Hypoxic Changes in Conducting Tissue of the Heart in Sudden Death in Infancy Syndrome

In a group of 50 sudden unexpected infant deaths serial sectioning of the hearts has revealed in 11 cases the presence of petechial haemorrhages in the region of the sinus node and internodal conducting tissue tracts. It is suggested that these findings indicate myocardial hypoxia and that such disturbance of the conducting system may well account for a failure to survive in the sudden death in infancy syndrome.     

Sudden and Unexpected Deaths in Infants: Histology and Virology

The histological appearance of lungs of children whose death had been sudden and unexpected has been studied in relation with the viruses found at necropsy. Fifty-one children were investigated and in 33 the lungs had the histological appearance widely accepted as characteristic of the condition previously termed “cot death.” Sixteen had the histological appearance of lymphocytic bronchiolitis, and it was from this group only that viruses were isolated. The viruses isolated were those associated with respiratory infections. Two patients showed the histological appearance of bacterial bronchopneumonia. Viruses are probably responsible for a substantial proportion of unexpected sudden deaths in infancy.     

Embryonic histogenesis of the atrioventricular segment of the heart conduction system of swine (Sus porcus L.)]

Histological, histochemical and neurochemical methods were used in order to study the features of the histogenesis of structures of the atrioventricular area of the conducting system of the heart and the formation of their cholinergic innervation in the postnatal period of the hog. Under study were 175 hearts of embryos of the hog at the age of 3, 4, 5, 6, 8, 10, 12, 14 and 15 weeks and 22 hearts of adult hogs. The formation of different areas of this system was shown to be asynchronous. The atrioventricular fascicle is formed during the 4th week, the atrioventricular node -- during the 6th week and the conducting muscle fibres--during the 8th week of embryogenesis. The fascicle and the node have a complicated structure and different cellular composition. In the process of prenatal ontogenesis the increased amount of glycogen and increased activity of phosphorylase were noted in the cytoplasm of myocytes of the atrioventricular area of the conducting system of the heart. The cholinergic nerve fibres grow up to the structures of the atrioventricular area of the conducting system of the heart during the 6th week of embryogenesis, and by the end of the prenatal development they form a thick network in all its structures.     

Respiratory viruses and cot death.

Respiratory viruses and histological appearances of the lung were studied prospectively in an unselected series of 104 children who died between 1 week and 2 years of age. Thirty-one of the cases were cot deaths. Seven of these showed evidence of active virus infection in the lower respiratory tract. Similar evidence was found in two children who died from known causes and did not have a severe respiratory illness terminally. Although in some cases of cot death respiratory viruses may be responsible for a severe and rapidly overwhelming illness, the present results are compatible with an alternative hypothesis-namely, that minor respiratory illness may trigger sudden apnoea.     

Role of respiratory viruses in childhood mortality.

Respiratory viruses have been identified at necropsy in the lungs of 13 out of 24 children who died with observed acute respiratory illness. The histological appearances of the lungs supported the association between virus and death in each of these 13 children and suggested an unidentified virus aetiology in a further five cases. Histological appearances compatible with bacterial infection were found in the lungs of only two of the 24 children. Similar virus and histological findings have been reported in about one-third of victims of the sudden infant death syndrome (cot deaths), indicating a rapid unobserved respiratory virus infection as the most likely mode of death in this group. Evidence that respiratory viruses may be involved in a larger proportion of sudden unexpected deaths, perhaps as antigens in a hypersensitivity reaction, is discussed. Respiratory viruses seem the major identifiable agents contributing to the maintenance of the postneonatal mortality rate since acute respiratory illness and the sudden infant death syndrome together account for about two-thirds of deaths at this age.     

Discrimination of Recent Ischemic Myocardial Changes in WHHLMI Rabbits from the Findings of Postmortem Degeneration.

To distinguish recent ischemic myocardial changes in myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbits from general postmortem myocardial degeneration, we examined hearts of WHHLMI rabbits after sudden death and postmortem hearts of non-atherogenic rabbits. Hearts of 8 WHHLMI rabbits were excised within 30 min of sudden death and hearts of 27 non-atherosclerotic rabbits were excised at designated periods after sacrifice. A large number of myocardial cells from WHHLMI rabbits exhibited features characteristic of ischemia (intercellular gap, intracellular edema, eosinophilia, disappearance of myocardial cells, indistinct nuclei, wavy myocardial fibers) simultaneously at regions close to proximal occluded coronary arteries. Although postmortem hearts of non-atherosclerotic rabbits exhibited similar characteristics, several features characteristic of autolyzed myocytes were also randomly observed in the left ventricle wall. Each feature was detected independently in myocardial cells or regions of the ventricle wall. In conclusion, we found several unique characteristics associated with myocardial infarction which enable discrimination between recent ischemic myocardial changes and myocardial degeneration following death.     

