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Transcript: Electrocardiographic Lead Systems Recording electrodes are configured to form various types of leads A lead records the fluctuation in extracellular voltage generated between its electrodes The standard clinical ECG includes recordings from 12 leads 6 in the frontal plane 3 bipolar leads or standard limb leads 3 modified (augmented) unipolar limb leads 6 in the transverse plane the unipolar precordial leads Limb leads Lead I -negative connection to right arm, positive connection to left arm -defines an axis in the frontal plane at 0 Lead II -negative to right arm, positive to left leg -defines an axis in the frontal plane at 60 Lead III -negative connection to left arm, positive connection to left leg -defines an axis in the frontal plane at 120 -The output – the potential difference between two limbs ECG Leads - Overview Each lead is an axis in one of the planes (frontal, transverse, sagittal) onto which the heart projects its electrical activity Each lead looks at the heart from a unique angle and plane it has its own unique point of view The recording from a single lead shows how that lead views the time-dependent changes in voltage of the heart Arrhythmias Conduction disturbances Myocardial ischemia Cardiac enlargement and hypertrophy Electrolyte disturbances Increased susceptibility to sudden death (QT-prolongation syndromes) Q wave: - Represents depolarisation in the septum. - The picture below shows this small negative wave immediately before the large QRS complex. Whilst the electrical stimulus passes through the bundle of His, and before it separates down the two bundle branches, it starts to depolarise the septum from left to right (shown by arrows). This is only a small amount of conduction (hence the Q wave is less than 2 small squares), It travels in the opposite direction to the main conduction (which is right to left) so the Q wave points in the opposite direction to the large QRS complex. P Wave R wave: As shown in the diagram; the R wave represents the electrical stimulus as it passes through the main portion of the ventricular walls. - The wall of the ventricles are very thick due to the amount of work they have to do and, consequently, more voltage is required. This is why the R wave is by far the biggest wave generated during normal conduction. More muscle means more cells. More cells mean more electricity . More electricity leads to a bigger wave. From Heart Vectors to ECG Waves The amplitude and polarity of the cardiac potentials sensed in a lead are proportional to the size of the projection of the heart vector on the lead vector a.The projection of the heart vector points toward the positive pole of the lead, the lead records a positive potential positive wave on ECG b.The projection is directed away from the positive pole of the lead the lead records a negative potential negative wave on ECG QRS Complex Nomenclature Q wave -Initial downward deflection -Duration: < 0.03 – 0.04 s; exception: in lead V1, V2 any Q is abnormal -Amplitude: < ¼ R wave, < 0.2 – 0.3 mV R wave -First upward deflection -Criteria for shape or size are not absolute; high amplitude in V5, V6 -A second upward deflection is designated R’ S wave -The second negative deflection if there is a Q wave, or the first downward deflection if not -Duration: < 0.04 s -High amplitude in V1, V2 = Repolarisation of ventricles Generally T wave = positive This is due to the repolarization of the membrane. (QRS wave), the heart depolarizes. Repolarization of the ventricle happens in the opposite direction of depolarization and is negative current. This double negative (direction and charge) is why the T wave is positive; although the cell becomes more negatively charged, the net effect is in the positive direction, and the ECG reports this as a positive spike. T-wave inversion (negative T waves) can be a sign of coronary ischemia, Wellens' syndrome, left ventricular hypertrophy, or CNS disorder. Tall and narrow ("peaked" or "tented") symmetrical T waves may indicate hyperkalemia. Flat T waves (less than 1 mV in the limb leads and less than 2 mV in the precordial leads) may indicate coronary ischemia or hypokalemia QRS WAVE: Definition: Represents ventricular depolarisation Description: At this point the electrical stimulus passes from the bundle of His into the bundle branches and Purkinje fibres. The amount of electrical energy generated is recorded as the QRS complex. More voltage is required to cause ventricular contraction and therefore the wave is much bigger. A non-invasive test of the electrical activity of heart's conduction system, which is transformed into recordings on graph paper – an electrocardiograph S wave: This is a small negative wave after the large R wave which represents depolarisation in the Purkinje fibres. The S wave travels in the opposite direction to the large R wave because, as can be seen on the earlier picture, the Purkinje fibres spread throughout the ventricles from top to bottom and then back up


