Study of 40 very serious condition ICU patients, 75% required invasive mechanical ventilation, 63% received vasoactive drugs, 50% received other treatments favoring QT prolongation. HC Q with or w/o AZ was given to 45% and 55% respectively. They showed an increase in QTc, more significant with the combination of HC Q+AZ where prolonged QTc was observed in 36% (10 with ΔQTc >60 milliseconds and 7 with QTc ≥500 milliseconds). No ventricular arrhythmia, including torsades de pointes, was recorded. While these results may not be generalizable outside the ICU, caution is recommended in use, especially with the combination.Appropriate use and careful analysis of contraindications, risks, and benefits are important. More recent and much larger studies have not shown significant safety concerns, including outpatient RCTs showing no serious adverse events, and even the RECOVERY trial which used an unusually high dose of HC Q (including 237 patients also receiving AZ) reports they "did not show any excess in ventricular tachycardia (including torsade de pointes) or ventricular fibrillation in the hydroxych loroquine arm", and "serious cardiovascular toxicity has been reported very rarely despite the high prevalence of cardiovascular disease in hospitalized patients, the common occurrence of myocarditis in COVID-19, and the extensive use of hydroxych loroquine and azithromycin together."