chapter 24 Exercise Related to ECG and Medications

chapter 24 Exercise Related to ECG and Medications David R. Bassett, Jr.

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

Coronary Blood Vessels Reprinted from J. E. Donnelly, 1990, Living anatomy, 2 nd 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 O 2 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 (ECG) A graphical recording of the heart’s electrical activity, obtained through the use of skin electrodes.

Lead Placement for CM 5 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, 11 th ed. (Los Altos, CA: Appleton & Lange), with permission of The Mc. Graw-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, 2 nd 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