Measurement of the QT Interval: Lessons from Thirty-Two Animal Species for the Correction of the QT Interval by Heart Rate

Background: The optimal method to correct the QT interval, an important indication of arrhythmia risk, for the impact of heart rate has been controversial. The fundamental biologic relationship of the QT interval-heart rate relationship has rarely been studied across different species. Methods: The literature on the QT and heart rate of 32 different species was examined specifically in the whales, dolphins, Asian elephants, rhinoceros, camels, brown bears, grizzly bear, lions, tigers, sea lions, seals, donkeys, ponies, horses, cows, sheep, goats, llamas & alpacas, swine, Minipigs, deer, dogs, cats, baboons, apes, monkeys, prairie dogs, marmot, rabbit, hamsters, guinea pigs and mice. Results: An inverse relationship between QT interval and heart rate was apparent across species. The relationship was poorly fit by a linear formula. The Bazett approach (square root of heart rate or RR interval) or the Fridericia approach (cubed root of the heart rate or RR interval) produced slight improvements. Second, third and fourth order polynomials produced a progressive greater improvement in the goodness of the fit of the relationship. The best fit of the relationship was attained by a nonlinear two-phase relationship identifying that there is one QT-heart rate relationship at slower heart rates and one at faster heart rates. Conclusion: The Bazett, Fridericia and linear formulae approaches to QT interval correction for the impact of heart are far from ideal. Nonlinear QT correction approaches are better approaches to correct the QT interval for heart rate.