Pathophysiology and etiology of sudden cardiac arrest - UpToDate shown to be the cause at autopsy, the most common underlying disorders were hypertrophic cardiomyopathy (36 percent, with possible HCM in another 10 percent), an anomalous coronary artery of wrong sinus origin (13 percent), and myocarditis (7 percent) [36]. (See "Athletes: Overview of sudden cardiac death risk and sport participation".) A different distribution of causes was noted in a series of 49 athletes under age 35 with SCD from northern Italy [37]. The most common causes were arrhythmogenic right ventricular cardiomyopathy (22 percent, which occurs more frequently in this region), coronary atherosclerosis (18 percent), anomalous origin of a coronary artery (12 percent), mitral valve prolapse (10 percent), myocarditis (6 percent), and hypertrophic cardiomyopathy (2 percent). Absence of structural heart disease In different reports, 10 to 12 percent of younger patients have VF in the true absence of structural heart disease [22,59], while a lower value of approximately 5 percent has been described when older patients are included [23,24]. This can occur in a variety of settings: Brugada syndrome (see "Brugada syndrome: Clinical presentation, diagnosis, and evaluation") Commotio cordis (see "Commotio cordis") Idiopathic VF, also called primary electrical disease (see "Approach to sudden cardiac arrest in the absence of apparent structural heart disease", section on 'Idiopathic VF') Catecholaminergic polymorphic VT (see "Catecholaminergic polymorphic ventricular tachycardia") Congenital or acquired long QT syndrome (see "Congenital long QT syndrome: Diagnosis" and "Acquired long QT syndrome: Definitions, pathophysiology, and causes") Short QT syndrome (see "Short QT syndrome") Wolff-Parkinson-White syndrome (see "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis") INFORMATION FOR PATIENTS UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." th th The Basics patient education pieces are written in plain language, at the 5 to 6 grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more th th sophisticated, and more detailed. These articles are written at the 10 to 12 grade reading https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 12/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate level and are best for patients who want in-depth information and are comfortable with some medical jargon. Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.) Basics topic (see "Patient education: Ventricular fibrillation (The Basics)") SUMMARY Background Sudden cardiac arrest (SCA) and sudden cardiac death (SCD) refer to the sudden cessation of organized cardiac electrical activity with hemodynamic collapse. The event is referred to as SCA (or aborted SCD) if an intervention (eg, defibrillation, cardioversion, antiarrhythmic drug) or spontaneous reversion restores circulation. The event is called SCD if the patient dies. However, the use of SCD to describe both fatal and nonfatal cardiac arrest persists by convention. (See 'Introduction' above.) Mechanisms The exact mechanism of collapse in an individual patient is often impossible to establish since, for the vast majority of patients who die suddenly, cardiac electrical activity is not being monitored at the time of their collapse. However, in studies of patients who were having cardiac electrical activity monitored at the time of their event, ventricular tachycardia (VT) or ventricular fibrillation (VF) accounted for the majority of episodes, with bradycardia or asystole accounting for nearly all of the remainder. (See 'Arrhythmic mechanisms' above.) Arrhythmic mechanisms In the majority of patients with VT/VF, sustained ventricular arrhythmia is preceded by an increase in ventricular ectopy and the development of repetitive ventricular arrhythmia, particularly runs of nonsustained VT. In approximately one-third of cases, the tachyarrhythmia is initiated by an early R on T PVC; in the remaining two-thirds, the arrhythmia is initiated by a late cycle PVC. (See 'Arrhythmic mechanisms' above.) Common causes There are many cardiac and noncardiac causes for a sustained ventricular tachyarrhythmia that can result in SCD ( table 1). Among all SCD in all age groups, the majority (65 to 70 percent) are related to coronary heart disease, with other structural cardiac disease (approximately 10 percent), arrhythmias in the absence of structural heart disease (5 to 10 percent), and noncardiac causes (15 to 25 percent) responsible for the remaining deaths. (See 'Etiology of SCD' above.) https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 13/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate ACKNOWLEDGMENT The UpToDate editorial staff thank Dr. Jie Cheng for his past contributions as an author to prior versions of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Kannel WB, Schatzkin A. Sudden death: lessons from subsets in population studies. J Am Coll Cardiol 1985; 5:141B. 2. Bay s de Luna A, Coumel P, Leclercq JF. 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Ventricular fibrillation and polymorphic ventricular tachycardia with critical coronary artery stenosis: does bypass surgery suffice? J Cardiovasc Electrophysiol 1994; 5:988. 54. Daoud EG, Niebauer M, Kou WH, et al. Incidence of implantable defibrillator discharges after coronary revascularization in survivors of ischemic sudden cardiac death. Am Heart J 1995; 130:277. 