Patients with acute chest pain are the most common group of patients in emergency medicine, and data show that patients with acute chest pain as the main complaint account for 5% to 20% of emergency medicine patients, and in tertiary hospitals it accounts for 20% to 30%. There are many causes of acute chest pain, different clinical manifestations, and large differences in risk, such as acute coronary syndrome (ACS), aortic coarctation, acute pulmonary embolism, tension pneumothorax and other high-risk diseases with time-dependent, that is, the earlier the diagnosis and the more timely the treatment, the better the prognosis, and the opposite brings catastrophic consequences. In order to identify these high-risk diseases among many patients presenting with acute chest pain and give timely and appropriate treatment, emergency physicians must be alert and make a rapid differential diagnosis. I. Differential diagnosis of acute chest pain 1. Cardiovascular system diseases Acute coronary syndrome: The typical symptom of unstable angina pectoris is crushing dull pain behind the sternum with a feeling of suffocation or tightness or frequent death, and the pain radiates to the back of the shoulder, the left upper arm, the jaw throat or the upper abdomen, etc., and lasts mostly for several minutes, accompanied by cold sweat or a feeling of fear. Sublingual nitroglycerin can provide rapid relief. Elderly, female, and diabetic patients may have only dull discomfort in the precordial region and posterior back. The electrocardiogram during the attack may show ST-segment downshift and may have transient arrhythmias. Myocardial biochemical markers are negative or not more than 2 times normal. Acute myocardial infarction pain is mostly in the precordial region and retrosternal region, but can also be located in the upper abdomen and back, and the nature of the pain is dull, crushing, stabbing or colic and cutting pain, which lasts more than 30 min and up to several hours. The pain may be accompanied by a drop in blood pressure, arrhythmia, heart failure, and cardiogenic shock. The electrocardiogram has a dynamic evolution and is positive for biochemical markers of the heart muscle. Acute aortic dissection: Acute aortic dissection (AAD) has an acute onset with sudden onset of severe burning or tearing pain in the precordial region or behind the sternum, radiating to the head, neck, upper extremities, back, lumbar, middle and lower abdomen, and even lower extremities, lasting from several hours to several days, and not relieved by nitroglycerin. Most of the patients have a history of hypertension or atherosclerosis, and their blood pressure is not controlled for a long time. There is no dynamic evolution of the electrocardiogram, a widening of the aortic shadow is seen on X-ray, and aortic reinforcement CT provides a clear diagnosis. Acute pericarditis: The disease causes more intense chest pain, mostly located in the precordial region, with persistent pain, which is aggravated by position change, deep breathing or coughing, and can be alleviated or relieved by anterior tilt position. It is often accompanied by fever. Pericardial friction sounds are an important sign of pericarditis. The electrocardiogram shows widespread ST-segment arch-dorsal downward elevation, normal myocardial biochemical markers, and effusion visible on x-ray and cardiac ultrasound. Aortic stenosis or insufficiency: typical angina symptoms may be present, with a characteristic murmur of aortic stenosis or insufficiency on auscultation, and the ECG shows left ventricular hypertrophy with secondary ST-T changes. Atrial fibrillation or ventricular arrhythmias may be present. Echocardiography is an important method to identify aortic valve lesions. Hypertrophic cardiomyopathy: The main symptoms are exertional chest pain with dyspnea, palpitations, syncope, and a jet systolic murmur on auscultation in the medial apical region or in the middle and lower sternal left margin. The ECG shows deep and narrow Q waves in leads II, III, aVF and V4-6, with upright T waves in the corresponding leads. Echocardiography can confirm the diagnosis. 2, respiratory disease Acute pulmonary embolism: sudden onset of chest pain, dyspnea, cyanosis, and even shock symptoms, occasionally accompanied by fever, cough, hemoptysis. There may be pleural friction sounds and wet woven 6 calling type of bun forgiveness (10) source disease MWEQIIP牡缤汲SⅠQⅢTⅢ pattern, electrical axis right deviation, pulmonary type P wave and right bundle branch conduction block pattern can be seen. x-ray wedge shadow. Arterial blood gas shows hypoxemia and hypocapnia with D-Dimer >500?g/L. Multi-row intensified CT can confirm the diagnosis. Spontaneous pneumothorax: The patient has sudden chest pain and dyspnea, and the chest pain worsens with deep breathing. Tension pneumothorax may have circulatory collapse or even coma. On examination, the affected side of the chest is full, the trachea is displaced to the healthy side, and the breath sounds are diminished or absent. x-ray shows increased translucency on the affected side, no lung texture is visible, and the lung is compressed. Pneumonia: