This chapter focuses on the epidemiology and pathophysiology of sudden cardiac death in adults and strategies for prevention and treatment. Discussions of sudden infant death syndrome and cardiac arrest in children are found in chapter 126, Congenital and Acquired Heart Disease, and chapter 127, Syncope, Dysrhythmias, and ECG Interpretation in Children. Chapters 22 and 23 discuss basic and advanced life support, respectively. Chapters 23 and 33 discuss defibrillation and cardioversion, and cardiac pacing, respectively.

Sudden, unexpected out-of-hospital cardiac arrest occurs in approximately 382,800 adult Americans each year.¹ Estimated national survival of EMS-treated cardiac arrest cases is 11.4%, yielding an estimated overall out-of-hospital cardiac arrest survival rate of 6.8% (EMS-treated plus deceased-on-EMS-arrival cases).¹ There is substantial variability in the odds for survival across various geographic locations.²

Most episodes of sudden cardiac death occur in the home, although victims who experience cardiac arrest in a public place have a much better chance of survival.³ The initial recorded cardiac arrest rhythm is more likely to be ventricular fibrillation when cardiac arrest occurs in a public location rather than in the home, likely because patients who experience cardiac arrest in the home are typically older and more likely to have one or more chronic diseases that limit or exclude participation in activities outside the home.³ Sudden cardiac death is 30% to 80% higher among residents in the lowest compared with the highest socioeconomic quartile.⁴ This association is likely due to lifestyle and healthcare disparity issues.

There is a circadian pattern of sudden cardiac death and acute myocardial infarction,^5,6 and both are most likely to occur within the first few hours after awakening from sleep, when there is increased sympathetic stimulation. β-Blockade provides some protection from sudden cardiac death, particularly in patients with known coronary artery disease who have had myocardial infarction and have a low ejection fraction.⁷

There are two peaks in the age-related prevalence of sudden cardiac death: infancy (representing sudden infant death syndrome) and age greater than 45 to 50 years, with 60% in males.⁴ There are multiple known factors contributing to the likelihood of sudden cardiac death (Table 11-1).

Coronary artery disease (which is often undiagnosed before the event) is the major cause of sudden cardiac death in adults and is present in 80% of cases, followed by cardiomyopathy (10% to 15%) and other miscellaneous conditions (e.g., hereditary channelopathies, valvular disease, congenital anomalies), which account for most of the remaining 5% to 10% of cases.⁴

CORONARY ARTERY DISEASE

Coronary atherosclerosis is present on autopsy in 80% of sudden cardiac death victims.⁸ Coronary artery disease is also found in 70% to 80% of cardiac arrest victims who survive and undergo coronary angiography.^9,10,11,12 Approximately one third have evidence of acute plaque rupture in areas of long-segment coronary stenosis.^10,11 A documented initial cardiac arrest rhythm of ventricular fibrillation (or shockable rhythm if an automated external defibrillator was applied) suggests that an acute coronary syndrome is the cause, since ventricular fibrillation is noted in the majority of cases in which a coronary occlusion is found on angiography.^9,10,11,12 However, ventricular fibrillation is present in only 23% of all cardiac arrests.¹³

SEVERE LEFT VENTRICULAR DYSFUNCTION

Severe left ventricular dysfunction with a reduced ejection fraction is currently the best available predictor of sudden death risk.⁴ Patients with an ejection fraction ≤35% are the primary candidates for an implantable cardioverter-defibrillator. However, almost half of sudden deaths occur in individuals with normal left ventricular function.

CARDIOMYOPATHY

Cardiomyopathy with reduced left ventricular function, regardless of cause or presence of decompensated heart failure, is another predictor of sudden cardiac death. Dilated ventricles promote dispersion of ventricular depolarization and/or repolarization, allowing “islands” of ventricular tissue to depolarize and repolarize at different rates. The lack of homogeneity in electrical activation and recovery fosters the development of circus movement reentry, which can initiate and sustain ventricular tachyarrhythmias. Myocardial ischemia and/or infarction can also transiently diminish the homogeneity of left ventricular depolarization and repolarization. Left ventricular hypertrophy (often a result of hypertension and/or valvular heart disease) or conduction disturbances (left or right bundle-branch block or a nonspecific intraventricular conduction disturbance) can create similar functional disturbances.

