diaphragmatic stimulation travels by the phrenic nerve, with the distribution of pain referred to the shoulder of the affected side The esophagus appears to be more pain sensitive in its proximal portion Pain is transmitted by afferents to corresponding spinal segments, with resultant anterior chest or neck pain The pericardium is innervated by portions of the phrenic, vagal, and recurrent laryngeal nerves, as well as by the esophageal plexus This appears to give rise to various sensations, including chest or abdominal pain, dull pressure, and even referred angina-like pain Other mediastinal structures, such as the aorta, have pain fibers in the adventitia of the vessel wall They transmit pain through the thoracic sympathetic chain to the spinal dorsal roots, giving rise to sharp, and variably localized chest pain Cardiac pain probably is transmitted by a number of routes, including the thoracic sympathetic chain and the cardiac nerves through the cervical and stellate ganglia It has been proposed that pain arises from abnormal ventricular wall movement and stimulation of the pericardial pain fibers These routes account for the sensation of cardiac chest pain as pressure or crushing substernal pain or as sharp pain in the shoulder, neck, or arm DIFFERENTIAL DIAGNOSIS A differential diagnosis of chest pain in children is included in Table 55.1 In the case of trauma, cardiac or pulmonary compromise may arise from direct injury to the heart, great vessels, or lung (see Chapter 115 Thoracic Trauma ) Most chest pain in the nontraumatized child is caused by acute respiratory disease, musculoskeletal injury, anxiety, or inflammation ( Table 55.2 ) Often, the physician does not make a causative diagnosis of the chest pain and calls it nonspecific or idiopathic in origin Occasionally, this idiopathic chest pain may be unrecognized organic disease, such as gastroesophageal reflux disease Chest pain in children usually occurs without associated cardiorespiratory signs or symptoms, often as an acute or chronic problem By the time of the ED visit, frequently the pain has resolved Although much less frequent, chest pain in association with cardiorespiratory distress demands immediate attention Table 55.3 lists the life-threatening causes of chest pain by disease and mechanisms for decompensation Chest pain in the dyspneic or cyanotic patient most often stems from a respiratory problem, such as pneumonia, asthma, pleurisy, or pneumothorax Rarely, severe chest pain in an acutely ill child results from myocardial infarction (MI) due to aberrant coronary vessels, cocaine abuse, Kawasaki disease, hyperlipidemia, or other underlying cardiac diseases (aortic stenosis, an acute arrhythmia, cardiomyopathy, or pericardial disease) Every