Transcript: ELECTRICAL CELLS pacemaker cells automaticity and conductivity generation and conduction of electrical impulses CARDIAC CELLS II (+) electrode V6 25 sm The limb electrodes RA - On the right arm, avoiding thick muscle LA – On the left arm this time. RL - On the right leg, lateral calf muscle LL- On the left leg this time. LL 5 Presented by: EMERGENCY ROOM DEPARTMENT Iligan Medical Center Hospital San Miguel Village, Pala-o, Iligan City Location: Right atrial wall inferior to the opening of SVC Function: Dominant pacemaker Physiologic heart rate Inherent rate: 60-100 beats/minute LEADS V1,V2,V3,V4,V5,V6 THEY ARE PLACED DIRECTLY ON THE CHEST. BECAUSE OF THEIR CLOSE PROXIMITY OF THE HEART, THEY DO NOT REQUIRE AUGMENTATION. Inferior to be continued... 25 sm HOW TO DO ELECTROCARDIOGRAPHY Sinus Node Standard Limb Leads Surface viewed Inferior 0.20s 1 The 6 chest electrodes V1 - Fourth intercostal space, right sternal border. V2 - Fourth intercostal space, left sternal border. V3 - Midway between V2 and V4. V4 - Fifth intercostal space, left midclavicular line. V5 - Level with V4, left anterior axillary line. V6 - Level with V4, left mid axillary line. The Electrocardiogram Analyzing a Rhythm Strip Atrial depolarization ANALYZING A RHYTHM STRIP Lead Left leg 1 The Electrical Conduction System Regularly Irregular V3 Right and Left (-) electrode Left arm Irregularly Irregular The Different Views Reflect The Angles At Which LEADS "LOOK" At The Heart And The Direction Of The Heart's Electrical Depolarization. Contraction of atria - P wave Ventricular depolarization - QRS complex Ventricular repolarization - T wave The ECG 12-lead system LA aVR aVL aVR aVF aVL LL Lateral RL V5 Note: Place the sensors on a smooth fleshy area of the upper arms and lower legs. Attach the limb leads. Left arm AV Node Assess the Rhythm 0.04 25 sm Left leg 25 sm MYOCARDIAL CELLS working cells mechanical cells contractility contraction and relaxation 4 Location: Interventricular septum Inherent rate: 20-40 beats/min Escape pacemaker 2 Records the hearts electrical activity The diagnostic tool of choice in order to investigate cardiac arrhythmias in most patients noninvasive and readily available THE SHAPE OF ECG V2 Time II 1 Record of electrical activity between 2 electrodes Has a negative (-) and positive (+) pole Types: 1. Standard limb leads 2. Augmented leads 3. Precordial leads (chest leads) 1. Place the patient in a supine or semi-Fowler's position. If the patient cannot tolerate being flat, you can do the ECG in a more upright position. 2. Instruct the patient to place their arms down by their side and to relax their shoulders. 3. Make sure the patient's legs are uncrossed. 4. Remove any electrical devices, such as cell phones, away from the patient as they may interfere with the machine. 5. If necessary shave the electrode areas before cleaning the exposed skin with alcohol for proper electrode adhesion. 6. If you're getting artifact in the limb leads, try having the patient sit on top of their hands. Causes of artifact: patient movement, loose/defective electrodes/apparatus, improper grounding. RA Sino-Atrial Node The electrocardiogram (ECG) is a representation of the electrical events of the cardiac cycle. Each event has a distinctive waveform the study of waveform can lead to greater insight into a patient’s cardiac pathophysiology. Bundle Branches (right and left) ECG Paper PRECORDIAL LEADS AV Junction 1 1 small square = 0.04 sec = 1 mm = 0.1 mV 1 big square = 0.2 sec 5 big squares = 1 sec 300 big squares = 1 min Ventricular Muscle CARDIAC CELLS These leads help to determine heart’s electrical axis. The limb leads and the augmented limb leads form the frontal plane. The precordial leads form the horizontal plane. Surface viewed Bundle of His What is an ECG? III Right arm Network of conducting strands beneath the ventricular myocardium Inherent rate: 20-40 beats/min Escape pacemaker Provides information about: Orientation of the heart in the chest Conduction disturbances Electrical effects of medications and electrolytes Presence of ischemic changes The ECG Waveforms BASIC ECG 1 Left arm I Learning Objectives (+) electrode RA Inferior The Electrocardiogram Left leg Assess the Rhythm V4 Atrioventricular node Lead The ECG Waveforms III Purkinje Fibers 3 V1 Voltage 25 sm Sino-atrial node 1mm or 0.1mV Rate, Rhythm and Waveforms aVF Right arm Define ECG and its importance Familiarize the Anatomy and Mechanism of Heart and its Conduction system Define terms related to ECG Demonstrate the proper ECG procedure and its Nursing Considerations Identify basic steps in analyzing a rhythm Identify common rhythm disturbances. Placement of electrodes Ventricular repolarization Augmented Leads The ECG and the 12-lead system Ventricular depolarization ANALYZING A RHYTHM STRIP LA Bundle of His Assess the Rhythm Measure the distance between 2 consecutive R-R intervals and compare that distance with the other R-R intervals PACEMAKERS OF THE HEART

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