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Cardiology 22.3
Cardiology 22.3 - slides 132 - 246
| Question | Answer |
|---|---|
| Learning Objective Slide 132 | Describe basic monitoring techniques that permit electrocardiogram (ECG) interpretation. Explain the relationship of the electrocardiogram tracing to the electrical activity of the heart. |
| Learning Objective | Describe in sequence the steps in electrocardiogram interpretation. Identify the characteristics of normal sinus rhythm. |
| ECG Monitoring | Graphic representation of electrical activity of heart Produced by electrical events in atria and ventricles Important diagnostic tool |
| ECG Monitoring | Helps to identify cardiac abnormalities Abnormal heart rates and rhythms Abnormal conduction pathways Hypertrophy or atrophy of portions of the heart Approximate location of ischemic or infarcted cardiac muscle |
| Evaluation of ECG requires systematic approach | Paramedic analyzes ECG, then relates it to clinical assessment of patient ECG tracing is only reflection of electrical activity of heart Does not provide information on mechanical events such as force of contraction or BP |
| ECG Monitoring Basic Concepts | Summation of all action potentials transmitted through heart during cardiac cycle can be measured on body surface |
| ECG Monitoring Basic Concepts | Measurement is obtained by applying electrodes to patient’s skin that are connected to ECG machine Voltage changes are fed to machine, amplified, and displayed visually on oscilloscope screen, graphically on ECG paper, or both |
| Voltage may be | Positive Seen as upward deflection on ECG tracing Negative Seen as downward deflection on ECG tracing Isoelectric When no electrical current is detected (seen as a straight baseline on ECG tracing) |
| ECG machines offer many views of electrical activity of heart | Monitor voltage changes between electrodes (leads) applied to body Modern ECG views electrical activity of heart from 12 leads 3 standard limb leads 3 augmented limb leads 6 precordial (chest) leads |
| ECG Leads | Standard limb leads: I, II, III Augmented limb leads: aVR, aVL, and aVF Precordial leads: V1 through V6 Each lead assesses electrical activity from slightly different view and produces different ECG tracings |
| Standard Limb Leads | Bipolar leads Use two electrodes of opposite polarity (one pole being positive and one pole being negative) to form lead |
| Standard Limb Leads | Standard limb leads record difference in electrical potential between left arm (+), right arm (–), and left leg (–) electrodes Lead I records difference in electrical potential between left arm (+) and right arm (–) electrodes |
| Standard Limb Leads | Lead II Records difference in electrical potential between left leg (+) and right arm (–) electrodes Lead III Records difference in electrical potential between left leg (+) and left arm (–) electrodes |
| Standard Limb Leads | Imaginary lines (axes) join positive and negative electrodes of each lead Form straight line between positive and negative poles These lines form equilateral triangle with heart at center (Einthoven’s triangle) - Slide 144 diagram |
| Placement of electrodes of bipolar leads | Lead I Positive electrode: left arm Negative electrode: right arm Lead II Positive electrode: left leg Negative electrode: right arm Lead III Positive electrode: left leg Negative electrode: left arm |
| Augmented Limb Leads | Record difference in electrical potential Are unipolar leads Have one electrode for positive pole Have no distinct negative pole Made by combining two negative electrodes Use three electrodes to provide their view of heart |
| Augmented Limb Leads | Magnify voltage of positive lead (which is usually small) Increases size of complexes seen on ECG Use same set of electrodes as standard limb leads |
| Augmented Limb Leads - Placement of electrodes | aVL Positive electrode: left arm Negative electrode: left leg and right arm aVR Positive electrode: right arm Negative electrode: left leg and left arm aVF Positive electrode: left leg Negative electrode: left arm and right arm |
| Augmented Limb Leads | Intersect at different angles than standard limb leads Produce three other intersecting lines of reference |
| Augmented Limb Leads | When combined with lines of reference of standard limb leads, form six lines of reference known as hexaxial reference system Important for advanced ECG interpretation - slide 150 diagram |
| Precordial Leads | 6 precordial leads or chest leads are unipolar leads that record electrical activity of heart in horizontal plane These leads are used in 12-lead ECG monitoring and measure amplitude of heart’s electrical current |
| Precordial Leads | Precordial leads are projected through anterior chest wall (through AV node) toward patient’s back Projection of leads separates body into upper and lower halves, providing transverse or horizontal plane |
| Precordial Leads | Electrodes on patient’s chest are considered positive, but they are considered negative posteriorly Chest leads are numbered from V1 to V6 Slide 153 diagram |
| Precordial Leads - When properly positioned on chest, chest leads surround heart from right to left side | Leads V1 and V2 are positioned over right side of heart V5 and V6 over left side of heart V3 and V4 over interventricular septum Right and left ventricle AV bundle Right and left bundle branches Slides 155 thru 157 diagrams |
