Recent advances in clinicohistopathologic correlates of sudden cardiac death

The cardiovascular risks of physical activity

The incidence of sudden death, serious arrhythmias, and myocardial infarction in connection with both recreational and rehabilitative physical activity is small. However, the incidence of e.g. sudden death is several times higher in exercise than at other times. This relative risk is highest in middle-aged men, and higher in strenuous than in nonstrenuous exercise. In the vast majority of the cases the underlying cause is advanced coronary heart disease, which in large proportion of the cases has been asymptomatic and has allowed regular strenuous training. Attempts to prevent the complications by special large scale screening programs would be ineffective and individual counselling limited by lack of resources. These measures should, however, be used in selected groups and individuals. Another approach is to inform the exercisers and their families at large by systematic, well-planned and repeated messages of the risks of physical activity, of the symptoms and findings indicating this risk, of the individual and environmental factors increasing the risk, and of the necessary measures to be taken to minimize the risk. Even if all available measures at present were used, the cardiovascular complications of physical activity could not be totally prevented. Fortunately, preliminary evidence suggests that at population level the cardiovascular hazards of physical activity are outweighed by its cardiovascular benefits.

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.

Changes in neural and humoral mechanisms of the heart in sudden death due to myocardial abnormalities

Quantitative neurohistochemical study of adrenergic elements of the myocardium and the adrenal medulla in victims of sudden death revealed an unequal and focal depletion of catecholamines attributable to prior pathologic processes in the myocardium. The greatest changes in cardiac innervation were found in cases of acute myocardial infarction and alcoholic cardiomyopathy, and the adrenergic plexuses were better preserved in cases of coronary heart disease without focal myocardial changes. Ultrastructural study of cardiac innervation in patients who died suddenly showed more pronounced changes in the nerve plexuses of the sinus node than in the perinodal nerves of the working myocardium. The changes in coronary artery innervation were usually related to the severity of stenosis due to fibrous plaque; desympathization of the vessels and the adjoining myocardial zone was also found in cases with 50% or greater occlusion of the lumen. The bulk of chromaffinocytes were depleted and weakly luminescent in the adrenal glands of patients with acute myocardial infarction who died suddenly. In contrast, chromaffinocytes with moderate and bright luminescence were prevalent in cases of sudden death with scarring from previous myocardial infarction and with alcoholic cardiomyopathy. Ultrastructural and histochemical examinations demonstrated that changes in the neurons of sympathetic ganglia increased with more severe atherosclerotic lesions of the aorta and with greater changes in the vessels supplying the ganglia. In experiments on rabbits and dogs, both coronary artery ligation and electrostimulation produced cardiac fibrillation followed by a local increase in luminescence intensity of the myocardial nerve plexuses when their density remained high. Chemoreceptors located along the coronary vessels and pulmonary artery in dogs included small cells with bright fluorescence and adrenergic nerve fibers.

Sudden death and vigorous exercise--a study of 60 deaths associated with squash

The circumstances surrounding 60 sudden deaths (59 men, one woman) associated with squash playing are described. The mean age (SD) of those who died was 46 (10.3) years (range 22-66 years). Necropsy reports were available in 51. The certified cause of death was coronary artery disease in 51 cases, valvar heart disease in four, cardiac arrhythmia in two cases, and hypertrophic cardiomyopathy in one case. There were only two deaths from non-cardiac causes. Forty five of those who died had reported prodromal symptoms, the most common of which was chest pain, and 22 were known to have had at least one medical condition related to the cardiovascular system during life, the most common of which was systemic hypertension (14 subjects). Those dying from coronary artery disease had a high frequency of risk factors. Some of these deaths might have been prevented by appropriate counselling of players after prospective medical screening, which would have detected most of the patients with overt cardiovascular disease and some of those with subclinical coronary artery disease.

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.

Exercise and heart disease. Epidemiology of the "exercise hypothesis"

The "exercise hypothesis" states that exercise protects against coronary heart disease. Reviewed herein is the epidemiologic evidence for and against the "exercise hypothesis." The weight of evidence supports the view that exercisers have a lower risk of coronary disease, but that vigorous exercise cannot always prevent progression of coronary atherosclerosis and does increase the risk of sudden death in persons with advanced coronary atherosclerosis. It is concluded that the "exercise hypothesis" is plausible, even likely, but still unproved.

Primary and secondary cardioneuropathies and their functional significance

For most functions of the heart its nerves are as important as its coronary arteries, but this is particularly true concerning cardiac rhythm, conduction and repolarization. It is thus paradoxical that postmortem correlative studies of sudden death virtually always include careful scrutiny of the coronary arteries but only rarely of the cardiac nerves or ganglia. In this review, abnormalities of the cardiac nerves and ganglia, collectively termed cardioneuropathies, are examined from the dual standpoint of their structural appearance and functional significance. Some cardioneuropathies are found in the absence of any other significant structural abnormality detectable in the heart and these are designated as primary cardioneuropathies. A viral etiology or some heritable disorder must rank high among possible causes. Secondary cardioneuropathies are those observed in association with almost every disease that can affect the heart; examples include myocardial infarction, infections, amyloidosis and cancer, but there are many others. Because abnormalities of the heart's nerves and ganglia not only have their own unstabilizing influence on cardiac electrical activity but can also profoundly alter a patient's responses to pharmacologic treatment, it is hoped that future clinicopathologic examinations will more often include their careful study and thereby add to our meager knowledge about these important structures.

The cardiac atrioventricular conduction system in familial amyloidosis with polyneuropathy. A clinico-pathologic study of six cases from Northern Sweden

Cardiac conduction disturbances are frequent in amyloidosis with cardiac involvement, but the pathogenesis of these electrocardiographic abnormalities is not clear. In the present study, the conduction systems in six patients with the Swedish variety of familial amyloidosis with polyneuropathy (FAP), have been analyzed. The results suggest that in FAP, direct amyloid infiltration of the atrioventricular conduction system accounts for the majority of the electrocardiographic disturbances.

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.