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Transcript
Electrocardiograph History • 1842- Italian scientist Carlo Matteucci realizes that electricity is associated with the heart beat • 1876- Irish scientist Marey analyzes the electric pattern of frog’s heart • 1895 - William Einthoven , credited for the invention of EKG • 1906 - using the string electrometer EKG, William Einthoven diagnoses some heart problems. Contd.. • 1924 - the noble prize for physiology or medicine is given to William Einthoven for his work on EKG • 1938 -AHA and Cardiac society of great Britan defined and position of chest leads • 1942- Goldberger increased Wilson’s Unipolar lead voltage by 50% and made Augmented leads • 2005- successful reduction in time of onset of chest pain and PTCA by wireless transmission of ECG on his PDA. Modern ECG Instrument Heart Functions • Heart has three functions: • Pumps oxygenated blood to all parts of the body • Has its’ own blood supply – called the coronary arteries • Has an electrical conduction system because cells are electrically charged and produce a wave form Bioelectricity in Tissues • Polarized = • high concentration of potassium inside the cell • high concentration of sodium outside the cell Contd… • Stimulation of cell/Depolarization = sodium rushes in and potassium rushes out • When depolarization is completed, sodium and potassium return to their normal places, bringing the cell back to rest called repolarization. • This process of depolarization and repolarization produces wave forms on the EKG • ECG shows repolarization → polarization with ECG complex. Impulse Conduction of Heart Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers Biopotential In Heart • SA node = Pacemaker of the heart (initiates the electricity that causes the heart to beat) • Rate=60-100 beats per minute (NSR) • Stimulates the right and left atrium to contract after depolarization of the cells Impulse travels to the: • AV Node= Functions as a delay, keeping the atria and ventricles from contracting at the same time. • Rate is 40-60 beats/minute • Bundle of His= Distal portion of the AV node • Splits into the Right and Left Bundle Branch, stimulating the right and left ventricle Contd… • Purkinje Fibers= Receives the electrical impulse from the Bundle of His • Fibers transmit through the walls of the ventricles • Rate is 20-40/min Definition of ECG • The ECG is a graphical representation of the electrical impulses that the heart generates during the cardiac cycle. • These electrical impulses are conducted to the body's surface, where they are detected by electrodes placed on the patient's limbs and chest. A NORMAL ECG WAVE Standard Lead System • The Standard ECG have 12 Leads • 6 Limbs Leads Limbs lead divided into Bipolar and Unipolar Leads 3 Bipolar Limb Leads 3 Unipolar Limb Leads • 6 Precordial Leads Bipolar Limb Leads • They are formed by voltage tracings between the limb electrodes (RA, LA, RLand LL). These are the only bipolar leads. Or • THE EINTHOVEN’S TRIANGLE – LEAD I – LEAD II – LEAD III 13-61 LEAD I • LA is connected to amplifier’s noninverting input, while RA is connected to inverting input. LEAD II • The LL is connected to amplifier’s noninverting input, while RA is connected to inverting input. LEAD III • The LL is connected to amplifier’s noninverting input, while LA is connected to inverting input. Unipolar Limb Leads • They are also derived from the limb electrodes, they measure the electric potential at one point with respect to a null point. They are the AUGMENTED LIMB LEADS. – aVR – aVL – aVF aVR aVL aVF aVR • RA is connected to noninverting input, while LA and LL are summed at inverting input. aVL • LA is connected to noninverting input, while RA and LL are summed at inverting input. aVF • LL is connected to noninverting input, while RA and LA are summed at inverting input. PRECORDIAL LEADS They are placed directly on the chest. Because of their close proximity of the heart, • V1 is recorded with the electrode in the 4th intercostals space just to the right of sternum. • V2 is recorded in the 4th intercostals space just to left of sternum. • V3 is recorded on a line midway between V2 and V4. • V4 is recorded in the midclavicular line in the fifth interspace. • V5 is recorded in the anterior axillary line at the same level as lead V4. • V6 is recorded in midaxillary line at the same level as V4 LA RA V1 RL V2 V3 V4V5 V6 LL ECG Waveform ECG • Three distinct wave are produced during cardiac cycle • P wave caused by atrial depolarization • QRS complex caused by ventricular depolarization • T wave results from ventricular repolarization P Wave • P wave represent the atrial depolarization. • P duration: < 3 small squares or 0.08 to 0.1 sec. • P amplitude : < 2.5 small squares or < 2.5 mm PR Interval • Represents the time between the onset of atrial depolarization (P wave) and the onset of ventricular depolarization (QRS Complex). • Normal duration = 0.12-2.0 sec (120-200 ms) (3-5 small squares of ECG paper) QRS Complex • Represent the Ventricular depolarization • Normal duration = 0.08-0.12 seconds ST Segment • Connects the QRS complex and T wave • Duration of 0.08-0.12 sec (80-120 msec) T Wave • It represents the ventricular depolarization and longer in duration than depolarization. QT interval • It represent the time for both ventricular depolarization and repolarization • Measured from beginning of QRS to the end of the T wave • Normal QT is usually about 0.40 sec • QT interval varies based on heart rate. Fig. 13.24b Fig. 13.24c Fig. 13.24d Fig. 13.24g Calibration • Check that your ECG is calibrated correctly • Height – 10mm = 1mV – Look for a reference pulse which should be the rectangular looking wave somewhere near the left of the paper. It should be 10mm (10 small squares) tall. • Paper speed – 25mm/ s – 25 mm (25 small squares / 5 large squares) equals one second ECG Paper