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A tool predicted whether patients with long QT syndrome (LQTS) are at risk of life-threatening events that could be prevented by an implantable cardioverter-defibrillator (ICD) or beta-blockers.

"This overall model shows that syncope and LQT3 genotype, especially, are associated with few-fold increases in life-threatening events. But the relative contribution of variables representing sex and age interaction is also important," Wojciech Zareba, MD, PhD, of the University of Rochester Medical Center in New York, reported at the .

For example, females in one group -- ages 13-20 with the LQT3 genotype, a QTc of 550 ms, and a history of syncope while on beta-blockers -- faced an especially high risk of life-threatening arrhythmic events over 5 years. The tool pegged their likelihood of these events at 26.5%, well over the 6% projected risk threshold that could represent an ICD indication.

"This tool could be a powerful adjunct to the role of individual clinical risk factors in the decision-making process for treatment of patients with LQTS," said HRS President Andrea Russo, MD, of Cooper Medical School of Rowan University in Camden, New Jersey. "Patients with long QT syndrome are often young, and we need to consider the impact of what it means for a young person to live with an ICD for many years over their lifetime. It's valuable to have better tools available for prediction of life-threatening arrhythmias in these patients."

QT prolongation has been a concern in COVID-19 patients who take hydroxychloroquine and azithromycin, which the FDA has warned about in a recent drug safety communication.

"This tool is not suitable in COVID-19 patients, but there are numerous publications identifying risk factors for drug-induced QT prolongation, which include female gender, older age, QTc>470 and even higher risk of QTc>500 ms, low potassium levels, and concomitant use of other drugs that could affect repolarization (dofetilide, sotalol)," Zareba said.

Zareba and colleagues developed their prediction model by prospectively analyzing a Rochester LQTS registry of 1,288 patients with single LQT1, LQT2, or LQT3 mutation. They validated the model in a cohort of 1,481 genotyped LQTS patients from Pavia, Italy.

The Rochester and Pavia cohorts had similar characteristics, such as gender (56% and 52% female, respectively), mean age at enrollment (20 and 21 years, respectively) and median years of follow-up (9.8 and 7.0, respectively). Fewer had the LQT3 genotype: 12% in both groups.

The researchers focused on a 5-year period of risk of aborted cardiac arrest, sudden cardiac death, or appropriate ICD shock because long-term outcomes are difficult to predict, Zareba told MedPage Today. "The 5-year period is more reliable, more predictable, and it is linked to therapeutic decisions for foreseeable future. Risk of sudden death >6% in 5 years is high, if we consider that six of 100 20-year-old individuals might die in 5 years."

The highest-risk patients were those with:

• Long QTc interval over 500 ms, but especially those above 550 ms
• Syncopal episodes, especially if occurring when patients already taking beta-blockers to prevent arrhythmias
• LQT3 genotype
• Adult females with LQT2 genotype

Among the lowest-risk patients were those with QTc <470 ms and males with LQT1 and LQT2 genotypes during adulthood.

Zareba said the calculator will become available publicly upon the study's publication in a medical journal.

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