From sting to pacemaker: a case of complete heart block following yellow scorpion envenomation—a case report

Abstract

Background

Scorpion envenomation is a significant medical concern in tropical and subtropical regions, with cardiovascular complications being among its most severe manifestations. While scorpion venom-induced cardiac dysfunction is well-documented, complete atrioventricular (AV) block is a rare occurrence. This case highlights a unique presentation of complete heart block following a yellow scorpion sting, emphasizing the importance of early recognition and management.

Case presentation

A 56-year-old Middle Eastern (Iranian) male presented to the emergency department with dizziness, syncope, and severe bradycardia following a yellow scorpion sting. Electrocardiographic evaluation revealed a complete atrioventricular block. Laboratory findings indicated elevated cardiac biomarkers, suggesting myocardial injury. Echocardiography demonstrated left ventricular dysfunction without significant structural abnormalities. The patient required temporary transvenous pacing for hemodynamic stabilization and was managed with supportive care, including intravenous fluids, atropine, and continuous cardiac monitoring. Over the course of hospitalization, his conduction abnormality resolved by permanent pacemaker, and he was discharged in stable condition.

Conclusions

This case underscores the potential for severe cardiac complications following scorpion envenomation, particularly conduction disturbances such as complete atrioventricular block. Although rare, healthcare providers should be aware of this life-threatening consequence and initiate prompt intervention to prevent adverse outcomes. Increased awareness and timely management can significantly improve prognosis in affected patients.

Introduction

Scorpion envenomation is a frequent medical emergency in tropical and subtropical regions, with over a million cases reported annually worldwide [1, 2]. Scorpion stings are a significant public health concern in Fars province, located in the southern part of Iran. This region, characterized by a warm climate, experiences a high incidence of scorpion stings, particularly during the hotter months, which corresponds to the peak activity of scorpions. The prevalence of scorpion stings is influenced by both geographical and seasonal factors, with higher sting rates reported in the spring and summer months [3]. The clinical presentation of scorpion envenomation varies widely, depending on the scorpion species involved [1].

Severe cardiovascular complications are commonly associated with species such as Androctonus and Buthus in North Africa, Leiurus quinquestriatus in the Middle East, Mesobuthus tamulus in India, and Tityus in Brazil. These effects may result from the venom’s direct action on the heart and blood vessels or indirectly via neurohormonal activation [2]. The clinical severity varies, with cardiovascular complications being a primary cause of mortality [4, 5]. The venom’s pathogenic mechanisms can include coronary spasm leading to myocardial ischemia, a direct toxic impact on the heart, and allergic reactions. Pulmonary edema, a critical cause of mortality in such cases, is often attributed to excessive catecholamine release following the sting [5]. Venom-induced autonomic disturbances result in a broad spectrum of cardiac effects, including arrhythmias, myocarditis, and acute heart failure [6–8]. Electrocardiography (ECG), a cost-effective and readily available diagnostic tool, is useful for predicting the severity of scorpion envenomation. Common abnormalities include sinus tachycardia, global ST-segment changes, and T-wave inversions, which are markers of moderate to severe envenomation [9]. Conduction blocks and ischemic patterns of electrocardiography (ECG), are critical in identifying and managing severe cases [10, 11]. This report presents a rare case of complete heart block following a scorpion sting, highlighting the importance of early recognition and intervention.

Case presentation

A 56-year-old Middle Eastern (Iranian) male presented to a rural hospital after being stung by a yellow scorpion on his right knee. He reported localized pain and swelling but denied systemic symptoms such as chest pain or dyspnea. The patient had no allergies and no previous past medical history such as hypertension or surgeries. He was not on any medications. Initial examination revealed a pulse rate of 35 bpm, with ECG findings consistent with complete heart block. (Fig. 1) On the basis of the patient’s electrocardiogram (ECG) findings, including bradycardia and atrioventricular (AV) dissociation, the diagnosis was consistent with complete heart block. This condition may occur owing to several underlying causes, such as directed toxin mediated depression of sinus node, myocarditis, parasympathetic over activity in the early phase of disease.

Fig. 1.

The first electrocardiography of the patient showing complete heart block (CHB)

He was promptly administered polyvalent scorpion antivenom immunoglobulin and a temporary pacemaker placed for him. (Fig. 2) The patient initially presented to the primary care center with symptom of dizziness. However, after administration of antivenom and implantation of a temporary pacemaker (TPM), his condition stabilized, and he remained symptom-free upon referral to the tertiary care center.

Fig. 2.

The electrocardiography after temporary pace-maker insertion

Upon transfer to a tertiary center, the patient remained hemodynamically stable with a pacemaker-dependent heart rate of 70 bpm and a blood pressure of 140/80 mmHg. Physical examination showed no additional abnormalities apart from localized tenderness and swelling at the sting site.

Laboratory studies revealed pancytopenia (WBC: 3.7 × 10³/µL, Hb: 13 g/dL, PLT: 88 × 10³/µL) and significantly elevated troponin levels (initial: 6.9 ng/mL, peak: 174.8 ng/mL, declining to 16.7 ng/mL). Pancytopenia was most likely related to a direct toxic effect of the scorpion venom on the bone marrow or a systemic inflammatory response, both of which have rarely been reported. Other causes such as viral infections or drug-induced cytopenia were excluded. Blood counts gradually improved during hospitalization, and by discharge, white blood cell and hemoglobin were normal, with platelets showing an upward trend.