In-hospital cardiac arrest patients with heart failure are more likely to have ventricular fibrillation as the initial documented cardiac arrest rhythm compared with non–heart failure patients.¹⁴ New York Heart Association functional class II (symptoms with moderate exertion) and III (symptoms with mild exertion) patients are at higher risk of sudden cardiac death than death from pump failure, whereas class IV patients (symptoms at rest) are more likely to die of pump failure than sudden cardiac death.^5,15

Hypertrophic cardiomyopathy is characterized by unexplained left ventricular hypertrophy associated with nondilated ventricular chambers.¹⁶ The disorder can cluster in families, and the risk of sudden cardiac death increases at a rate of approximately 1% per year.¹⁶ Hypertrophic cardiomyopathy is the most common cardiovascular cause of sudden cardiac death in young athletes, accounting for one third of such events, and its presence disqualifies affected individuals from competitive sports.¹⁶ Implantable cardioverter-defibrillator placement is recommended for individuals with prior documented cardiac arrest; ventricular fibrillation; hemodynamically significant or nonsustained ventricular tachycardia; patients with a first-degree relative who has had sudden cardiac death; one or more recent, unexplained episodes of syncope; a maximum left ventricular wall thickness ≥30 mm; an abnormal blood pressure response to exercise in the presence of other sudden death risk factors or modifiers; or high-risk children with unexplained syncope, massive left ventricular hypertrophy, or family history of sudden cardiac death.¹⁶

Arrhythmogenic right ventricular cardiomyopathy is a hereditary form of cardiac muscle disease that is characterized by right-sided heart failure, ventricular arrhythmias of right ventricular origin (i.e., ventricular tachycardia with a left bundle-branch block morphology), syncope, and sudden cardiac death.^17,18 The electrocardiogram typically shows T-wave inversion in the right precordial leads (V_1-3). Severe right heart failure develops in the majority of cases. Patients suspected of having this disorder should be referred for cardiology evaluation. Implantable cardioverter-defibrillator placement is often the treatment of choice since β-blockers and other antiarrhythmics do not usually prevent symptomatic ventricular arrhythmias in these patients.¹⁷

CONGENITAL HEART DISEASE

Congenital heart disease occurs in approximately 0.8% of all live births.¹⁹ Because many children with congenital heart disease survive to adulthood as a result of improvements in cardiac surgery, sudden cardiac death is a frequent cause of later morbidity and mortality. Congenital heart defects commonly associated with sudden cardiac death in children and adults are listed in Table 11-2.¹⁹

The most frequent coronary artery anomaly associated with sudden cardiac death is anomalous origin of the left coronary artery from the pulmonary artery syndrome, which results in the left coronary artery traversing between the aorta and main pulmonary artery. This disorder is being diagnosed more frequently in adults by cardiac CT and MRI.²⁰ Ischemic symptoms, ventricular arrhythmias, and sudden death can be triggered during exercise as a result of increasing venous return, which dilates the main pulmonary artery and compresses the anomalous coronary artery in the space between the aorta and main pulmonary artery. Treatment is surgical correction.

The greatest risk of sudden cardiac death in children and adults with congenital heart disease exists in those with left heart obstructive lesions (e.g., aortic stenosis, aortic coarctation) and cyanotic defects (e.g., Ebstein’s anomaly, corrected transposition of the great vessels, tetralogy of Fallot).¹⁹ Most sudden death events in this population occur during exercise, with half of cases resulting from ventricular fibrillation.¹⁹ Nonventricular arrhythmias (e.g., sinus node dysfunction, atrioventricular block, supraventricular tachyarrhythmias) are also common, even after surgical correction.¹⁹

VALVULAR HEART DISEASE

Hemodynamically severe aortic stenosis can cause effort-induced dyspnea, myocardial ischemia, and ventricular arrhythmias, which can trigger syncope and sudden cardiac death. The most common causes of aortic stenosis are a congenitally bicuspid aortic valve that typically calcifies and narrows its orifice in mid-adulthood or sclerosis/calcification of a tricuspid aortic valve, which can occur in individuals who are older than 70 or 80 years of age. A harsh, late-peaking systolic murmur at the upper-right sternal border with radiation to the neck is a typical finding in hemodynamically significant aortic stenosis.

CARDIAC PACEMAKER AND CONDUCTING SYSTEM DISEASE

Sick sinus syndrome affects the heart’s primary pacemaker and can cause intermittent lightheadedness, syncope, or sudden cardiac death. Although it is more common with advancing age, primary electrical failure of the heart can occur in infants and children. The cause is unknown, but pathologic studies reveal histologic degeneration of the sinoatrial node. In addition, the disorder often involves the atrioventricular node and the conduction tissue between the sinoatrial and atrioventricular nodes. Therefore, sick sinus syndrome should be thought of as a diffuse degenerative disease of the heart’s electrical generation and conduction system. Idiopathic sclerodegeneration of the AV node and the bundle branches (Lenègre’s disease) or invasion of the conduction system by fibrosis or calcification spreading from adjacent cardiac structures (Lev’s disease) can lead to bradyasystolic heart block with or without cardiac arrest. In rare cases, a clinical presentation resembling the sick sinus syndrome can occur when the heart’s electrical system is affected by systemic disease, vascular compromise, or tumor. Symptomatic bradycardia is treated with pacemaker placement.

HEREDITARY CHANNELOPATHIES