Which patient would be least likely to develop a decrease in heart rate with a high (C8) level spinal anesthesia?

Which patient would be least likely to develop a decrease in heart rate with a high (C8) level spinal anesthesia?

• A. A 15-year-old female with Wolff-Parkinson-White syndrome
• B. A 73-year-old patient with glaucoma treated with pilocarpine eye drops
• C. A 33-year-old with a T6 paraplegia
• D. A 45-year-old diabetic man with orthostatic hypotension

Answer: (D)

The main factor is how much the heart’s sympathetic input can be blocked and how well the body can compensate with reflexes. A high spinal block at the level that reaches the cardioaccelerator fibers (the T1–T4 region) removes sympathetic stimulation to the heart. With that input gone, the heart rate tends to fall due to unopposed parasympathetic (vagal) influence. In a diabetic patient with autonomic neuropathy presenting with orthostatic hypotension, these autonomic reflexes are blunted. The sympathetic system’s ability to respond to reduced blood pressure or to a spinal block is diminished, and the baroreceptor reflex is impaired. As a result, the heart rate is less able to decrease further in response to the block, making a significant bradycardic effect less likely in this patient compared with others who have relatively intact autonomic function. By contrast, the other scenarios involve either normal autonomic function or factors that would augment vagal dominance or preserve sympathetic pathways to the heart. A young patient with WPW typically has intact autonomic control; a pilocarpine-treated patient has heightened muscarinic (parasympathetic) activity that can promote bradycardia; and a person with a T6 spinal injury may still have usable heart sympathetic input that can be blocked by the high spinal, leading to bradycardia.

The main factor is how much the heart’s sympathetic input can be blocked and how well the body can compensate with reflexes. A high spinal block at the level that reaches the cardioaccelerator fibers (the T1–T4 region) removes sympathetic stimulation to the heart. With that input gone, the heart rate tends to fall due to unopposed parasympathetic (vagal) influence.

In a diabetic patient with autonomic neuropathy presenting with orthostatic hypotension, these autonomic reflexes are blunted. The sympathetic system’s ability to respond to reduced blood pressure or to a spinal block is diminished, and the baroreceptor reflex is impaired. As a result, the heart rate is less able to decrease further in response to the block, making a significant bradycardic effect less likely in this patient compared with others who have relatively intact autonomic function.

By contrast, the other scenarios involve either normal autonomic function or factors that would augment vagal dominance or preserve sympathetic pathways to the heart. A young patient with WPW typically has intact autonomic control; a pilocarpine-treated patient has heightened muscarinic (parasympathetic) activity that can promote bradycardia; and a person with a T6 spinal injury may still have usable heart sympathetic input that can be blocked by the high spinal, leading to bradycardia.