Kounis Syndrome

Kounis syndrome, also known as allergic myocardial infarction, presents as the concurrent occurrence of acute coronary syndrome (ACS) and hypersensitivity reactions ^[6]D. Clinical manifestations range from mild allergic symptoms to life-threatening cardiogenic shock ^[6]D. Symptoms typically manifest rapidly, often within 20 minutes of exposure to a trigger such as bee stings or medications like Diclofenac 50 mg ^[2][4]D.

Clinical Features

Chest pain is the most frequent symptom, reported in 36% of cases triggered by insect bites ^[3]. Other common features include anaphylaxis (29%), dyspnea, and palpitations ^[3]. Electrocardiographic findings frequently demonstrate ST-segment elevation, occurring in over 70% of patients ^[3]. While the syndrome can affect any age, the median age of presentation is 57 years, with a male predominance of 68.5% ^[6]D.

Classification

Kounis syndrome is classified into three distinct variants based on the underlying coronary anatomy and the mechanism of ischemia ^[6]D:

• Type I (49.7%): Occurs in patients with normal or nearly normal coronary arteries. The primary mechanism is coronary vasospasm induced by inflammatory mediators ^[6]D.
• Type II (27.2%): Occurs in patients with pre-existing coronary artery disease . Allergic reactions trigger plaque rupture or erosion, leading to acute myocardial infarction ^[6]D.
• Type III (5.9%): Involves drug-eluting stent thrombosis or restenosis. Histological analysis typically reveals mast cells and eosinophils within the thrombus ^[6]D.

Diagnosis of Kounis syndrome requires identifying concurrent acute coronary syndrome (ACS) and hypersensitivity ^[6]D. Clinical manifestations often include chest pain (36%) and anaphylaxis (29%) ^[3]. A thorough history is vital, as only 12% of patients have a known history of allergy ^[3].

Electrocardiography

Ischemic changes are the most frequent finding ^[2]. ST-segment elevation occurs in >70% of cases triggered by insect bites ^[3]. These changes typically manifest within 20 minutes of exposure to a suspected trigger, such as diclofenac or bee venom ^[2][4]D. Continuous monitoring is necessary as complications, including arrhythmias, occur in 15% of cases ^[3].

Laboratory Investigations

Cardiac biomarkers, specifically troponin, confirm myocardial injury ^[1]. Clinicians must measure markers of mast cell activation to distinguish Kounis syndrome from standard ACS ^[5]D. Serum tryptase levels peak 1–2 hours after the reaction. Histamine levels rise rapidly but normalize within 30–60 minutes.

Imaging and Invasive Studies

Echocardiography assesses regional wall motion abnormalities. Coronary angiography is essential to classify the syndrome into variants based on coronary anatomy and the presence of stents ^[6]D.

The management of Kounis syndrome requires a delicate balance between treating systemic anaphylaxis and managing acute myocardial ischemia ^[5]D[10]C. Clinicians face a therapeutic dilemma: medications used for allergic reactions may worsen cardiac status, while cardiac treatments may exacerbate systemic hypotension ^[10]C[11]C.

Allergic Reaction Control

Standard anaphylaxis therapy remains the priority, though modifications are often necessary.

• Epinephrine: While it is the first-line treatment for anaphylaxis, it can induce coronary vasoconstriction, increase myocardial oxygen demand, and worsen ischemia ^[7]D[11]C. In severe cases, low-dose continuous intravenous titration may be preferred over bolus administration to minimize cardiac stress ^[11]C.
• Corticosteroids: Hydrocortisone or methylprednisolone are administered to suppress the inflammatory cascade ^[8]C.
• Antihistamines: Combined H1 and H2 receptor antagonists are utilized to block histamine-mediated effects ^[8]C.

Cardiac Stabilization

Vasodilators are indicated for coronary vasospasm but must be used cautiously to avoid profound hypotension ^[10]C.

• Nicorandil: This coronary vasodilator may be beneficial as it has a limited effect on systemic blood pressure compared to nitrates ^[11]C.
• Nitrates: Useful for vasospasm but contraindicated in patients with low systemic blood pressure.
• Monitoring: Routine cardiac investigations, including ECG and troponin, are mandatory for any patient with grade 4 anaphylaxis or chest pain following an allergic event to rule out the ATAK complex (Adrenaline, Takotsubo, Anaphylaxis, and Kounis) ^[9]C.

The prognosis of Kounis syndrome is generally favorable with prompt recognition and management, though the clinical course varies significantly by variant ^[13]C. Type I (vasospastic) typically carries a better prognosis than Type II (plaque rupture) or Type III (stent thrombosis) ^[12]D. However, the condition can lead to fatal outcomes if the underlying anaphylaxis or myocardial ischemia is not recognized ^[15]C.

Acute Complications

Complications involve acute cardiac events triggered by the release of inflammatory mediators. These include:

• Acute Myocardial Infarction (AMI): Myocardial damage can occur in patients with normal coronary arteries (Type I) or those with pre-existing atherosclerosis (Type II) ^[1], ^[12]D.
• Cardiogenic Syncope: Severe hypersensitivity can lead to sudden loss of consciousness due to reduced cardiac output ^[15]C.
• Stent Thrombosis: In Type III KS, eosinophilic and mast cell infiltration can cause acute or recurrent occlusion of coronary stents ^[12]D, ^[13]C.
• Arrhythmias: Allergic insults may trigger life-threatening rhythm disturbances ^[12]D.

Long-term Outlook and Recurrence

Recurrence is a significant concern, particularly if the inciting allergen is not identified and avoided ^[13]C. Patients with Type III KS may experience multiple episodes of stent thrombosis if the allergic trigger persists ^[13]C. Long-term outcomes depend on the extent of myocardial injury and the success of secondary prevention strategies.