De subitaneis mortibus. XVII. Multifocal stenoses due to fibromuscular dysplasia of the sinus node artery

Histopathology of the Cardiac Conduction System in the Investigation of Sudden Unexpected Death

When a gross and microscopic autopsy, drug screen, and past medical history fail to yield a cause of death, the forensic pathologist may opt to study the cardiac conduction system. This paper describes the excision of the SA (sinoatrial) node and AV(atrioventricular) node-containing areas of the heart and the microscopic appearance of normal SA and AV nodes, His bundle and bundle branches. Conduction system findings that have been reported to be significant include fibromuscular hyperplasia (often mislabeled dysplasia) of the SA and AV nodes arteries, persistent fetal dispersion of the AV node and His bundle, accessory pathways, ganglionitis and neuritis near the SA node, fibrosis and fatty infiltration of the conducting tissue, AV node tumor, left-sided His bundle, and AV node fibrosis. In an otherwise normal autopsy, AV node tumors, severe fibromuscular hyperplasia of the AV node artery and AV node fibrosis are sufficient to cause death. Other findings, particularly Mahaim tracks, are competent causes of death if they correlate with premortem electrocardiographic findings. Conduction system examination, although a low-yield procedure, is a worthwhile endeavor. Care must be taken to not overestimate the significance of the findings.

Early atherosclerotic lesions of the cardiac conduction system arteries in infants

INTRODUCTION

Although several studies have described initial atherosclerotic lesions of the coronary arteries, already detectable in infancy and even during the intrauterine life, little, if any, attention has been given to the possible involvement of the cardiac conduction system arteries. In particular, to the best of our knowledge, none has considered the lesions of the cardiac conduction arteries as an initial stage of atherosclerosis.

METHODS

The cardiac conduction system of 70 infants dying suddenly and unexpectedly was removed in two blocks for paraffin embedding and serially cut.

RESULTS

The histological study of the cardiac conduction arteries of the 70 cases examined showed a normal structure in 55 cases (78.57%). In 15 cases (21.43%), there was a thickening of the sinoatrial node and/or atrioventricular artery associated with a thickening of varying severity in coronary artery walls. The lesions were marked by thickening and deposits of amorphous material and mainly lipids in the intima, as well as fragmentation of the elastic fiber system. A significant correlation was evident between early atherosclerotic lesions and both formula feeding and parental cigarette smoking (P<.05, chi(2) test).

CONCLUSIONS

The combination of both the considered risk factors seems to increase the early atherogenic effect of each noxa because the coronary lesions were more diffused in formula-fed infants whose parents both smoked.

Crib death: further support for the concept of fatal cardiac electrical instability as the final common pathway

This work intends to be a review of the current status of knowledge on the cardiac conduction system in the crib death as well as remaining challenges, including reflections upon authors' personal works as well as many studies by others. The cardiac conduction system findings of resorptive degeneration, His bundle dispersion, Mahaim fibers, cartilaginous meta-hyperplasia, persistent fetal dispersion, left sided His bundle, hemorrhage of the atrio-ventricular junction, septation of the bifurcation, atrio-ventricular node dispersion, sinus node hypoplasia, Zahn node, His bundle hypoplasia, atrio-ventricular node and His bundle dualism are hereby discussed by the authors. The cardiac hypotheses postulating that crib death could be due to lethal cardiac arrhythmias or heart block were considered of great interest in the 1970s. After a general abandon of the conduction studies in crib death, the cardiac concept of crib death is gathering a renewed interest, as well as the occurrence of infantile junctional tachycardia. Both the morphological and functional derangement underlying crib death remain poorly understood, assuring that it remains to be a major medical and social problem. Despite the non-specificity of most of the cardiac conduction findings in crib death, we believe that they, in association with altered neurovegetative stimuli, could underlie potentially malignant arrhythmias, providing a morphologic support for the cardiac concept of crib death.

Intramural coronary artery dysplasia of the ventricular septum and sudden death

We report four cases of sudden unexpected death in three males and one female aged 12 to 31 years. Death occurred during exercise in three of four cases, and there was no history of sudden death or previous cardiac history in any patient. At autopsy, there was marked intramural coronary artery dysplasia of the ventricular septum, accompanied in three of the four cases by myocardial fibrosis. The arterial dysplasia was characterized by severe medial thickening with smooth muscle cell disorganization and marked luminal narrowing. There was no evidence of myofiber disarray or asymmetric septal hypertrophy to suggest hypertrophic cardiomyopathy. Other than an ostium secundum type atrial septal defect in one case, there were no associated cardiac or extracardiac lesions found at complete autopsy of these individuals. We conclude that small vessel disease of intramural coronary arteries of the ventricular septum may be an isolated finding leading to sudden cardiac death in young adults.