55. Uretsky BF, Thygesen K, Armstrong PW, et al. Acute coronary findings at autopsy in heart failure patients with sudden death: results from the assessment of treatment with lisinopril and survival (ATLAS) trial. Circulation 2000; 102:611. 56. Burke AP, Farb A, Liang YH, et al. Effect of hypertension and cardiac hypertrophy on coronary artery morphology in sudden cardiac death. Circulation 1996; 94:3138. 57. Viskin S, Belhassen B. Idiopathic ventricular fibrillation. Am Heart J 1990; 120:661. 58. Rodriguez RM, Montoy JCC, Repplinger D, et al. Occult Overdose Masquerading as Sudden Cardiac Death: From the POstmortem Systematic InvesTigation of Sudden Cardiac Death Study. Ann Intern Med 2020; 173:941. 59. Topaz O, Edwards JE. Pathologic features of sudden death in children, adolescents, and young adults. Chest 1985; 87:476. Topic 974 Version 31.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 18/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate GRAPHICS Continuous electrocardigraphic (ECG) strip during an episode of ventricular fibrillation (VF) that progresses to fine VF and then asystole At the onset of ventricular fibrillation (VF), the QRS complexes are regular, widened, and of tall amplitude, suggesting a more organized ventricular tachyarrhythmia. Over a brief period of time, the rhythm becomes more disorganized with high amplitude fibrillatory waves; this is coarse VF. After a longer period of time, the fibrillatory waves become fine, culminating in asystole. Graphic 67777 Version 3.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 19/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate ECG 12-lead ventricular fibrillation 12-lead ECG showing course ventricular fibrillation. ECG: electrocardiogram. Graphic 118944 Version 1.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 20/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate Major causes of sudden death Ischemic heart disease Coronary artery disease with myocardial infarction or angina Coronary artery embolism Nonatherogenic coronary artery disease (arteritis, dissection, congenital coronary artery anomalies) Coronary artery spasm Nonischemic heart disease Hypertrophic cardiomyopathy Dilated cardiomyopathy Valvular heart disease Congenital heart disease Arrhythmogenic right ventricular dysplasia Myocarditis Acute pericardial tamponade Acute myocardial rupture Aortic dissection No structural heart disease Primary electrical disease (idiopathic ventricular fibrillation) Brugada syndrome (right bundle branch block and ST segment elevation in leads V1 to V3) Long QT syndrome Preexcitation syndrome Complete heart block Familial sudden cardiac death Chest wall trauma (commotio cordis) Noncardiac disease Pulmonary embolism Intracranial hemorrhage Drowning Pickwickian syndrome Drug-induced https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 21/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate Central airway obstruction Sudden infant death syndrome Sudden unexplained death in epilepsy (SUDEP) Graphic 62184 Version 3.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 22/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate Incidence of sudden death in men and women increases with age During a 38-year follow-up of subjects in the Framingham Heart Study, the annual incidence of sudden death increased with age in both men and women. However, at each age, the incidence of sudden death is higher in men than women. Data from Kannel WB, Wilson PWF, D'Agostino RB, et al. Am Heart J 1998; 136:205. Graphic 59028 Version 4.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 23/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate Risk of SCD is related to clinical manifestations of CHD During a 38-year follow-up of subjects in the Framingham Heart Study, the annual incidence of sudden cardiac death (SCD) in both men and women was related to the clinical manifestations of coronary heart disease (CHD). It was highest in those with a myocardial infarction, intermediate in those with angina and no prior infarction, and lowest in those without overt CHD. Data from: Kannel WB, Wilson PWF, D'Agostino RB, et al. Am Heart J 1998; 136:205. Graphic 52309 Version 2.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 24/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate Heart failure predicts increased sudden cardiac death and overall mortality During a 38-year old follow-up of subjects in the Framingham Heart Study, the presence of heart failure (HF) significantly increased sudden death and overall mortality in both men and women. p <0.01. p <0.001. Data from: Kannel WB, Wilson PWF, D'Agostino RB, et al. Am Heart J 1998; 136:205. Graphic 58658 Version 4.0 https://www.uptodate.com/contents/pathophysiology-and-etiology-of-sudden-cardiac-arrest/print 25/26 7/6/23, 1:41 PM Pathophysiology and etiology of sudden cardiac arrest - UpToDate Contributor Disclosures Philip J Podrid, MD, FACC No relevant financial relationship(s) with ineligible companies to disclose. Brian Olshansky, MD Other Financial Interest: AstraZeneca [Member of the DSMB for the DIALYZE trial]; Medtelligence [Cardiovascular disease]. All of the relevant financial relationships listed have been mitigated. Scott Manaker, MD, PhD Other Financial Interest: Expert witness in workers' compensation and in medical negligence matters [General pulmonary and critical care medicine]; National Board for Respiratory Care [Director]. All of the relevant financial relationships listed have been mitigated. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. 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