Transtheoretical Model of Behavior Change
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Tachycardia Lois Jane Heller Department of Biomedical Sciences, University of Minnesota Medical School – Duluth, Duluth, MN, USA
Definition The word “tachycardia” means rapid heart rate. This condition is more precisely defined as a heart rate that is above the age-adjusted range of normal heart rates (see Table 1). Children normally have higher heart rates than adults and can tolerate rapid heart rates more easily.
Description Normal Determinants of Heart Rate Heart rate is normally established by the rate of spontaneous generation of an electrical signal
Tachycardia, Table 1 Age-associated upper limit to normal human heart rates (Adapted from Greene, 1991) Less than 1 year 1–2 years 3–5 years 6–12 years 12–15 years 15 years through adulthood
170 bpm 150 bpm 135 bpm 130 bpm 120 bpm 100 bpm
(action potential) by “pacemaker” cells located in the sinoatrial (SA) node of the heart (in the wall of the right atrium near the entry of the superior vena cava) (Mohrman & Heller, 2011). These electrical signals are normally generated at a rate of 60–100 beats per min in a human adult. They are propagated from the SA node through the atrial and ventricular muscle cells in a set pathway that stimulates contraction in a pattern that optimizes pumping of blood from the heart. Most other cardiac muscle cells have the potential to act as pacemakers, but the SA nodal cells drive the heart at a slightly faster rate than any of these other “latent” pacemakers. The normal fluctuations in heart rate that occur in response to normal changes in the body’s metabolic demands are accomplished by altering autonomic neural influences on the SA nodal pacemaker cells from the parasympathetic and sympathetic nervous system. Increased sympathetic activity causes an increase in heart rate whereas increase in parasympathetic activity causes a decrease in heart rate. Symptoms of Tachycardia A person with significant tachycardia may or may not be aware that their heart rate is fast without actually measuring their pulse rate (Valentin, O’Rourke, Walsh, & Poole-Wilson, 2008). However, tachycardia often results in a feeling of light-headedness, dizziness, tunnel vision, or fainting. Other symptoms may include muscle weakness, nervousness, sweating, pallor, or a feeling of fullness in the chest. The cause of
M.D. Gellman & J.R. Turner (eds.), Encyclopedia of Behavioral Medicine, DOI 10.1007/978-1-4419-1005-9, # Springer Science+Business Media New York 2013
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many of these symptoms is often related to a decrease in arterial blood pressure and therefore blood flow to the brain and other tissues. Physiological Cause of the Symptoms The amount of blood that the heart pumps in a minute is called the cardiac output (Mohrman & Heller, 2011). This is determined by the volume of blood ejected in each beat (stroke volume) and the number of beats per minute (heart rate): Cardiac output ¼ stroke volume heart rate One might predict from this equation that the cardiac output would increase whenever heart rate increased. This is true over the normal
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