Arrhythmias are often difficult to manage clinically and are one of the serious risks for patients. Many retrospective and prospective clinical studies have been and are being conducted on the causes and management of arrhythmias, especially regarding life-threatening ventricular tachyarrhythmias. Given that tachyarrhythmias can lead to sudden cardiac death before the patient is asymptomatic, it is extremely critical to identify which patients are at high risk, even if asymptomatic. Sudden cardiac death can be prevented. Early identification of high-risk patients and their referral to a qualified hospital and consultation with a cardiac electrophysiologist can help reduce the incidence of sudden cardiac death. A large body of literature has been published on the risk factors for sudden cardiac death. The definition of sudden cardiac death (SCD) has been discussed in different ways, but all of them include the following points: sudden loss of consciousness within 1 h after the onset of acute symptoms due to cardiac causes, resulting in an unexpected natural death. The incidence of sudden cardiac death in the United States is estimated to be 300,000 to 400,000 per year, accounting for more than 50% of all cardiac deaths, and the incidence of sudden cardiac death in the United States is 84-200 cases per 100,000 population; in European countries, it is about 20-159 cases per 100,000 population. The incidence of SCD is higher in men than in women. Although there is a lack of accurate statistics on the incidence of SCD in China, the absolute number of SCD is estimated to be large because the incidence of coronary heart disease is about 50% of that in the United States, and the total population is 6 times larger than that in the United States. III. Clinical risk factors for sudden cardiac death Previous survivors of cardiac arrest, previous episodes of ventricular tachycardia, previous myocardial infarction, coronary artery disease, family history of cardiac arrest, low left ventricular ejection fraction from any cause, patients with chronic ischemic heart disease with premature ventricular beats, ventricular hypertrophy, hypertrophic obstructive cardiomyopathy, dilated cardiomyopathy and heart failure, acute heart failure, the long QT syndrome, arrhythmogenic right ventricular dysplasia, and Brugada syndrome. Syncope of unknown origin, although not classified as a risk factor, is a warning sign of cardiac quenching, especially in patients with severe heart failure. Overall, individual risk factors are of greater predictive value for sudden cardiac death when combined with other risk factors. The highest risk for SCD in cardiac arrest survivors is a prior cardiac arrest, as 50% of cardiac arrest survivors will experience another cardiac arrest within 1 year. However, only 1-20% of cardiac arrests that occur outside the hospital survive, so it is important to identify other risk factors. Previous history of ventricular tachycardia Myerburg et al. (1993, 1997), Kannel et al. (1975), Goldstein et al. (1985), Bigger et al. (1984), Ruberman et al. (1981), Echt et al. (1991), and many others have reported ventricular tachyarrhythmias (ventricular tachycardia and/or ventricular fibrillation), the risk of recurrence of ventricular tachycardia is high, and recurrence is accompanied by a 20% to 41% mortality rate, even if the patient is treated with antiarrhythmic drugs. Ventricular tachycardia with reduced left ventricular ejection fraction or old myocardial infarction has a risk of sudden cardiac death of between 20% and 50%, depending on the circumstances accompanying the ventricular tachyarrhythmia. 3. old myocardial infarction Although sudden cardiac death is the first clinical manifestation of coronary artery disease in any country, accounting for approximately 20% to 50% of all those who experience sudden cardiac death, old myocardial infarction can be found in 75% of patients who experience sudden cardiac death. Old myocardial infarction as a single risk factor increases the risk of sudden cardiac death by 5%, whereas when combined with a reduced left ventricular ejection fraction or complex premature ventricular beats, it increases the risk of sudden cardiac death by 10% to 15% (Futterman et al. 1997; Demirovic et al. 1984; Bigger et al. 1984; Echt et al. 1991 ; Shen et al, 1991; Moss et al, 1996). Such a high incidence of old myocardial infarction in victims of sudden cardiac death has prompted researchers to make every effort to find predictive methods in post-myocardial infarction patients as well as in patients with other clinical manifestations of coronary artery disease. 