A Comprehensive Guide to Basic Medical Research and Diagnosis of Coronary Artery Disease: From the Mechanisms of Atherosclerosis to Holter Monitoring and the Gold Standard for Coronary Angiography

Section 3 Coronary Heart Disease 1. What is Coronary Heart Disease? Coronary heart disease, also known as coronary atherosclerotic heart disease, refers to the blood vessels that supply blood to the heart, called the coronary arteries. If the heart is likened to a green mountain, then the coronary arteries are like the irrigation canals that irrigate it. At birth, the inner lining of the coronary arteries is thin and smooth, and the canals are unobstructed. With age, under the influence of various harmful factors such as hypertension, hyperlipidemia, and diabetes, lipids in the blood gradually deposit under the inner lining. Simultaneously, the proliferation of smooth muscle cells and fibrous matrix components causes the inner lining to bulge and the lumen to narrow, much like sediment gradually depositing at the bottom of a canal. These raised plaques form a yellowish, porridge-like substance; when cut open, a yellowish, millet-porridge-like lipid substance flows out, called "atherosclerotic plaques." As these plaques enlarge, the lumen becomes increasingly narrow, and blood flow decreases. When the blood flow cannot meet the normal needs of the myocardium, myocardial ischemia and hypoxia occur, a condition known as coronary heart disease, which seriously threatens the patient's health and life.

2. What are the different types of coronary heart disease? In real life, many people are diagnosed with coronary heart disease. However, careful friends will find that their symptoms are very different. Some are almost no different from normal people, while others have attacks every few days. Some attacks can be relieved after a few minutes of rest, while others are so severe that they need to be rushed to the hospital for emergency treatment. In fact, coronary heart disease is just a general term. It includes many types, each with its own characteristics and varying degrees of severity. Friends with coronary heart disease should understand the classification of their disease, which will be more conducive to targeted prevention and treatment. Clinically, coronary heart disease is often divided into five types. (1) Asymptomatic coronary heart disease. Also known as latent coronary heart disease, patients have no symptoms, but at rest or after a stress test, there are ECG changes such as ST segment depression, T wave flattening, and inversion, which indicate myocardial ischemia. Pathological examination shows no obvious changes in myocardial cell morphology. (2) Angina pectoris type coronary heart disease. There is paroxysmal retrosternal pain, which is caused by transient myocardial ischemia. Pathological examination showed no obvious changes in myocardial cell morphology or fibrotic changes. (3) Myocardial infarction type coronary heart disease. Severe symptoms, caused by acute ischemic necrosis of the myocardium due to coronary artery occlusion. (4) Ischemic cardiomyopathy type coronary heart disease. Manifested as cardiac enlargement, heart failure and arrhythmia, caused by myocardial fibrosis due to long-term myocardial ischemia. Clinically similar to primary dilated cardiomyopathy. (5) Sudden death type coronary heart disease. Sudden death due to primary cardiac arrest, mostly caused by local electrophysiological disturbances in ischemic myocardium, resulting in severe ventricular arrhythmias. The above five types of coronary heart disease can occur together. In the past decade, it has been recognized that unstable angina is a special type and very common, with an incidence rate several times higher than that of acute myocardial infarction, and different in pathogenesis, diagnosis and treatment. Therefore, coronary heart disease is now divided into: stable angina, acute coronary syndrome, heart failure, sudden death and painless myocardial ischemia. In cases of heart failure due to coronary artery disease, if the patient has no clinical or electrocardiographic evidence of myocardial infarction, the diagnosis is purely hypothetical. Additionally, tachycardia can be the only symptom of coronary artery disease. In such cases, unless coronary angiography confirms coronary artery disease, the diagnosis remains hypothetical.

3. What are the commonly used methods for diagnosing coronary heart disease? You probably already know that when you experience chest pain and suspect coronary heart disease, you should go to the hospital for an electrocardiogram (ECG). However, an ECG is only a relatively simple and commonly used method for confirming coronary heart disease. There are many more complex and accurate methods for diagnosing coronary heart disease. When a routine ECG is normal, the following methods can be used to determine whether atherosclerotic plaques have appeared in the coronary arteries: 24-hour Holter monitoring, treadmill exercise test, and coronary angiography.

