Chapter 49

• The Electrocardiogram

  • Strength or voltage of electrical impulse determines size of deflection. 
• Polarity: having 2 seperate poles

  1 NEGATIVE

  1 POSITIVE
• If no energy is sensed, ECG equipment records a flat line (isoelectric line). 
• MYOCARDIAL IN RESTING PHASE- it is polarized because of it negative internal charge and its positive external charge.
• Myocardium: the muscular tissue of the heart. (heart muscle)
• As the cells depolarize, artia and ventricles contract, blood is pushed out of heart and into the circulatory system.
• End of contraction - Myocardium relaxes and rests
• During Relaxation- cells become repolarized
• The cycle of the eletrical impulses (depolarization and repolarization) represents one heartbeat.
• Normal eletrical cardiac cycle (1 heartbeat) is traced on electrocardiogram as one set of PQRST waves.
• P - Atrial depolarization
• QRS- Ventricular depolarization
• T- Repolarization
• ECG Horizontal Line- represents time
• Recordings are made from variety of perspectives or angles (leads)
• Each lead recors a specific combination of sensors
• When completed- 12- Lead ECG produces 3D record of cardiac impulses
• P-R intervals is between 0.12 & 0.20
• Interval represents the time it takes for impulses to cross atria and atrial-ventricular (AV) node and reach the ventricles
• P Wave - Atrial contraction initiated by electrical impulses from SA node. (Atrial depolarization)
• QRS Complex- Ventricular contraction of heart. (Ventricular depolarization)
• T Wave- completion of ventricular contraction; cells begin their resting phase before process restarts. (Ventricular repolarization)
• U Wave- Sometimes present; represents further relaxation of the ventricles; continuation of ventricular repolariztion.
• ECG MACHINES- Calibrated to align with the international standard.
• ECG MACHINE- Standardization is verifying each machine deflects 10 mm in repsonse to 1 mV of electricity in sensitvity.
• ECG MACHINE- Computerized models have automatic features.
• ECG MACHINES- All 10 electrode sensors are placed on the patient at the beginning of the procedure.
• Standard (limb) Leads- Records from 2 sensors placed on all extremities
• Augmented Leads- Records from midpoint between 2 limb sensors to 3rd limb sensor.
• Chest Leads (precordial leads)- Record from various positions on the thorax
• Sensitivity Control- Allows operator to increase or decrease recording size to enlarge or shrink deflections to fit on the paper
• Electrocardiogram Paper- Pressure & photo sensitive
• Electrocardiogram Paper- Must be handled carefully
• Electrocardiogram Paper- If exposed to light for long time the markings will fade
• Electrocardiogram Paper- "Time" marks (3 second markers) are small squares with a light line & large squares with darker line
• Electrocardiogram Paper- Paper records both time (horizontally) and voltage (vertivcally)
• Vertical - Voltage

  Horizontal- Time
• Precordial Lead- Chest Sensor
• V1- 4th Intercostal space; right sternal border
• V2- 4th intercostal space, left sternal border