Preservation of pre-excitation despite acute myocardial infarction complicated by complete heart block.

In a 53-year-old man with ventricular pre-excitation (normal PR interval, QRS interval of 0.12 seconds and delta-waves) acute inferior wall myocardial infarction was complicated by, successively, first-degree atrioventricular block, second-degree atrioventricular block (Wenckebach type) and complete heart block. The QRS pattern of pre-excitation was preserved throughout these events. The classification of ventricular pre-excitation is reviewed and the correlation between the various electrocardiographic patterns (the Wolff-Parkinson-White syndrome and its variants and the Lown-Ganong-Levine syndrome) and the anomalous conduction pathways of Kent, James and Mahaim are discussed. In this case the best possible explanation for preservation of pre-excitation during complete heart block was the existence of accessory fibres of Mahaim.     

Cytofluorometric nuclear DNA determinations on the atrioventricular nodal cells in human hearts

In the human heart, it is well known that the polyploidization of working heart-muscle cells increases in proportion to increases in heart weight, but there has been no investigation of the process of polyploidization in the specialized heart-muscle cells of the cardiac conduction system which have a nerve-like function. In order to investigate the process of polyploidization in these cells, the nuclear DNA content of atrioventricular nodal cells was measured using cytofluorometry. Tissue samples taken from autopsied hearts without arrhythmias were embedded in paraffin blocks after Carnoy fixation. Blocks containing the atrioventricular conduction system were cut according to the serial sectioning method of Lev et al. The compact atrioventricular nodes were removed from thick paraffin sections (150 micron) under a stereomicroscope. The cells were then isolated by enzyme digestion and ultrasonic treatment. Smears of the isolated cells were double stained with azocarmin-G and acriflavine-Feulgen. Cytofluorometric DNA determinations of the DNA content of atrioventricular nodal cells were performed. Atrioventricular nodes were found to be composed of a large number of diploid cells and a small number of tetraploid cells. No octaploid cells were found. These findings reveal that the process of polyploidization in atrioventricular nodal cells is different from that found in working heart-muscle cells.     

Aerial release of bacteria from cot mattress materials and the sudden infant death syndrome

AIM: To investigate aerial release of bacteria from used cot mattresses and to assess factors that may influence this process. METHODS AND RESULTS: Movement on used mattresses, simulating that of an infant's head, significantly enhanced aerial release of naturally acquired bacteria from the polyurethane foams (total count data, P = 0.008; Staphylococcus aureus, P = 0.004) or from polyvinyl chloride covers (total count data, P = 0.001). Aerial release of naturally acquired bacteria from used cot mattresses showed high variability and was poorly correlated (R2 < or = 0.294) with bacterial cell density within the materials. In experiments involving inoculation of S. aureus and Escherichia coli onto the polyurethane of unused cot mattresses, aerial release of the species correlated well (R2 > or = 0.950) with inoculation density when simulated infant head movement was applied. Aerial release of these bacterial species from the material decreased with increase in width or aqueous content of the material, and was lower from polyurethane foam of a used cot mattress. CONCLUSIONS: Simulated infant movement and mattress related factors influence aerial release of bacteria from cot mattress materials. With simulated infant movement on cot mattress polyurethane foam, levels of airborne bacteria above the material are proportional to bacterial population levels inoculated onto the material. SIGNIFICANCE AND IMPACT OF THE STUDY: Cot mattresses harbouring relatively high levels of naturally acquired toxigenic bacteria, such as S. aureus, could pose a relatively high risk of infection to the infant's respiratory tract through increased aerial contamination. This has impact in the context of recent findings on cot mattress related risk factors for sudden infant death syndrome.     

May fever trigger ventricular fibrillation?

