All of the following can cause tachycardia except?

NHM UP Staff Nurse - 2016

Applied Physiology

Medium

Appeared in: NHM UP Staff Nurse - 2016

Explanation

Parasympathetic nervous system stimulation, often called the 'rest and digest' system, acts to slow down bodily functions, including heart rate.
Stimulation of the vagus nerve (a key component of the parasympathetic system) releases acetylcholine.
Acetylcholine slows the firing rate of the sinoatrial (SA) node, the heart's natural pacemaker.
This action results in bradycardia (a heart rate below 60 bpm), which is the opposite of tachycardia.

Option A: Fever increases the body's metabolic rate, which in turn increases the heart rate to meet higher oxygen demands and help dissipate heat.
Option B: Exercise increases the body's demand for oxygenated blood. The sympathetic nervous system responds by increasing the heart rate to boost cardiac output.
Option C: The sympathetic nervous system is the primary 'accelerator' for the heart. Its stimulation (the 'fight or flight' response) directly causes an increase in heart rate.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Regulation of heart rate by the autonomic nervous system and other physiological factors as background academic context rather than a clinical decision trigger.
Understanding the causes of tachycardia is crucial for nurses to differentiate between normal physiological responses (like exercise) and pathological signs that require intervention (like in heart failure or infection).
When a patient presents with tachycardia, a nurse's first steps include assessing for common causes like fever, pain, anxiety, dehydration, or medication side effects.
What if? - If a patient with tachycardia is also taking a beta-blocker medication (which blocks sympathetic effects), the heart rate may not be as high as expected for the clinical situation. This 'relative bradycardia' can mask the severity of an underlying problem, requiring astute nursing assessment.

How to Approach the Question

First, identify the keyword 'except'. This means you are looking for the option that does NOT cause the condition mentioned.
Next, define the main term in the question: 'Tachycardia' is a heart rate greater than 100 beats per minute.
Evaluate each option one by one to determine its effect on heart rate.
Option A, Fever: Recall that fever increases metabolism, thus increasing heart rate. So, it causes tachycardia.
Option B, Exercise: Recall that physical exertion requires more oxygen, leading to an increased heart rate. So, it causes tachycardia.
Option C, Sympathetic stimulation: Recall the 'fight or flight' response, which directly increases heart rate. So, it causes tachycardia.

Concept Tested & Keywords

Concept Tested: Regulation of heart rate by the autonomic nervous system and other physiological factors.
Stem keywords: tachycardia, cause
Lead-in keywords: except
Negative lead-in flag: The question asks for the EXCEPTION among the causes of tachycardia.

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