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Transcript
chapter 24 Exercise Related to ECG and Medications David R. Bassett, Jr. 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. Coronary Blood Vessels Reprinted from J.E. Donnelly, 1990, Living anatomy, 2nd ed. (Champaign, IL: Human Kinetics), 199. Reprinted by permission of Joeseph Donnelly. 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. 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. Steps in an ECG Cycle Electrical Conduction System of the Heart Electrocardiogram Electrocardiogram (ECG) A graphical recording of the heart’s electrical activity, obtained through the use of skin electrodes. Lead Placement for CM5 Adapted from M. Ellestad, 1994, Stress testing: Principles and practice (Philadelphia: Davis). 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. ECG Wave Forms • P wave: atrial depolarization • QRS complex: ventricular depolarization (continued) ECG Wave Forms (continued) • T wave: ventricular repolarization Normal Sinus Rhythm In this example, the heart rate is 71 beats · min–1. Sinus Bradycardia In this example, the heart rate is 35 beats · min–1. Sinus Tachycardia In this example, the heart rate is 143 beats · min–1. First-Degree AV Block Note the prolonged P-R interval (0.28 sec in this example). Second-Degree AV Block (Mobitz Type I, or Wenckebach) There is a gradually lengthening P-R interval until finally a QRS complex is skipped. Second-Degree AV Block (Mobitz Type II) Occasionally, and without lengthening of the P-R interval, QRS complexes are skipped. 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. Premature Atrial Contractions The arrow indicates a premature diphasic P wave coming from an ectopic focus in the atria. 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. Atrial Fibrillation A jagged baseline and irregularly spaced QRS complexes are seen with atrial fibrillation. Premature Junctional Contractions (PJCs) The arrow indicates a premature, inverted P wave coming from the AV node. Premature Ventricular Contractions (PVCs) The arrows indicate premature ventricular contractions coming from a single ectopic focus in the ventricles (unifocal premature ventricular contractions). Ventricular Tachycardia A succession of three or more premature ventricular contractions in a row is seen in ventricular tachycardia. Ventricular Fibrillation When there are no discernible P waves or QRS complexes, the heart contracts in a disorganized, quivering manner. Myocardial Ischemia Myocardial Infarction Reprinted, by permission, from E. Stein, 1992, Rapid analysis of electrocardiograms, 2nd ed. (Philadelphia, PA: Lea & Febiger), 150. Cardiovascular Medications • • • • • Beta-blockers Nitrates Calcium channel blockers Antiarrhythmic medications Digitalis (continued) Cardiovascular Medications (continued) • • • • • Antihypertensives Lipid-lowering agents Anticoagulants Nicotine patches and gums Bronchodilators