Residency · Residency · Pathology

Sudden Cardiac Death and Cardiovascular Autopsy Pathology

Introduction

Sudden cardiac death (SCD) accounts for a significant proportion of unexpected deaths encountered at autopsy. The pathologist must conduct a systematic cardiovascular examination to identify structural, ischemic, inflammatory, and inherited causes while recognizing that some cases require molecular autopsy for definitive diagnosis.

Definition and Epidemiology

Defining Sudden Cardiac Death

Sudden cardiac death is unexpected death from a cardiac cause occurring within 1 hour of symptom onset (when witnessed) or within 24 hours of last being seen alive (when unwitnessed). It accounts for approximately 300,000-400,000 deaths annually in the United States. There is a bimodal age distribution affecting young adults (under 35) and older adults (over 35), with a male predominance particularly in younger age groups.

Age-Related Etiologic Differences

In individuals under 35, the predominant causes are cardiomyopathies (HCM, ARVC), congenital coronary anomalies, myocarditis, channelopathies, and aortic dissection (Marfan syndrome). In those over 35, coronary artery disease is the dominant cause, responsible for approximately 80% of cases. In athletes, the leading causes include hypertrophic cardiomyopathy, anomalous coronary arteries, commotio cordis, and arrhythmogenic cardiomyopathy.

Cardiovascular Autopsy Technique

Heart Examination Protocol

The heart is weighed (normal adult: 250-350 g in women, 300-400 g in men, adjusted for body size). The epicardial coronary arteries are examined in situ before removal, noting dominance (right, left, or codominant). Serial cross-sections of the coronary arteries are made at 3-mm intervals, documenting stenosis percentage, plaque morphology, and thrombosis. The heart is opened following the flow of blood: right atrium, tricuspid valve, RV, pulmonary valve, left atrium, mitral valve, LV, and aortic valve. Wall thickness is measured: LV free wall (normal: 1.3-1.5 cm), RV free wall (normal: 0.3-0.5 cm), and interventricular septum. The valves, endocardium, myocardium, and conduction system region are all examined.

Histologic Sampling

Standard sections include the anterior, lateral, posterior, and septal LV walls; RV free wall; and interventricular septum including the SA and AV node regions. All areas of gross abnormality are sectioned, along with coronary arteries at sites of maximal stenosis or thrombosis. Special stains such as Masson trichrome (fibrosis), Congo red (amyloid), PAS (glycogen storage), and iron stain are applied as indicated.

Coronary Artery Disease

Acute Coronary Syndromes

Acute plaque rupture shows a disrupted fibrous cap exposing the lipid core with an overlying thrombus. Plaque erosion involves a thrombus overlying an intact but denuded plaque surface and is increasingly recognized. Calcified nodule is rare and features a protruding calcification disrupting the intimal surface. Thrombus age is assessed as fibrin-platelet (acute), organized (days), or recanalized (weeks to months).

Acute Myocardial Infarction at Autopsy

In the first 0-4 hours, there are no gross or microscopic changes, and diagnosis may require clinical correlation. At 4-12 hours, wavy fibers and early coagulative necrosis appear, with contraction band necrosis at the periphery. By 12-24 hours, coagulative necrosis with neutrophilic infiltrate is present, and gross pallor may be subtle. At 1-3 days, there is a prominent neutrophilic infiltrate and gross yellow-tan discoloration. From 3-7 days, macrophage infiltration and early granulation tissue at the edges appear. At 1-3 weeks, granulation tissue is prominent, and this is the peak risk period for myocardial rupture. Over weeks to months, dense scar formation with fibrosis develops.

Chronic Ischemic Heart Disease

Chronic ischemic heart disease features healed myocardial infarction as a white fibrous scar replacing the myocardium, along with severe coronary stenosis (greater than 75% cross-sectional area narrowing) in one or more vessels. The LV may show dilation and hypertrophy with wall thinning in scarred areas, and a left ventricular aneurysm or mural thrombus may be present.

Cardiomyopathies

Hypertrophic Cardiomyopathy (HCM)

HCM is the most common cause of SCD in young athletes. Heart weight is increased, and there is asymmetric septal hypertrophy (septum-to-free-wall ratio greater than 1.3). Microscopically, myocyte disarray (affecting more than 5% of the septum), interstitial fibrosis, and small vessel disease are the hallmarks. The condition is genetic, with mutations in sarcomeric proteins (MYH7 and MYBPC3 being most common). LVOT obstruction and systolic anterior motion (SAM) of the mitral valve may be present.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

ARVC features fibrofatty replacement of the RV myocardium in the triangle of dysplasia (inflow, outflow, and apex). LV involvement is increasingly recognized, including biventricular and left-dominant forms. Desmosomal gene mutations include PKP2, DSP, DSG2, DSC2, and JUP. Histology shows residual myocytes embedded in adipose and fibrous tissue, and inflammation may be present. The Task Force Criteria integrate imaging, ECG, histology, genetics, and family history.

