Electrocardiography or electrocardiogram (ECG)
The electrocardiogram (ECG) records from the body surface and registers the differences in electrical potential generated by the heart. The signal recorded is determined by action potentials generated by millions of individual cells and their sequence of activation. A multitude of factors, both cardiac and extra cardiac, alter the final electrical signal. For instance, the electrical forces generated by the heart are subsequently altered by the position of the heart within the body, the nature of the intervening tissue, and the distance to the recording electrode. Since the final, recorded electrical signal does not faithfully reflect the electrical activity of individual cells, the student should not expect the ECG necessarily to provide an exact anatomic or physiologic: “picture” of the heart. Nevertheless, as the result of careful correlation of electrocardiographic patterns with observed anatomic, pathologic, and physiologic data, it is now possible to deduce, with a high grade of accuracy, the state of the heart from the surface ECG. While it is true that the ECG may be normal despite an abnormal heart, or abnormal with a normal heart, it is equally true that the ECG often provides an important indication of a cardiac abnormality, and even allows a fairly accurate appraisal of the anatomic and physiologic significance of that abnormality. Furthermore, the ECG is by far the best method of analysis of disturbances of the cardiac rhythm.
Different phases of a cardiac cycle
ECG records the heart activity. It records the electrical activity generated by heart muscle depolarizations, which propagate in pulsating electrical waves towards the skin. Although the electricity amount is in fact very small, it can be picked up reliably with ECG electrodes attached to the skin (data unit: microvolt, uV). The full ECG setup comprises at least four electrodes which are placed on the chest or at the four extremities according to standard nomenclature (RA = right arm; LA = left arm; RL = right leg; LL = left leg). Of course, variations of this setup exist in order to allow more flexible and less intrusive recordings, for example, by attaching the electrodes to the forearms and legs. ECG electrodes are typically wet sensors, requiring the use of a conductive gel to increase conductivity between skin and electrodes.
ECGs serve many roles in the research and development process of a drug:
• Cardiac safety has become the number one reason for drug withdrawals and labeling changes during the past several years. This has resulted in greater regulatory scrutiny for all new compounds and greater concern among pharma in regard to the potential effect of their compounds on the heart
• They generally are required as part of the screening, selection, and enrollment process for study participants; they assist in assessing the cardiac safety of the investigational drug; they provide efficacy data for cardiovascular-related compounds; and they provide indirect benefits to the subject and his or her physician in diagnosing undetected structural or electrical cardiac diseases, as well as detecting progression of cardiac disease during the course of the clinical trial.
• Significance of QT interval in drug development: The duration of QT interval of the surface electrocardiogram (ECG) reflects the ventricular action potential duration (APD) which is determined mainly by the rapid component of the outward repolarizing current (IKr). This current is mediated primarily by the delayed rectifying potassium channel. Thus, the QT interval is congenitally prolonged when this current is diminished as a result of genetic mutations of this channel as for example in the Romano–Ward syndrome 1. Reduction in this current and hence, the prolongation of the QT interval may also be acquired, resulting from electrolyte imbalance (especially hypokalemia and/or hypomagnesaemia), endocrine dysfunction (e.g. hypothyroidism), autonomic imbalance, various disease states or most frequently, following clinical administration of drugs.
• Currently, most view the main role of ECGs as the tool that best assesses the effect of investigational drugs on the electrical functions of the heart. In particular, ECGs are used to gather information on changes in the QT interval, the best surrogate marker for the possibility that an investigational drug may cause Torsade de Pointes, a life threatening arrhythmia. ECGs also gather information on heart rate effects, atrioventricular conduction, depolarization, and changes in ECG morphology that may indicate pathological cardiac changes.
The purpose of this lab exercises is to understand the function and the importance of an electrocardiogram. This lab will demonstrate how stress levels or different elevations can affect human rate. Furthermore, the equipment used in the experiment will show the function in the right and left arm, as well as in the right and left ankles. Finally, the lab will serve a purpose as a way to know how to read an electrocardiogram and how to calculate the heart rate.
Beginning of the lab involved a reading from the electrocardiogram and then calculating the heart rate by comparing the waves to what the electrocardiogram reading said. The electrocardiogram is divided into five main parts. The first small peak is the P wave; it represents the atrial depolarization. Next is the QRS complex; the QRS consist of the Q,R and S. The complex occurs because of the electrical events produced as the ventricles depolarized. Lastly there is the T wave; it represents the ventricular repolarization.
Purpose of the lab was to teach someone how to read an electrocardiogram as well to know how to calculate heart rate. If there was vibration in the table or the position in which someone was standing/laying the it can affect the reading of the electrocardiogram.