Bradycardia is a heart rate below 60 beats per minute. There are several factors that can decrease heart rate and cause bradycardia. How sensitive a person is to these factors depends on how healthy she is. Medication, disease processes and physical stress can slow the heart rate. Even breathing can cause a slight decrease in heart rate.
Physical Exertion
Donna D. Ignatavicius, MS RN, and M. Linda Workman, Ph.D, authors of "Medical-Surgical Nursing: Critical Thinking for Collaborative Care," explain that in an unhealthy heart, the increased demand for oxygen caused by physical strain may fatigue the heart and cause bradycardia. Patients with unstable congestive heart failure and cardiomyopathy (enlarged heart) are prone to this.
Opposite to this picture is the very fit individual. A well-trained athlete like a long-distance runner may develop a very slow heart rate. However, this happens because the heart muscle is very powerful and effective at pumping blood to the body; it does not need a fast heart rate to meet the body's oxygen demands.
Vagal Stimulation
Vagal stimulation involves special sensors in the body that are attuned to blood pressure changes. One example of this is baroreceptors. These sensors are located in the aortic arch and respond to changes in blood pressure. When baroreceptors sense an increase in blood pressure, they signal the heart to slow down its rate so as to lower the blood pressure. Vagal stimulation can occur when a person bears down. For example, when a person has a bowel movement or delivers a baby, there is an increase in intra-abdominal pressure. This stimulates the baroreceptors, causing the heart rate to slow down.
Medications
Beta blockers and digitalis preparations are medications that are used to treat various heart conditions. Scott and White Hospital explains that beta blockers slow the heart rate. Digitalis also slows the heart rate. Some herbal preparations available on the market also decrease the heart rate, and when taken with beta blockers and digitalis medications, they can dangerously slow the heart rate.
Septic Shock
Barbara McLean, CCNP, and Janice Zimmerman, MD, authors of "Fundamental Critical Care Support," discuss how septic shock results in bradycardia, which when it occurs, is an ominous sign of cardiovascular collapse. When an infection overcomes the body's defense system, the person becomes septic. This means the infection has spread throughout the entire body. Sepsis can lead to shock. A serious warning sign of septic shock is a slowing heart rate. Bradycardia heralds circulatory collapse. Emergency intervention is needed to prevent cardiac arrest and death.
Sick Sinus Syndrome
The American Heart Association explains that heart muscle damage from atherosclerosis (plaque buildup in arteries), heart attack, and viral or bacterial illness can lead to a condition called sick sinus syndrome. Sick sinus syndrome affects the natural pacemaker of the heart. Bradycardia can occur. If left untreated, severe bradycardia can lead to cardiac arrest. Treatment involves medications and often insertion of a pacemaker to regulate the heart rate.
References
- "Medical-Surgical Nursing - Critical Thinking for Collaborative Care"; Donna D. Ignatavicius MS RN, & M. Linda Workman Ph.D; 2006
- "Fundamental Critical Care Support (4th ed.)"; McLean, B. & Zimmerman, J. L.; 2007
- Scott and White Hospital: Drug Treatments: Beta Blockers
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