| Precordial leads are placed on chest in reference to thoracic landmarks | Proper placement of chest leads at specific intercostal spaces is essential for accurate reading |
| One method to locate appropriate intercostal spaces | Locate jugular notch and move downward until sternal angle is found Follow articulation to right sternal border to locate second rib Just below second rib is second intercostal space |
| One method to locate appropriate intercostal spaces Method (cont'd) | Move down two intercostal spaces and position V1 electrode in fourth intercostal space, just to right of patient’s sternum Move across sternum to corresponding intercostal space and position V2 to left of patient’s sternum |
| One method to locate appropriate intercostal spaces Method (cont'd) | From V2, palpate down one intercostal space and follow fifth intercostal space to midclavicular line to place V4 electrode |
| One method to locate appropriate intercostal spaces Method (cont'd) | Place lead V3 midway between V2 and V4 Place V5 in anterior axillary line in straight line with V4 (where arm joins chest) Place V6 in midaxillary line, level with V4 and V5 |
| One method to locate appropriate intercostal spaces Method (cont'd) | May be more convenient to place V6 first, and then V5 In women, place V4 to V6 electrodes under left breast to avoid any errors in ECG tracing that may occur from breast tissue Lift breast away using back of hand Slide 161 |
| Routine monitoring of cardiac rhythm in prehospital setting, emergency department, or coronary care unit usually is obtained in lead II or MCL1 | Best leads to monitor for dysrhythmias because of their ability to display P waves (atrial depolarization) on ECG tracing |
| Much information can be gathered from single monitoring lead, and in many cases, cardiac monitoring by a single lead is sufficient | Paramedic also can determine how long conduction lasts in different parts of heart Single-lead monitoring does have limitations and may fail to reveal various cardiac abnormalities |
| Much information can be gathered from single monitoring lead, and in many cases, cardiac monitoring by a single lead is sufficient | In most EMS systems that provide advanced life support, 12-lead ECG is standard in monitoring patients with chest pain of cardiac origin Most commonly used electrodes for continuous ECG monitoring are pre-gelled stick-on disks |
| Observe guidelines to minimize artifacts in signal and to make effective contact between electrode and skin | Choose appropriate area of skin, avoiding large muscle masses and large quantities of hair, which may prevent electrode from lying flat against skin Cleanse area with alcohol to remove dirt and body oil |
| Observe guidelines to minimize artifacts in signal and to make effective contact between electrode and skin | When attaching electrodes to extremities, use inner surfaces of arms and legs If necessary, trim excess body hair before placing electrodes |
| Observe guidelines to minimize artifacts in signal and to make effective contact between electrode and skin | If patient is extremely diaphoretic, use tincture of benzoin to aid in securing application or use diaphoretic electrodes |
| Monitoring Electrodes Application Guidelines (cont'd) | Attach electrodes to prepared site Attach ECG cables to electrodes Most cables are marked for right arm, left arm, and left leg application |
| Monitoring Electrodes Application Guidelines (cont'd) | Turn on ECG monitor and obtain baseline tracing If signal is poor, recheck cable connections and effectiveness of patient’s skin contact with electrodes |
| Monitoring Electrodes Application Guidelines (cont'd) | Other common causes of poor signal include body hair, dried conductive gel, poor electrode placement, and diaphoresis |
| Paper used in recording ECGs is standardized to allow comparative analysis of an ECG wave | Divided into squares 1 mm in height and width Paper is divided further by darker lines every fifth square vertically and horizontally Each large square is 5 mm high and 5 mm wide Slide 171 diagram |
| As graph paper moves past needle or pen of ECG machine, it measures time and amplitude | Time is measured on horizontal plane (side to side) When ECG is recorded at standard paper speed of 25 mm per second |
| ECG Graph Paper | Each small square = 1 mm (0.04 second) Each large square (the dark vertical lines) = 5 mm (0.20 second) Squares measure length of time it takes electrical impulse to pass through specific part of heart |
| Amplitude is measured on vertical axis (top to bottom) of graph paper | Each small square = 0.1 mV Each large square (five small squares) = 0.5 mV |
| Sensitivity of 12-lead ECG machine is standardized | When properly calibrated, a 1-mV electrical signal produces 10-mm deflection (two large squares) on ECG tracing |
| Sensitivity of 12-lead ECG machine is standardized | ECG machines equipped with calibration buttons should have calibration curve placed at beginning of first tracing (generally 1-mV burst, represented by 10-mm “block” wave) |
| Time-interval markings denoted by short vertical lines and usually located on top of ECG graph paper | When ECG is recorded at standard paper speed of 25 mm/second, distance between each short vertical line = 75 mm (3 seconds) |
| Time-interval markings denoted by short vertical lines and usually located on top of ECG graph paper | Each 3-second interval contains 15 large squares (0.2 second x 15 squares = 3 seconds) Used as method of heart rate calculation |
| Slide 176 |
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zach918