The clinical precipitants of ventricular fibrillation (VF) remain poorly understood. Clinical factors such as hypoxemia, acidosis or electrolyte imbalance, drug-related toxicity, autonomic nervous system disorders as well as viral myocarditis have been proposed to be associated with sudden cardiac death particularly in patients with structural heart disease. However, In the Brugada syndrome, concurrent febrile illness has been reported to unmask the electrocardiographic features of the Brugada syndrome and be associated with an increased propensity for VF. More recently, a febrile illnesses of infectious etiology was associated to polymorphic ventricular tachycardia or VF in patients with normal hearts and without known repolarization abnormality. In this review we detail this phenomenon and its putative mechanisms.     

Cytofluorometric nuclear DNA determinations on the atrioventricular nodal cells in human hearts

Summary In the human heart, it is well known that the polyploidization of working heart-muscle cells increases in proportion to increases in heart weight, but there has been no investigation of the process of polyploidization in the specialized heart-muscle cells of the cardiac conduction system which have a nerve-like function. In order to investigate the process of polyploidization in these cells, the nuclear DNA content of atrioventricular nodal cells was measured using cytofluorometry. Tissue samples taken from autopsied hearts without arrhythmias were embedded in paraffin blocks after Carnoy fixation. Blocks containing the atrioventricular conduction system were cut according to the serial sectioning method of Lev et al. The compact atrioventricular nodes were removed from thick paraffin sections (150 m) under a stereomicroscope. The cells were then isolated by enzyme digestion and ultrasonic treatment. Smears of the isolated cells were double stained with azocarmin-G and acriflavine-Feulgen. Cytofluorometric DNA determinations of the DNA content of atrioventricular nodal cells were performed. Atrioventricular nodes were found to be composed of a large number of diploid cells and a small number of tetraploid cells. No octaploid cells were found. These findings reveal that the process of polyploidization in atrioventricular nodal cells is different from that found in working heart-muscle cells.     

Cot mattresses as reservoirs of potentially harmful bacteria and the sudden infant death syndrome

Cot mattress materials were investigated as potential reservoirs of bacteria in relation to the sudden infant death syndrome (SIDS). The sleeping position of the infant significantly influenced bacterial population density of cot mattress polyurethane foams (p<0.0000001) and their covers (p<0.004). Staphylococcus aureus was isolated at significantly higher frequency (p<0.03) from the infant's head region of cot mattress materials. Significantly higher bacterial population densities (p<0.001) were associated with polyurethane foams from non-integral mattresses (exposed polyurethane foam), when compared to those from mattresses completely covered by polyvinyl chloride (integral type mattress). The frequency of isolation of S. aureus from polyurethane foams from non-integral mattresses was also significantly higher (p=0.03) than from foams from the integral type. The following factors were significantly associated with increased frequency of isolation of S. aureus: from the polyurethane foam, previous use of non-integral mattresses by another child (p=0.03 for all sample sites, p=0.01 for torso region); from the covers, sleeping in the prone position (p=0.003 head region, p=0.001 torso region). Prone sleeping was also significantly associated with increased bacterial population levels (p=0.01) and increased frequency of isolation of Escherichia coli (p=0.02) from the torso region of cot mattress covers. These findings could explain some recently identified risk factors for SIDS associated with type and previous use of cot mattresses. Clostridium perfringens was isolated at very low frequency and Streptococcus pyogenes was not isolated from any cot mattress materials tested.     

Growth and survival of bacteria implicated in sudden infant death syndrome on cot mattress materials

AIMS: To compare growth and survival of selected bacteria implicated in sudden infant death syndrome (SIDS) on cot mattress polyurethane (PU) inner-foams and on different types of cot mattress cover materials. METHODS AND RESULTS: Escherichia coli, Staphylococcus aureus or Streptococcus pyogenes were inoculated onto swatches of new-unused cot mattress PU inner-foam and onto three types of cot mattress covers (polyvinyl chloride, cotton and polyester). The influence of inoculation cell density, relative humidity (RH) and temperature of incubation on survival was assessed by recovery of cells in 0.85% NaCl, with viable cell enumeration by plate counting on selective and differential media. Utilization of carbon and nitrogen sources within cot mattress PU was assessed by following growth on aqueous leachate from PU, and by colorimetric determination of aromatic amines. Good survival capability (>206 d) was shown by all three test species on PU inner-foam and on polyester mattress cover at high RH (75%), but only by Staph. aureus on PU at low RH (25%). Aqueous soluble material from PU foam supports bacterial growth; removal of aromatic amines from aqueous leachate from PU accompanies growth of Staph. aureus. CONCLUSIONS: Staphylococcus aureus has good survival capability on cot mattress PU foam, even at low RH. Soluble material within PU can serve as carbon and nitrogen sources for bacterial growth. SIGNIFICANCE AND IMPACT OF THE STUDY: Prolonged survival of Staph. aureus on PU at low RH could explain, in the context of the common bacterial toxins hypothesis, an increased risk of SIDS associated with used infant mattresses.     

