The Practical on Electrocardiogram Cardiopulmonary Physiology - Term Paper Example

Name Course Institution Instructor DATE HET241 Cardiopulmonary physiology Abstract This report summarizes the practical done on Electrocardiogram (ECG). The practical was done in two parts. Part one involved the recording of the electrical activity of the heart in which the direction of its current in the frontal plane was determined by analyzing the QRS direction and magnitude in limb leads. The goal was to become familiar to the following leads systems: l, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6, and to estimate the magnitude and direction of the (frontal plane) cardiac vector. The electrical activity of the human heart is observed by using 12 channel computerized ECG instrument. By using this method Einthonven’s law is verified where the complex in lead II is equal to the sum of the corresponding complexes in lead I and II. The voltage recorded along a particular lead axis at a particular time is obtained by taking a projection onto that axis of the vector representing the magnitude and direction of depolarization at that time. The second part enables one to demonstrate the use of the Interpretative ECG and provide an opportunity to analyze the system as it is used to record various simulated cardiac arrhythmias provided by an ECG Waveform Simulator. Introduction An electrocardiogram (ECG or EKG) is a recording of the electrical activity of the heart using an electrocardiograph. It is used to evaluate the electrical events within the heart through the skin electrodes. The potential action of cardiac-muscle cell cause electric charges to move throughout the body fluids. These moving charges represent the sum of the action potentials occurring simultaneously in many individuals’ cells, which is detected by recording electrodes using electrode leads placed at the surface of the skin (Iaizzo, 2005). The electrical activity of the heart (cardiac vector) is the movement of an electrical dipole consisting of negative and positive charges. Cardiac vector is fully described by its magnitude and direction. In the frontal plane ECG, the cardiac vector is described by the three vectors which are 600 to each other. The resulting triangle, shown below, is called Eindhoven’s triangle (Iaizzo, 2005). The three possible combinations of the three electrodes sites are lead I, II and III. If the amplitude of the signals in three leads is measured at any time during the cardiac cycle and plotted on the Eindhoven’s triangle, the duration and the amplitude of the cardiac vector can be found. The first part of this practical involves the study of the electrical activities of the heart by placing six lead electrodes on different parts of the skin. The activities of the heart results are obtained on a graph on calibrated paper. These graphs are used in monitoring the contraction of the cardiac muscles by measuring the propagation of electrical depolarization and repolarization in the atria and ventricles (Chung, 1989). The first deviation from the Isoelectric line is P wave and lasts about 0.04 seconds. It is caused by the depolarization of the atria and is associated with the contraction of the atria. After a return to the Isoelectric line there is a short delay while the heart’s AV node depolarizes and sends a signal along the atrioventricular bundle of conducting fibers to the Purkinje fibers, which bring depolarization to all parts of the ventricles almost simultaneously (Chung, 1989). After the AV node depolarizes there is a downward pulse called the Q wave. Shortly after the Q wave there is a rapid upswing of the line called the R wave followed by a strong downswing of the line called the S wave and then a return to the Isoelectric line. These three waves together are called the QRS complex. This complex is caused by the depolarization of the ventricles and is associated with the contraction of the ventricles (Iaizzo, 2005). T wave indicates repolarization of the ventricles. The sequence from P wave to T wave represents one heart cycle. The time from one P wave to the next P wave is the period of the heartbeat. The heart rate is the reciprocal of the period of the heartbeat. The number of such cycles in a minute is called the heart rate and is typically 70-80 heartbeats per minute at rest (Speck, 2005). The figure below shows the components of ECG signal. The electrode at the center of the Einthoven’s triangle is at zero potential. The direction of these leads is from the “center” of the heart radially outward and includes the precordial (chest) leads and limb leads— VL, VR, & VF. The latter, in contrast, have both the electrodes at some potential and the direction of the corresponding