At a time when the anti-malarial drug hydroxychloroquine (HCQ) is being touted as a 'wonder drug' to treat critical COVID-19 patients, a new US study has found evidence suggesting that patients who received hydroxychloroquine for COVID-19 were at an increased risk of electrical changes to the heart and cardiac arrhythmias.

Cardiac arrhythmia refers to a group of conditions that cause the heart to beat irregular, too slowly, or too quickly.

The combination of hydroxychloroquine with azithromycin was linked to even greater changes compared to hydroxychloroquine alone, according to the researchers from Beth Israel Deaconess Medical Center (BIDMC) in the US.

"While hydroxychloroquine and azithromycin are generally well-tolerated medications, increased usage in the context of COVID-19 will likely increase the frequency of adverse drug events (ADEs)," said study co-author Nicholas J Mercuro from BIDMC.

"This is especially concerning given that that patient with underlying cardiac co-morbidities appear to be disproportionately affected by COVID-19 and that the virus itself may damage the heart," Mercuro added.

According to the study, published in the journal JAMA Cardiology, HCQ and azithromycin each can cause an electrical disturbance in the heart known as a QTc prolongation, indicated by a longer space between specific peaks on an electrocardiogram.

QTc prolongation denotes that the heart muscle is taking milliseconds longer than normal to recharge between beats. The delay can cause cardiac arrhythmias, which in turn increases the likelihood of cardiac arrest, stroke or death.

In this single-centre, retrospective, observational study, the research team evaluated 90 adults with COVID-19 who were hospitalised at BIDMC between March 1 and April 7 and received at least one day of hydroxychloroquine.

More than half of these patients also had high blood pressure, and more than 30 per cent had diabetes.

Seven patients (19 per cent) who received hydroxychloroquine alone developed prolonged QTc of 500 milliseconds or more, and three patients had a change in QTc of 60 milliseconds or more.

Of the 53 patients who also received azithromycin, 21 per cent had prolonged QTc of 500 milliseconds or more, and 13 per cent experienced a change in QTc of 60 milliseconds or more.

"In our study, patients who were hospitalised and receiving hydroxychloroquine for COVID-19 frequently experienced QTc prolongation and adverse drug events," said study researcher Christina F Yen.

"One participant taking the drug combination experienced a potentially lethal tachycardia called torsades de pointes, which to our knowledge has yet to be reported elsewhere in the peer-reviewed COVID-19 literature," Yen added.

In 2003, preliminary data suggested hydroxychloroquine may be effective against SARS-CoV-1, a fatal but hard-to-transmit respiratory virus related to the coronavirus that causes COVID-19.

More recently, a small study of patients with COVID-19 appeared to benefit from the anti-malarial drug. Subsequent research, however, has failed to confirm either finding.

In light of their data, the research team urge caution and careful consideration before administering hydroxychloroquine as a treatment for COVID-19.

Meanwhile, the US Food and Drug Administration (FDA) has granted Emergency Use Authorisation (EUA) for the experimental anti-viral drug remdesivir to treat COVID-19.

The number of COVID-19 cases in the US has reached 1,100,197 as of Friday, according to the Johns Hopkins University. The death toll from the disease in the country hit 64,789.

New York remains the hardest-hit state, with 308,314 cases and 24,039 deaths, followed by New Jersey with 121,190 cases and 7,538 deaths.