4. The Value of Routine Electrocardiogram (ECG) in Diagnosing Coronary Artery Disease (CAD): Routine ECG is a simple and convenient method, currently the most commonly used method for diagnosing CAD. The typical ECG manifestation of myocardial ischemia is a horizontal or downsloping ST segment depression of more than 0.1 mV in the corresponding lead at the cardiac anatomical location. However, its sensitivity and specificity are not 100%; in typical angina patients, half or more may have a normal resting ECG. ECG changes related to symptoms that return to normal as symptoms disappear strongly suggest myocardial ischemia. The presence of ST-T changes on a resting ECG is related to the location, extent, and severity of myocardial ischemia; the presence of ST-T changes indicates a poor prognosis. In addition, angina patients may also present with complete left bundle branch block or left anterior fascicular block. The former suggests multi-vessel disease or left ventricular dysfunction, or a history of myocardial damage; the latter is seen in CAD and left ventricular hypertrophy. If these occur during an attack, they have diagnostic significance. The ST segment and T wave on the ECG represent ventricular repolarization. Repolarization is influenced by many factors, which can be functional or organic. ST-segment elevation can be caused by normal repolarization, acute pericarditis, acute myocardial infarction, acute cor pulmonale, hyperkalemia, hypothermia, cardiac tumors, or aneurysms. ST-segment depression can be caused by myocardial ischemia, ventricular hypertrophy, medications (such as digoxin), ectopic rhythms, or electrolyte imbalances. Don't be alarmed if your ECG report shows ST-T changes. While ECG is an important clinical reference for diagnosing coronary artery disease (CAD), it is not the only diagnostic criterion. Clinically, a comprehensive assessment based on medical history, symptoms, and certain specific examinations is necessary. Therefore, an abnormal ECG does not necessarily mean you have heart disease. Furthermore, because the heart and coronary circulation have significant compensatory capacity, over 50% of patients with stable CAD may have normal ECGs. Often, an exercise stress test is needed to detect the true ECG changes. Therefore, a normal ECG does not mean you don't have heart disease.

5. What are the advantages of Holter monitoring? When an electrocardiogram (ECG) is insufficient for diagnosis, doctors often recommend Holter monitoring. This is a continuous 24-hour ECG recorder connected to simple electrodes. While it uses fewer electrodes than a standard ECG, their placement is more representative and can essentially reflect the condition of the entire heart. Furthermore, because it records continuously for 24 hours, it offers unparalleled advantages over a standard ECG. Continuous 24-hour ECG recording helps detect myocardial ischemia and can be used for suspected angina patients whose resting ECG shows no abnormalities. Observing the frequency and duration of myocardial ischemia episodes during daily activities can identify asymptomatic myocardial ischemia. By comparing ECG changes with the patient's activity and symptoms in conjunction with their daily diary, the triggers for ischemia can be identified. The characteristics and related analyses of ST segment changes help determine the type of myocardial ischemia and select appropriate medications. In addition, it can detect the type and frequency of arrhythmias accompanying myocardial ischemia and predict the likelihood of sudden cardiac death, facilitating early intervention and prevention.

6. What is an electrocardiogram (ECG) stress test? For patients highly suspected of having coronary artery disease (CAD) but whose routine ECG shows no evidence of myocardial ischemia, an ECG stress test is often necessary. This is because ECG changes only appear during myocardial ischemia, and some patients with mild lesions do not experience myocardial ischemia normally, making a routine ECG difficult to diagnose. In such cases, an ECG stress test can be performed to increase the myocardial load through exercise, medication, or other methods, inducing myocardial ischemia and thus making a diagnosis. The most commonly used method is the exercise stress test. This increases the cardiac load through exercise to induce myocardial ischemia. The main methods are treadmill running or cycling, with the intensity gradually increasing. The specificity of the stress test for diagnosing CAD is 67%–97%, with a false positive rate of 15%. False positives are more common in women, especially young women, and young men also have a relatively high false positive rate. Therefore, diagnosing CAD solely based on a stress test is inappropriate.

7. Can patients with unstable angina undergo exercise testing? Patients with unstable conditions and uncontrolled angina may experience sudden cardiac death during exercise testing. However, if the patient has not experienced an angina attack for 24-48 hours and their electrocardiogram is stable, the risk of exercise testing is extremely low. Symptom-limited exercise testing before and shortly after discharge is a necessary examination for these patients unless there are specific contraindications. If the patient can tolerate the exercise test well, their prognosis is good. Severe ischemia during exercise, even with minimal exercise, indicates a very poor short-term prognosis; in such cases, coronary angiography and interventional treatment should be performed as soon as possible.

8. What is the significance of coronary angiography? Many patients may have heard of coronary angiography (CHA). With the advancement of medical technology, this method, known as the "gold standard" for diagnosing coronary heart disease, is increasingly used in clinical practice. Coronary angiography is a valuable technique for diagnosing coronary heart disease. The procedure involves inserting a catheter into the patient's femoral or radial artery. With the aid of X-rays, the tip of the catheter is guided to the coronary arteries of the heart. Contrast agent is then injected, and angiography is performed on both the left and right coronary arteries. This clearly distinguishes whether there is stenosis in the coronary arteries and their branches, the location and degree of stenosis, as well as the status of collateral circulation and left ventricular function. This not only provides a direct and accurate diagnosis of coronary heart disease but also provides a basis for cardiac surgery. This examination provides direct and realistic visualization of the coronary arteries, undoubtedly making it more accurate and reliable for diagnosing coronary heart disease than other examinations. It is a necessary preoperative examination, especially for patients requiring coronary artery bypass grafting or coronary angioplasty.