RR Interval

The determinant that mostly influences the QT interval duration is cycle length (RR interval) the longer the RR interval, the longer the QT interval and vice versa. Therefore, a number of formulas (see [94] for a list) are used to normalize the QT interval for heart rate and obtain a corrected QT interval (QTc), a key issue especially... 

Physiological these include heart rate, stroke volume, blood pressure, Rr intervals, vector cardiograms, and 3-D vector cardiograms. 

Hamlin RL, Kijtawomrat A, Keene BW, Hamlin DM (2003) QT and RR intervals in conscious and anesthetized guinea pigs with highly varying RR intervals and given QTc-lengthening test articles. Toxicological Sciences 76(2) 437-442... 

Heart rate or RR interval (defined as 60 divided by the heart rate) correction plays a very important role in the analysis of QT/QTc data. Baseline corrections depend heavily on the clinical assumptions that the baseline data represent the subjects physiological condition in drug-free conditions, and that the QT/HR relationship stays the same before and after drug administration, whether or not the heart rate changes. With this assumption, QT values are corrected for HR in order to summarize and compare QTc values across different subjects, trials, or conditions. 

The objective of correcting the QT interval for HR or RR is to obtain a corrected QT interval that is statistically independent of the HR or RR interval. Figure 40.2 shows the dependence of QT on HR. In order to eliminate the dependence of QT on heart rate, numerous HR or RR correction formulas have been proposed in the ECG literature, reflecting the variety of statistical models that have been ht to the data. The reader should be aware that there is no best QT interval correction method for heart rate, but there are some practical methods. The most popular corrections are the Bazett (3) and Fridericia (4) formulas. Both are based on the simple power model QTc = QT/RR that is, calculation of the QTc is equal to the observed QT in milliseconds divided by the term of a root of the RR interval in milliseconds. 

Akhtar M, Saha N, Roy A, Pillai KK. Effect of sparfloxacin and terfenadine combination on QT-intervals at various RR-intervals. Inditm J Pharmacol (2002) 34,264-8. 

Standard deviation of all normal RR intervals in the entire 24-hour ECG recording. 

Root mean square successive difference, the square root of the mean of the squared differences between adjacent normal RR intervals over the entire 24-hour ECG recording. 

Symptomatic sinus bradycardia in the adolescent with longest RR interval <3 s... 

The following ECG parameters were obtained heart rate, PR interval, QT interval, QTc, QRS duration, RR interval, P-QRS-T axes, P amplitude, Q amplitude, R amplitude, S amplitude, T amplitude and ventricular activation time. 

Figure 1.9 RR interval by age, each curve corresponding to the indicated percentile level ( = mean). The RR interval decreases slightly from birth to ages 7-30 days and 1 -3 months. From that age forward, the RR interval increases with a wider range along with increasing age until adolescence.

Cardiovascular The effect of nelfinavir on the QT interval has been evaluated in a randomized, foiu -way crossover, third-party-blinded study in 68 healthy subjects with moxifloxacin as a positive control. Nelfinavir had no effect on the QT or QT intervals or the RR interval, even in poor metabolizers of CYP2C19, in whom exposure was high [189 ]. 

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