Cardiogenic shock requiring VA-ECMO therapy in scorpionism-induced myocarditis

Abstract

It is estimated that approximately 1.2 million scorpion stings occur globally each year. However, the true incidence is likely underestimated due to underreporting, particularly in endemic regions with limited access to healthcare systems. While the vast majority of stings result in only local symptoms, approximately 5% of patients develop systemic manifestations, and up to 1% progress to life-threatening complications such as acute heart failure, arrhythmias and cardiogenic shock.¹

Scorpion envenomation represents a significant public health issue in tropical and subtropical regions, including parts of Latin America. This case occurred in Córdoba, Argentina, a temperate region in the central part of the country characterized by hot summers and mild winters. The city of Córdoba, where the patient was treated, is a large urban centre surrounded by hilly terrain and natural scorpion habitats. Tityus trivittatus, the most medically relevant scorpion species in Argentina, is endemic to the area, with increasing reports of envenomation during the warm season.²

Cardiovascular complications are among the most severe and life-threatening effects of systemic scorpion envenomation. In a systematic review of over 700 reported cases of scorpion-related myocarditis, pulmonary oedema occurred in approximately 60.7% of cases, and hypotension or cardiogenic shock in 45.8%. Sinus tachycardia was the most common ECG abnormality (82%), followed by ST-T changes (64.6%), with less frequent findings such as ventricular arrhythmias and atrioventricular blocks. Echocardiographic evaluations often reveal global or regional hypokinesia, ventricular dilation and reduced left ventricular ejection fraction (EF)—frequently below 40%. Right ventricular dysfunction and functional mitral or tricuspid regurgitation may also be observed. Despite the severity of these manifestations, many patients—particularly children—exhibit rapid and complete recovery with timely supportive care.^{3, 4}

Although the use of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) has been documented in paediatric patients with severe envenomation, no previous cases have been reported in adults.⁵ We present what is, to our knowledge, the first documented case of successful VA-ECMO support in an adult patient with cardiogenic shock secondary to Tityus trivittatus envenomation, underscoring the importance of early recognition and aggressive intervention in such critical scenarios.

A 21 year-old female with no significant past medical history presented to the emergency department with acute onset of sharp pain in the right foot, radiating proximally along the lower limb, accompanied by sudden-onset vomiting. On admission, she was haemodynamically stable with normal vital signs. According to the patient and her family, the symptoms began approximately 4 h following a suspected scorpion sting to the right foot.

During the initial evaluation, the patient exhibited progressive clinical deterioration characterized by respiratory distress, tachypnoea (respiratory rate: 32 breaths/min), hypotension (blood pressure: 81/56 mmHg) and hypoxemia. She was promptly transferred to the intensive care unit (ICU), where she required endotracheal intubation and initiation of mechanical ventilation. Laboratory investigations revealed marked leukocytosis (35 600/mm³ with 83% neutrophils), severe hyperglycaemia (408 mg/dL) and pronounced lactic acidosis (8.8 mmol/L), prompting an initial working diagnosis of diabetic ketoacidosis.

However, this diagnosis was subsequently ruled out: urinary ketones were negative, viral serologies were non-reactive and laboratory parameters demonstrated elevated liver enzymes, lactate dehydrogenase (LDH), ultrasensitive troponin and creatine phosphokinase (CPK). Chest computed tomography revealed bilateral ground-glass opacities, predominantly affecting the right lung (Figure 1). Considering the initial lower limb pain, recent sting history and clinical evolution, severe scorpion envenomation was suspected, and specific antivenom [purified F (ab′)₂ polyclonal antibodies targeting Tityus trivittatus] were administered.

The patient developed signs of cardiogenic shock with low cardiac output, including cold extremities, oliguria, altered mental status, hypotension and tachycardia. Transthoracic Doppler echocardiography demonstrated severe global hypokinesis with an EF below 10% and a velocity-time integral of 7 cm measured at the left ventricular outflow tract; the left and right ventricles were of normal size; the LV showed akinesia of basal and mid-segments with preserved apical motion; diastolic function was pseudonormal; all cardiac valves were morphologically normal, as were atrial sizes and the pericardium; no signs of elevated pulmonary pressures were observed.. Pharmacologic support with norepinephrine and dobutamine was initiated. Despite these measures, the patient remained in a state of refractory hypoperfusion, with a delta CO₂ of 12, central venous oxygen saturation of 55%, persistent hyperlactataemia and haemodynamic parameters consistent with mixed shock (cardiac output: 2.17 L/min, cardiac index: 1.4 L/min/m²; pulmonary capillary wedge pressure: 32 mmHg; systemic vascular resistance: 400 dyn·s/cm⁵). Consequently, an intra-aortic balloon pump was inserted, followed by the initiation of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) for circulatory support.

Alternative aetiologies were thoroughly excluded: autoimmune and rheumatologic serologies were negative, blood cultures showed no microbial growth and the endocrine profile was within normal limits. Subsequently, a specimen of Tityus trivittatus was identified at the patient's residence, confirming the diagnosis (Figure 2).