Chest pain on the affected side, which may radiate to the shoulder, with an acute onset, accompanied by high fever, chills, blood in the sputum, and in some patients, especially the elderly, the body temperature may not rise. There are faint or flaky shadows on X-ray or CT. Laboratory tests sputum smear or culture with growth of pathogenic bacteria. Pleurisy: tingling sensation on breathing with coughing and fever, normal ECG, chest radiograph helps to diagnose. Lung cancer, metastatic lung cancer and mediastinal tumor: chest pain is non-specific, may be accompanied by cough, hemoptysis and fever, tumor compression of the esophagus may cause dysphagia, hoarseness when compressing the recurrent laryngeal nerve, infiltrative shadows, cornu foci and cavities are seen on X-ray and CT. Metastatic signs include enlarged lymph nodes in the hilum and mediastinum. Sputum cytology is important for lung cancer. 3.Digestive system diseases Reflux esophagitis or esophageal spasm: Reflux esophagitis is mostly seen as pain behind the sternum or under the glabella, with acid reflux, burning sensation or difficulty in swallowing. It is aggravated when lying down and relieved when standing upright. Esophagoscopy reveals esophageal mucosa congestion, edema, erosion, ulceration, bleeding, sometimes visible niches, and positive esophageal acid drip test. Esophageal spasm with swallowing chest pain with dysphagia, resembling angina pectoris because nitroglycerin can relieve it, but no ischemic changes on ECG, and barium meal can confirm the diagnosis. Esophageal hiatal hernia and esophageal cancer: the chest pain is often located behind the sternum, and it mostly attacks or worsens when swallowing, accompanied by dysphagia. Middle and advanced esophageal cancer can be seen as wasting, anemia, and enlarged supraclavicular lymph nodes. Barium meal of upper gastrointestinal tract and endoscopy can confirm the diagnosis. Gallstone and acute cholecystitis: the pain is often in the upper abdomen and lower right chest, and radiates to the shoulders and back, and may be accompanied by chills, high fever, nausea and vomiting. It can also appear similar to angina attack called “biliary heart syndrome”, the electrocardiogram can appear ST-T changes, and long-term misdiagnosis as coronary angina, but everything returns to normal after cholecystectomy. 4. Bone and chest wall lesions Costal chondromalacia: tenderness, pain related to body position. ECG is normal. Intercostal neuralgia: stabbing or burning pain and distributed along the intercostal nerve with localized pressure pain, more obvious in the paravertebral, axillary midline and parasternal. The chest pain caused by benign and malignant intercostal nerve tumors is persistent and often more intense, and local examination may reveal the presence of the tumor. Herpes zoster: This disease can cause severe chest pain with multiple scattered, fused papules or small vesicular rashes on the skin of the diseased side, distributed along the intercostal nerve without crossing the midline, or involving only a small portion of the contralateral skin. The electrocardiogram is normal. 5.Psychiatric disorders Autonomic dysfunction: the symptoms are many but not typical. In addition to complaints of chest pain, they are accompanied by chest tightness, panic, dizziness and tinnitus or mental discomfort, often triggered by mental stimulation or stressful life. Some patients are accompanied by chronic insomnia. There may be slight ST-T changes in the ECG. Depression: persistent heaviness in the chest, unrelated to activity, with normal ECG examination. Factors to be considered in diagnosis and differential diagnosis 1. Medical history and concomitant conditions: When receiving patients with acute chest pain, we should use the limited time to take a careful history and conduct physical examination as much as possible, which is the basis for us to make a correct diagnosis. When asking the present medical history, we need to pay attention to the factors triggering and aggravating the chest pain; the location, nature, duration, method of relief, whether it is radiating, concomitant symptoms, etc. We also need to inquire about the presence of hypertension, diabetes mellitus, coronary artery disease in the patient’s past medical history and how well these diseases are controlled, and ask about any recent surgery, trauma, bed rest, etc. During the physical examination, we emphasize the need to be both comprehensive and targeted, paying particular attention to the changes in vital signs. Some diseases can be characterized by careful physical examination, such as the disappearance of breath sounds on one side suggesting pneumothorax, asymmetric pulses and strong vascular murmurs suggesting aortic coarctation in those with severe chest pain, pericardial friction sounds are important signs of pericarditis, aortic stenosis or incomplete closure have characteristic murmurs, and local tenderness is diagnostic of skeletal chest wall disorders. 