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Indian Pediatr 2015;52: 291-292 |
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Myocardial Dysfunction in Children with
Scorpion Sting Envenomation
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*OP Mishra and Rajniti Prasad
Department of Pediatrics, Institute of Medical
Sciences, Banaras Hindu University,
Varanasi, India.
Email: [email protected]
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Scorpion sting envenomation with systemic
manifestations is a life threatening emergency and poses a significant
health problem in children. Mesobuthus tumulus or Indian red
scorpion, the most toxic species in India, is abundantly found in
coastal areas and para-Gangetic regions. In envenomed children, serum
venom concentration peaks at about 2 hours, and its level is directly
related to clinical manifestations [1] which also depend upon the age of
the patient, the season of the sting and the time lapse between the
sting and the hospitalization. Children are more likely to develop rapid
deterioration because of their lesser body weight. The critical time
period in cardiopulmonary dysfunction ranges from two to several hours
after the sting.
Mesobuthus tumulus venom is a potent sodium
channel activator which results in autonomic storm. It initially leads
to a transient cholinergic phase followed by sustained adrenergic
hyperactivity, which is a venom dose-dependent phenomenon. The severity
of envenomation and mortality are related to hemodynamic and
cardio-respiratory dysfunctions with cardiac failure and pulmonary edema.
The myocarditis is due to the direct effect of venom on the myocardium,
hypoxia in the presence of increased catecholamines, and altered
permeability of myocardial cell membrane affecting electrical properties
and abnormalities in electrolytes fluxes. Coronary microvascular spasm
due to catecholamine overstimulation may be the underlying
pathophysiology triggering the myocardial perfusion derangement [2].
Pulmonary edema may be due to direct effect of the toxin on the
myocardium and impairment in the clearance of alveolar fluid mediated by
epithelial sodium channel and sodium–potassium pump (Na +/K+-ATPase)
[3]. Furthermore, a-toxin
causes a massive release of vasoactive peptide hormones, including
endothelin-1, which impairs the clearance of alveolar fluid.
Prazosin has been reported to be effective in
reducing preload and improving left ventricular function. However,
cardiotoxicity is due to sustained beta-receptor stimulation leading to
exhaustion of the heart, consequent to a decrease in left ventricular
function. Dobutamine is required in order to improve cardiac function
until catecholamine stores are replenished [4,5]
Specific scorpion antivenom (SAV) therapy is a widely
accepted and is still the single major therapeutic strategy against the
envenomation. The late administration of SAV may not be effective as the
venom might have already reached the target site and not accessible to
the antivenom for neutralization [5]. However, apart from the action on
neutralizing circulating unbound venom, antivenom also creates a
concentration gradient between plasma and target tissue. The venom bound
to antivenom gets excreted and the toxin in the tissues moves down the
concentration gradient into the blood and gets bound by the antivenom.
Therefore, even if the venom is not immediately neutralized by
antibodies, its removal from tissue may cause relief in symptoms [6].
Ananda Kumar, et al. [7], in a study published
in this issue of Indian Pediatrics, observed an increase in
cumulative proportion of children without myocardial dysfunction after
combined administration of SAV and prazosin therapy. They also reported
that late admission to hospital (>4 hours) after the sting, hypotension
at admission, and not using SAV in grade-2 envenomation were
significantly associated with myocardial dysfunction. On multivariate
logistic regression analysis, the independent predictors of myocardial
dysfunction were longer time between sting and admission and
hypotension. However, the main limitation of study was lesser number of
patients in higher grades of envenomation and non-availability of a test
to detect venom antigen to find out the dose-response relationship in
these cases.
Echocardiography is a useful tool for evaluating the
various parameters of cardiac function. It has been used to document
myocarditis in scorpion sting envenomation. Left ventricular systolic
dysfunction is the predominant finding along with left ventricular
dilatation, and regional wall motion abnormalities have been described
infrequently. However, its routine use in emergency is limited by
non-availability [8]. Cardiac troponin (cTn I) has become an important
diagnostic and prognostic tool in acute coronary syndromes as well as
myocarditis. Its measurement and benefits in scorpion sting envenomation
has been reported by Meki, et al. [8]. It showed 100% specificity
and sensitivity for the diagnosis of myocardial injury in relation to
the echocardiographic findings in the envenomed victims. In severe
cases, cTnI was found to be positively correlated with left ventricular
ejection fraction (LVEF). The normal levels of cTnI is an important
indicator of non-involvement of myocardium, when echocardiography is not
available. Left ventricular global hypokinesia, LVEF less than 30% and
right ventricular dysfunction contribute to hypotension in envenomed
patients. These patients are benefitted by the early use of vasopressors
and inotropes. The normal echocardiography and serum level of cTnI also
favor an early discharge from hospital [8,9]. Echocardiography should be
done routinely in all patients with grade 2-4 envenomation to predict
outcome and discharge from hospital. Moreover, early hospitalization
after sting, and administration of SAV are the key factors in reducing
the myocardial dysfunction, and hence related morbidity and mortality.
Funding: None; Competing interests: None
stated.
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