What are the causes of sudden cardiac death?

Causes of Sudden Cardiac Death

Primary Mechanism

Malignant ventricular arrhythmias—specifically ventricular fibrillation and ventricular tachycardia—are the terminal rhythm in 75-80% of sudden cardiac death cases, making them the predominant mechanism across all age groups. 1, 2

Age-Dependent Etiologies

Adults Over 35-40 Years

• Coronary artery disease is the overwhelming cause, accounting for 50-60% of all sudden cardiac deaths in adults. 1, 2
• Acute thrombotic coronary occlusion with plaque rupture occurs in 57-89% of sudden death victims at autopsy, even in those without prior myocardial infarction. 1
• Active coronary lesions are found in 46-50% of hearts with only healed infarction or no infarction at all, indicating acute ischemia as a trigger even without new infarct. 1
• In the post-thrombolytic era, arrhythmic death occurs in approximately 2% of post-MI patients at 2.5 years, with 60% preceded by symptoms of myocardial ischemia. 1

Young Adults and Athletes (<35-40 Years)

• Hypertrophic cardiomyopathy is the single most frequent cause in young trained athletes, accounting for up to one-third of sudden deaths. 1, 2
• Congenital coronary artery anomalies—particularly anomalous origin of the left main coronary artery from the right sinus of Valsalva—are the second most common cause. 1
• Primary electrical diseases (Long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT) are not identifiable at routine autopsy and require pre-existing ECG analysis for diagnosis. 1
• Arrhythmogenic right ventricular cardiomyopathy is a major cause in the pre-coronary disease age group, with sudden death occurring more frequently in patients with extensive right ventricular changes and left ventricular involvement. 1

Cardiomyopathies

Dilated Cardiomyopathy

• Sudden cardiac death accounts for 20-30% of all deaths in dilated cardiomyopathy patients. 1
• Malignant ventricular arrhythmia remains the commonest single cause of sudden death in dilated cardiomyopathy, accounting for the majority of deaths in patients with less severe disease. 1
• In advanced disease, bradyarrhythmias, pulmonary or systemic embolization, and electromechanical dissociation contribute to up to 50% of cardiac arrests. 1
• Ejection fraction consistently predicts sudden death risk, though predictive accuracy varies widely (13-59% for EF <20%). 1
• Syncope is a powerful predictor: 70% of dilated cardiomyopathy patients with sustained VT or sudden death had prior syncope. 1

Bradyarrhythmic Mechanisms

• Bradyarrhythmias account for 15-20% of all sudden cardiac deaths. 1
• In acute myocardial infarction with right coronary artery involvement, heart block or asystole may be the terminal event rather than ventricular fibrillation. 1
• Following AV node ablation, 2-3% of patients suffer sudden death, likely due to bradycardia-dependent prolongation of repolarization in the first 24 hours. 1
• Among paced patients, 12-31% experience sudden death months or years after implantation, with a three-fold higher rate in the first year. 1

Non-Arrhythmic Cardiac Causes

• Pulmonary thromboembolism and cardiac tamponade from aortic dissection or cardiac rupture cause mechanical sudden death without shockable rhythms. 3
• Degenerative valve diseases—particularly severe aortic stenosis and mitral valve prolapse—predominate in elderly populations. 3

Genetic and Familial Factors

• Up to 40% of dilated cardiomyopathy cases are familial, with predominantly autosomal dominant inheritance (2-5% X-linked). 1
• In families with clustering of cardiac arrests, monogenic disorders (Brugada syndrome, Long QT syndrome, hypertrophic cardiomyopathy) should be evaluated, particularly with juvenile arrests. 1
• Hypertrophic cardiomyopathy affects approximately 1 in 500 persons in the general population. 2

Critical Clinical Pitfalls

• Do not assume modest troponin elevations after sustained ventricular arrhythmias indicate acute MI as the cause—prolonged arrhythmias elevate biomarkers through supply-demand mismatch without acute coronary occlusion. 2
• Propafenone and other antiarrhythmics can cause proarrhythmic sudden death, including ventricular fibrillation, torsade de pointes, and asystole, with 92% of proarrhythmic events occurring in patients with prior VT history. 4
• In athletes over 35 years, do not dismiss all bradycardia as benign—coronary artery disease becomes the predominant cause of sudden death in this age group. 1, 5
• Brugada syndrome may be unmasked by drugs like propafenone; obtain ECG after initiation and discontinue if suggestive changes appear. 4