Ecg Signal Processing for Detection and Classification of Cardiac Diseases

International Journal of Electronics and Communication Engineering & Technology (IJECET), International Journal of Electronics and Communication ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep – Oct (2010), © IAEME Engineering & Technology (IJECET) ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct Oc t (2010), pp. 33-43 ©IAEME © IAEME, http://www.iaeme.com/ijecet.html

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ECG SIGNAL PROCESSING FOR DETECTION AND CLASSIFICATION OF CARDIAC DISEASES Ms Kavita L.Awade Dr Babasaheb Ambedkar Technological University, Raigad E-Mail: [email protected]

ABSTRACT: This paper contains brief

introduction of the conduction of the heart, its

periodicity and stability for the normal sinus rhythm. Any disorder in the cardiac rhythm may cause heart failure .In this classification of different cardiac disease like ventricular and super ventricular fibrillation [SVF], arterial flutter/Fibrillation [AF], ventricular fibrillation, [VF], Premature ventricular contraction [PVC], is chemia, Mayocardial Infraction [MI] etc. is covered This work presents the approach followed for the assessment of cardiac arrhythmias, with clinical relevance for heart failure prevention. The results figures are produced for the detection of the arrhythmia using Pan Tompkins algorithm .MIT BHI database is use for the detection of arrhythmia and the verified with the physionet.org ATM.

INTRODUCTION: More than 35 % of all deaths in Asia are due to cardiovascular disease (CVD) and more than 20% of all asian citizens suffer from a chronic CVD, such as myocardial infarction, arrhythmias and congestive heart failure. Despite the advances in the treatment of heart failure (HF), it is observed that the mortality rate continues to be high. Now a days, close to 40% of deaths in HF are thought to occur suddenly. The principal cause of mortality in HF is not absolutely clear, but the presence of cardiac arrhythmias suggests a reserved prognosis. Atrial fibrillation (AF) and ventricular tachyarrhythmia (VA) are the most significant rhythm disturbances found in ventricular dysfunction (decompensation) both in terms of the number of patients affected and the associated mortality and morbidity

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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 VF detection, and only few methods consider the problem of ECG analysis as a global/integrated procedure.

1 ANATOMY OF THE HEART The heart consists of four compartments: the right and left atria and ventricles. It serves as a four-chambered pump for the circulatory system, as shown in Figure 1. The main pumping function is supplied by the ventricles, and atria are merely used to store blood when the ventricles are pumping. The walls of the heart are composed of cardiac muscle, 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 of

blood flow within the heart. Opening and closing of the valves is controlled by the pressures 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 contraction phase, ejection phase, resting phase, and ¯ lling phase. The resting and ¯ falling phase is called called diastole; the pumping phase (contraction and ejection) is called systole. The atria systole is followed by ventricular systole, and then ventricular diastole.

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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 initiated by a coordinated series of events taking place in the 'specialized conduction system' of the 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 pathways between the SA and AV nodes, a common bundle called the bundle of His, and its branches, Purkinje ¯ bers, as shown in Figure 2. Cardiac contraction is stimulated by impulses generated in pacemaker cells in the SA node, which are self-excitatory and generate an action potential at a rate of about 70/min. The impulses are conducted through the atria to the AV node, which has an intrinsic frequency of about 50 pulses/min. There the passage of the impulses are delayed. Then the propagation goes through the bundle of His, the left and right bundle branches and the Purkinje ¯ bers, which further transmit the impulses impulses to the ventricular myocardium. Thus, via the the cardiac conduction system, the heartbeats are spread to all parts of the myocardium.

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3 PROPERTIES OF CARDIAC MUSCLE CELLS In the heart muscle cell, or myocyte, electric activation takes place due to the in°ow of sodium ions ( Na+) across the cell membrane. membrane. Myocardial ¯ bers have a resting membrane potential of approximately -90 mV . As shown in Figure 3, the transmembrane action 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 the repolarisation is due to net K + out flow. The waveforms of action potential observed in representative cells of different cardiac tissues show different characteristics, as we can see in Figure 2 (right part). For example, cells within the SA node are called primary pacemaker , which do not have a constant resting potential. Instead, they generate regular,

spontaneous action potentials. The depolarizing current is carried primarily by relatively slow, inward Ca2+ currents instead of by fast Na+ currents. The bottom trace of Figure 2 also shows the sum of electrical activity of all the cardiac muscle, which is the Electrocardiogram (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 threedimensional view.