The patient showed progressive clinical improvement, including a marked reduction in vasopressor and inotropic support, along with recovery of ventricular function on follow-up echocardiography (Video S1). VA-ECMO was successfully weaned after 50 h and 30 min of support (Table 1).

At 72 h, an extubation attempt was unsuccessful due to the development of acute respiratory distress syndrome, necessitating prone positioning, neuromuscular blockade and prolonged mechanical ventilation. The course was further complicated by ventilator-associated pneumonia, requiring tracheostomy and a total ICU stay of 31 days.

Following clinical stabilization, a comprehensive cardiac magnetic resonance imaging (MRI) study was performed. The MRI demonstrated preserved left ventricular EF (62%) with normal global and segmental wall motion. However, myocardial tissue characterization was abnormal. Quantitative mapping revealed elevated native T1 values (1285 ms), increased T2 relaxation times (70.8 ms) and a globally increased extracellular volume fraction (38%), all consistent with diffuse myocardial inflammation. In addition, T2-weighted STIR sequences showed increased signal intensity in the anterolateral wall, confirming the presence of myocardial oedema. Late gadolinium enhancement imaging revealed limited subepicardial enhancement in the mid-anterolateral and inferolateral segments, as well as at the inferior right ventricular insertion point. These findings fulfil the updated Lake Louise Criteria for acute non-ischaemic myocarditis (Figure 3).

Endomyocardial biopsy was initially considered, but we decided against it based on several clinical factors. The diagnosis of cardiogenic shock due to scorpion envenomation was strongly supported by the clinical context, including the temporal relationship with the sting, the absence of prior cardiac disease and cardiac MRI findings consistent with toxic myocarditis. There was no diagnostic uncertainty or suspicion of an alternative treatable cause such as giant cell or eosinophilic myocarditis, for which histological confirmation would have altered therapeutic management. Furthermore, the patient remained haemodynamically unstable during the critical phase, increasing the procedural risk.

After 16 additional days in the medical ward, the patient was discharged with no residual deficits except for mild critical illness myopathy, for which she was prescribed outpatient physiotherapy.

Cardiovascular involvement is one of the most critical and potentially fatal complications of scorpion envenomation, resulting either from direct myocardial toxicity or venom-induced myocarditis. Myocarditis in this context is primarily mediated by a massive release of catecholamines and vasoactive peptides triggered by neurotoxins acting on voltage-gated sodium and potassium channels, leading to excessive sympathetic and parasympathetic stimulation. The resulting catecholaminergic storm increases afterload, myocardial contractility and oxygen demand, contributing to myocardial ischaemia. Additionally, the venom may exert a direct cytotoxic effect on cardiomyocytes by disrupting intracellular ion homeostasis.^6-8

These pathophysiological mechanisms may lead to fulminant myocarditis with severe ventricular dysfunction, as observed in our patient. While this condition predominantly affects paediatric populations (98% of reported cases), our patient's low body mass index (19.53) may have contributed to increased venom toxicity and severity of clinical presentation. Her clinical findings—respiratory distress, tachycardia, pulmonary oedema and shock—are consistent with the most commonly reported manifestations in the literature.⁹

The absence of clinical improvement following antivenom administration in this case can be attributed to several key factors. First, commercial antivenoms may have low immunoreactivity against the small molecular weight neurotoxins (3–15 kDa) that constitute the most clinically relevant components of the venom, particularly those affecting sodium and potassium channels.^{10, 11} Furthermore, the efficacy of antivenom is highly time-dependent, and it is most effective when administered shortly after envenomation, before systemic complications develop. In our case, by the time of administration, the patient had already progressed to severe cardiogenic shock with established tissue injury. Together, these factors likely explain the poor clinical response to antivenom in this patient.¹²

The management of severe cardiogenic shock requires an aggressive, multidisciplinary approach. In this case, despite optimal pharmacologic support, the patient's haemodynamic instability persisted, necessitating the use of advanced circulatory support with intra-aortic balloon pump and VA-ECMO. Mechanical support was instrumental in stabilizing her cardiopulmonary status and allowing time for myocardial recovery.

A notable strength of our approach was the early recognition of cardiogenic shock and the prompt initiation of ECMO, which likely contributed to the favourable outcome. Limitations include the rarity of this presentation in adults, which poses challenges for early diagnosis and delays in considering extracorporeal support in this context.

To our knowledge, this is the first reported case of VA-ECMO use in an adult patient with cardiogenic shock secondary to scorpion envenomation. While prior literature has described similar interventions in paediatric populations, there is a lack of documented evidence in adults. This case highlights the importance of considering ECMO in severe, refractory cardiovascular compromise due to scorpion venom, and it suggests that body size may influence disease severity.

This case highlights the potential for severe cardiovascular complications following Tityus trivittatus envenomation, even in adult patients. Fulminant myocarditis leading to refractory cardiogenic shock may require advanced circulatory support. The successful use of VA-ECMO in this patient illustrates that timely mechanical support can be lifesaving and facilitate complete myocardial recovery. Clinicians should maintain a high index of suspicion for cardiac involvement in scorpionism and consider ECMO as a therapeutic option in selected critically ill patients.

The patients have allowed personal data processing, and informed consent was obtained from all individual participants included in the study.

The authors declare no conflicts of interest.