The heart is an organ that pumps and circulates blood all over the body through a circulatory system to supply nutrients and oxygen to the body tissues and excrete carbon dioxide alongside other wastes.The human heart is in the chest where it lies between the lungs and above the diaphragm, just behind the sternumand is encased by the pericardium that protects it and supports the inside part of the chest. Heart’s size is that of a fist, and the weight is about two hundred and eighty to three hundred and forty grams in men and in women it is between two hundred and thirty to two hundred and eighty grams. There are four chambers in the human heart, two on the upper side (atria) and other two on the lower side (ventricles). Further, the heart is divided into left and right side by the septum which is a muscle wall. The right side is made up of the right ventricle and the right atrium while the left atriums with the right ventricle are on the left side of the heart (Lewis). Similarly, the heart has four valves: the tricuspid valve is between the right atrium and right ventricle, and the mitral valve is at the center of the left ventricle and atrium. The pulmonary valve is located between the pulmonary artery and the right ventricle and the aorta valve that is on the tract that flows out of the left ventricle.Additionally, the wall of the heart has three layers: the epicardium which is the outer layer, myocardium which is in the middle has contracting muscle and the inner layer that contacts blood is called the endocardium.
In between the epicardium, parietal pericardium, and the endocardium, there is the serous pericardium which contains a pericardial fluid that aids in the lubrication of the heart during the movements and contractions of the diaphragm and the lungs.There are two pathways of circulating blood in the heart that is the systematic circuit and the pulmonary circuit. For the pulmonary circuit, deoxygenated blood from the right ventricle passes through the pulmonary artery to the lungs while the oxygenated blood enters the left atrium through the pulmonary vein. On the other hand, in the systematic circuit, it is through the left ventricle where oxygenated blood moves to the aorta and again into the capillaries and arteries thus supplying oxygen to the body tissues (Lewis). After there the oxygen-deficit blood flows back through the veins into the vena cava and re-enters the right atrium of the heart.
Human heart (Balance, Drrofi)
Cardiac Muscle Cell
The heart walls are made up of cardiac muscle(myocardium) and skeletal muscle like striations. The cardiac muscle tissue consists of heart muscle fibers or cells that interlock giving properties to the fabric. There is a single nucleus in each muscle fiber which is striated because when it looked through a microscope, it appears to have dark and light bands. The muscles are spirally oriented in four groups divisions where two fiber groups curl around the outer side of both ventricles(Balance). Underneath the first two groups of fibers, there is the third group and the fourth group winds around the left ventricle only. Given that the orientation of the muscle cells is tangential, and the tissue resistivity is lower in the fiber direction, this is significant in electrocardiography.
Electric signal Conduction of the Heart
Electrical activation just like the nerve cell mechanism takes place in the myocyte or heart muscle cell. Similarly, the action potential amplitude is alike for both muscle and nerve which is around 100 mV. However, the cardiac muscle impulse duration is longer than that in either skeletal muscle or nerve cell by a magnitude of two orders.A plateau phase follows cardiac depolarization and after that repolarization happens where the repolarization is as a result of potassium ions ( K+) outflow and the impulse action duration is usually 300 ms.Cardiac muscle cell electric activation is associated with its mechanical contraction, and this occurs a while after. The sinus node, crescent in shave and with an approximate length of fifteen millimeters and a width of five millimeters is found at the superior vena cava in the right atrium and hasmuscle cells that are specialized( Sun et al., 28). The cells of the sinoatrial node are pacemakers and self-excitatory and generate a seventy per minute action potential. Activation propagates from the SA node through the atria though it cannot spread directly across ventricles and atria boundaries. In between the border of the ventricles and atria, there is the atrioventricular node which has 50pulses per minute frequency.When the AV node is prompted with a frequency that is high, a higher rate follows.For a normally functioning heart, the atrioventricular node gives a conducting path to the ventricles from the atria.
There is a conduction system that provides the spread from the atrioventricular node to the ventricles which comprises a typical bundle named “bundle of His” which takes the name after Wilhelm His, a German physician. The bundle further separates into a pair of bundle branches that spread along the septum sides making up left and right bundle branches.The conduction system based propagation happens at high speed when at the ventricular region whereas before there, it is at a low velocity. The underlying high sinus node rate is the setter of the whole heart’s activation frequency. In case the atria to AV node connection fail, an intrinsic frequency is adopted by the AV nodes, and when at the bundle of His the conduction system fails, he region of the ventricles determine the beating rate which is at a high frequency. For a healthy heart, there are five contraction stages: the early diastole which is the first stage where the heart relaxes, then the atrial systole when the atrium contracts pushing blood into the ventricle. After that, the ventricles contract without any change in volume, continue with the contraction at an empty state then stop and relax, and the cycle starts again.