Sudden death caused by stricture of the sinus node artery

The sudden unexpected deaths of two young people and the findings in their hearts at autopsy are described. The striking feature was marked narrowing of the sinus node arteries by fibromuscular dysplasia. There were no other histological abnormalities present elsewhere. The observations suggest that pathological changes of the sinus node arteries might lead to a terminal cardiac arrhythmia acting as the mechanism of death.

Fibromuscular dysplasia of coronary arteries as a rare cause of death

A case of fibromuscular dysplasia of the coronary arteries in a 15-year-old boy is reported. After a quarrel involving no violence the boy suddenly suffered from ventricular fibrillation, collapsed and was initially successfully defibrillated. After 37 days of deep unconsciousness the boy died of bronchopneumonia. The cause of the ventricular fibrillation was clarified only after histological investigations. Fibromuscular dysplasia of the coronary arteries with narrowing was found, which has very occasionally been described in the literature. However, its localization in the A-V node artery, as described here, only seems to have been observed once.

Anomalous connection between the sinus node artery and the A-V node artery

Anomalous connection between the sinus node artery and A-V node artery is an extremely rare coronary variant. Angiographic and clinical data from an adult with this finding are reported. Coronary embryogenesis and normal nodal arterial blood supply are reviewed.

Nonatherosclerotic narrowing of the atrioventricular node artery and sudden death

OBJECTIVES

This study was undertaken to determine whether thickening of the atrioventricular (AV) node artery is a cause of sudden cardiac death.

BACKGROUND

Thickening of the AV node artery has been implicated as a cause of sudden death primarily on the basis of case reports. Few pathologic studies have compared subjects who died of sudden cardiac death with normal control subjects who died traumatically.

METHODS

The AV node artery in 27 patients with unexplained sudden cardiac death (mean age 24.8 +/- 7.4 years) was compared with that in 17 control subjects who died traumatically (mean age 25.6 +/- 7.0 years). No anatomic cause of death was found at autopsy in the subjects with sudden death, all of whom died of presumed cardiac arrhythmias. The conduction system of all hearts was studied by semiserial sections and Movat pentachrome stains. At the point of greatest narrowing of the AV node artery, the outer circumference and lumen outline were traced by computerized morphometry, the ratio of outer vessel area to lumen area was calculated and the histopathologic changes were noted.

RESULTS

The rank-sum of ratios was significantly greater in the sudden death group than in the control group (p = 0.031, Wilcoxon rank-sum/Mann-Whitney statistic). A dysplastic AV node artery with significant acid mucopolysaccharide deposition was seen almost exclusively in the sudden death group (12 of 27 vs. 1 of 17, p = 0.006). In 10 subjects with sudden death a dysplastic AV node artery was narrowed > 2 SD over the control value; half of this subgroup died during exercise and one third had a family history of sudden unexplained cardiac death.

CONCLUSIONS

Dysplasia of the AV node artery may contribute to death in a substantial portion of patients with unexplained sudden death, and such death is often associated with exercise and a family history of unexplained sudden death.

Morphologic characteristics and functional significance of focal fibromuscular dysplasia of small coronary arteries

Focal fibromuscular dysplasia of small coronary arteries is not so rare as it is unrecognized. Although sometimes occurring as an isolated abnormality, it more often accompanies a variety of other lesions including inflammation or infiltration. In this review based on personal study of over 1,000 human hearts, the 3 topics include a description of the morphologic characteristics of the lesion, a discussion of its functional consequences affecting coronary flow, and an iteration of theoretical explanations for its development. The typical lesion is focal in distribution, is comprised of both fibrous and smooth muscle elements, and the histologic organization is one of dysplastic array. Included among the subjects discussed in functional consequences are coronary spasm, coronary reserve, chest pain, electrical instability of the heart, and comments on the role of focal fibromuscular dysplasia of small coronary arteries in hypertension, myocardial hypertrophy and heart failure. Theories as to its development include primary faults of smooth muscle or collagen, and focal abnormalities of clotting or neurovascular relation, but it is likely that the cause is multifactorial.

