Relationship between RR and QT Intervals in Normal and Pacing-induced Heart Failure Dogs

This study was conducted to determine the effects of rapid ventricular pacing on cardiac function and hemodynamics, and to determine the most suitable QTc formula for the effects of alterations in the RR interval on the QT interval of conscious dog with heart failure (HF). Electrocardiograms were acquired from dogs (n=18) at baseline and after rapid ventricular pacing (6, 9, 12 weeks). RR and QT intervals were measured and QTc intervals were calculated using 3 common formulae (Bazett, Fridericia and Van de Water). HF was confirmed by reduced left ventricular fractional shortening (p<0.05), significantly faster heart rate (p<0.001) and significantly changed QT and QTc intervals (p<0.001) when compared to the baseline. This model also demonstrated decreased systolic arterial pressure (p<0.01) and increased BNP (p<0.05). The appropriate regression equations were QT = 152.4+0.08RR for normal dogs and QT = 32.3 (RR) 0.29 for HF dogs. In normal dogs, the Van de Water formula reveals the least dependency of QTc on RR interval. In HF dogs, the Fridericia formula appears to be the best equation to remove the influence of heart rate.