoms ranging from mild chest discomfort on exertionto the crushing chest pain of an infraction. Changes in the resting potential and in therepolarisation of the muscle cells occur, which is mostly seen as changes in the ST: eitherST elevation (transmural ischemia) or ST depression (sub end cordial ischemia).5.3 MYOCARDIAL INFARCTION (MI) After longer period of ischemia, myocardial infarction can appear. The oxygensupply is terminated in a certain area, leading to irreversible changes and death ofmyocardial cells in that region. An infarct area is electrically silent since it has lost itsexcitability.5.3 ARRHYTHMIAS The rhythm of the heart is normally generated and regulated by pacemaker cellswithin the SA node. The SA nodal pacemaker activity controls the rhythm of the atria andventricles. Normal heart rhythm is very regular, with minimal fluctuation. When thisrhythm becomes irregular, too fast (tachycardia) or too slow (bradycardia), or thefrequency of the atrial and ventricular beats are different, we call it an arrhythmia. Inanother word, arrhythmias are pathological changes in cardiac impulse generation orconduction that can be visualized by ECG[3]. Depending on the severity of thearrhythmia, patients may experience shortness of breath, fainting, fatigue, heart failuresymptoms, chest pain or cardiac arrest. Basically, the most common arrhythmias can beclassified as supraventricular (above the ventricles) and ventricular arrhythmias.SUPRAVENTRICULAR ARRHYTHMIAS 1. Sinus Arrhythmias Sinus tachycardia is when the sinus rhythm rises to 100/min or higher, due to physical exercise, stress, emotion, fever or hyperthyroidism. Sinus 38
  • 7. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME bradycardia is when the heart rate falls below 60/min, due to the disrupted electrical impulses at the nodes or along the pathways. In both cases the rhythm is regular. Sinus arrhythmias can be physiological and respiration dependent (heart rate is increased during inspiration and decreased during expiration). 2. Paroxysmal Atrial Tachycardia Rapid discharge of impulses from an atrial focus, which triggers the AV node or ventricles to generate ectopic impulses at a rate usually between 160 and 200/min. The P waves are a result of a circular movement in the atria involving the AV node, which leads to a high rate of activation. The isoelectric baseline may be seen between the T- wave and the next P-wave. 3. Atrial Flutter A very rapid and regular mapping contraction of the atria, beating at a rate of 200-350 beats/min. The AV node and the ventricles are generally activated by every second or every third atrial impulse. In the ECG, the isoelectric interval between the end of T and beginning of P disappears. [Figure 5 (A)] Figure 5 (A) Atrial flutter; (B) Atrial fibrillation. 1. Atrial Fibrillation A weak and uncoordinated twitching of atria in the baseline at the rate up to 500 beats/min. The ventricular rate is thus rapid and irregular, though the QRS usually appears normal. [Figure 5 (B)] 39
  • 8. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME 2. Atrial Extra systole Impulses from the SA node stimulates the AV node prematurely. The P wave on the ECG is distorted while the QRS complex remains normal.VENTRICULAR ARRHYTHMIASIn ventricular arrhythmias, ventricular activation is not originated from the AV node andusually proceeds in the ventricles in an abnormal way. 1. Premature Ventricular Contraction (PVC) An ectopic pacemaker within the ventricle or specialized conduction system may discharge, generating an extra beat, or extra systole that interrupts the normal rhythm. It is characterized by distorted and widened QRS complexes in the ECG. [Figure 6 (A)] 2. Ventricular Tachycardia A rapid train (100-200/min) of impulses originating from a ventricular focus, usually caused by a slower conduction in the ischemic ventricular muscle, leading to circular activation (re-entry). On the ECG it is characterized by rapid, bizarre and widened QRS. [Figure 6 (B)] Figure 6 (A) A Premature ventricular contraction; (B) Ventricular tachycardia; (C) Ventricular fibrillation. 40
  • 9. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME 3. Ventricular Fibrillation when ventricular depolarization occurs chaotically, theventricles twitch in a very weak and uncoordinated way with no blood pumped from theheart. It is caused by multiple re-entry loops usually involving diseased myocardium, andmay lead to loss of consciousness and death within minutes. The ventricular fibrillationmay be stopped with an external de fibrillate pulse. On the ECG, it appears to beextremely frequent and uncoordinated and lacks QRS waves.[Figure 6 (C)]4. Thyrotoxic Heart DiseaseEvery aspect of the metabolism including the heart rate, is regulated by thyroid hormonesi.e T3, T4 and TSH. Hyperthyroidism can lead to some heart diseases, includingtachycardia, atrial fibrillation, congestive heart failure and cardiac enlargementRESULT:The following record of ecg is processed with the help of MATLAB 7.8 tools The resultare shown in the figure [6].Database Used : MITBHIECG Record : 100Domain Name : Physionet.org.Result obtained : Arrhythmia is detectedSampling rate : 360 signals /samplesThe work is done by using the Pan Tompkin algorithm for the QRS detection. The Figure[6] shows the waveforms for the 5 sec duration. 41
  • 10. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME Figure 6: (A) Original and Normalized ECG signal (B) Filterd Squared and Averaged ECG signal; (C) Histogram or calculated RR intervalCONCLUSION: With the basic knowledge of the conduction system of the heart, how the ECG isoriginated, and how it looks like under normal condition and in different kinds of heartdiseases, we can come back to this scenario. As we know, atrial fibrillation, congestiveheart failure, and ventricular flutter or fibrillation are complications of hyperthyroidism.And when ventricular ¯ fibrillation occurs, patients may die almost immediately. Ischemiaor infarction can also occur without any warning symptoms (silent ischemia or MI). The 42
  • 11. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEMEthyroid is a butterfly-shaped endocrine gland located in the base of the neck. had veryweak, slow and irregular pulses. It is probably caused by an AV block, or sinusbradycardia. Bradycardia can be developed with aging, coronary artery disease and MI,orhypothyroidism, etc. An artificial pacemaker, an implanted device that consists of a pulsegenerator and leads sending small electrical impulses to the heart muscle to maintain asuitable heart rate, should be used.REFERENCES: 1).”ELECTROCARDIOGRAM (ECG) SIGNAL PROCESSING” LEIF SO RNMO Lund University Sweden 2. Assessment of Arrhythmias for Heart Failure Management J. Henriques, P. Carvalho , M. Harris, M. Antunes1, R. Couceiro, M. Brito, R. Schmidt #Center for Informatics and Systems, University of Coimbr 3.”BiomedicalSignal Processing”. By Rangayan”Biomedical Signal Processing”.By Tompkin 4. The weighted diagnostic distortion (WDD) measure for ECG signal compression. IEEE Trans. Biomed. Eng. 2000; 47: 1422–1430. G. J. Balm, 5.”.Crosscorrelation techniques applied to the electrocardiogram interpretation problem.” IEEE Trans. Biomed.Eng. 1967; 14:258–262..J. C. Huhta and J. G. Webster, 6.”60-Hz interference in electrocardiography”IEEE Trans. Biomed. Eng. 1973; 43:91–101.C. D. McManus, D. Neubert, and E. Cramer, 7. Characterization and elimination of AC noise in the electrocardiogram: a comparison of digital filtering methods. Comput. Biomed. Res. 1993; 26:48–67. P. S. Hamilton, 8. A comparison of adaptive and non adaptive filters for the reduction of power line interference in the ECG.IEEE Trans. Biomed. Eng. 1996; 43:105–109. 43