The spectrum of diseases of small coronary arteries and their physiologic consequences

There is a wide spectrum of abnormalities in the structure of small coronary arteries, with regard both to the portion of the arterial wall involved and to the histologic nature of the disease. A fuller understanding of this spectrum permits more useful interpretation of the pathophysiologic basis for the functional consequences of small coronary artery disease. In this review based on personal observations during examination of more than 1,000 human hearts postmortem there is initially a description of the wide variety of structural abnormalities, then a discussion of the functional consequences of these abnormalities and finally a section of general comments to weave together the structural and functional discussion in the context of clinical evaluation of patients who have small coronary artery disease. Future studies should apply fractal analysis and quantitative topology, methods that lend themselves particularly well to an investigation of the progressively smaller branching of the human coronary tree.

Non-uniform fine structural alteration in the sinus node after cessation or reduction of blood flow

The sinus node of the dog was examined, using a large-specimen resin-embedding method for combined light and electron microscopy, after 30-240 min of total in vitro ischaemia and after 15-180 min of reduced blood flow in hearts with 2:1 AV block. Although progressive fine structural alteration was observed in the in vitro series, not all cells developed changes at the same rate. Complete loss of glycogen stores and swelling of organelles could be seen in many after only 30 min, whilst others retained their glycogen and showed minimal alteration even after 90 min. Despite relatively severe alteration throughout the node after 120 or more min, some groups of cells showed more extreme degrees of swelling and surface bleb formation than others. In the partially ischaemic in vivo series focal alteration, consisting chiefly of mitochondrial swelling and/or gross dilatation of sarcoplasmic reticulum vesicles, was detectable after 20 min and increased little in extent or degree during longer periods of reduced blood flow. This non-uniform response of sinus nodal cells to ischaemic injury parallels that of contractile atrial muscle cells.

Arterial fibromuscular dysplasia

Fibromuscular dysplasia is a nonatherosclerotic, noninflammatory vascular disease that involves primarily the renal and internal carotid arteries and less often the vertebral, iliac, subclavian, and visceral arteries. Although its pathogenesis is not completely understood, humoral, mechanical, and genetic factors as well as mural ischemia may play a role. The natural history is relatively benign, with progression occurring in only a minority of the patients. Typical clinical manifestations are renovascular hypertension, stroke, subarachnoid hemorrhage, abdominal angina, or claudication of the legs or arms. In patients with symptoms, percutaneous transluminal angioplasty has emerged as the treatment of choice in most involved vascular beds.

Intramural ("small vessel") coronary artery disease in hypertrophic cardiomyopathy

Many patients with hypertrophic cardiomyopathy have signs and symptoms of myocardial ischemia and dysfunction. Although hypertrophy and increased left ventricular pressure can account for such abnormalities, altered small intramural coronary arteries have also been described in such patients. To determine the prevalence and extent as well as the clinical relevance of abnormal intramural coronary arteries, a histologic analysis of left ventricular myocardium obtained at necropsy was performed in 48 patients with hypertrophic cardiomyopathy (but without atherosclerosis of the extramural coronary arteries) and in 68 control patients with either a normal heart or acquired heart disease. In hypertrophic cardiomyopathy, abnormal intramural coronary arteries were characterized by thickening of the vessel wall and a decrease in luminal size. The wall thickening was due to proliferation of medial or intimal components, or both, particularly smooth muscle cells and collagen. Of the 48 patients with hypertrophic cardiomyopathy, 40 (83%) had abnormalities of intramural coronary arteries located in the ventricular septum (33 patients), anterior left ventricular free wall (20 patients) or posterior free wall (9 patients); an average of 3.0 +/- 0.7 abnormal arteries were identified per tissue section. Altered intramural coronary arteries were also significantly more common in tissue sections having considerable myocardial fibrosis (31 [74%] of 42) than in those with no or mild fibrosis (31 [30%] of 102; p less than 0.001). Abnormal intramural coronary arteries were also identified in three of eight infants who died of hypertrophic cardiomyopathy before 1 year of age. In contrast, only rare altered intramural coronary arteries were identified in 6 (9%) of the 68 control patients (0.1 +/- 0.05 abnormal arteries per section; p less than 0.001) and those arteries showed only mild thickening of the wall and minimal luminal narrowing. Moreover, of those patients with abnormal intramural coronary arteries, such vessels were about 20 times more frequent in patients with hypertrophic cardiomyopathy (0.9 +/- 0.2/cm2 myocardium) than in control patients (0.04 +/- 0.02/cm2 myocardium). Hence, abnormal intramural coronary arteries with markedly thickened walls and narrowed lumens are present in increased numbers in most patients with hypertrophic cardiomyopathy studied at necropsy and may represent a congenital component of the underlying cardiomyopathic process.(ABSTRACT TRUNCATED AT 400 WORDS)