2.Use of auxiliary examinations to help differential diagnosis The characteristics of emergency medicine determine that we should handle patients with acute chest pain with the principle of quick and convenient, and complete the tests to clarify the diagnosis or exclude the diagnosis in the shortest possible time, “only necessary, not demanding comprehensive”. The most commonly used tests are electrocardiogram, laboratory tests, imaging and ultrasound. 2.1 Electrocardiogram: For a patient with acute chest pain, electrocardiogram is the first test to be done. Ischemic chest pain can be identified or excluded by ECG. If there is a high clinical suspicion of ischemic chest pain and the first ECG is normal, the ECG should be kept and repeated within a short period of time. The ECG should be read in comparison with the previous ECG to detect new changes, and even subtle changes, such as mild ST elevation, decrease or improvement, T-wave inversion or change to upright, should be taken seriously. The first ECG must be done in 18 leads to avoid missing infarcts in the posterior wall and right ventricle. 2.2 Laboratory tests: About 5% to 15% of patients with acute myocardial infarction have atypical electrocardiographic changes. For patients who cannot exclude ischemic heart disease, blood should be drawn for myocardial biochemical markers. The rapid bedside combined test of CK-MB, MYO and CTnT or CTnI in the emergency department is worth promoting. MYO can be used to rule out infarction or to infer the time of infarction based on the values of the three tests to guide the choice of treatment plan; it can also be used to risk stratify patients with angina pectoris to decide whether to go home, stay in the emergency department or be hospitalized. D-Dimer can be used to rule out acute pulmonary embolism if the D-Dimer is less than 500 μg/L in both measurements, but a diagnosis of pulmonary embolism cannot be confirmed if the D-Dimer is greater than 500 μg/L. D-Dimer is also elevated in other embolic diseases such as deep vein thrombosis. D-Dimer is not elevated in spontaneous pneumothorax and aortic coarctation. Blood gas analysis is necessary in patients with suspected pulmonary embolism, and most patients may present with varying degrees of hypoxemia with hypocarbia. hypoxemia and hypocarbia may also be present in ACS and aortic coarctation, which are generally not characteristic, but are associated with acute left heart failure. 2.3 Imaging: X-ray chest radiographs can confirm the diagnosis of pneumothorax and show the degree of lung compression, according to which doctors can develop different treatment plans. Pneumonia and chest tumor have characteristic changes on chest X-ray, and CT examination is available if necessary. In acute pulmonary embolism, a wedge-shaped shadow pointing to the lung door can be seen on a plain chest X-ray, but the sensitivity and specificity are not high, so it is only used in emergency medicine for bedside examination of patients with hemodynamic instability and suspected pulmonary embolism. Multi-row spiral CT pulmonary arteriography is the main method for diagnosing pulmonary embolism because of its high sensitivity and specificity. Patients with pulmonary embolism can see filling defects in the pulmonary arteries and their branches. Pulmonary ventilation-flow scans also have high specificity and sensitivity for the diagnosis of pulmonary embolism. A normal pulmonary perfusion scan is usually sufficient to rule out the diagnosis of pulmonary embolism. Multi-row spiral CT coronary angiography can be used to identify patients with acute chest pain and to rapidly exclude ACS mainly in patients with low likelihood of ACS (normal ECG and normal markers of myocardial necrosis.) Confirmation of acute aortic coarctation relies on enhanced CT or magnetic resonance imaging, which can show the site of the fissure and the true and false lumen. 2.4 Ultrasound: Ultrasound can clarify the diagnosis of cholelithiasis cholecystitis. In acute myocardial infarction, echocardiography shows segmental dyskinesia of the ventricular wall, loss of motion or paradoxical motion. However, if the diagnosis of acute infarction can be confirmed by history, ECG and myocardial biochemical markers, and there are no complications, it is not necessary to force the ultrasound results in the acute phase, but should be performed after the condition is stabilized. Ultrasound is very helpful in diagnosing acute pulmonary embolism, sometimes detecting emboli in the right atrial right ventricle or pulmonary artery, and also non-invasively determining pulmonary artery pressure. The diagnosis of submassive pulmonary embolism relies mainly on the manifestation of right ventricular dyskinesia under ultrasound. Ultrasound can also detect thrombus within the peripheral deep veins, which is indirectly helpful in the suspected diagnosis of pulmonary embolism. Ultrasound Doppler can be used for the examination of aortic coarctation, but it has limitations, only the ascending aorta and the vessels in the abdomen and iliac region can be seen. The main signs are significant widening of the aorta and separation of the aortic wall to form a true and false lumen. Aortic stenosis or insufficiency of closure and hypertrophic cardiomyopathy are then diagnosed mainly by echocardiography.