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5 ECG DIAGNOSIS OF CARDIAC DISEASES Since many parts of the heart have an inherent rhythm, any part under abnormal conditions can become the dominant cardiac pacemaker. This can happen when the SA node activity is depressed, when the bundle of His is interrupted or damaged, or when an ectopic focus in the atria or in specialized conduction system tissue in the ventricles discharges at a rate faster than the SA node. These abnormal rhythms are normally be rejected 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 PQ

interval is progressively prolonged until the arterial impulse fails to conduct to the ventricle. The lengthened but otherwise normal impulse conduction in the AV node is rst-degree ree AV block (PQ interval >200ms). Second-degree AV block is when called ¯ rst-deg

every second or third impulse is conducted. A complete block of signals from the atria to the ventricles is called third-degree AV block. There is total disjunction .between the QRS complex and P waves: the P wave is at a normal sinus rate, while the QRS's is either in a AV rhythm (40-55/min) or a ventricular rhythm (25-40/min). Artificial pacemaker should then be used. (See Figure 4).

Figure 4 (A) First-degree AV block; (B) Second-degree AV block; (C) T hird-degree AV block .

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2. Bundle Branch: Block Disturbance of conduction in a branch of the bundle of

His. If the two bundle-branches are blocked simultaneously, the activation from the atria to the ventricles is completely prohibited. Bizarrely shaped QRS complexes of abnormally long duration occur on the ECG.

5.2 ISCHEMIA Ischemia is an inadequate flow of blood to the cardiac muscle caused by occlusion of coronary arteries. It is most likely to occur when the heart demands extra oxygen. Ischemia can present symptoms ranging from mild chest discomfort on exertion to the crushing chest pain of an infraction. Changes in the resting potential and in the repolarisation of the muscle cells occur, which is mostly seen as changes in the ST: either ST 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 oxygen supply is terminated in a certain area, leading to irreversible changes and death of myocardial cells in that region. An infarct area is electrically silent since it has lost its excitability.

5.3 ARRHYTHMIAS The rhythm of the heart is normally generated and regulated by pacemaker cells within the SA node. The SA nodal pacemaker activity controls the rhythm of the atria and ventricles. Normal heart rhythm is very regular, with minimal fluctuation. When this rhythm becomes irregular, too fast ( tachycardia) or too slow ( bradycardia), or the frequency of the atrial and ventricular beats are different, we call it an arrhythmia. In another word, arrhythmias are pathological changes in cardiac impulse generation or conduction that can be visualized by ECG[3]. Depending on the severity of the arrhythmia, patients may experience shortness of breath, fainting, fatigue, heart failure symptoms, chest pain or cardiac arrest. Basically, the most common arrhythmias can be classified 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

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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)]

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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 ARRHYTHMIAS In ventricular arrhythmias, ventricular activation is not originated from the AV node and usually 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 .

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3. Ventricular Fibrillation when ventricular depolarization occurs chaotically, the ventricles twitch in a very weak and uncoordinated way with no blood pumped from the heart. It is caused by multiple re-entry loops usually involving diseased myocardium, and may lead to loss of consciousness and death within minutes. The ventricular fibrillation may be stopped with an external de fibrillate pulse. On the ECG, it appears to be extremely frequent and uncoordinated and lacks QRS waves.[Figure 6 (C)]

4. Thyrotoxic Heart Disease Every aspect of the metabolism including the heart rate, is regulated by thyroid hormones i.e T3, T4 and TSH. Hyperthyroidism can lead to some heart diseases, including tachycardia, atrial fibrillation, congestive heart failure and cardiac enlargement

RESULT: The following record of ecg is processed with the help of MATLAB 7.8 tools The result are shown in the figure [6]. Database Used

: MITBHI

ECG Record

: 100

Domain Name

: Physionet.org.

Result obtained : Arrhythmia is detected Sampling rate

: 360 signals /samples

The work is done by using the Pan Tompkin algorithm for the QRS detection. The Figure [6] shows the waveforms for the 5 sec duration.

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Figure 6: (A) Original and Normalized ECG signal (B) Filterd Squared and Averaged ECG signal; (C) Histogram or calculated RR interval

CONCLUSION: With the basic knowledge of the conduction system of the heart, how the ECG is originated, and how it looks like under normal condition and in different kinds of heart diseases, we can come back to this scenario. As we know, atrial fibrillation, congestive heart failure, and ventricular flutter or fibrillation are complications of hyperthyroidism. And when ventricular ¯ fibrillation occurs, occurs, patients may die almost immediately. immediately. Ischemia or infarction can also occur without any warning symptoms (silent ischemia or MI). The

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thyroid is a butterfly-shaped endocrine gland located in the base of the neck. had very weak, slow and irregular pulses. It is probably caused by an AV block, or sinus bradycardia. Bradycardia can be developed with aging, coronary artery disease and MI,or hypothyroidism, etc. An artificial pacemaker, an implanted device that consists of a pulse generator and leads sending small electrical impulses to the heart muscle to maintain a suitable heart rate, should be used.

REFERENCES: 1).”ELECTROCARDIOGRAM 1).”ELECTROCARDIOGRAM (ECG) SIGNAL PROCESSING” 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.

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Ecg Signal Processing for Detection and Classification of Cardiac Diseases

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