Atherosclerotic involvement of coronary branch vessels

The atherosclerotic involvement of coronary branch vessels (first diagonal, first septal, posterior descending, left and right marginals, conus and the vessels supplying the conduction system) was investigated in 450 apparently healthy subjects aged 11-55 years who died of accidental causes. In subjects 35-55 years old, 1 out of every 3 persons with atherosclerotic plaques in the major coronary arteries also had atherosclerotic plaques in coronary branch vessels; the respective relation for fatty streaks was 1 out of every 12 subjects, for intimal necrotic areas 1 out of every 7 subjects and for incorporated microthrombi 1 out of every 9 subjects. One out of every 3 subjects 51-55 years old had more than 50% lumen reduction in the undistended major coronary arteries, compared to 1 out of every 6 subjects in undistended coronary branch vessels. A small subgroup (8.2%) showed more severe stenotic lesions in coronary branch vessels than in coronary major arteries. The atherosclerotic plaques of coronary branch vessels appeared as 'underdeveloped', lacking a thick fibrohyaline cap, a large detritus cavity, abundant lipid deposition, cholesterol crystals, basal vascularization, intraplaque hemorrhage, ulceration, calcification, occlusive thrombosis. On the other hand the stenotic character of these plaques was often severe (more than 75% lumen reduction). The questionable value of the estimation of the ischemic significance of a coronary stenosis in the absence of available data on the development of a compensatory collateral circulation is discussed.

Cardiac atrioventricular junctional tissues in hearts from infants who died suddenly

The cause of sudden infant death syndrome is not known at present. Most agree that in the majority of cases it involves primary apnea. However, cardiac abnormalities probably account for a subset of these deaths. An investigation into the structure of the atrioventricular (AV) junctional tissues of the heart would provide insight into the frequency of sudden death in infants that might result from abnormal cardiac morphology. The hearts of seven infants who died from diagnosed sudden infant death syndrome were examined by serially sectioning and studying this critical region of the heart. The hearts of these infants could be divided into three groups on the basis of their morphologic features. In the first group, represented by two cases, there were marked variations from normal, the most striking feature being the presence of accessory pathways. In the second group, represented by four cases, the AV junctional tissues were not fully mature and clusters of AV nodal and bundle cells were dispersed throughout the anulus fibrosus. In the third group, the structure of the junctional tissues was normal. There remains a distinct subset of infants who might have died suddenly and unexpectedly from cardiac abnormalities that needs to be more completely defined.

Cardiac conduction system abnormalities as a possible cause of sudden death in young athletes

Histologic examination of serial sections of the conduction system of the hearts of three young persons who died suddenly while engaged in active sports was performed. In no case were electrocardiogram tracings available. One patient, an 11-year-old girl, had micro-Ebstein's anomaly of the tricuspid valve associated with a septoseptal Kent fascicle through a wide gap of the central fibrous annulus and upper Mahaim fibers. Another patient, a 24-year-old football player, had a focal, 75 per cent obstructing atherosclerotic plaque in the proximal descending coronary artery, with scattered band necrosis and patchy myocardial fibrosis; upper and lower Mahaim fibers joined the atrioventricular node and the left bundle branch with the crest of the interventricular septum. The third patient, a 26-year-old cycling champion, had a conspicuous atrial fascicle of ordinary and transitional myocardium bypassing the atrioventricular node to anastomose with the His bundle (James accessory atrioventricular pathway). These findings indicate that atrioventricular conduction system abnormalities may play a fatal arrhythmogenic role in sudden death and raise questions regarding the prevention of electrical instability in young people engaged in active sports.

