The electrocardiogram (abbreviated as ECG or EKG) represents an electrical tracing of the heart and is recorded non-invasively from the surface of the body. The word ECG derives from the German language. In German, it is elektro-kardiographie. In 1902, the Dutch physician Einthovan invented ECG, and his tremendous input in the clinical studies for about ten years led to full recognition of the clinical potential of the technique. Many arrhythmias and EKG changes associated with angina and atherosclerosis were identified by 1910. William Einthoven was named the "father of electrocardiography" and was awarded Nobel Prize in Medicine in 1924 for his hard work that laid the foundation of the most fundamental technique of investigating heart disorders. ECG was soon recognized as a robust screening and a clinical diagnostic tool, and today it is used globally in almost every healthcare setting.
ECG is a non-invasive diagnostic modality that has a substantial clinical impact on investigating the severity of cardiovascular diseases. ECG is increasingly being used for monitoring of patients on antiarrhythmics and other drugs, as an integral part of preoperative assessment of patients undergoing non-cardiac surgery, and for screening individuals in high-risk occupations and those who are participating in sports. Also, EKG serves as a research tool for surveillance and experimental trials of drugs with recognized cardiac effects. Cardiovascular disease, as the number one cause of death, puts a great emphasis on health-care providers to develop skills and knowledge in interpreting ECGs to provide the best care promptly. Many health-care providers find the advanced interpretation of ECG findings a complicated task. Errors in the analysis can lead to misdiagnosis resulting in delaying the appropriate treatment. This activity seeks to provide a general understanding of the ECG mechanisms, interpretation techniques, and commonly encountered ECG findings.
A basic understanding of cardiac anatomy and coronary distribution is essential to understand the electrocardiographic findings.
The heart is a vital organ of the body and occupies the space in the central chest between the lungs. Together with the blood vessels and blood, it constitutes the circulatory system of the body. The heart is a muscular organ comprised of four chambers that includes two atria (right and left) opening into right and left ventricles via tricuspid and mitral valves, respectively. A wall of muscle called septum separates all the four chambers. The heart receives deoxygenated blood from the whole body via superior and inferior vena cava, which first enters the right atrium. From here, it transits through the right ventricle and then passes into the lungs via right and left pulmonary arteries, where it is oxygenated. The oxygenated blood from the lungs pours into the left atrium through the right and left pulmonary veins, and from here, it is pumped by the left ventricle into the aorta to the rest of the body. The heart derives its blood supply from the coronary arteries that branch off from the aorta. The right and left coronary arteries lie on the surface of the heart. With considerable heterogeneity among the general population, different regions of the heart receive vascular supply by the various branches of the coronary arteries. This anatomic distribution is significant because these cardiac regions are assessed by a 12-lead ECG to help localize and diagnose ischemic or infarcted areas. Written below are the following regions supplied by the different coronary arteries.
The heart is a mechanical pump whose activity is governed by the electrical conduction system. It is essential to have a good understanding of the physiology of the cardiac cells as this will help the reader appreciate how the heart works and the implications of findings on the ECG. The heart is made up of specialized cardiac muscle, which is striated and organized into sarcomeres. These muscle fibers contain a single central nucleus, numerous mitochondria, and myoglobin molecules. Extensive branching of the cardiac muscle fibers and their end to end connection with each other through intercalated discs make them contract in a wave-like fashion. This mechanical work of pumping blood to the whole body occurs in a synchronized manner and is under the control of the cardiac conduction system. It is comprised of two types of cells, pacemaker and non-pacemaker cells. Pacemaker cells are located primarily in the SA and AV node, and it is the SA node, which drives the rate and rhythm of the heart. The AV node gets suppressed by the more rapid pace of the SA node.  The specialized function associated with the pacemaker cells is their spontaneous depolarization with no true resting potential. When spontaneous depolarization reaches the threshold voltage, it triggers a rapid depolarization followed by repolarization. The non-pacemaker cells mainly comprise the atrial and ventricular cardiac muscle cells and Purkinje fibers of the conduction system. They consist of true resting membrane potential, and upon initiation of an action potential, rapid depolarization is triggered, followed by a plateau phase and subsequent repolarization. Action potentials are generated by ion conductance via the opening and closing of the ion channels. Knowing which ECG leads corresponds to specific arteries helps in localizing the obstruction in acute ST-elevation MI or an age-indeterminate Q-wave infarction by observing predictable patterns on the ECG.
The evolution of EKG from a string galvanometer to the modern-day advanced computerized machine has led to its use as a diagnostic and screening tool, making it the gold standard for diagnosing various cardiac diseases.
Owing to its widespread use in the field of medicine, the EKG has several indications listed below:
There are no absolute contraindications for EKG. The relative contraindications to its use include:
The American College of Cardiology (ACC), in conjunction with American Heart Association (AHA) and the Heart Rhythm Society (HRS), has formulated guidelines and also set technical standards for ECG equipment . With advancements, most of the EKG machines are digital and can autogenerate preliminary findings based on the morphology criteria.
The conventional ECG machine consists of 12 leads, which divide into two groups, i.e., limb leads and precordial leads. Limb leads are further categorized as standard bipolar limb leads I, II and III, and augmented unipolar leads aVL, aVF, and aVR. The precordial leads include V1 to V6. The limb leads view the heart in a vertical plane, and the precordial leads record the electrical activity of the heart in the horizontal plane. The ECG represents a graphic recording of the electrical cardiac activity tracing on the electrocardiograph paper. The fundamental principles behind the recording of an ECG is an electromagnetic force, current or vector that has both magnitude and direction. When a current of depolarization travels towards the electrode, it gets recorded as a positive deflection, and when it moves away from the electrode, it appears as a negative deflection.
