Topic: Regulation of BP and heart rate
Question: Define sinus arrhythmia. How is it produced and what is its clinical significance?
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Sinus arrhythmia refers to a normal variation in the heart rate that occurs during the respiratory cycle. It is a normal physiological phenomenon and not a cardiac arrhythmia.
It is produced by the influence of the respiratory system on the sinoatrial node of the heart. During inspiration, the heart rate increases slightly due to increased venous return to the heart. During expiration, the heart rate decreases slightly. This cyclical increase and decrease in heart rate corresponds with the respiratory cycle and is known as sinus arrhythmia.
The clinical significance of sinus arrhythmia is:
- It is a normal finding, especially in young healthy adults and athletes. It does not require any treatment.
- It indicates that the sinoatrial node is responsive to autonomic influences like respiration. An absence of sinus arrhythmia may indicate decreased responsiveness of the sinoatrial node.
- In some elderly patients, excessive sinus arrhythmia may be associated with heart block or pacemaker dysfunction. If very symptomatic, a pacemaker may be needed.
- The degree of sinus arrhythmia reflects the balance between the parasympathetic and sympathetic systems. Greater variations reflect increased parasympathetic tone relative to sympathetic tone.
- Sinus arrhythmia usually disappears with tachycardia, stress or exercise as the heart rate increases. It is most prominent at slower heart rates.
- Certain drugs like atropine that block the parasympathetic system may decrease or abolish sinus arrhythmia.
So in summary, sinus arrhythmia is a normal physiological phenomenon that reflects the influence of respiration on the heart rate. It indicates an intact autonomic nervous system and a healthy heart. But excessive or symptomatic sinus arrhythmia may rarely require treatment.
