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Chapter 37

Chapter 37. Electrocardiography. Anatomy of the Heart. Four chambers Atria: two upper chambers Ventricles: two lower chambers Deoxygenated and oxygenated blood Cycle begins with each heartbeat Coronary arteries. Electrical Conduction System of the Heart.

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Chapter 37

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  1. Chapter 37 Electrocardiography

  2. Anatomy of the Heart • Four chambers • Atria: two upper chambers • Ventricles: two lower chambers • Deoxygenated and oxygenated blood • Cycle begins with each heartbeat • Coronary arteries

  3. Electrical Conduction System of the Heart • Sinoatrial (SA) node: body’s natural pacemaker • Atrioventricular (AV) node: responds to signals from SA node • Bundle of His and Purkinje fibers: disperses electrical impulses

  4. Electrical Conduction System of the Heart • Systole: contraction • Diastole: relaxation • ECG cycle • Graphic representation of cardiac cycle • Electrical impulses recorded on ECG paper or displayed on oscilloscope

  5. The Cardiac Cycle and the ECG Cycle • Baseline or isoelectric line • Positive and negative deflection • P, QRS, T waves: depolarization and repolarization of myocardial cells • Each cardiac cycle takes about 0.8 second

  6. Electrical impulses in cardiac cycle The Cardiac Cycle and the ECG Cycle

  7. Calculation of Heart Rate • On ECG graph paper: • Every fifth line darker than other lines (squares 5 X 5 mm) • Time measured on horizontal line • Voltage measured on vertical line

  8. Types of Electrocardiographs • Multichannel ECG • Automatic ECG machines • Single-channel ECG >>

  9. Types of Electrocardiographs • ECG telephone transmissions • Facsimile electrocardiograph • Interpretive electrocardiograph

  10. ECG Equipment • Electrocardiograph paper • Black or dark blue • Wax or plastic coated • Heat and pressure sensitive • Heat of stylus can be adjusted to obtain sharp tracing

  11. ECG Equipment • Electrolyte • Applied with each electrode to pick up electrical current • In form of gel, lotion, paste, or pre-saturated pads, contained within adhesive sensors

  12. ECG Equipment • Sensors or electrodes • Detect electrical impulses on body surface; relay them through cables, or lead, wires to ECG machine • Disposable sensors (electrodes) contain layer of electrolyte gel on adhesive surface; used on limbs and chest

  13. ECG Equipment • Lead wires • Once self-adhesive sensors are placed, lead wires from ECG machine are connected to them

  14. ECG Equipment • Electrocardiograph machine • Electrical activity from body small; made larger by amplifier of ECG machine • Care of equipment • Remove lead wires from sensors • Remove sensors from patient • Dispose of sensors • Change paper when necessary

  15. Lead Coding • 12 leads recorded using 10 lead wires • Necessary for identification and mounting purposes • Newer ECGs automatically mark (code) each lead

  16. The Electrocardiograph and Sensor Placement • 10 sensors that record 12 leads of heart’s electrical activity • Allows for 3D interpretation of activity • Electrodes placed on patient’s four limbs and chest

  17. The Electrocardiographand Sensor Placement • Types of leads • Standard limb or bipolar leads • Augmented leads • Chest leads or precordial leads

  18. Standardization and Adjustment of the Electrocardiograph • Value of recording depends on accuracy • Universal measurements • One millivolt (mV) of cardiac electrical activity will deflect stylus exactly 10 mm high

  19. Standard Resting Electrocardiography • Patient preparation • Placement of limb and chest leads • Attachment of lead wires • Elimination of artifacts vary little from one electrocardiograph to another

  20. Mounting the ECG Tracing • Commercially prepared mounting forms • Mount completed tracing after provider has reviewed entire recording • Patient’s name, date, address, age, sex, blood pressure, height and weight, cardiac medications

  21. Interference or Artifacts • Somatic tremor artifacts: muscle tremor • Alternating current (AC) interference: electrical interference • Wandering baseline artifacts: stylus moves from center of ECG paper

  22. Interference or Artifacts • Interrupted baseline artifacts: break seen between waves • Patients with unique problems

  23. Myocardial Infarctions (Heart Attacks) • Number one cause of death in United States • Behaviors to adopt for healthy heart

  24. Cardiac Arrhythmias • Atrial arrhythmias • Premature atrial contractions (PAC) • Paroxysmal atrial tachycardia (PAT) • Atrial fibrillation

  25. Cardiac Arrhythmias • Ventricular arrhythmias • Premature ventricular contractions (PVCs) • Ventricular tachycardia • Ventricular fibrillation

  26. Defibrillation • Electrical device that applies countershocks to heart through electrodes or pads placed on chest wall • Can convert cardiac arrhythmia to normal sinus rhythm • Automated external defibrillators (AED)

  27. Other Cardiac Diagnostic Tests • Holter monitor (portable ambulatory electrocardiograph) • Portable continuous recording of cardiac activity for 24-hour period • Noninvasive test helps to diagnose cardiac arrhythmias • Digital, three-channel ECG; Windows-based software • Electrode placement not the same as for standard 12-lead resting ECG

  28. Other Cardiac Diagnostic Tests • Holter monitor • Prepare patient • Instruct patient • Check and replace battery • Apply and remove monitor

  29. Other Cardiac Diagnostic Tests • Holter monitor • Patient activity diary • Record all activities, emotional states, time of their occurrence • Record chest pain and other symptoms and time of occurrence • Removal • Patient returns to office • Tape analyzed by scanner or computer

  30. Other Cardiac Diagnostic Tests • Loop ECG • Uses only two electrodes • Records few minutes of ECG at a time on computer chip • Recorded event transmitted by telephone to provider

  31. Other Cardiac Diagnostic Tests • Treadmill stress test or exercise tolerance ECG • Diagnose heart disorders • Probable cause of patient’s chest pain • Assess patient’s cardiac ability following cardiac surgery • Noninvasive test • Patient exercises on treadmill at prescribed rates of speed

  32. Other Cardiac Diagnostic Tests • Treadmill stress test or exercise tolerance ECG • Complications ( myocardial infarction or serious arrhythmia) can occur during testing • Further diagnostic tests such as cardiac catheterization (angiogram) may be necessary

  33. Other Cardiac Diagnostic Tests • Thallium stress test • Similar to treadmill stress • Patient given injection of radioactive (thallium) • Test shows how well blood flows to heart muscle

  34. Other Cardiac Diagnostic Tests • Echocardiography/ultrasonography • Noninvasive, diagnostic test • Ultrasound to image internal structures of heart • CT and MRI coronary imaging • Identify location and thickness of cardiac muscle scars due to damage

  35. Cardiac Procedures • Percutaneous transluminal coronary angioplasty (PTCA) • Widens narrowed or blocked coronary artery • Balloon angioplasty • Stents: small mesh tubes compressed around balloon; permanent intervention

  36. Cardiac Procedures • Atherectomy and laser angioplast • Coronary artery bypass • Heart valve: repaired or replaced • Procedures for arrhythmias

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