4. coronary heart disease Autopsies of sudden cardiac death victims have shown that 90% of sudden cardiac deaths have coronary heart disease (Myerburg et al. 1997; Demirovic et al. 1994; Kannel et al. 1975). more than 50% of sudden cardiac deaths do not have any clinical manifestations of coronary heart disease during life (Moss et al. 1996; Friedlander et al. 1998). Many studies have shown that the first clinical manifestation of sudden cardiac death is in as many as 20% to 50% of patients with heart disease (Futterman et al., 1997; de Vreede et al., 1997; Shen et al., 1991). 5. Family history of sudden cardiac death Over the years, many researchers have suggested that family history plays an important role in sudden cardiac death. A recent study (Friedlander et al., 1998) testing the family history hypothesis showed that first-generation relatives of sudden cardiac death victims have a 50% higher risk of myocardial infarction or primary cardiac arrest. Studies specifically for sudden cardiac death are also needed. For patients with chronic ischemic heart disease and sudden cardiac death due to other causes, a significant decrease in left ventricular ejection fraction is one of the most powerful predictors. Ejection fraction ≤0.30 is the most obvious risk factor for SCD, but its specificity is low because most studies have shown that more than 50% of SCD victims have an LV ejection fraction >0.30 (G01dman et al. 1993). During the follow-up period, SCD occurred in 13% to 19% of patients. 7, . Premature ventricular contractions in patients with chronic ischemic heart disease Frequent and/or complex premature ventricular contractions are an independent risk factor for the development of SCD in patients after myocardial infarction. Frequent ventricular premature beats are defined as ≥10 ventricular premature beats per hour on the dynamic ECG, and complex ventricular premature beats are defined as paired ventricular premature beats and/or more than 3 consecutive ventricular premature beats, i.e., nonsustained ventricular tachycardia (without deterioration of the patient’s hemodynamic status). a study by Ruberman et al. (1991) showed that patients with complex ventricular premature beats maintained over a 5-year follow-up period patients with premature ventricular contractions had a 6 to 25% increase in mortality due to SCD. The purpose of the Antiarrhythmic Drug Suppression Trial (CAST) was to determine whether suppression of mildly symptomatic or asymptomatic ventricular arrhythmias in post-myocardial infarction patients could attenuate sudden arrhythmic death. This study found that the overall morbidity and mortality rate was 6% in the 2 drug treatment groups (flecainide and inconazole) during a 10-month follow-up period, and 66% of these deaths were arrhythmia-induced (Echt et al., NEnglJMed, 1991, 324: 781-788). The rate of morbidity and mortality was higher in the drug-treated group than in the control group. 8. ventricular hypertrophy and hypertrophic cardiomyopathy left ventricular hypertrophy is an independent risk factor for SCD. the Framingham study showed that left ventricular hypertrophy was present in 19% of SCD victims (Gordon et al., JAMA, 1971). In patients with hypertrophic cardiomyopathy, SCD is the most common cause of death. 254 patients with hypertrophic cardiomyopathy in Goodwin (1982), followed for a mean of 6 years, had a mortality rate of 14% due to SCD. Shah et al. (1974) reported a 15% incidence of SCD in another group of 190 patients with hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy is the most common cause of SCD in athletes under 35 years of age, while in athletes over 35 years of age, ischemic heart disease is the most common cause of SCD. 9. dilated cardiomyopathy and heart failure Recent literature has reported that up to 47% of deaths in the dilated cardiomyopathy patient population are due to sudden death from arrhythmias and that the risk of SCD increases with worsening left ventricular function (Myerburg et al. 1997; Middlekauf et al. 1993; Stevenson et al. 1993). In patients with cardiac function class II-IV (NYHA), syncope of unknown cause reliably predicts SCD (Middlekauf et al., 1993). There have been several other ongoing studies in heart failure, including the Sudden Cardiac Death ln Heart Failure Trial (SCD-HEFT), a trial designed to discover which treatments significantly reduce morbidity and mortality in patients with congestive heart failure (National Institutes of Health. NIH, 1997). Acute heart failure from any cause can lead to SCD if not treated appropriately, either due to circulatory failure or secondary arrhythmias (Myerburg et al., 1997). 