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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
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Beta-blockers
Nitrates
Calcium channel blockers
Antiarrhythmic medications
Digitalis
(continued)
Cardiovascular Medications (continued)
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Antihypertensives
Lipid-lowering agents
Anticoagulants
Nicotine patches and gums
Bronchodilators