Successful Management of Refractory Torsades De Pointes Due to Drug-Induced Long QT Syndrome Guided by Point-of-Care Monitoring of Ionized Magnesium

Ionized magnesium (iMg) is the physiologically active fraction, although total magnesium (tMg) is often used clinically because a dedicated electrode is required to measure the iMg concentration. The tMg concentration is not correlated with the iMg concentration, especially in severely ill patients. In this report, a case of refractory torsades de pointes (TdP) due to drug-induced long QT syndrome was successfully treated with high-dose magnesium sulfate guided by point-of-care monitoring of the iMg concentration. A woman in her 60s had taken osimertinib for two months to treat lung cancer. TdP occurred after the operation of a thoracic compression fracture under general anesthesia. She was diagnosed with drug-induced long QT syndrome. TdP continued, despite treatment with 6 g magnesium sulfate. The iMg value on the admission to the intensive care unit was 0.92 mmol/L, but TdP occurred intermittently and circulatory dynamics were unstable. After an additional intravenous administration of 1 g magnesium sulfate, continuous intravenous administration was initiated at 1 g/h. TdP terminated when the iMg concentration reached 1.31 mmol/L. Then, the target iMg was set to 1.3 mmol/L. The iMg concentration was measured every two hours to adjust the continuous dose of magnesium sulfate. Magnesium administration was tapered, and she was transferred to a general ward on the third day. She was discharged without complications on the 11th day. Point-of-care monitoring of the iMg concentration and observation of the patient's clinical symptoms were important for the effective and safe treatment of TdP due to drug-induced long QT syndrome.