11, QT interval prolongation Primary long QT syndrome is an inherited disorder that can cause unexplained syncope, convulsions, and sudden cardiac death (Schwart2 et al, 1997; Smith et al, 1980; Carson et al, 1993). There are two congenitally inherited forms, one is Jervell-Lange-Nielsen syndrome, which was first reported in 1975 and is clinically characterized by deafness and prolonged QT, and is an autosomal recessive disorder. The other, known as Ward-Romano syndrome, was first reported in 1964 and is characterized clinically by prolonged QT interval with normal hearing and is an autosomal dominant disorder. Both types of congenital long QT syndrome can also occur in the same family. Some patients are never asymptomatic during their lifetime, while others are prone to develop symptomatic and fatal arrhythmias, especially the tip-twisting ventricular tachycardia of ventricular tachycardia (Smith et al., 1980). 39% of patients with long QT syndrome have a family member who has also been found to have the disease, while 60% of patients with long QT syndrome have a positive history of cardiac arrest or long QT syndrome The other type of long QT syndrome was found in 1 family member. Another type of long QT syndrome is caused by certain drugs (especially antiarrhythmic drugs and drugs for psychiatric disorders), electrolyte balance disorders, hypothermia, toxic substances and central nervous system damage and can be called acquired long QT syndrome. If the underlying cause can be identified and corrected, tip-twisting ventricular tachycardia and sudden death can be avoided. 12. arrhythmogenic arrhythmogenic ventricular dysplasia (ARVD) is characterized by replacement of right ventricular myocardial tissue by fibrofatty tissue and is clinically prone to sudden death (Dalar et al., 1994). Many patients have no symptoms prior to the onset of quenching and the diagnosis is often made by autopsy findings (Corrado et al., 1997fFurlanello et al., 1989).ARVD is most common in healthy young athletes and also has a familial tendency, although ARVD can be seen in patients of different ages.An autopsy study by Corrado et al. (1997) found that autopsy (1997) found that 29% of patients with a diagnosis of ARVr) had sudden death as their first clinical presentation. In another 71% of patients, there were symptoms of palpitations during life and 26% had at least one episode of syncope of unknown origin prior to the cardiac arrest event. 13, Brugada syndrome A new syndrome characterized by right bundle branch block with ST-segment pick-up in leads Vl-V2 with syncopal episodes or quenching was identified in 1992 in a structurally normal heart with an electrocardiogram (Brugada P, Brugada J. J Am CollCardiol, 1992) and is now widely known as Brugada syndrome. This syndrome is widespread. Its incidence is difficult to estimate. It is found more frequently in Southeast Asian countries, where it is locally known as “death in sleep”. In Thailand and Laos, this syndrome causes 4 to 10 cases of sudden death per 10,000 people per year. The diagnosis of Brugada syndrome is based on a history of surviving cardiac arrest, with typical STvl-v3 elevation, with or without right bundle branch block and episodes of ventricular tachycardia or ventricular fibrillation. However, there are insidious or intermittent forms of this syndrome, making it difficult to diagnose in some patients. brugada syndrome is an autosomal dominant form of a genetically determined condition, and 3 different mutations have been identified. All 3 mutations affect the structure and function of the sodium channel determined by the gene SCN5A, thus affecting the action potential of cardiac myocytes. Recent data suggest that only the right ventricular epicardium loses its action potential plateau phase, while the endocardial action potential plateau remains and forms the basis for the ST-segment elevation seen in this syndrome. This electrical inhomogeneity present in the right ventricular endocardium and epicardium leads to premature beats with short pairwise intervals, which contribute to the development of ventricular tachycardia or ventricular fibrillation via a 2-phase foldback mechanism. Currently, implantation of a cardioverter-defibrillator (ICD) is the only effective treatment to prevent sudden death.