The sympathetic cardiac nerves are the superior, middle and inferior cervical cardiac nerves from the three cervical sympathetic ganglia, together with the thoracic cardiac branches from the upper four or five thoracic ganglia. They descend to the cardiac plexus at the base of the heart, where they mix with the vagal cardiac branches. They speed the heart, increase the force of contraction and carry pain fibres from the heart.
| Origin | Superior, middle and cervicothoracic (stellate) ganglia and the upper four or five thoracic sympathetic ganglia |
|---|---|
| Course | Descend through the neck alongside the carotid sheath and from the thoracic sympathetic trunk to join the superficial and deep parts of the cardiac plexus around the aortic arch and tracheal bifurcation |
| Motor |
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| Sensory |
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Pain fibres from the heart travel back with these nerves to the T1-T4 spinal segments, which explains why angina and myocardial infarction are felt in the chest, the inner arm and the jaw. Surgical removal of the lower half of the left stellate ganglion and the upper thoracic ganglia (left cardiac sympathetic denervation) reduces dangerous arrhythmias in long QT syndrome and catecholaminergic ventricular tachycardia. A transplanted heart loses these nerves, so its rate rises slowly with exercise and ischaemia is often painless.
Ischaemic pain carried by the sympathetic cardiac nerves to the upper thoracic segments is felt in the chest, left arm, neck and jaw rather than in the heart itself.
The donor heart has no cardiac nerve supply, so its resting rate is high, its response to exercise depends on circulating adrenaline, and angina may be absent even with significant coronary disease.
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