Saroja Bharati.
Maurice Lev Congenital Heart and Conduction System Center, The Heart Institute for
Children, Hope Children's Hospital, Christ Hospital and Medical Center, Oak Lawn, Rush
Medical College, Rush University, Rush-Presbyterian-St. Luke's Medical Center, Chicago,
Clinical Professor of Pathology, Finch University of Health Sciences, Chicago Medical
School, North Chicago, University of Illinois at Chicago, Chicago, USA
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The conduction system has been infrequently dealt with
when death occurs suddenly in the athlete both in the human and the sled dog. In general,
when death occurs suddenly, especially in the athlete, we examine the heart for the
obvious abnormalities such as: hypertrophic cardiomyopathy, Marfan's syndrome, and
coronary artery anomalies. It is self evident that after having ruled out the above
abnormalities it is also equally important that we should look for congenital
abnormalities with or without associated acquired pathological changes that may be present
to a varying degree in the conduction system. These pathological and/or congenital
anomalies of the conduction system may remain silent especially in an athlete for a long
time and during an altered physiological state may create arrhythmias that may end
fatally. It is, therefore, important that after ruling out all possible causes of sudden
death in the athlete including the gross, microscopic, as well as the toxicological
examination, every effort should be made to study the conduction system.
We had the opportunity of studying the conduction system in athletes who died suddenly
as well as Alaskan sled dogs who died suddenly, either during the Iditarod race and/or
during training. First I will briefly discuss the conduction system in sudden death in
athletes and later discuss the conduction system findings in the sled dogs and then
compare the findings between the two.
The heart was hypertrophied and enlarged to a varying degree in all athletes who died
suddenly. The conduction system in all athletes demonstrated varying degrees of
abnormalities including both the congenital and the acquired pathologic changes. The
congenital abnormalities include: abnormally developed SA node and its approaches, the AV
node and its approaches, the AV bundle and the bundle branches. In addition, there were
abnormalities in the central fibrous body and the membranous part of the ventricular
septum. There were also anomalous connections such as atrio-His bundle connection or left
atrial or node like structures entering the central fibrous body that eventually joined
the AV node at varying levels. The acquired pathological changes included mononuclear cell
infiltration in the approaches to the SA node, the SA node, the AV node, fat and fibrosis
to a varying degree in all parts of the conduction system and the surrounding myocardium
with or without focal fibrotic scars in the ventricular septum both on the left as well as
the right side.
The conduction system in sudden death in sled dogs revealed considerable fibrosis of
the SA node and/or its approaches, with narrowing of the SA nodal artery, marked fatty
infiltration and fibrosis in and around the AV node in all with almost isolation of the AV
node from its surrounding approaches in some, or fat and fibrosis in the AV bundle and
bundle branches to a varying degree with focal fibrotic scars in the left ventricle with
fat and/or myocardial disarray.
The acquired pathological findings in both the human and the sled dogs appear to be
more or less similar, but definitely not identical. It is of interest to note that there
were no congenital anomalies of the conduction system in the Alaskan sled dogs.
It is obvious that the above anatomic and/or pathological findings were present in the
human athletes and the sled dogs for a long period of time, but nevertheless, they were
able to continue with their strenuous physical activity without symptoms. It is
conceivable that although they were considered "asymptomatic", they might have
experienced symptoms "that were probably considered not significant". On the
other hand, one may hypothesize that the pathological and/or the congenital findings in
the conduction system may indeed alter its function during an altered physiological and/or
metabolic state and may initiate varying types of arrhythmias, such as, premature
ventricular contractions that may proceed to ventricular tachycardia, fibrillation and
sudden death. It is also understood that there may be a genetic tendency to sudden death
in some.
In conclusion, when death occurs suddenly either in human athletes and/or heavily
trained sled dogs during the Iditarod race and/or during training, significant
pathological findings in the conduction system and the surrounding myocardium, are present
to a varying degree and the above findings during an altered physiological state may form
a milieu for an arrhythmic event that may promote a reentry mechanism or any other
mechanism resulting in ventricular tachycardia, fibrillation and sudden death. It is
emphasized that although varying types of congenital anomalies of the conduction system
are found in some of the human athletes, such findings were not seen in the sled dogs who
died suddenly.
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