Abnormal myocardial lipid composition in an infant with type II glutaric aciduria

We have analyzed the myocardial lipids of an infant with glutaric aciduria type II (GAII) who died from sudden cardiac failure and of five infants who died suddenly from indeterminate causes (sudden infant death syndrome, SIDS). Histology of the SIDS hearts was normal, but there was marked fatty deposition in the GAII heart. Fatty acid composition of myocardial lipids was determined by thin-layer chromatography-gas-liquid chromatography. Total lipid was elevated 20-fold in the GAII heart. Of total fatty acids, 75% was derived from phospholipids in SIDS heart and 89% from neutral lipids in GAII heart. Increased levels of free oleic acid and a 6-fold elevation in the (n-6)/(n-3) fatty acid ratio in phospholipid were noted in GAII heart compared to SIDS hearts.     

Development of the Hearts of Lizards and Snakes and Perspectives to Cardiac Evolution

Birds and mammals both developed high performance hearts from a heart that must have been reptile-like and the hearts of extant reptiles have an unmatched variability in design. Yet, studies on cardiac development in reptiles are largely old and further studies are much needed as reptiles are starting to become used in molecular studies. We studied the growth of cardiac compartments and changes in morphology principally in the model organism corn snake (Pantherophis guttatus), but also in the genotyped anole (Anolis carolinenis and A. sagrei) and the Philippine sailfin lizard (Hydrosaurus pustulatus). Structures and chambers of the formed heart were traced back in development and annotated in interactive 3D pdfs. In the corn snake, we found that the ventricle and atria grow exponentially, whereas the myocardial volumes of the atrioventricular canal and the muscular outflow tract are stable. Ventricular development occurs, as in other amniotes, by an early growth at the outer curvature and later, and in parallel, by incorporation of the muscular outflow tract. With the exception of the late completion of the atrial septum, the adult design of the squamate heart is essentially reached halfway through development. This design strongly resembles the developing hearts of human, mouse and chicken around the time of initial ventricular septation. Subsequent to this stage, and in contrast to the squamates, hearts of endothermic vertebrates completely septate their ventricles, develop an insulating atrioventricular plane, shift and expand their atrioventricular canal toward the right and incorporate the systemic and pulmonary venous myocardium into the atria.     

Involvement of neuroleptic drugs in selenium deficiency and sudden death of cardiac origin: study and human post-mortem examination

The involvement of psychotropic drugs in sudden deaths has been highlighted. The objective of this work was to establish a link between selenium levels in heart tissue, psychotropic treatment and sudden death. Selenium levels were measured by electrothermal atomic absorption spectroscopy post-mortem in heart, brain and liver. Histological examination evidenced dilated cardiomyopathy in 45% of cases, left ventricular hypertrophy in 36%, and ischemic coronaropathy in 18%. A significant reduction of myocardial selenium levels compared to controls was seen in patients treated with neuroleptic drugs or meprobamate. No changes in brain or liver selenium levels were seen. These results suggest that selenium deficiency can facilitate sudden death in patients on psychotropic drugs. The reduced activity of glutathione peroxidase due to selenium deficiency can result in augmented oxidative stress in myocardial cells and myocardiopathy leading to sudden death.     

Mechanism of facilitation of conduction in Purkinje fibers with sequential pacing

Clinical studies have demonstrated that retrograde conduction of a premature beat through the His-Purkinje system can be facilitated by atrioventricular sequential pacing. Several possible mechanisms of facilitation have been proposed. No studies, however, have shown the occurrence of this phenomenon or its mechanism in isolated Purkinje fibers. The present study demonstrated that facilitation of conduction of a premature beat can indeed occur in isolated canine Purkinje fibers during sequential pacing. When a premature beat showed conduction delay during unidirectional pacing, its conduction consistently improved during sequential pacing. This improvement of conduction was related to a greater membrane recovery of a portion of the Purkinje fiber, i.e., the portion that was pre-excited by the sequential mode of stimulation. These findings suggest that an important mechanism of the facilitation of conduction observed clinically may be similar; i.e., pre-excitation and consequent earlier recovery from refractoriness of portions of the His-Purkinje system during atrioventricular sequential pacing.     

