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Understanding Heart's Electrophysiology and Medications

Delve into the intricate electrical conduction system of the heart and familiarize yourself with various ECG waveforms. Explore common cardiovascular medications used in clinical practice. Learn about myocardial ischemia and infarction.

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Understanding Heart's Electrophysiology and Medications

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  1. chapter24 Exercise Related to ECG and Medications David R. Bassett, Jr.

  2. Heart Chambers and Valves Reprinted from J.E. Donnelly, 1990, Living anatomy, 2nd ed. (Champaign, IL: Human Kinetics), 199. Reprinted by permission of Joeseph Donnelly.

  3. Coronary Blood Vessels Reprinted from J.E. Donnelly, 1990, Living anatomy, 2nd ed. (Champaign, IL: Human Kinetics), 199. Reprinted by permission of Joeseph Donnelly.

  4. Oxygen Use by the Heart • The myocardium relies on ATP for contraction. • In the heart, 40% of the muscle cells are mitochondria. • Even at rest, the heart muscle extracts 75% of the O2 delivered to it.

  5. Electrophysiology of the Heart • At rest, the insides of heart muscle cells are negatively charged. • When depolarized, the insides of the cells become positively charged. • If a wave of depolarization travels toward a positive electrode on the ECG, an upward deflection occurs.

  6. Steps in an ECG Cycle

  7. Electrical Conduction Systemof the Heart

  8. Electrocardiogram Electrocardiogram (ECG) A graphical recording of the heart’s electrical activity, obtained through the use of skin electrodes.

  9. Lead Placement for CM5 Adapted from M. Ellestad, 1994, Stress testing: Principles and practice (Philadelphia: Davis).

  10. ECG Complex Showing Time and Voltage Scales Adapted from M.J. Goldman, 1982, Principles of clinical electrocardiography, 11th ed. (Los Altos, CA: Appleton & Lange), with permission of The McGraw-Hill Companies.

  11. ECG Wave Forms • P wave: atrial depolarization • QRS complex: ventricular depolarization (continued)

  12. ECG Wave Forms (continued) • T wave: ventricular repolarization

  13. Normal Sinus Rhythm In this example, the heart rate is 71 beats · min–1.

  14. Sinus Bradycardia In this example, the heart rate is 35 beats · min–1.

  15. Sinus Tachycardia In this example, the heart rate is 143 beats · min–1.

  16. First-Degree AV Block Note the prolonged P-R interval (0.28 sec in this example).

  17. Second-Degree AV Block(Mobitz Type I, or Wenckebach) There is a gradually lengthening P-R interval until finally a QRS complex is skipped.

  18. Second-Degree AV Block(Mobitz Type II) Occasionally, and without lengthening of the P-R interval, QRS complexes are skipped.

  19. Third-Degree AV Block There is no relationship between the atrial rate (e.g., 94 beats · min–1) and the ventricular rate (e.g., 36 beats · min–1), indicating complete blockage of the atrioventricular node.

  20. Premature Atrial Contractions The arrow indicates a premature diphasic P wave coming from an ectopic focus in the atria.

  21. Atrial Flutter In atrial flutter, the atrial rate is 200 to 350 beats · min–1 (300 beats · min–1 in this example), but the ventricular rate is much slower.

  22. Atrial Fibrillation A jagged baseline and irregularly spaced QRS complexes are seen with atrial fibrillation.

  23. Premature Junctional Contractions (PJCs) The arrow indicates a premature, inverted P wave coming from the AV node.

  24. Premature Ventricular Contractions(PVCs) The arrows indicate premature ventricular contractions coming from a single ectopic focus in the ventricles (unifocal premature ventricular contractions).

  25. Ventricular Tachycardia A succession of three or more premature ventricular contractions in a row is seen in ventricular tachycardia.

  26. Ventricular Fibrillation When there are no discernible P waves or QRS complexes, the heart contracts in a disorganized, quivering manner.

  27. Myocardial Ischemia

  28. Myocardial Infarction Reprinted, by permission, from E. Stein, 1992, Rapid analysis of electrocardiograms, 2nd ed. (Philadelphia, PA: Lea & Febiger), 150.

  29. Cardiovascular Medications • Beta-blockers • Nitrates • Calcium channel blockers • Antiarrhythmic medications • Digitalis (continued)

  30. Cardiovascular Medications (continued) • Antihypertensives • Lipid-lowering agents • Anticoagulants • Nicotine patches and gums • Bronchodilators

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