What is the diagnosis and treatment for SCDT (Sudden Cardiac Death Syndrome)?

Diagnosis and Treatment of Sudden Cardiac Death Syndrome (SCDT)

Sudden Cardiac Death Syndrome (SCDT) is primarily diagnosed through post-mortem examination and treated preventively with implantable cardioverter-defibrillators (ICDs) in high-risk patients, with early defibrillation being the most effective intervention for witnessed cardiac arrest.

Diagnosis of SCDT

• Sudden cardiac death (SCD) is defined as natural unexpected death occurring within 1 hour of symptom onset in witnessed cases or within 24 hours in unwitnessed cases 1
• Post-mortem examination is essential for diagnosis, with expert cardiac pathologists examining the heart both macroscopically and microscopically 1
• The most common finding in SCD is Sudden Arrhythmic Death Syndrome (SADS) with morphologically normal heart (53%), which may be underlaid by cardiac channelopathies 1
• Cardiomyopathies account for 22% of SCD cases, followed by ischemic heart disease (9%), valve disease (3%), congenital heart disease (3%), and myocarditis/sarcoidosis (3%) 1
• Genetic testing (molecular autopsy) should be integrated with family screening in the assessment of SCD victims 1

Underlying Causes

• In patients aged 50 years and older, coronary artery disease plays a dominant role in over 75% of SCD cases, either through acute ischemia leading to ventricular fibrillation or chronic scar formation causing reentrant ventricular tachycardia 2
• In younger patients, SCD may occur with structurally normal hearts due to arrhythmogenic disorders such as long and short QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and early repolarization syndrome 2
• In children and adolescents, hypertrophic cardiomyopathy and coronary artery anomalies are the most common causes of SCD 3
• Arrhythmogenic right ventricular dysplasia and long QT syndrome are the most common primary arrhythmic causes of SCD in young people 3

Mechanisms of SCD

• SCD is most frequently caused by ventricular tachyarrhythmias: monomorphic and polymorphic ventricular tachycardia, torsade de pointes, and ventricular fibrillation 2
• Pulseless electrical activity (PEA) is increasingly seen, particularly in patients with advanced chronic heart disease 2
• Bradyarrhythmia in the form of asystole (usually complete heart block without escape rhythm) causes only 10-15% of SCD cases 2
• Ventricular tachyarrhythmias at the cellular level may involve mechanisms such as phase 2 reentry and reflection 2

Treatment and Prevention

Primary Prevention in High-Risk Patients

• Implantable cardioverter-defibrillator (ICD) is the most effective treatment for prevention of SCD in high-risk patients 4
• For post-MI patients with non-sustained ventricular tachycardia and ejection fraction ≤0.35, ICD implantation is recommended 4
• In patients with hypertrophic cardiomyopathy who are at high risk for SCD, ICD therapy should be considered 4
• Beta-blockers should be considered first-line therapy for symptomatic ventricular arrhythmias, especially when associated with heightened adrenergic tone 5
• Amiodarone may be considered for patients with structural heart disease and symptomatic ventricular arrhythmias that persist despite beta-blockers 5

Secondary Prevention

• In survivors of sustained and hemodynamically non-tolerated ventricular arrhythmias, ICD should be considered as the first treatment option in most cases 4
• Exceptions to routine ICD treatment for secondary prevention include patients who refuse therapy or have limited life expectancy due to another disease 4
• ICD treatment should be discouraged when the precipitating cause of arrhythmia is due to a transient and correctable factor (e.g., electrolyte imbalance, ischemia, drug-related adverse effects) 4

Emergency Management

• Early defibrillation is crucial and should be integrated into an effective emergency cardiac care system 4
• All emergency ambulances that respond to or transport cardiac patients should be equipped with a defibrillator 4
• Defibrillation should be a core competence of all healthcare professionals including nurses, and defibrillators should be widely available on general hospital wards 4
• Early cardiopulmonary resuscitation and widespread availability of automatic external defibrillators could prevent about 25% of pediatric sudden deaths 3

Special Considerations for Specific Conditions

Brugada Syndrome

• Brugada syndrome is responsible for 4-12% of all sudden deaths and around 20% of deaths in patients with structurally normal hearts 6
• It is characterized by a distinct ECG pattern of right bundle-branch block with ST segment elevation in leads V1-V3 and normal QT interval in the absence of structural heart disease 6
• The syndrome has male predominance with arrhythmic events appearing at an average age of 40 years 6
• Antiarrhythmic drugs have limited use in preventing recurrences of ventricular arrhythmias, making ICD the best therapy to prevent sudden death in these patients 6

Aortic Stenosis

• In aortic stenosis, both syncope and SCD are often exertional, though it's unclear if syncope predicts SCD 4
• Ventricular tachyarrhythmias are the predominant mechanism of SCD in aortic stenosis, with bradyarrhythmias being less common 4
• Restriction of physical activity should be advised in patients with moderate and especially severe aortic stenosis 4
• Surgical treatment should be undertaken as soon as symptoms develop 4

Mitral Valve Prolapse

• Although mitral valve prolapse (MVP) is generally benign, it has been associated with SCD in rare cases 4
• Among young people with sudden cardiovascular death, MVP was the only cardiac pathology in approximately 10% of cases 4
• Patients with redundant leaflets may be at higher risk for SCD compared to those with non-redundant leaflets 4

Risk Stratification

• ECG signs and clinical features indicating high risk for SCD have been identified and should be assessed 2
• Extended monitoring (>24 hours) should be considered for patients with intermittent symptoms like palpitations or lightheadedness 5
• Exercise stress testing may be useful to determine if arrhythmias are exacerbated or suppressed with exercise and to evaluate for underlying ischemia 5
• Cardiac magnetic resonance imaging (CMR) may be considered if echocardiography is inconclusive or to assess for subtle structural abnormalities 5