The Pathologic Basis of Cardiac Arrhythmias

Age-related histologic features of the sinoatrial node from normal human hearts during the first 10 decades of life: a study of 200 cases

Knowledge of the histologic constituency of the sinoatrial (SA) node is based on small studies with unevenly distributed ages and subjective assessments of nodal composition, leading to difficulties in interpreting what constitutes true pathology of the SA node. SA nodes from two-hundred normal hearts (10 male and 10 female from each of the first 10 decades of life) were digitally analyzed to assess their histologic composition. Both nodal area and nodal fat content (≥5%) showed a quadratic relationship with age, peaking in the fifth to eighth decades of life. Increased fat content was also more prevalent with increased BMI (≥25 kg/m²). No differences between sexes were observed. Mean nodal collagen ranged from 7.1% to 50.3%, without a statistically significant differences by age or body mass index (BMI). The data suggests that the designation of pathologic fibrosis should be reserved for SA nodes with >50% collagen content. These findings expand and refine our understanding of the anatomy of the SA node.

Anatomopathological changes of the cardiac conduction system in sudden cardiac death, particularly in infants: advances over the last 25 years

Sudden cardiac death (SCD) is defined as the unexpected death without an obvious noncardiac cause that occurs within 1 h of witnessed symptom onset (established SCD) or within 24 h of unwitnessed symptom onset (probable SCD). In the United States, its incidence is 69/100,000 per year. Dysfunctions of the cardiac conduction and autonomic nervous systems are known to contribute to SCD pathogenesis, even if most clinicians and cardiovascular pathologists lack experience with detailed examination of the cardiac conduction system and fail to recognize lesions that are crucial to explain the SCD itself. In this review, we sought to describe the advances over the last 25 years in the study of the anatomopathological changes of the conducting tissue, in SCD, in mature hearts and particularly in sudden infant death syndrome (SIDS) and sudden intrauterine unexpected death syndrome (SIUDS), through the articles published in our journal Cardiovascular Pathology (CVP). We carried out an extensive Medline search to retrieve and review all articles published in CVP in which the sudden unexpected death of one or more subjects believed healthy was reported, especially if associated with lesions of the conducting tissue in settings that revealed no other explained causes of death, particularly in infants and fetuses. The cardiac conduction findings of resorptive degeneration, His bundle dispersion, Mahaim fibers, cartilaginous meta-hyperplasia, persistent fetal dispersion, left-sided His bundle, septation of the bifurcation, atrioventricular node dispersion, sinus node hypoplasia, Zahn node, His bundle hypoplasia, atrioventricular node, and His bundle dualism were similarly detected in SIDS and SIUDS victims.

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.

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.

Sudden Infant Death Syndrome (SIDS): a study of cardiac conduction system

The theory that Sudden Infant Death Syndrome (SIDS) may be related to lethal cardiac arrhythmias or heart block due to structural abnormalities of the conduction system is attractive and still of particular interest. We analyze 69 autopsied cases of SIDS (46 males and 23 females, infants ranging in age from 3 to 365 days) and 24 age-matched cases of explained death (ED) as controls (16 males and 8 females), infants who died from extracardiac cause (cerebral and respiratory). SIDS and ED groups were divided into three subgroups according to the age: (A) from 3 to 60 days; (B) from 61 to 120 days; (C) from 121 to 365 days. Histological observations were focused on the cardiac conduction system (CCS) which was examined on serial sections with the technique devised by one of the present authors (L. Rossi). The following findings were observed: resorptive degeneration (97.10% of SIDS, 75% of ED), His bundle dispersion (33. 33% of SIDS, 16.66% of ED), Mahaim fibers (21.73% of SIDS, 8.3% of ED), cartilaginous meta-hyperplasia (5.79% of SIDS, 4.16% of ED), persistent fetal dispersion (24.63% of SIDS, 16.66% of ED), intramural right bundle (20.29% of SIDS, 25% of ED), left sided His bundle (20.29% of SIDS and 8.3% of ED), hemorrhage of the atrio-ventricular junction (15.94% of SIDS), septation of the bifurcation (13.04% of SIDS), atrio-ventricular node (AVN) dispersion (7.24% of SIDS), sino-atrial node hypoplasia (5.79% of SIDS), Zahn node (1.45% of SIDS), His bundle hypoplasia (1.45% of SIDS), intramural left bundle (1.45% of SIDS), AVN dualism (2.89% of SIDS), and His bundle dualism (2.89% of SIDS, 4.16% of ED). Only the presence of resorptive degeneration was significantly higher in SIDS than in ED cases (p = 0.004). Regarding the subgroups, the only significant difference was the higher presence of intramural right bundle in SIDS-A than in SIDS-B (p = 0.01). Despite the non-specificity of most of these findings, we believe that these changes, associated with particular conditions and/or neurovegetative stimuli, could cause potentially malignant arrhythmias. These data suggest the need for an accurate approach and examination of the cardiac conduction system in all cases of sudden death in infancy