These concepts are easily applied to the heart while recording the ECG. There are several types of ECG monitoring equipment available, including continuous ECG monitoring, hardwire cardiac monitoring, telemetry, ambulatory electrocardiography, transtelephonic monitoring, and wireless mobile cardiac monitoring systems, etc. Furthermore, a duo of ECG and electronic stethoscope has been designed into a portable, handheld device that can review ECG rhythms and intervals at the bedside for analysis. With the evolution of technology, there are electronic wristwatches that can also provide monitoring of the heart rate and rhythm and have proven to be of value in detecting atrial fibrillation. The accuracy of these devices, however, may be somewhat inferior when compared to a 12-lead ECG; and when prompted for abnormal findings, these require confirmation by standardized clinical testing available in the Cardiology office.
The equipment for performing a conventional 12-lead ECG includes:
The medical personnel that can perform the ECG procedure includes a doctor, nurse, or a qualified technician. Usually, it is performed by the technicians either in the clinics or hospitals and then interpreted by physicians. Often, these findings are confirmed by a cardiologist in a hospital-based setting.
ECG merely requires special preparation. Before the procedure, a brief history regarding drugs and allergy to adhesive gel is necessary. The temperature of the room must be kept optimal to avoid shivering. The patient should be in a gown, and electrode sites identified. For good contact between body surface and electrodes, it is advised to shave the chest hair and then apply the electrocardiographic adhesive gel for electrodes. Any metallic object like jewelry or watch requires removal, if possible. Limb and precordial leads should be accurately placed to avoid vector misinterpretation. The patient must lie down and relax before recording the standard 10-second strip.
ECG machines are designed to record changes in the electrical activity by drawing a trace on a moving electrocardiograph paper. The electrocardiograph moves at a speed of 25mm/sec. Time is plotted on the x-axis and voltage on the y-axis. In the x-axis, 1 second is divided into five large squares, each of which represents 0.2 sec. Each large square is further divided into five small squares of 0.04 sec each. The EKG machine is calibrated in such a way that an increase of voltage by one mVolt should move the stylus by 1 cm. The conventional 12-lead EKG consisting of six limbs and six precordial leads is organized into ten wires. The limb leads include I, II, III, aVL, aVR, and aVF and named as RA, LA, RL, and LL. The limb leads are color-coded to avoid misplacement (red- right arm, yellow- left arm, green- left leg, and black- right leg). The precordial leads V1 to V6 are attached to the surface of the chest. For the correct location, the "Angle of Louis" method is an option, and the exact placement is as follows:
ECG is a safe, non-invasive, painless test with no major risks or complications. An allergic reaction or skin sensitivity to the adhesive gel can occur and usually resolves as soon as the electrode patches are removed, and in most cases, do not require any treatment. Artifacts and distortions pose serious diagnostic difficulties and may result in an inaccurate interpretation of the ECGs that may potentially result in an adverse therapeutic intervention.
The goal of the ECG interpretation is the ability to determine whether the ECG waves and intervals are normal or pathological. Electrical signal interpretation gives a good approximation of heart pathology. A standard 12 lead ECG is shown in [Figure 1]. The best way to interpret an ECG is to read it systematically:
ECG monitoring goals from simple heart rate and essential rhythm monitoring have been expanded significantly to the interpretation of complex arrhythmias, myocardial infarction, and other ECG abnormalities. The rapid detection of myocardial infarction has reduced the door-to-balloon time for reperfusion therapy substantially. Nurses' skills regarding assessment and comprehensive knowledge of the dysrhythmias can prevent stroke in atrial fibrillation and improve patient outcomes from the emergency department presentation through discharge and follow-up. Cardiology board-certified pharmacists can make appropriate medication recommendations for several medications, in particular, antiarrhythmics, based on ECG readings and patient history, working in conjunction with the cardiologist.
ECG outcomes in management are noticeable from observation to the critical care floors. An interaction among physicians, nurses, patient care assistants, pharmacists, and ECG technicians is critical to provide the most effective patient care. Interprofessional collaboration and teamwork in the hospital setting prevents significant medical errors by multiple checkpoints and also ensures timely emergency care in cardiac emergencies. For better outcomes, excellent professional ethics, evaluating patients satisfaction, and proficiency of the staff in evaluating ECGs are mandatory. There should be effective communication with appropriate role clarity, shared policies, and strategies to improve system-related issues. [Level V]
Continuous EKG monitoring is one of the current technologies being used in the emergency department, intensive, post-anesthesia, and cardiac care units, and often, nurses are the first care responders in these hospital settings. The first interaction of the EKG view puts great responsibility on the nurses in managing technical aspects of the EKG monitoring and also decision-making on the clinical grounds with information received from the monitor. The current practice involved is that nurses initially interpret the EKG and gather data and timely notify the physician-in-charge, to ensure an appropriate management plan.
Among the healthcare providers in a hospital setting, especially in intensive and cardiac care units where round the clock monitoring of critical patients is required, nurses play a very crucial role in cardiac monitoring. It is the responsibility of the nurse to assess the patient's clinical condition, monitor, and make sure that an excellent quality of care is delivered. The nurses' should monitor the continuous EKG monitoring very carefully and have competency in initial interpretation. Their knowledge about correct EKG leads placement, analysis, and providing thrombolytic treatment in acute coronary syndrome patients have significant implications in reducing morbidity and mortality.
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