Enzyme histochemical studies on the Purkinje fibres of canine, bovine and porcine hearts

Synopsis Whereas in ungulates the Purkinje fibres of the atrioventricular conducting system are highly characteristic cells, those in the canine heart are poorly differentiated and accordingly they cannot always be readily identified in histological sections. Consequently in this paper the results of various histochemical tests on bovine and porcine hearts have been compared with the view of evaluating them as dependable methods for identifying Purkinje fibres that are microscopically poorly differentiated.It appeared that, histochemically, canine Purkinje fibres differ consistently in similar ways and as markedly from the common myocardial fibres as the morphologically typical conducting fibres in bovine and porcine hearts. The conducting fibres distinguish themselves from the myocardium proper in containing more glycogen and fewer lipids, in possessing higher activities of the enzymes -glucan phosphorylase,l-glycerol-3-phosphate:menadione oxidoreductase, myosin adenosine triphosphatase and monoamine oxidase, as well as in possessing lower activities of several dehydrogenases, cytochrome oxidase, peroxidase and mitochondrial adenosine triphosphatase. The relatively high activity of -glucan phosphorylase in particular is striking. As the activity of this enzyme persists during periods of up to 20 min after death, the staining method for this enzyme provides a valuable technique for identifying Purkinje fibres even if they are cytologically poorly differentiated.It is of interest in relation to electrophysiological data that the histochemical properties are similar in Purkinje fibres derived from widely differing levels of the conducting system. From the present histochemical findings it may be assumed that, as compared with the myocardium proper, the Purkinje fibres have a higher rate of anaerobic and a lower rate of aerobic metabolism. Furthermore, it is pointed out that histochemically the differences between Purkinje fibres and common myocardial cells on the one hand, and those between white (Type II) and red (Type I) striated muscle fibres on the other, are essentially similar.     

Effects of voltage sensitive dye di-4-ANEPPS on guinea pig and rabbit myocardium

Voltage-sensitive dyes (VSDs) are used to record transient potential changes in various cardiac preparations. In our laboratory, action potentials have been recorded by optical probe using di-4-ANEPPS. In this study, the effects of two different ways of staining were compared in guinea pig and rabbit isolated hearts perfused according to Langendorff: staining either by coronary perfusion with low dye concentration or with concentrated dye as a bolus into the aorta. Staining with low dye concentration lead to its better persistence in the tissue. Electrogram and coronary flow were monitored continuously. During the staining and washout of the dye, prominent electrophysiological changes occurred such as a decrease in spontaneous heart rate, partial atrioventricular block and changes of ST-T segment, accompanied by a decrease in mean coronary flow. No production of hydroxyl radicals was found by HPLC which excluded significant ischemic damage of the myocardium. Good viability of the stained preparation was supported by unchanged electron microscopy. Since in rabbit hearts the VSD-induced arrhythmogenesis was less pronounced, we conclude that the rabbit myocardium is more resistant to the changes triggered by VSD application. It may be due to different properties of the membrane potassium channels in the cardiomyocytes of these two species.     

Identification of infants destined to die unexpectedly during infancy: evaluation of predictive importance of prolonged apnoea and disorders of cardiac rhythm or conduction.

Twenty four hour tape recordings of electrocardiogram and breathing movement were made prospectively in 6914 full term and 2337 preterm infants or infants of low birth weight during their first six weeks of life. These recordings included 40 obtained in 29 infants who subsequently suffered the sudden infant death syndrome and 13 obtained in 10 other infants who died suddenly and unexpectedly. None of the recordings obtained in the infants who suffered the sudden infant death syndrome showed prolonged apnoea (cessation of breathing movement for 20 seconds or more) or pre-excitation. One infant had multiple ventricular premature beats (38/hour). Compared with recordings obtained in 211 control infants who did not die none of the recordings obtained in the infants who suffered the syndrome showed abnormal prolongation of the QT interval.