Dilated Cardiomyopathy

Dilated cardiomyopathy produces an enlarged heart with biventricular dilation and thinned walls. Microscopically, myocyte hypertrophy, interstitial fibrosis, and patchy myocyte degeneration are seen. Ischemic, valvular, and other secondary causes must be excluded. The condition is familial in 30-50% of cases, with TTN (titin) mutations being most common.

Restrictive and Infiltrative Cardiomyopathies

Cardiac amyloidosis shows Congo red positive deposits with apple-green birefringence (AL or ATTR type). Cardiac sarcoidosis features non-caseating granulomas in a patchy distribution that may involve the conduction system. Hemochromatosis produces iron deposition in myocytes visible with Prussian blue stain. Fabry disease causes lysosomal glycolipid accumulation with lamellar bodies on electron microscopy.

Myocarditis

Etiologies and Diagnosis

Viral myocarditis is the most common form, caused by coxsackievirus B, adenovirus, parvovirus B19, HHV6, and SARS-CoV-2. Giant cell myocarditis is aggressive, featuring multinucleated giant cells with necrosis and high mortality without transplant. Eosinophilic myocarditis results from hypersensitivity (drug-related) or hypereosinophilic syndrome. The Dallas criteria require a myocardial inflammatory infiltrate with associated myocyte necrosis or degeneration. At least 3-5 endomyocardial biopsies are recommended because sensitivity is limited by patchy involvement.

Congenital and Structural Anomalies

Anomalous Coronary Arteries

The most dangerous anomaly is left coronary artery from the right sinus (ALCA), which has an intramural aortic course with a slit-like ostium and may cause exertional sudden death in young individuals. Right coronary from left sinus is less commonly fatal. Careful examination of coronary ostia at autopsy is essential.

Aortic Pathology

Aortic dissection involves an intimal tear with blood tracking through the media and is classified as Stanford type A (ascending) or type B (descending). It is associated with hypertension, Marfan syndrome (FBN1), Loeys-Dietz syndrome, and bicuspid aortic valve. Cystic medial degeneration features loss of smooth muscle cells, fragmentation of elastic fibers, and Alcian blue-positive mucopolysaccharide accumulation.

The Molecular Autopsy

Channelopathies and Autopsy-Negative SCD

Autopsy-negative SCD occurs when no structural cause is found, which happens in up to 30% of young SCD cases. Channelopathies should be considered, including long QT syndrome (KCNQ1, KCNH2, SCN5A), Brugada syndrome (SCN5A), and CPVT (RYR2). Molecular autopsy involves postmortem genetic testing on DNA extracted from blood, tissue, or stored specimens. The yield of pathogenic variants in autopsy-negative SCD is approximately 15-30%. Results inform genetic counseling and screening of surviving family members.

Clinical Pearls

Coronary artery disease accounts for approximately 80% of sudden cardiac death in adults over 35, while cardiomyopathies and congenital anomalies predominate in younger individuals. Myocyte disarray involving greater than 5% of the septum is the histologic hallmark of hypertrophic cardiomyopathy and should be distinguished from normal septal architecture. Autopsy-negative sudden cardiac death in young individuals warrants molecular autopsy (postmortem genetic testing) to identify inherited channelopathies and guide family screening. Systematic coronary artery sectioning at 3-mm intervals is essential for identifying plaque rupture, erosion, and thrombosis as the cause of acute coronary death.

References

1. Basso C, et al. Guidelines for autopsy investigation of sudden cardiac death: 2017 update from the Association for European Cardiovascular Pathology. Virchows Arch. 2017;471(6):691-705.
2. Maron BJ, et al. Assessment of the 12-lead ECG as a screening test for detection of cardiovascular disease in healthy general populations of young people. Circulation. 2014;130(15):1303-1314.
3. Tester DJ, Ackerman MJ. The role of molecular autopsy in unexplained sudden cardiac death. Curr Opin Cardiol. 2006;21(3):166-172.
4. Sheppard MN. Approach to the cardiac autopsy. J Clin Pathol. 2012;65(6):484-495.

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