Changes in autonomic function can do what to reentry?

• A. Initiate or stop reentry
• B. Always increase reentry
• C. Have no effect
• D. Cause immediate arrest

Answer: (A)

Changes in autonomic tone shift conduction velocity and refractoriness in cardiac tissue, which in turn alters the likelihood of reentry. Reentry needs a circuit where the impulse can reexcite tissue after it has recovered; autonomic influences that shorten the refractory period or speed conduction shorten the wavelength of excitation, making reentry more likely to occur. Conversely, autonomic changes that lengthen refractoriness or slow conduction increase the wavelength, making it harder for a circulating impulse to persist and often terminating an existing reentrant circuit. Because these effects can either promote or prevent reentry depending on the specific tissue and circuit, autonomic changes can initiate or stop reentry rather than always increasing it or causing arrest.