The conduction system findings in sudden cardiac death

This is a brief review of the findings in the conduction system in cases of sudden death victims who were living "normal" active lives. Twenty-two representative samples from more than 100 cases of sudden cardiac death, especially in young and asymptomatic individuals, revealed a plethora of findings that varied from normal to congenital and acquired changes, in most cases either at the gross or microscopic level, especially in the conduction system to a varying degree. Despite these changes, the individuals were living normal, symptom-free lives and were not clinically diagnosed to have lethal cardiac problems. This suggests that these individuals might have experienced lethal arrhythmias in the past, which might have been "silent" in nature. Innovative new methodologies must be developed to detect the silent lethal arrhythmic focus that may lead to sudden cardiac death.

Electrophysiologic-structural correlations in chagasic aneurysms causing malignant arrhythmias

We studied the structure and ultrastructure of three chagasic aneurysms, the excision of which abolished malignant arrhythmias. Chronic recurrent ventricular tachycardia often occurs in patients with chagasic aneurysms, and ventricular mapping indicates that these arrhythmias originate in regions adjacent to those aneurysms. In our patients, ventricular tachycardia had been refractory to medical treatment. During surgery, epicardial and endocardial mapping showed abnormal potentials. Sutures were placed in the areas of resection, their sizes approximating those of earliest activation so that these sites could be identified. The myocardium showed chronic inflammatory reaction, myocytolysis and fibrosis. The presence of "islets" was common (normal, "early" damaged or "established" necrotic myocytes surrounded by fibrous tissue). The "early" lesions were predominant at the previously identified areas of arrhythmogenic activity. The ultrastructural studies showed hypertrophy of myocytes and partial or complete loss of myofibrils, swelling of mitochondria and disruption of mitochondrial cristae, accumulation of lipofuscin granules, and intracellular oedema. A most striking alteration was the thickening of the basement membranes of myocytes and vascular endothelial and smooth muscle cells. The interlaced fronts of respectively healthy (fast conducting) and "early" damaged (slow conducting) myocytes seen in serial sectioning produced an ideal configuration for reentry circuits. The final proof that the arrhythmias originated in these endocardial regions was their abolition by resection of the aneurysm.

Cardioneuropathy and extracardiac neural disease

The pathology of cardiac innervation, both intrinsic and external to the heart (aortopulmonary glomera included), is scarcely known, yet it can be critical to life-threatening disorders in cardiac performance, or to reflexes discharging outside the heart, or both. Evidence has been supplied in cardiac neuroanatomy relevant to cardioneuropathy. The arrhythmogenic potential of imbalanced autonomic input in the heart has been corroborated by histopathologic findings in intrinsic plexuses. In turn, significant neurogenic substrates for cardiomyopathy have not been confirmed. Changes in the extrinsic sympathetic chain (left stellate ganglion) and in the prevailing vagal cardiac plexus were found in subjects with arrhythmias (with long QT interval and ventricular tachycardia/fibrillation, respectively). In myocardial infarction with sudden cardiac death, a complicating mediastinitis often presented and was seen to produce focal inflammation of mediastinal nerve plexus and paraganglia. This can worsen the imbalance in autonomic control of the performance of the heart and interfere with barochemoreflex regulation of the systemic or coronary circulation, or both. Such ill-understood sequelae of infarction as the shoulder-hand, chest pain and Dressler syndromes might also correlate with the newly described neuromediastinitis.

Anatomic and electrophysiologic substrate of the permanent form of junctional reciprocating tachycardia

Data are reported on three patients with the permanent form of junctional reciprocating tachycardia, in whom conduction over a slow accessory pathway was observed after His bundle ablation. Tachycardia was almost incessant and showed a retrograde P wave (P') and RP' interval longer than P'R interval in all patients; during sinus rhythm, the PR interval was normal and there was no evidence of a delta wave. An accessory pathway with a long conduction time located in the posterior pyramidal space provided the retrograde limb of the reentry circuit. After His bundle ablation, the accessory pathway was capable of conducting in both anterograde and retrograde directions with decremental properties in all patients. Postmortem documentation of the accessory pathway was achieved in one patient. Serial sections revealed an accessory atrioventricular connection composed of ordinary myocardium joining the lower rim of the coronary sinus outlet to the uppermost ventricular muscle. This anomalous atrioventricular connection pursued a sinuous, tortuous path. As a result of changing cross-sectional area, such an accessory pathway might exhibit slow conduction, thus explaining its decremental characteristics.