Diabetic autonomic neuropathy and silent myocardial ischaemia
Core concept
- Cardiac autonomic neuropathy (CAN) damages the afferent sensory fibres that carry anginal pain
- Nociceptive afferents from the myocardium run with sympathetic fibres to T1-T4
- Length-dependent axonal loss -> raised anginal threshold or complete loss of pain perception
- -> silent (painless) myocardial ischaemia and infarction
- The efferent arm is damaged too, and in a defined order
- Parasympathetic (vagal) fibres fail first - the vagus is the longest autonomic nerve
- -> resting tachycardia (~90-100), loss of heart rate variability, loss of sinus arrhythmia
- Sympathetic failure follows - orthostatic hypotension, exercise intolerance, blunted HR response
- Late: a fixed, denervated heart with a resting rate of ~80-90 that does not vary
- Parasympathetic (vagal) fibres fail first - the vagus is the longest autonomic nerve
3 more sections, plus exam facts
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