Makindo Medical Notes

Related Subjects: |ECG-QT interval |Brugada Syndrome |Long QT syndrome (LQTS) Acquired |Long QT syndrome (LQTS) Congenital |Torsades de Pointes |Ventricular Fibrillation |Ventricular Tachycardia |Resuscitation - Adult Tachycardia Algorithm |Automatic Implantable Cardioverter Defibrillator (AICD)

Sudden cardiac death (SCD) refers to an unexpected death caused by a sudden loss of heart function. While SCD in young individuals is rare, it is often traumatic and highly publicized. In older adults, SCD is primarily due to coronary artery disease (CAD), whereas in younger populations, it is more commonly associated with cardiomyopathies and ion-channelopathies.

About

• SCD is significantly more prevalent in young males.
• College athletes have a 2-3 times higher incidence of SCD compared to the general population, often due to conditions like arrhythmogenic right ventricular cardiomyopathy (ARVC).

Heritable Causes

• Hypertrophic Cardiomyopathy (HCM): Occurs in approximately 1 in 500 individuals.
• Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): Characterized by fibrofatty replacement of the right ventricular myocardium.
• Dilated Cardiomyopathy: Enlargement and weakening of the heart's ventricles.
• Left Ventricular Non-Compaction Cardiomyopathy: Involves excessive trabeculation of the left ventricle.
• Heritable Channelopathies:
  • Long QT Syndrome (LQTS): Present in approximately 1 in 2,000 individuals.
  • Short QT Syndrome: Associated with an increased risk of ventricular arrhythmias.
  • Brugada Syndrome (BrS): Identified by characteristic ECG patterns and associated with ventricular fibrillation.
  • Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT): Triggered by physical activity or emotional stress.

Structural Congenital Heart Disease (CHD)

• Ventricular dysfunction combined with scarring, hypertrophy, and fibrosis increases the risk of SCD in patients with severe or mild forms of CHD.
• Tetralogy of Fallot: A well-studied CHD with SCD rates averaging 0.1-0.2% per year, even after surgical correction.

Structurally Normal Heart

• Brugada Syndrome: Characterized by ST-segment elevation in leads V1-V3 and a high risk of ventricular fibrillation.
• Congenital Long QT Syndrome: Prolonged QT intervals increase the risk of torsades de pointes.
• Acquired Long QT Syndrome: Caused by medications or electrolyte imbalances.
• Pre-Excitation Syndromes (e.g., Wolff-Parkinson-White [WPW]): Can lead to atrial fibrillation with rapid ventricular response.
• Commotio Cordis: Sudden blunt chest trauma during a vulnerable phase of the cardiac cycle, often seen in sports.
• Catecholamine-Induced Ventricular Tachycardia: Triggered by excessive catecholamines.

Structurally Abnormal Heart

• Ischaemic Heart Disease (IHD): Acute myocardial infarction (MI) or acute coronary syndrome (ACS) can precipitate SCD.
• Arrhythmogenic Right Ventricular Dysplasia: Fibrofatty infiltration of the right ventricle leading to arrhythmias.
• Hypertrophic Cardiomyopathy: Thickened ventricular walls increase the risk of arrhythmias.
• Aortic Stenosis: Severe obstruction to left ventricular outflow can lead to fatal arrhythmias.

Causes of Sudden Cardiac Death

Investigations

• Comprehensive cardiovascular screening strategies include:
  • Electrocardiogram (ECG): A sensitive and efficient screening tool for most conditions leading to SCD in young individuals. It can identify abnormalities such as long QT syndrome (LQTS), Wolff-Parkinson-White (WPW) syndrome, hypertrophic cardiomyopathy (HCM), and Brugada syndrome (BrS).
  • History and Physical Examination: Detailed patient history and thorough physical examination to identify risk factors and signs of underlying cardiac conditions.
  • Echocardiography: Provides detailed images of heart structure and function, aiding in the diagnosis of structural heart diseases and cardiomyopathies.

ECG Findings Associated with Increased Risk of SCD

• Prolonged QT Interval: A corrected QT interval (QTc) >450 ms in men and >470 ms in women is associated with a three-fold increased risk of SCD, especially in individuals over 55 years of age.
• T-Wave Inversions, Wide QRS-T Angle, and Prolonged QRS Duration: These can result from left bundle branch block (LBBB) or intraventricular conduction delays, increasing the risk of arrhythmias.
• Non-Sustained Ventricular Tachycardia (VT): Episodes of VT detected on ECG indicate an elevated risk of SCD.
• Poor Left Ventricular Function: Identified via echocardiography, associated with a higher likelihood of arrhythmic events.

Management

• Implantable Cardioverter-Defibrillator (ICD):
  • Consideration for patients identified as high-risk for SCD. ICDs can provide life-saving defibrillation in the event of ventricular arrhythmias.
  • Weighing the risk-to-benefit ratio is crucial, as the long-term benefits in preventing SCD must be balanced against potential complications.
• Device-Related Complications:
  • Children and young adults may experience higher rates of complications such as inappropriate shocks, lead malfunctions, and difficulties in device placement due to smaller intracardiac anatomy.

References

• Sudden Cardiac Death in the Young
• NICE Guidelines on Sudden Cardiac Death