electrode is from the electrode at lower potential to the one at higher potential, e.g., in limb lead I, the direction is from left to right. These include the limb leads--I, II, and III (Chung, 1989). Diagram: Frontal Plane Leads Normal electrocardiogram from a healthy subject. Sinus rhythm is present with a heart rate of 75 beats per minute. PR interval is 0.16 s; QRS interval (duration) is 0.08 s; QT interval is 0.36 s; QTc is 0.40 s; the mean QRS axis is about +70°. The precordial leads show normal R-wave progression with the transition zone (R wave = S wave) in lead V3, (Speck, 2005).. The second part of this lab was a computer simulation program to illustrate cardiac arrhythmias in an ECG Waveform. An arrhythmia is any disorder of the heart rate or rhythm. It means that the heart beats too quickly, too slowly or with an irregular pattern. The P waves in leads I and II was upright (positive), this is because it is coming from the sinus node. A problem with any part of this process can cause an arrhythmia. For example, in atrial fibrillation a common type of arrhythmia, electrical signals travel through the atria in a fast and disorganized way. This causes the atria to quiver instead of contract (Chung, 1989). Materials and Methods In order to carry out the electrocardiogram experiment a number of materials needed to be obtained. Three disposable electrodes (self-adhesive electrodes) were needed. The disposable 2m self-adhesive electrodes are position on each wrist and ankle. The electrode is then placed at each side of the precordial by attaching precordial list (v1-6) electrode to the participant chest. They are then connected to their respective input connections on the lead switch box. Other lead wires are connected to their respective inputs labels on the switch box to their respective sites on the subject. For example LL-Left Leg and RA- Right. Switch box In the second part the device used was the Mortara ELI100 12-lead Interpretative ECG used to prints out the ECG report in a 108 mm thermal sensitive paper format using a dot array of 200 dpi or 200 dots per 2.5cm. An “emergency” standard 12 lead ECG was obtained from a volunteer subject to review electrode placement and system operation A patient lead was connected to ELI100, and powered. The lead was then placed on the volunteer and ECG test is done. Operation of the system was observed and the nature of display is noted. The “simulated” arrhythmia was obtained from an Automated Safety Analyzer. This device was used to check the safety of electrical instruments to internationally recognized standards. This particular unit has a “simulation Waveform” option which produces a series of standard electrical signals, normal sinus rhythm in a range of bpm, as well as a small range of abnormal patterns. Purpose built ECG waveform simulators are specialized devices which provide a much wider range of waveforms and heart rate options. Most of the modern simulators used D/A techniques to generate the waveforms from stored digitized patterns. The patient lead of ELI100 is connected to the Bio-Tek 601 safety analyzer. Using emergency recording technique, different waveform were acquired and printed. The acquisition was repeated with a simulated patient entered into ECG. A report with the interpretation information on ELI100 was printed out Results In the ECG reading, a P, QRS, and T wave were visibly present. The P wave is caused by the contraction and depolarization of the atria. When the ventricles depolarized and contracted, this produced the QRS wave. The final wave exhibited is the T wave. This is the result of the relaxation of ventricles and also of their repolarization (Lewis, 2010). Leads V1, V2, and V3 are referred to as the right precordial leads and V4, V5, and V6 are referred to as the left precordial leads. The QRS complex is negative in lead V1 and positive in lead V6. The QRS complex shows a gradual transition from negative to positive between leads V2 and V4. There is a gradual increase in the amplitude of the R wave between leads V1 and V4. This is known as R wave progression. Poor R wave progression is a nonspecific finding. It can be caused by conduction abnormalities, myocardial infarction, cardiomyopathy, and other pathological conditions (Lewis, 2010). The QRS complex has duration of < 0.10 sec. it is illustrated below. Its amplitude varies from person to person and corresponds to the depolarization of the ventricles. The figure below illustrates the electrocardiogram the condition of the human heart. It shows the simple beats per second along with how fast it travels. Heart Rate: 60 - 100 bpm, PR Interval: 0.12 - 0.20 sec, QRS Duration: 0.06 - 0.10 sec and QT Interval (QTc Read More