WEEK4: ELECTROCARDIOGRAPHY

• In 1786, Luigi Aloisio Galvani observed that when a frog's heart was disconnected from its conductor and touched by a scalpel, all the muscles of the legs seemed to contract again and again as if they were affected by powerful cramps.
• In 1856, Rudolph von Koelliker and Heinrich Müller confirmed that an electrical current accompanies each heart beat by applying a galvanometer to the base and apex of an exposed ventricle.
• U wave results from slow repolarization of ventricular Purkinje fibers.
• QT interval represents total time required for ventricular depolarization and repolarization, from the beginning of QRS complex to the end of T wave.
• T wave represents ventricular repolarization.
• Normal QT interval is 0.36 to 0.45 sec.
• ST segment represents early ventricular repolarization.
• Carlo Matteucci, an Italian scientist, realized in 1842 that electricity is associated with the heartbeat.
• In 1876, Mary analyzed the electric pattern of a frog's heart.
• William Einthoven, an Irish scientist, is credited for the invention of the electrocardiogram (EKG) in 1895.
• Using the string electrometer EKG, William Einthoven diagnosed some heart problems in 1906.
• In 1924, the Nobel Prize for Physiology or Medicine was given to William Einthoven for his work on the electrocardiogram.
• In 1938, the American Heart Association and the cardiac society of Great Britain defined and position of chest leads.
• Goldberger increased Wilson's Unipolar lead voltage by 50% and made augmented leads in 1942.
• Electrocard>The machine and electrodes are applied at specific locations on the patient's chest wall and extremities to view the heart's electrical activity from different angles and planes.
• Electrode position V6 is at the same level as V4 and V5, mid-axillary line.
• Limb leads are bipolar and include Standard limb leads (I, II, III) and Unipolar Augmented leads (aVR, aVL, aVF).
• Lead wires or cable connections include clip and snap.
• Electrode position V2 is in the 4th intercostal space in the left sternal border.
• Rarely, the adhesive can cause allergic reactions or rashes, which may not be obvious until about 24 hours after the test.
• Electrode position V4 is in the 5th intercostal space in the left midclavicular line.
• Electrocardiography is a safe test that does not cause health complications.
• Electrode position V5 is at the same level as V4, anterior axillary line.
• P wave represents atrial contraction.
• The purpose of an ECG is to verify these alterations in heart rhythm, provide information about the specific type of heart disease, and provide information about which region in the heart is affected.
• Electrode position V3 is midway between V2 and V4.
• During the test, the technician attaches a total of ten electrodes with a sticky, but easy-to-remove adhesive, one electrode on each arm and leg, and six on the chest.
• PR interval is measured from the beginning of P wave to the beginning of QRS complex and the normal PR interval is 0.12 - 0.2 sec, represented by 3 - 5 small squares.
• QRS complex represents ventricular depolarization and is composed of 3 waves: Q wave is the first negative deflection, R wave is the first positive deflection after the P wave, and S wave is the negative deflection following R wave.
• Indications for an ECG include heart arrhythmias, conduction abnormalities, Myocardial infarction, CAD, hypertrophic cardiomyopathy, signs of congenital electrical abnormalities, electrolyte imbalances, congenital heart defects, and infections involving the heart.
• Chest leads (V1, V2, V3, V4, V5, V6) are unipolar.
• An electrocardiogram or ECG is a graphic recording of the electrical activity of the heart.
• Electrode position V1 is in the 4th intercostal space in the right sternal border.
• An ECG is done if the patient had heart disease in the past, if the patient has a medical condition that predisposes to heart disease, such as hypertension, diabetes, high cholesterol, or inflammatory disease, if the patient has other significant risk factors for cardiac disease, and an ECG is also required prior to any type of heart surgery.
• Electrocardiography converts the heart’s electrical activity into lines called “waveforms” which can be seen on a monitor or printed out on paper.
• The ECG is made up of 12 characteristic views of the heart: 6 from limb leads and 6 from chest leads.
• The responsibilities of ECG technicians include reminding the patients to lie flat and relaxed as possible, and not to wear jewelries/metal during ECG.
• ECG paper is a graph paper used to measure rates of impulse formation and the duration of the electrical events that occur in the heart.
• Modern ECG machine has evolved into compact electronic systems that often include computerized interpretation of the electrocardiogram.