CARDIAC PAIN 309 



the upper four thoracic segments, it is in these areas that 

 referred pains might be expected to occur in cardiac 

 disturbances. 



In later attacks of angina pectoris, the pain tends to radiate 

 from the praecordia down the medial side of the left arm, and, 

 in this case, there is no doubt that the condition exemplifies 

 the viscero-sensory reflex (p. 192), since the painful areas are 

 innervated by the first and second thoracic nerves (Fig. 67). 



If a "focus of irritation " (p. 195) is established in the upper 

 thoracic segments of the spinal medulla, areas of cutaneous 

 hyperalgesia (p. 195) may be found in the regions supplied by 

 the nerves arising from the segments affected. In the same 

 way, the muscles supplied by these segments may be very 

 tender on deep pressure, and this muscular hyperalgesia is 

 observed best in the pectoralis major and minor, which receive 

 branches from the first thoracic nerve through the medial 

 anterior thoracic nerves. In some cases where an area of 

 cutaneous hyperalgesia is present, it is possible to induce a 

 severe attack of cardiac pain by such a simple peripheral 

 stimulus as lightly stroking the hyperaesthetic area. 



The posterior rami (primary divisions) of the upper thoracic 

 nerves are much less frequently the site of referred cardiac 

 pain than are the anterior rami. In angina pectoris, however, 

 it is sometimes possible to demonstrate areas of hyperaesthesia 

 or hyperalgesia over the spines of the upper four thoracic 

 vertebrae or in the adjoining region. 



Afferent impulses from the heart travel not only by the 

 sympathetic but also by the vagus, and it is, therefore, possible 

 for a " focus of irritation " to arise in the medulla oblongata 

 in cardiac disturbances. The sensory nucleus of the vagus is 

 practically continuous with the posterior column of grey 

 matter in the spinal medulla, and a "focus of irritation" may 

 spread downwards and cause an increased excitability of the 

 sensory nerve-cells in the upper cervical segments. In angina 

 pectoris, the pain may radiate into the left side of the neck 

 and involve the areas supplied by the cutaneous branches of 



