In sinus arrhythmia, what is the primary factor that causes variability in heart rate?

Study for the MedCa Electrocardiogram (EKG) Exam. Use flashcards and multiple choice questions, each question includes hints and explanations. Prepare yourself for the test!

In sinus arrhythmia, the primary factor that causes variability in heart rate is related to the respiratory cycle, specifically inspiration. During inspiration, the intrathoracic pressure decreases, leading to an increase in venous return to the heart. This physiological response stimulates the baroreceptors and can activate the sympathetic nervous system, resulting in an increase in heart rate. Conversely, during expiration, the heart rate tends to decrease. This natural variation in heart rate with the phases of respiration is what characterizes sinus arrhythmia, distinguishing it from other types of arrhythmias that may not be influenced by breathing patterns.

This phenomenon is commonly seen in younger populations, where it is considered a normal variation and not indicative of any underlying pathology. Understanding the role of inspiration in sinus arrhythmia helps clarify how the heart's rate can fluctuate in a healthy manner, particularly in response to changes in thoracic pressure related to breathing.

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