Quinine‑related cardiac arrhythmia - Symptoms, Causes, Treatment & Prevention

Overview

Quinine‑related cardiac arrhythmia is an abnormal heart rhythm that occurs as an adverse reaction to quinine, a medication originally derived from the bark of the cinchona tree. Quinine is most commonly used today to treat uncomplicated malaria and, in some countries, to relieve nocturnal leg cramps. While quinine is generally safe when used as prescribed, it can interfere with the electrical conduction system of the heart, leading to potentially serious arrhythmias such as ventricular tachycardia, atrial fibrillation, or QT‑interval prolongation.

**Who it affects** – Anyone taking quinine can be at risk, but certain populations are more vulnerable:

• Adults ≥ 65 years old
• Patients with pre‑existing cardiac disease (e.g., heart failure, prior arrhythmia, coronary artery disease)
• Individuals with electrolyte disturbances (low potassium, magnesium, or calcium)
• People taking other QT‑prolonging drugs (macrolide antibiotics, antifungals, certain anti‑psychotics)
• Patients with renal or hepatic impairment, which can increase quinine plasma levels

**Prevalence** – True incidence is difficult to capture because quinine is often prescribed for short courses. In a 2020 review of adverse drug reactions reported to the FDA’s FAERS, quinine‑induced arrhythmias accounted for < 0.1 % of all cardiac adverse events, but the mortality associated with severe cases was as high as 8–12 % ¹. In malaria‑endemic regions, studies estimate that 1–3 % of patients receiving quinine develop electrocardiographic changes, with a smaller fraction progressing to symptomatic arrhythmia ².

Symptoms

Symptoms can range from subtle palpitations to life‑threatening cardiac arrest. Because arrhythmias may be silent, any new cardiac symptom in a person taking quinine warrants evaluation.

Common symptoms

• Palpitations – a sensation of skipped beats, fluttering, or “racing” heart.
• Chest discomfort – pressure, tightness, or pain that may mimic angina.
• Dizziness or light‑headedness – due to reduced cardiac output.
• Syncope (fainting) – sudden loss of consciousness, often preceded by a rapid heartbeat.
• Shortness of breath – especially on exertion.
• Fatigue – persistent tiredness not explained by other causes.

Less common but alarming symptoms

• Sudden visual disturbances or “flashing lights” (possible cerebral hypoperfusion).
• Seizures (rare, usually secondary to severe arrhythmia).
• Cardiac arrest – no pulse, unresponsiveness, and apnea.

Causes and Risk Factors

Quinine interferes with cardiac ion channels, chiefly the delayed‑rectifier potassium current (I_Kr), which prolongs the repolarization phase of the cardiac action potential. The resulting QT interval lengthening predisposes the heart to torsades de pointes and other ventricular arrhythmias.

Primary causes

• Therapeutic dose toxicity – Even standard dosing (e.g., 600 mg loading, then 300 mg q8h for malaria) can cause QT prolongation in susceptible individuals.
• Overdose – Intentional or accidental ingestion of > 2 g within 24 h markedly raises plasma concentrations.
• Drug‑drug interactions – Concomitant use of CYP3A4 inhibitors (ketoconazole, erythromycin) raises quinine levels; other QT‑prolonging agents have additive effects.
• Electrolyte imbalance – Hypokalemia, hypomagnesemia, or hypocalcemia amplify QT prolongation.

Risk factors

• Age ≥ 65 years
• Pre‑existing structural heart disease or prior arrhythmia
• Renal insufficiency (eGFR < 30 mL/min/1.73 m²) or hepatic dysfunction (Child‑Pugh B/C)
• Concurrent QT‑prolonging medication
• Genetic predisposition (e.g., congenital long QT syndrome)
• Electrolyte disturbances
• High‑dose or prolonged quinine therapy (> 7 days)

Diagnosis

Diagnosis hinges on linking the arrhythmia to quinine exposure while ruling out other causes.

Clinical assessment

• Detailed medication history (including over‑the‑counter supplements)
• Review of symptom onset relative to quinine start date
• Physical exam focusing on heart rate, rhythm, blood pressure, and signs of heart failure

Electrocardiography (ECG)

• Baseline ECG before quinine initiation is recommended for high‑risk patients.
• Key findings: QTc > 450 ms (men) or > 470 ms (women), T‑wave flattening or inversion, ventricular ectopy.
• Serial ECGs every 48–72 h during therapy help detect evolving changes.

Laboratory tests

• Serum quinine level (rarely available, but useful in overdose)
• Electrolytes (K⁺, Mg²⁺, Ca²⁺)
• Renal and hepatic panels
• Cardiac biomarkers (troponin) if myocardial injury is suspected

Advanced cardiac monitoring

• Telemetry or continuous Holter monitoring for patients with symptomatic arrhythmia.
• Electrophysiology study (ES) – only when the mechanism remains unclear after non‑invasive testing.

Exclusion of other causes

Conditions such as acute coronary syndrome, myocarditis, electrolyte abnormalities unrelated to quinine, and other drug toxicities must be ruled out.

Treatment Options

Management focuses on immediate stabilization, removal of the offending agent, and correction of precipitating factors.

Immediate interventions

• Discontinue quinine promptly – the cornerstone of therapy.
• Administer intravenous magnesium sulfate 2 g over 15 min for torsades de pointes, even if serum Mg is normal.
• Correct electrolyte abnormalities (e.g., potassium > 4.5 mmol/L, magnesium > 2 mg/dL).
• Provide cardioversion for hemodynamically unstable tachyarrhythmias (synchronised shock for SVT, unsynchronised for VF/VT).

Pharmacologic therapy

• Beta‑blockers (metoprolol, esmolol) – useful for rate control in atrial arrhythmias.
• Class III antiarrhythmics (amiodarone) – can be considered if arrhythmia persists after quinine cessation, but beware of additional QT prolongation.
• Lidocaine** (IV) for ventricular ectopy when amiodarone contraindicated.