Sudden death in three teenagers: conduction system studies

The pathologic substrate for sudden death in the middle-aged or elderly adult is usually ischemic heart disease. In contrast, few data are available regarding the pathology of sudden death in teenagers. This report describes three teenagers without clinically suspected heart disease dying suddenly. Patient 1 (age 15, male) was known to have right ventricular premature ventricular beats. Postmortem examination revealed marked premature aging, sclerosis of the cardiac skeleton extending to the right side of the summit with fibrosis of the left and right bundle branches. Patient 2 (age 17, male) was a trained athlete who died during football scrimmage. Autopsy revealed moderate mitral valve prolapse and marked premature aging, sclerosis of the left side of the cardiac skeleton, which extended to the right ventricular side, and secondary involvement of the trifascicular conduction system with mononuclear cell infiltration. Patient 3 (age 19, female) died suddenly at home. Autopsy revealed mitral valve prolapse, thrombosis of the sinoatrial (SA) node artery, and premature aging, sclerosis of the left side of the cardiac skeleton, with involvement of the ventricular septum more on the right ventricular side and involvement of the atrioventricular bundle and trifascicular conduction system. In conclusion, unexpected deaths in three teenagers occurred with demonstrable pathologic findings in the heart. Two of the three patients had mitral valve prolapse, one of whom also had thrombosis or embolism of the sinoatrial node artery. All three had sclerosis of not only the left side but also the right side of the ventricular septum with involvement of the conduction system. The anatomic substrate demonstrated in these three patients could relate to lethal bradyarrhythmia or tachyarrhythmia, or both.

Chance and sudden death

An aura of mystery has always surrounded the subject of sudden unexpected death. Part of the explanation is an absence of a single or unusual explanation, although electrical instability of the heart does serve as a unifying concept for the final common pathway. In this review, emphasis is placed on the random aggregation of a wide variety of contributing factors in the pathogenesis of sudden death. Such factors include coronary disease, platelet aggregation, neural control of the heart, apoplexy of the heart, normal and abnormal variations in the structure of the atrioventricular junction, lessons from certain rare cardiac tumors and the nature of ventricular fibrillation. Useful thinking about these and related causes should employ both a horizontal (concurrence of events) and vertical (sequence of events) matrix, in all of which chance plays a major role. One impediment to understanding sudden death associated with coronary disease is the prevalent assumption that one is due to the other without proper examination of the other factors involved, some of which may be more susceptible to intervention or modification. The multifactorial nature of the pathogenesis of sudden death and the recognition that chance is a major determinant of which factors convene and when they will aggregate in the victim are essential elements to consider if more effective means of treatment and prevention are to be obtained.

Pathologic changes in the cardiac conduction and nervous system in sudden coronary death

The arrhythmogenic substrates for sudden coronary death were studied in 13 autopsied hearts and in 2 left stellate ganglia (surgically excised). Diffuse or segmentary obstruction of nutritional arteries accounted for acute ischemic injury of the conduction system, which was the underlying cause of high-risk bradycardic arrhythmias in one-third of the cases. However, in one-quarter of the cases the survival of anoxia-resistant subendocardial specialized fibers was probably responsible for reentrant lethal tachycardic arrhythmias. In other cases, early infarct damage could have fatal arrhythmias of either type. Intrinsic and/or extrinsic neuropathologic changes, unbalancing the autonomic action on the heart, were often seen to participate in the arrhythmogenic features of sudden coronary death.

Sudden death from occlusive disease of the atrioventricular node artery

Non-atherosclerotic focal occlusive disease of the atrioventricular node artery was the only significant pathological lesion found at autopsy in 2 individuals aged 40 and 17 yr who died suddenly and unexpectedly. The cases were observed amongst 115 autopsies categorized as sudden cardiac death and performed during an 18 mth period. Occlusive disease of the atrioventricular node artery is a poorly documented entity of unknown aetiology and pathogenesis. We believe it is a more frequent pathological finding in sudden cardiac death than has been previously recognized and that it deserves more attention than it currently receives.

Sinus bradycardia in the aged

In the aged, sinus bradycardia represents the sinus-node-dysfunction component of diffuse conduction system disease associated with coronary and cerebral arteriosclerosis. Findings are presented on 15 patients whose ages ranged from 69 to 93 years at the time of admission to a home for the aged. They remained under observation (with electrocardiographic data) for from less than 1 year up to 18 years. The findings illustrate the evolution of conduction system abnormalities, including sinus node dysfunction, occurring either as an initial or an interval event. These abnormalities represent positive indications for pacemaker insertion in the aged.

The sinus node

This discussion of the sinus node begins with a description of its normal anatomy, particularly in the human heart, and then proceeds to a review of the several pathologic changes known to affect the sinus node. The latter include diseases of the sinus node artery, changes in the normal collagen framework of the node, pericarditis and certain infiltrative processes. The concluding section combines an examination of function and structure of the sinus node on the basis of experimental observations. Some new laws of the heart dealing with governance of normal cardiac rhythm are presented.