Electrocardiogram (ECG) is a signal that varies with time reflecting the flow of ionic current that causes the subsequent contraction and relaxation of the cardiac fibers. Two electrodes are placed on the skin, and then the ECG on the surface is acquired by recording the electrodes potential difference. The signal gives different reports of the human heart. It provides information about electrolyte concentrations changes, myocardial ischemia extent, conduction disturbances and the rhythm of the heart. Likewise, it offers the recording of the effects of drugs on the heart, the origin, and propagation of the heart impulse, the size of the chamber and the position of the heart (Sun et al., 28). It is at the QRS complex where the ECG signal energy is mostly concentrated though there are other crucial changes in the P and T waves, and PQ and ST intervals which are of small amplitude and could be hidden by the noise of the EMG.
The cardiac cycle tracing of an ECG comprises of a T wave, U wave, P-wave and a QRS complex.First, the electrical impulse is transmitted to other heart parts causing it to contract, and once the electrodes are placed on the skin, they sense the potentials of the mill volt that are caused by muscle depolarization with each heartbeat (The electrocardiogram, ECG). Every muscle cell is charged on its outer cell membrane and its reduction to zero results to depolarization, activating cells mechanism that results in chamber contraction. Each healthy heart heartbeat interval possesses a depolarization wave progression triggered by sinoatrial node cells that propagate all the way to the ventricles through intrinsic “conduction pathways”. Fundamentally, ECG signal and electricity concept is that a positive deflection appears on ECG as an impulse tends to a positive electrode. ECGs use is widespread and ubiquitous among providers mostly the tertiary care hospitals.
Specifically, Mayo Clinic performs around two hundred and forty thousand ECG tests yearly and the predicted growth of ECG machines global market by the year 2020 is over five billion. An ECG test detects the abnormalities of the heart by measuring the heart contractions that generate the electrical activity (AHA).According to Walters, ECG machines differ according to the physical footprint, diagnostic ability and price where currents and the devices are classified as either incumbent products or the upcoming disruptive products that are less expensive and portable. The incumbent class consists of around sixteen manufacturers in the developed countries like Philips, Schiller, Burdick, GE, Welch Allyn, and Nihon Kohden, which use 12-leads and can print. On the other part, the disruptive class is from the developing countries’ manufacturers such as ECG Check, PC-80, AliveCor, MD100E, REKA E100, and ReadMyHeart.
Willem Einthoven and the first ECG
Willem Einthoven was born in Java Island in Semarang previously known as Dutch East Indies and is currently called Indonesia in the year 1860 May 21. His parents were Jacob Einthoven, a parish doctor, and Louise de Vogel. He was born in a family of six children being the third born and the eldest son. Willem’s father, Jacob passed on when he was six years old and after four years they moved to Holland with his mother and siblings.After completing his secondary school education, he joined the University of Utrecht to study medicine where his intentions were following the footsteps of his father (Willem Einthoven – Biographical). Willem worked under Snellen Sr. who was an ophthalmologist and after that he carried out two investigations. Einthoven talent came up when he started using a capillary electrometer to record the sounds of the heart. He did a survey of the instrument’s theoretical principles and came up with mathematics errors correction methods. With these methods, he ventured into an analysis of the A.DWaller’s electrocardiogram and this motivated him to make his research thorough. Finally, he was able to devise a string galvanometer to evade mathematical corrections that were complex.
Galvanometer (first ECG)
The galvanometer passed currents between magnets using a conductive wire thin filament where on the passage of current through the filament the string would move because of the creation of a magnetic field. The limitations of the galvanometer are that it was supposed to be cooled with water because of the powerful electromagnet, it had a weight of two hundred and seventy kilograms and for it to be operated there had to be five people present. Willem identified wave types using the letters P, Q, R and S. He modified the galvanometer and used it to record ECG signals. He Received a Nobel Prize award in medicine for his contribution to the invention of the first electrocardiography system that is used for medical diagnosis.
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Sun, Yan, Kap Chan, and Shankar Krishnan. BMC Cardiovasc Disord 5.1 (2005): 28. Web. 20
The electrocardiogram, ECG. Nobelprize.org. Nobel Media AB 2014. Web. 20 May 2016.
Walters, Austin. “Global Healthcare: ECG Tech From India Could Save U.S. $50 Million Today”. Globalhealth.care. N.P., 2015. Web. 20 May 2016.
Willem Einthoven – Biographical. Nobelprize.org. Nobel Media AB 2014. Web. 19 May 2016.