Serum sodium, potassium, calcium, and magnesium levels were within normal limits throughout hospitalization. No electrolyte abnormalities contributed to conduction defects.

Echocardiography revealed a reduced ejection fraction (45%) with global hypokinesia especially in the base of the inferior and the inferoseptal wall and mild valvular regurgitation. Coronary angiography excluded significant coronary artery disease. (Fig. 3) First, the patient was managed conservatively and was closely observed, but owing to the persistence of complete heart block for 13 days without recovery, a permanent pacemaker was implanted. (Fig. 4) The patient was discharged in stable condition and referred for outpatient follow-up.

Fig. 3.

Coronary angiography showing no significant coronary artery stenosis. A Selective left circumflex angiography at LAO projection which shows normal left circumflex artery. Lead of temporary pace maker is also seen. B Normal left coronary system (left anterior descending and left circumflex arteries) at LAO- Caudal projection (spider view). Lead of temporary pace maker is also seen. C Normal right coronary artery at LAO projection. Lead of temporary pace maker is also seen

Fig. 4.

A The electrocardiography after permanent pacemaker implantation which shows normal ventricular-paced rhythm. B The chest X-ray after a dual chamber permanent pacemaker implantation

The patient was followed for 6 months. During this period, no return of intrinsic AV conduction was observed, and pacemaker function remained stable, and the patient reported no significant limitations in daily activities The initial echocardiogram showed EF 45% with global hypokinesia. Follow-up echocardiography at three months demonstrated EF improvement to 55% and resolution of wall motion abnormalities, suggesting recovery of myocardial function.

Discussion

Scorpion venom exerts potent effects on the cardiovascular system through its action on sodium and potassium ion channels, triggering a massive release of catecholamines and acetylcholine. This “autonomic storm” leads to vasoconstriction, myocardial ischemia, and conduction system dysfunction [2, 12, 13]. Initial cardiovascular dysfunction, termed the “vascular phase,” is driven by catecholamine-induced vasoconstriction. This increases left ventricular (LV) afterload, obstructing LV ejection and raising filling pressure. This is followed by a “myocardial phase,” characterized by reduced LV contractility, low cardiac output, and systemic hypotension. Similar reversible dysfunction is observed in the right ventricle. These cardiac effects closely resemble takotsubo cardiomyopathy (stress cardiomyopathy), driven by excessive catecholamine release, causing myocardial ischemia through coronary vasomotor disturbances. Treatment typically focuses on managing pulmonary edema and improving hemodynamic status, often using dobutamine to enhance cardiac function [2]. Bradyarrhythmias, including the complete heart block observed in this case, are linked to parasympathetic overactivity [13].

Studies on cardiac manifestations

Several studies have explored the cardiovascular manifestations of scorpion envenomation, underscoring its variability and severity:

1. Myocarditis and cardiac dysfunction

   Bahloul et al. examined 50 patients with scorpion envenomation-induced myocarditis and reported that 44% experienced left ventricular dysfunction, with 16% progressing to pulmonary edema [5].

2. Electrocardiographic changes

   Research has demonstrated that sinus tachycardia is the most frequently observed ECG abnormality in scorpion envenomation, affecting approximately 82% of cases. However, more severe arrhythmias, such as ventricular fibrillation, atrial fibrillation, and conduction blocks, including complete heart block, are less common but carry significant prognostic implications [7].

Case comparisons

Sharifkazemi et al. (2003): this case described a 55-year-old woman who developed transient complete heart block following a scorpion sting. Despite severe bradycardia, the heart block resolved without the need for pacing, highlighting the potential for spontaneous recovery in milder cases [13].

Maharat Nakhon Ratchasima Hospital Journal (2010): a 45-year-old male presented with complete heart block and cardiogenic shock. Temporary pacing was employed, and the conduction abnormality resolved within 48 hours, suggesting reversible toxic effects on the conduction system [14].

To our knowledge, no prior report has described irreversible AV block requiring permanent pacemaker implantation. This makes our case unique, and this point has been emphasized in the Abstract and Discussion.

In contrast to the cases described above, our patient exhibited persistent complete heart block requiring permanent pacemaker implantation. The elevated troponin levels and echocardiographic findings further indicated significant myocardial injury, which could reflect more severe venom toxicity or individual susceptibility.

Conclusion

Scorpion envenomation can result in significant cardiac complications, including complete heart block. This case highlights the importance of recognizing and managing these complications promptly, particularly in regions where scorpion stings are endemic. Multidisciplinary collaboration and timely intervention, including pacemaker therapy when indicated, are critical for improving patient outcomes.

Author contributions

M.Z.: case diagnosis, evaluation, and editing; Z.A.: case presentation, imaging; A.R.: editing; M.B.: conceptualization, writing, and editing. All authors reviewed and approved the final manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

All data generated or analyzed during this study are included in this published article.

Declarations

Ethics approval and consent to participate

All experiments involving human samples were conducted in accordance with relevant guidelines and regulations. The study protocol was reviewed and approved by the Ethics Committee of Shiraz University of Medical Sciences (SUMS). All procedures were performed in compliance with the Declaration of Helsinki, and written informed consent was obtained from all participants and/or their legal guardians prior to their inclusion in the study.

Consent for publication

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

Competing interests

The authors declare no conflicts of interest related to this case report.